Revert json ops (#2814)

* Revert "port more ops to JSON (#2809)"

This reverts commit 137f33733d365026903d40e7cde6e34ac6c36dcf.

* Revert "port ops to JSON: compiler, errors, fetch, files (#2804)"

This reverts commit 79f82cf10ed1dbf91346994250d7311a4d74377a.

* Revert "Port rest of os ops to JSON (#2802)"

This reverts commit 5b2baa5c990fbeae747e952c5dcd7a5369e950b1.

45 files changed, 1978 insertions, 1055 deletions

diff --git a/cli/deno_error.rs b/cli/deno_error.rs
index 3b7dbcde8..e024a396c 100644
--- a/cli/deno_error.rs
+++ b/cli/deno_error.rs
@@ -205,18 +205,6 @@ impl GetErrorKind for ReadlineError {
   }
 }
 
-impl GetErrorKind for serde_json::error::Error {
-  fn kind(&self) -> ErrorKind {
-    use serde_json::error::*;
-    match self.classify() {
-      Category::Io => ErrorKind::InvalidInput,
-      Category::Syntax => ErrorKind::InvalidInput,
-      Category::Data => ErrorKind::InvalidData,
-      Category::Eof => ErrorKind::UnexpectedEof,
-    }
-  }
-}
-
 #[cfg(unix)]
 mod unix {
   use super::{ErrorKind, GetErrorKind};
@@ -263,11 +251,6 @@ impl GetErrorKind for dyn AnyError {
       .or_else(|| self.downcast_ref::<uri::InvalidUri>().map(Get::kind))
       .or_else(|| self.downcast_ref::<url::ParseError>().map(Get::kind))
       .or_else(|| self.downcast_ref::<ReadlineError>().map(Get::kind))
-      .or_else(|| {
-        self
-          .downcast_ref::<serde_json::error::Error>()
-          .map(Get::kind)
-      })
       .or_else(|| unix_error_kind(self))
       .unwrap_or_else(|| {
         panic!("Can't get ErrorKind for {:?}", self);
diff --git a/cli/main.rs b/cli/main.rs
index a601e68af..2e82b8ee8 100644
--- a/cli/main.rs
+++ b/cli/main.rs
@@ -32,6 +32,7 @@ mod http_body;
 mod http_util;
 mod import_map;
 pub mod msg;
+pub mod msg_util;
 pub mod ops;
 pub mod permissions;
 mod progress;
diff --git a/cli/msg.fbs b/cli/msg.fbs
index a7359c527..3a40b80f5 100644
--- a/cli/msg.fbs
+++ b/cli/msg.fbs
@@ -1,14 +1,48 @@
 union Any {
+  Accept,
+  ApplySourceMap,
+  Cache,
   Chdir,
   Chmod,
   Chown,
+  Close,
   CopyFile,
+  CreateWorker,
+  CreateWorkerRes,
   Cwd,
   CwdRes,
+  Dial,
+  Fetch,
+  FetchSourceFile,
+  FetchSourceFileRes,
+  FetchRes,
+  FormatError,
+  FormatErrorRes,
+  GetRandomValues,
+  GlobalTimer,
+  GlobalTimerRes,
+  GlobalTimerStop,
+  HostGetMessage,
+  HostGetMessageRes,
+  HostGetWorkerClosed,
+  HostPostMessage,
+  Kill,
   Link,
+  Listen,
+  ListenRes,
   MakeTempDir,
   MakeTempDirRes,
+  Metrics,
+  MetricsRes,
   Mkdir,
+  NewConn,
+  Now,
+  NowRes,
+  Open,
+  OpenRes,
+  PermissionRevoke,
+  Permissions,
+  PermissionsRes,
   Read,
   ReadDir,
   ReadDirRes,
@@ -17,11 +51,30 @@ union Any {
   ReadlinkRes,
   Remove,
   Rename,
+  ReplReadline,
+  ReplReadlineRes,
+  ReplStart,
+  ReplStartRes,
+  Resources,
+  ResourcesRes,
+  Run,
+  RunRes,
+  RunStatus,
+  RunStatusRes,
   Seek,
+  SetEnv,
+  Shutdown,
+  Start,
+  StartRes,
   Stat,
   StatRes,
   Symlink,
   Truncate,
+  HomeDir,
+  HomeDirRes,
+  WorkerGetMessage,
+  WorkerGetMessageRes,
+  WorkerPostMessage,
   Write,
   WriteRes,
 }
@@ -114,6 +167,25 @@ table Base {
   inner: Any;
 }
 
+table Start {
+  unused: int8;
+}
+
+table StartRes {
+  cwd: string;
+  pid: uint32;
+  argv: [string];
+  main_module: string; // Absolute URL.
+  debug_flag: bool;
+  deps_flag: bool;
+  types_flag: bool;
+  version_flag: bool;
+  deno_version: string;
+  v8_version: string;
+  no_color: bool;
+  xeval_delim: string;
+}
+
 table FormatError {
   error: string;
 }
@@ -122,15 +194,138 @@ table FormatErrorRes {
   error: string;
 }
 
+// Create worker as host
+table CreateWorker {
+  specifier: string;
+  include_deno_namespace: bool;
+  has_source_code: bool;
+  source_code: string;
+}
+
+table CreateWorkerRes {
+  rid: uint32;
+}
+
+table HostGetWorkerClosed {
+  rid: uint32;
+}
+
+// Get message from guest worker as host
+table HostGetMessage {
+  rid: uint32;
+}
+
+table HostGetMessageRes {
+  data: [ubyte];
+}
+
+// Post message to guest worker as host
+table HostPostMessage {
+  rid: uint32;
+  // data passed thru the zero-copy data parameter.
+}
+
+// Get message from host as guest worker
+table WorkerGetMessage {
+  unused: int8;
+}
+
+table WorkerGetMessageRes {
+  data: [ubyte];
+}
+
+// Post message to host as guest worker
+table WorkerPostMessage {
+  // data passed thru the zero-copy data parameter.
+}
+
+table FetchSourceFile {
+  specifier: string;
+  referrer: string;
+}
+
+table FetchSourceFileRes {
+  // If it's a non-http module, moduleName and filename will be the same.
+  // For http modules, module_name is its resolved http URL, and filename
+  // is the location of the locally downloaded source code.
+  module_name: string;
+  filename: string;
+  media_type: MediaType;
+  data: [ubyte];
+}
+
+table ApplySourceMap {
+  filename: string;
+  line: int;
+  column: int;
+}
+
+table Cache {
+  extension: string;
+  module_id: string;
+  contents: string;
+}
+
 table Chdir {
   directory: string;
 }
 
+table GlobalTimer {
+  timeout: int;
+}
+
+table GlobalTimerRes { }
+
+table GlobalTimerStop { }
+
+table SetEnv {
+  key: string;
+  value: string;
+}
+
 table KeyValue {
   key: string;
   value: string;
 }
 
+table Permissions {}
+
+table PermissionRevoke {
+  permission: string;
+}
+
+table PermissionsRes {
+  run: bool;
+  read: bool;
+  write: bool;
+  net: bool;
+  env: bool;
+  hrtime: bool;
+}
+
+// Note this represents The WHOLE header of an http message, not just the key
+// value pairs. That means it includes method and url for Requests and status
+// for responses. This is why it is singular "Header" instead of "Headers".
+table HttpHeader {
+  is_request: bool;
+  // Request only:
+  method: string;
+  url: string;
+  // Response only:
+  status: uint16;
+  // Both:
+  fields: [KeyValue];
+}
+
+table Fetch {
+  header: HttpHeader;
+}
+
+table FetchRes {
+  header: HttpHeader;
+  body_rid: uint32;
+}
+
 table MakeTempDir {
   dir: string;
   prefix: string;
@@ -189,6 +384,35 @@ table ReadlinkRes {
   path: string;
 }
 
+table ReplStart {
+  history_file: string;
+  // TODO add config
+}
+
+table ReplStartRes {
+  rid: uint32;
+}
+
+table ReplReadline {
+  rid: uint32;
+  prompt: string;
+}
+
+table ReplReadlineRes {
+  line: string;
+}
+
+table Resources {}
+
+table Resource {
+  rid: uint32;
+  repr: string;
+}
+
+table ResourcesRes {
+  resources: [Resource];
+}
+
 table Symlink {
   oldname: string;
   newname: string;
@@ -221,6 +445,22 @@ table Truncate {
   len: uint;
 }
 
+table HomeDir {}
+
+table HomeDirRes {
+  path: string;
+}
+
+table Open {
+  filename: string;
+  perm: uint;
+  mode: string;
+}
+
+table OpenRes {
+  rid: uint32;
+}
+
 table Read {
   rid: uint32;
   // (ptr, len) is passed as second parameter to Deno.core.send().
@@ -239,10 +479,103 @@ table WriteRes {
   nbyte: uint;
 }
 
+table Close {
+  rid: uint32;
+}
+
+table Kill {
+  pid: int32;
+  signo: int32;
+}
+
+table Shutdown {
+  rid: uint32;
+  how: uint;
+}
+
+table Listen {
+  network: string;
+  address: string;
+}
+
+table ListenRes {
+  rid: uint32;
+}
+
+table Accept {
+  rid: uint32;
+}
+
+table Dial {
+  network: string;
+  address: string;
+}
+
+// Response to Accept and Dial.
+table NewConn {
+  rid: uint32;
+  remote_addr: string;
+  local_addr: string;
+}
+
+table Metrics {}
+
+table MetricsRes {
+  ops_dispatched: uint64;
+  ops_completed: uint64;
+  bytes_sent_control: uint64;
+  bytes_sent_data: uint64;
+  bytes_received: uint64;
+}
+
+enum ProcessStdio: byte { Inherit, Piped, Null }
+
+table Run {
+  args: [string];
+  cwd: string;
+  env: [KeyValue];
+  stdin: ProcessStdio;
+  stdout: ProcessStdio;
+  stderr: ProcessStdio;
+  stdin_rid: uint32;
+  stdout_rid: uint32;
+  stderr_rid: uint32;
+}
+
+table RunRes {
+  rid: uint32;
+  pid: uint32;
+  // The following stdio rids are only valid if "Piped" was specified for the
+  // corresponding stdio stream. The caller MUST issue a close op for all valid
+  // stdio streams.
+  stdin_rid: uint32;
+  stdout_rid: uint32;
+  stderr_rid: uint32;
+}
+
+table RunStatus {
+  rid: uint32;
+}
+
+table RunStatusRes {
+  got_signal: bool;
+  exit_code: int;
+  exit_signal: int;
+}
+
+table Now {}
+
+table NowRes {
+  seconds: uint64;
+  subsec_nanos: uint32;
+}
+
 table Seek {
   rid: uint32;
   offset: int;
   whence: uint;
 }
 
+table GetRandomValues {}
+
 root_type Base;
diff --git a/cli/msg.rs b/cli/msg.rs
index db4c771f8..51726b572 100644
--- a/cli/msg.rs
+++ b/cli/msg.rs
@@ -1,8 +1,22 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 #![allow(dead_code)]
 #![cfg_attr(feature = "cargo-clippy", allow(clippy::all, clippy::pedantic))]
+use crate::state;
 use flatbuffers;
+use std::sync::atomic::Ordering;
 
 // GN_OUT_DIR is set either by build.rs (for the Cargo build), or by
 // build_extra/rust/run.py (for the GN+Ninja build).
 include!(concat!(env!("GN_OUT_DIR"), "/gen/cli/msg_generated.rs"));
+
+impl<'a> From<&'a state::Metrics> for MetricsResArgs {
+  fn from(m: &'a state::Metrics) -> Self {
+    MetricsResArgs {
+      ops_dispatched: m.ops_dispatched.load(Ordering::SeqCst) as u64,
+      ops_completed: m.ops_completed.load(Ordering::SeqCst) as u64,
+      bytes_sent_control: m.bytes_sent_control.load(Ordering::SeqCst) as u64,
+      bytes_sent_data: m.bytes_sent_data.load(Ordering::SeqCst) as u64,
+      bytes_received: m.bytes_received.load(Ordering::SeqCst) as u64,
+    }
+  }
+}
diff --git a/cli/msg_util.rs b/cli/msg_util.rs
new file mode 100644
index 000000000..e37a91f3a
--- /dev/null
+++ b/cli/msg_util.rs
@@ -0,0 +1,124 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+// Helpers for serialization.
+use crate::msg;
+use deno::ErrBox;
+use flatbuffers;
+use http::header::HeaderName;
+use http::uri::Uri;
+use http::Method;
+use hyper::header::HeaderMap;
+use hyper::header::HeaderValue;
+use hyper::Body;
+use hyper::Request;
+use hyper::Response;
+use std::str::FromStr;
+
+type Headers = HeaderMap<HeaderValue>;
+
+pub fn serialize_key_value<'bldr>(
+  builder: &mut flatbuffers::FlatBufferBuilder<'bldr>,
+  key: &str,
+  value: &str,
+) -> flatbuffers::WIPOffset<msg::KeyValue<'bldr>> {
+  let key = builder.create_string(&key);
+  let value = builder.create_string(&value);
+  msg::KeyValue::create(
+    builder,
+    &msg::KeyValueArgs {
+      key: Some(key),
+      value: Some(value),
+    },
+  )
+}
+
+pub fn serialize_request_header<'bldr>(
+  builder: &mut flatbuffers::FlatBufferBuilder<'bldr>,
+  r: &Request<Body>,
+) -> flatbuffers::WIPOffset<msg::HttpHeader<'bldr>> {
+  let method = builder.create_string(r.method().as_str());
+  let url = builder.create_string(r.uri().to_string().as_ref());
+
+  let mut fields = Vec::new();
+  for (key, val) in r.headers().iter() {
+    let kv = serialize_key_value(builder, key.as_ref(), val.to_str().unwrap());
+    fields.push(kv);
+  }
+  let fields = builder.create_vector(fields.as_ref());
+
+  msg::HttpHeader::create(
+    builder,
+    &msg::HttpHeaderArgs {
+      is_request: true,
+      method: Some(method),
+      url: Some(url),
+      fields: Some(fields),
+      ..Default::default()
+    },
+  )
+}
+
+pub fn serialize_fields<'bldr>(
+  builder: &mut flatbuffers::FlatBufferBuilder<'bldr>,
+  headers: &Headers,
+) -> flatbuffers::WIPOffset<
+  flatbuffers::Vector<
+    'bldr,
+    flatbuffers::ForwardsUOffset<msg::KeyValue<'bldr>>,
+  >,
+> {
+  let mut fields = Vec::new();
+  for (key, val) in headers.iter() {
+    let kv = serialize_key_value(builder, key.as_ref(), val.to_str().unwrap());
+    fields.push(kv);
+  }
+  builder.create_vector(fields.as_ref())
+}
+
+// Not to be confused with serialize_response which has nothing to do with HTTP.
+pub fn serialize_http_response<'bldr>(
+  builder: &mut flatbuffers::FlatBufferBuilder<'bldr>,
+  r: &Response<Body>,
+) -> flatbuffers::WIPOffset<msg::HttpHeader<'bldr>> {
+  let status = r.status().as_u16();
+  let fields = serialize_fields(builder, r.headers());
+  msg::HttpHeader::create(
+    builder,
+    &msg::HttpHeaderArgs {
+      is_request: false,
+      status,
+      fields: Some(fields),
+      ..Default::default()
+    },
+  )
+}
+
+pub fn deserialize_request(
+  header_msg: msg::HttpHeader<'_>,
+  body: Body,
+) -> Result<Request<Body>, ErrBox> {
+  let mut r = Request::new(body);
+
+  assert!(header_msg.is_request());
+
+  let u = header_msg.url().unwrap();
+  let u = Uri::from_str(u).map_err(ErrBox::from)?;
+  *r.uri_mut() = u;
+
+  if let Some(method) = header_msg.method() {
+    let method = Method::from_str(method).unwrap();
+    *r.method_mut() = method;
+  }
+
+  if let Some(fields) = header_msg.fields() {
+    let headers = r.headers_mut();
+    for i in 0..fields.len() {
+      let kv = fields.get(i);
+      let key = kv.key().unwrap();
+      let name = HeaderName::from_bytes(key.as_bytes()).unwrap();
+      let value = kv.value().unwrap();
+      let v = HeaderValue::from_str(value).unwrap();
+      headers.insert(name, v);
+    }
+  }
+  Ok(r)
+}
diff --git a/cli/ops/compiler.rs b/cli/ops/compiler.rs
index 39d3a6d7f..efdcd2c9b 100644
--- a/cli/ops/compiler.rs
+++ b/cli/ops/compiler.rs
@@ -1,68 +1,86 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{Deserialize, JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::*;
+use crate::deno_error;
+use crate::msg;
 use crate::state::ThreadSafeState;
 use crate::tokio_util;
 use deno::*;
-
-#[derive(Deserialize)]
-#[serde(rename_all = "camelCase")]
-struct CacheArgs {
-  module_id: String,
-  contents: String,
-  extension: String,
-}
+use flatbuffers::FlatBufferBuilder;
+use futures::Future;
 
 pub fn op_cache(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: CacheArgs = serde_json::from_value(args)?;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let inner = base.inner_as_cache().unwrap();
+  let extension = inner.extension().unwrap();
+  // TODO: rename to something with 'url'
+  let module_id = inner.module_id().unwrap();
+  let contents = inner.contents().unwrap();
 
-  let module_specifier = ModuleSpecifier::resolve_url(&args.module_id)
+  let module_specifier = ModuleSpecifier::resolve_url(module_id)
     .expect("Should be valid module specifier");
 
   state.ts_compiler.cache_compiler_output(
     &module_specifier,
-    &args.extension,
-    &args.contents,
+    extension,
+    contents,
   )?;
 
-  Ok(JsonOp::Sync(json!({})))
-}
-
-#[derive(Deserialize)]
-struct FetchSourceFileArgs {
-  specifier: String,
-  referrer: String,
+  ok_buf(empty_buf())
 }
 
 pub fn op_fetch_source_file(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: FetchSourceFileArgs = serde_json::from_value(args)?;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  if !base.sync() {
+    return Err(deno_error::no_async_support());
+  }
+  assert!(data.is_none());
+  let inner = base.inner_as_fetch_source_file().unwrap();
+  let cmd_id = base.cmd_id();
+  let specifier = inner.specifier().unwrap();
+  let referrer = inner.referrer().unwrap();
 
   // TODO(ry) Maybe a security hole. Only the compiler worker should have access
   // to this. Need a test to demonstrate the hole.
   let is_dyn_import = false;
 
   let resolved_specifier =
-    state.resolve(&args.specifier, &args.referrer, false, is_dyn_import)?;
+    state.resolve(specifier, referrer, false, is_dyn_import)?;
 
   let fut = state
     .file_fetcher
-    .fetch_source_file_async(&resolved_specifier);
+    .fetch_source_file_async(&resolved_specifier)
+    .and_then(move |out| {
+      let builder = &mut FlatBufferBuilder::new();
+      let data_off = builder.create_vector(out.source_code.as_slice());
+      let msg_args = msg::FetchSourceFileResArgs {
+        module_name: Some(builder.create_string(&out.url.to_string())),
+        filename: Some(builder.create_string(&out.filename.to_str().unwrap())),
+        media_type: out.media_type,
+        data: Some(data_off),
+      };
+      let inner = msg::FetchSourceFileRes::create(builder, &msg_args);
+      Ok(serialize_response(
+        cmd_id,
+        builder,
+        msg::BaseArgs {
+          inner: Some(inner.as_union_value()),
+          inner_type: msg::Any::FetchSourceFileRes,
+          ..Default::default()
+        },
+      ))
+    });
 
   // WARNING: Here we use tokio_util::block_on() which starts a new Tokio
   // runtime for executing the future. This is so we don't inadvernently run
   // out of threads in the main runtime.
-  let out = tokio_util::block_on(fut)?;
-  Ok(JsonOp::Sync(json!({
-    "moduleName": out.url.to_string(),
-    "filename": out.filename.to_str().unwrap(),
-    "mediaType": out.media_type as i32,
-    "sourceCode": String::from_utf8(out.source_code).unwrap(),
-  })))
+  let result_buf = tokio_util::block_on(fut)?;
+  Ok(Op::Sync(result_buf))
 }
diff --git a/cli/ops/dispatch_flatbuffers.rs b/cli/ops/dispatch_flatbuffers.rs
index bd0158751..b9dd4d9fa 100644
--- a/cli/ops/dispatch_flatbuffers.rs
+++ b/cli/ops/dispatch_flatbuffers.rs
@@ -6,12 +6,29 @@ use deno::*;
 use flatbuffers::FlatBufferBuilder;
 use hyper::rt::Future;
 
-use super::files::{op_read, op_write};
+use super::compiler::{op_cache, op_fetch_source_file};
+use super::errors::{op_apply_source_map, op_format_error};
+use super::fetch::op_fetch;
+use super::files::{op_close, op_open, op_read, op_seek, op_write};
 use super::fs::{
   op_chdir, op_chmod, op_chown, op_copy_file, op_cwd, op_link,
   op_make_temp_dir, op_mkdir, op_read_dir, op_read_link, op_remove, op_rename,
   op_stat, op_symlink, op_truncate,
 };
+use super::metrics::op_metrics;
+use super::net::{op_accept, op_dial, op_listen, op_shutdown};
+use super::os::{op_home_dir, op_set_env, op_start};
+use super::performance::op_now;
+use super::permissions::{op_permissions, op_revoke_permission};
+use super::process::{op_kill, op_run, op_run_status};
+use super::random::op_get_random_values;
+use super::repl::{op_repl_readline, op_repl_start};
+use super::resources::op_resources;
+use super::timers::{op_global_timer, op_global_timer_stop};
+use super::workers::{
+  op_create_worker, op_host_get_message, op_host_get_worker_closed,
+  op_host_post_message, op_worker_get_message, op_worker_post_message,
+};
 
 type CliDispatchFn = fn(
   state: &ThreadSafeState,
@@ -125,24 +142,61 @@ pub fn serialize_response(
 /// Standard ops set for most isolates
 pub fn op_selector_std(inner_type: msg::Any) -> Option<CliDispatchFn> {
   match inner_type {
+    msg::Any::Accept => Some(op_accept),
+    msg::Any::ApplySourceMap => Some(op_apply_source_map),
+    msg::Any::Cache => Some(op_cache),
     msg::Any::Chdir => Some(op_chdir),
     msg::Any::Chmod => Some(op_chmod),
     msg::Any::Chown => Some(op_chown),
+    msg::Any::Close => Some(op_close),
     msg::Any::CopyFile => Some(op_copy_file),
+    msg::Any::CreateWorker => Some(op_create_worker),
     msg::Any::Cwd => Some(op_cwd),
+    msg::Any::Dial => Some(op_dial),
+    msg::Any::Fetch => Some(op_fetch),
+    msg::Any::FetchSourceFile => Some(op_fetch_source_file),
+    msg::Any::FormatError => Some(op_format_error),
+    msg::Any::GetRandomValues => Some(op_get_random_values),
+    msg::Any::GlobalTimer => Some(op_global_timer),
+    msg::Any::GlobalTimerStop => Some(op_global_timer_stop),
+    msg::Any::HostGetMessage => Some(op_host_get_message),
+    msg::Any::HostGetWorkerClosed => Some(op_host_get_worker_closed),
+    msg::Any::HostPostMessage => Some(op_host_post_message),
+    msg::Any::Kill => Some(op_kill),
     msg::Any::Link => Some(op_link),
+    msg::Any::Listen => Some(op_listen),
     msg::Any::MakeTempDir => Some(op_make_temp_dir),
+    msg::Any::Metrics => Some(op_metrics),
     msg::Any::Mkdir => Some(op_mkdir),
+    msg::Any::Now => Some(op_now),
+    msg::Any::Open => Some(op_open),
+    msg::Any::PermissionRevoke => Some(op_revoke_permission),
+    msg::Any::Permissions => Some(op_permissions),
     msg::Any::Read => Some(op_read),
     msg::Any::ReadDir => Some(op_read_dir),
     msg::Any::Readlink => Some(op_read_link),
     msg::Any::Remove => Some(op_remove),
     msg::Any::Rename => Some(op_rename),
+    msg::Any::ReplReadline => Some(op_repl_readline),
+    msg::Any::ReplStart => Some(op_repl_start),
+    msg::Any::Resources => Some(op_resources),
+    msg::Any::Run => Some(op_run),
+    msg::Any::RunStatus => Some(op_run_status),
+    msg::Any::Seek => Some(op_seek),
+    msg::Any::SetEnv => Some(op_set_env),
+    msg::Any::Shutdown => Some(op_shutdown),
+    msg::Any::Start => Some(op_start),
     msg::Any::Stat => Some(op_stat),
     msg::Any::Symlink => Some(op_symlink),
     msg::Any::Truncate => Some(op_truncate),
+    msg::Any::HomeDir => Some(op_home_dir),
     msg::Any::Write => Some(op_write),
 
+    // TODO(ry) split these out so that only the appropriate Workers can access
+    // them.
+    msg::Any::WorkerGetMessage => Some(op_worker_get_message),
+    msg::Any::WorkerPostMessage => Some(op_worker_post_message),
+
     _ => None,
   }
 }
diff --git a/cli/ops/errors.rs b/cli/ops/errors.rs
index cd21a3880..a27f3656e 100644
--- a/cli/ops/errors.rs
+++ b/cli/ops/errors.rs
@@ -1,56 +1,88 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{Deserialize, JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::*;
+use crate::deno_error;
 use crate::fmt_errors::JSError;
+use crate::msg;
 use crate::source_maps::get_orig_position;
 use crate::source_maps::CachedMaps;
 use crate::state::ThreadSafeState;
 use deno::*;
+use flatbuffers::FlatBufferBuilder;
 use std::collections::HashMap;
 
-#[derive(Deserialize)]
-struct FormatErrorArgs {
-  error: String,
-}
-
 pub fn op_format_error(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: FormatErrorArgs = serde_json::from_value(args)?;
-  let error = JSError::from_json(&args.error, &state.ts_compiler);
-
-  Ok(JsonOp::Sync(json!({
-    "error": error.to_string(),
-  })))
-}
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let inner = base.inner_as_format_error().unwrap();
+  let json_str = inner.error().unwrap();
+  let error = JSError::from_json(json_str, &state.ts_compiler);
+  let error_string = error.to_string();
+
+  let mut builder = FlatBufferBuilder::new();
+  let new_error = builder.create_string(&error_string);
+
+  let inner = msg::FormatErrorRes::create(
+    &mut builder,
+    &msg::FormatErrorResArgs {
+      error: Some(new_error),
+    },
+  );
+
+  let response_buf = serialize_response(
+    base.cmd_id(),
+    &mut builder,
+    msg::BaseArgs {
+      inner_type: msg::Any::FormatErrorRes,
+      inner: Some(inner.as_union_value()),
+      ..Default::default()
+    },
+  );
 
-#[derive(Deserialize)]
-struct ApplySourceMap {
-  filename: String,
-  line: i32,
-  column: i32,
+  ok_buf(response_buf)
 }
 
 pub fn op_apply_source_map(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: ApplySourceMap = serde_json::from_value(args)?;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  if !base.sync() {
+    return Err(deno_error::no_async_support());
+  }
+  assert!(data.is_none());
+  let inner = base.inner_as_apply_source_map().unwrap();
+  let cmd_id = base.cmd_id();
+  let filename = inner.filename().unwrap();
+  let line = inner.line();
+  let column = inner.column();
 
   let mut mappings_map: CachedMaps = HashMap::new();
   let (orig_filename, orig_line, orig_column) = get_orig_position(
-    args.filename,
-    args.line.into(),
-    args.column.into(),
+    filename.to_owned(),
+    line.into(),
+    column.into(),
     &mut mappings_map,
     &state.ts_compiler,
   );
 
-  Ok(JsonOp::Sync(json!({
-    "filename": orig_filename.to_string(),
-    "line": orig_line as u32,
-    "column": orig_column as u32,
-  })))
+  let builder = &mut FlatBufferBuilder::new();
+  let msg_args = msg::ApplySourceMapArgs {
+    filename: Some(builder.create_string(&orig_filename)),
+    line: orig_line as i32,
+    column: orig_column as i32,
+  };
+  let res_inner = msg::ApplySourceMap::create(builder, &msg_args);
+  ok_buf(serialize_response(
+    cmd_id,
+    builder,
+    msg::BaseArgs {
+      inner: Some(res_inner.as_union_value()),
+      inner_type: msg::Any::ApplySourceMap,
+      ..Default::default()
+    },
+  ))
 }
diff --git a/cli/ops/fetch.rs b/cli/ops/fetch.rs
index e2ab81a81..7661eb6e9 100644
--- a/cli/ops/fetch.rs
+++ b/cli/ops/fetch.rs
@@ -1,57 +1,38 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{Deserialize, JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::CliOpResult;
 use crate::http_util;
+use crate::msg;
+use crate::msg_util;
 use crate::resources;
 use crate::state::ThreadSafeState;
 use deno::*;
-use http::header::HeaderName;
-use http::uri::Uri;
-use http::Method;
+use flatbuffers::FlatBufferBuilder;
 use hyper;
-use hyper::header::HeaderValue;
 use hyper::rt::Future;
-use hyper::Request;
 use std;
 use std::convert::From;
-use std::str::FromStr;
-
-#[derive(Deserialize)]
-struct FetchArgs {
-  method: Option<String>,
-  url: String,
-  headers: Vec<(String, String)>,
-}
 
 pub fn op_fetch(
   state: &ThreadSafeState,
-  args: Value,
+  base: &msg::Base<'_>,
   data: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: FetchArgs = serde_json::from_value(args)?;
-  let url = args.url;
+) -> CliOpResult {
+  let inner = base.inner_as_fetch().unwrap();
+  let cmd_id = base.cmd_id();
+
+  let header = inner.header().unwrap();
+  assert!(header.is_request());
+  let url = header.url().unwrap();
 
   let body = match data {
     None => hyper::Body::empty(),
     Some(buf) => hyper::Body::from(Vec::from(&*buf)),
   };
 
-  let mut req = Request::new(body);
-  let uri = Uri::from_str(&url).map_err(ErrBox::from)?;
-  *req.uri_mut() = uri;
-
-  if let Some(method) = args.method {
-    let method = Method::from_str(&method).unwrap();
-    *req.method_mut() = method;
-  }
-
-  let headers = req.headers_mut();
-  for header_pair in args.headers {
-    let name = HeaderName::from_bytes(header_pair.0.as_bytes()).unwrap();
-    let v = HeaderValue::from_str(&header_pair.1).unwrap();
-    headers.insert(name, v);
-  }
+  let req = msg_util::deserialize_request(header, body)?;
 
-  let url_ = url::Url::parse(&url).map_err(ErrBox::from)?;
+  let url_ = url::Url::parse(url).map_err(ErrBox::from)?;
   state.check_net_url(&url_)?;
 
   let client = http_util::get_client();
@@ -61,22 +42,32 @@ pub fn op_fetch(
     .request(req)
     .map_err(ErrBox::from)
     .and_then(move |res| {
-      let status = res.status().as_u16();
-      let mut res_headers = Vec::new();
-      for (key, val) in res.headers().iter() {
-        res_headers.push((key.to_string(), val.to_str().unwrap().to_owned()));
-      }
+      let builder = &mut FlatBufferBuilder::new();
+      let header_off = msg_util::serialize_http_response(builder, &res);
       let body = res.into_body();
       let body_resource = resources::add_hyper_body(body);
+      let inner = msg::FetchRes::create(
+        builder,
+        &msg::FetchResArgs {
+          header: Some(header_off),
+          body_rid: body_resource.rid,
+        },
+      );
 
-      let json_res = json!({
-        "bodyRid": body_resource.rid,
-        "status": status,
-        "headers": res_headers
-      });
-
-      futures::future::ok(json_res)
+      Ok(serialize_response(
+        cmd_id,
+        builder,
+        msg::BaseArgs {
+          inner: Some(inner.as_union_value()),
+          inner_type: msg::Any::FetchRes,
+          ..Default::default()
+        },
+      ))
     });
-
-  Ok(JsonOp::Async(Box::new(future)))
+  if base.sync() {
+    let result_buf = future.wait()?;
+    Ok(Op::Sync(result_buf))
+  } else {
+    Ok(Op::Async(Box::new(future)))
+  }
 }
diff --git a/cli/ops/files.rs b/cli/ops/files.rs
index c02a69b9c..023bd65f9 100644
--- a/cli/ops/files.rs
+++ b/cli/ops/files.rs
@@ -1,6 +1,5 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 use super::dispatch_flatbuffers::serialize_response;
-use super::dispatch_json::{Deserialize, JsonOp, Value};
 use super::utils::*;
 use crate::deno_error;
 use crate::fs as deno_fs;
@@ -15,22 +14,17 @@ use std;
 use std::convert::From;
 use tokio;
 
-#[derive(Deserialize)]
-#[serde(rename_all = "camelCase")]
-struct OpenArgs {
-  promise_id: Option<u64>,
-  filename: String,
-  mode: String,
-}
-
 pub fn op_open(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: OpenArgs = serde_json::from_value(args)?;
-  let (filename, filename_) = deno_fs::resolve_from_cwd(&args.filename)?;
-  let mode = args.mode.as_ref();
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+  let inner = base.inner_as_open().unwrap();
+  let (filename, filename_) =
+    deno_fs::resolve_from_cwd(inner.filename().unwrap())?;
+  let mode = inner.mode().unwrap();
 
   let mut open_options = tokio::fs::OpenOptions::new();
 
@@ -81,39 +75,44 @@ pub fn op_open(
     }
   }
 
-  let is_sync = args.promise_id.is_none();
   let op = open_options.open(filename).map_err(ErrBox::from).and_then(
     move |fs_file| {
       let resource = resources::add_fs_file(fs_file);
-      futures::future::ok(json!(resource.rid))
+      let builder = &mut FlatBufferBuilder::new();
+      let inner =
+        msg::OpenRes::create(builder, &msg::OpenResArgs { rid: resource.rid });
+      Ok(serialize_response(
+        cmd_id,
+        builder,
+        msg::BaseArgs {
+          inner: Some(inner.as_union_value()),
+          inner_type: msg::Any::OpenRes,
+          ..Default::default()
+        },
+      ))
     },
   );
-
-  if is_sync {
+  if base.sync() {
     let buf = op.wait()?;
-    Ok(JsonOp::Sync(buf))
+    Ok(Op::Sync(buf))
   } else {
-    Ok(JsonOp::Async(Box::new(op)))
+    Ok(Op::Async(Box::new(op)))
   }
 }
 
-#[derive(Deserialize)]
-struct CloseArgs {
-  rid: i32,
-}
-
 pub fn op_close(
   _state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: CloseArgs = serde_json::from_value(args)?;
-
-  match resources::lookup(args.rid as u32) {
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let inner = base.inner_as_close().unwrap();
+  let rid = inner.rid();
+  match resources::lookup(rid) {
     None => Err(deno_error::bad_resource()),
     Some(resource) => {
       resource.close();
-      Ok(JsonOp::Sync(json!({})))
+      ok_buf(empty_buf())
     }
   }
 }
@@ -203,32 +202,27 @@ pub fn op_write(
   }
 }
 
-#[derive(Deserialize)]
-#[serde(rename_all = "camelCase")]
-struct SeekArgs {
-  promise_id: Option<u64>,
-  rid: i32,
-  offset: i32,
-  whence: i32,
-}
-
 pub fn op_seek(
   _state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: SeekArgs = serde_json::from_value(args)?;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let inner = base.inner_as_seek().unwrap();
+  let rid = inner.rid();
+  let offset = inner.offset();
+  let whence = inner.whence();
 
-  match resources::lookup(args.rid as u32) {
+  match resources::lookup(rid) {
     None => Err(deno_error::bad_resource()),
     Some(resource) => {
-      let op = resources::seek(resource, args.offset, args.whence as u32)
-        .and_then(move |_| futures::future::ok(json!({})));
-      if args.promise_id.is_none() {
+      let op = resources::seek(resource, offset, whence)
+        .and_then(move |_| Ok(empty_buf()));
+      if base.sync() {
         let buf = op.wait()?;
-        Ok(JsonOp::Sync(buf))
+        Ok(Op::Sync(buf))
       } else {
-        Ok(JsonOp::Async(Box::new(op)))
+        Ok(Op::Async(Box::new(op)))
       }
     }
   }
diff --git a/cli/ops/metrics.rs b/cli/ops/metrics.rs
index e1a23f6c8..76f36c390 100644
--- a/cli/ops/metrics.rs
+++ b/cli/ops/metrics.rs
@@ -1,21 +1,31 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::*;
+use crate::msg;
 use crate::state::ThreadSafeState;
 use deno::*;
-use std::sync::atomic::Ordering;
+use flatbuffers::FlatBufferBuilder;
 
 pub fn op_metrics(
   state: &ThreadSafeState,
-  _args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let m = &state.metrics;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
 
-  Ok(JsonOp::Sync(json!({
-    "opsDispatched": m.ops_dispatched.load(Ordering::SeqCst) as u64,
-    "opsCompleted": m.ops_completed.load(Ordering::SeqCst) as u64,
-    "bytesSentControl": m.bytes_sent_control.load(Ordering::SeqCst) as u64,
-    "bytesSentData": m.bytes_sent_data.load(Ordering::SeqCst) as u64,
-    "bytesReceived": m.bytes_received.load(Ordering::SeqCst) as u64
-  })))
+  let builder = &mut FlatBufferBuilder::new();
+  let inner = msg::MetricsRes::create(
+    builder,
+    &msg::MetricsResArgs::from(&state.metrics),
+  );
+  ok_buf(serialize_response(
+    cmd_id,
+    builder,
+    msg::BaseArgs {
+      inner: Some(inner.as_union_value()),
+      inner_type: msg::Any::MetricsRes,
+      ..Default::default()
+    },
+  ))
 }
diff --git a/cli/ops/mod.rs b/cli/ops/mod.rs
index 4636754c9..240132960 100644
--- a/cli/ops/mod.rs
+++ b/cli/ops/mod.rs
@@ -34,40 +34,6 @@ pub const OP_IS_TTY: OpId = 4;
 pub const OP_ENV: OpId = 5;
 pub const OP_EXEC_PATH: OpId = 6;
 pub const OP_UTIME: OpId = 7;
-pub const OP_SET_ENV: OpId = 8;
-pub const OP_HOME_DIR: OpId = 9;
-pub const OP_START: OpId = 10;
-pub const OP_APPLY_SOURCE_MAP: OpId = 11;
-pub const OP_FORMAT_ERROR: OpId = 12;
-pub const OP_CACHE: OpId = 13;
-pub const OP_FETCH_SOURCE_FILE: OpId = 14;
-pub const OP_OPEN: OpId = 15;
-pub const OP_CLOSE: OpId = 16;
-pub const OP_SEEK: OpId = 17;
-pub const OP_FETCH: OpId = 18;
-pub const OP_METRICS: OpId = 19;
-pub const OP_REPL_START: OpId = 20;
-pub const OP_REPL_READLINE: OpId = 21;
-pub const OP_ACCEPT: OpId = 22;
-pub const OP_DIAL: OpId = 23;
-pub const OP_SHUTDOWN: OpId = 24;
-pub const OP_LISTEN: OpId = 25;
-pub const OP_RESOURCES: OpId = 26;
-pub const OP_GET_RANDOM_VALUES: OpId = 27;
-pub const OP_GLOBAL_TIMER_STOP: OpId = 28;
-pub const OP_GLOBAL_TIMER: OpId = 29;
-pub const OP_NOW: OpId = 30;
-pub const OP_PERMISSIONS: OpId = 31;
-pub const OP_REVOKE_PERMISSION: OpId = 32;
-pub const OP_CREATE_WORKER: OpId = 33;
-pub const OP_HOST_GET_WORKER_CLOSED: OpId = 34;
-pub const OP_HOST_POST_MESSAGE: OpId = 35;
-pub const OP_HOST_GET_MESSAGE: OpId = 36;
-pub const OP_WORKER_POST_MESSAGE: OpId = 37;
-pub const OP_WORKER_GET_MESSAGE: OpId = 38;
-pub const OP_RUN: OpId = 39;
-pub const OP_RUN_STATUS: OpId = 40;
-pub const OP_KILL: OpId = 41;
 
 pub fn dispatch(
   state: &ThreadSafeState,
@@ -93,155 +59,9 @@ pub fn dispatch(
     OP_EXEC_PATH => {
       dispatch_json::dispatch(os::op_exec_path, state, control, zero_copy)
     }
-    OP_HOME_DIR => {
-      dispatch_json::dispatch(os::op_home_dir, state, control, zero_copy)
-    }
     OP_UTIME => {
       dispatch_json::dispatch(fs::op_utime, state, control, zero_copy)
     }
-    OP_SET_ENV => {
-      dispatch_json::dispatch(os::op_set_env, state, control, zero_copy)
-    }
-    OP_START => {
-      dispatch_json::dispatch(os::op_start, state, control, zero_copy)
-    }
-    OP_APPLY_SOURCE_MAP => dispatch_json::dispatch(
-      errors::op_apply_source_map,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_FORMAT_ERROR => dispatch_json::dispatch(
-      errors::op_format_error,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_CACHE => {
-      dispatch_json::dispatch(compiler::op_cache, state, control, zero_copy)
-    }
-    OP_FETCH_SOURCE_FILE => dispatch_json::dispatch(
-      compiler::op_fetch_source_file,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_OPEN => {
-      dispatch_json::dispatch(files::op_open, state, control, zero_copy)
-    }
-    OP_CLOSE => {
-      dispatch_json::dispatch(files::op_close, state, control, zero_copy)
-    }
-    OP_SEEK => {
-      dispatch_json::dispatch(files::op_seek, state, control, zero_copy)
-    }
-    OP_METRICS => {
-      dispatch_json::dispatch(metrics::op_metrics, state, control, zero_copy)
-    }
-    OP_FETCH => {
-      dispatch_json::dispatch(fetch::op_fetch, state, control, zero_copy)
-    }
-    OP_REPL_START => {
-      dispatch_json::dispatch(repl::op_repl_start, state, control, zero_copy)
-    }
-    OP_REPL_READLINE => {
-      dispatch_json::dispatch(repl::op_repl_readline, state, control, zero_copy)
-    }
-    OP_ACCEPT => {
-      dispatch_json::dispatch(net::op_accept, state, control, zero_copy)
-    }
-    OP_DIAL => dispatch_json::dispatch(net::op_dial, state, control, zero_copy),
-    OP_SHUTDOWN => {
-      dispatch_json::dispatch(net::op_shutdown, state, control, zero_copy)
-    }
-    OP_LISTEN => {
-      dispatch_json::dispatch(net::op_listen, state, control, zero_copy)
-    }
-    OP_RESOURCES => dispatch_json::dispatch(
-      resources::op_resources,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_GET_RANDOM_VALUES => dispatch_json::dispatch(
-      random::op_get_random_values,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_GLOBAL_TIMER_STOP => dispatch_json::dispatch(
-      timers::op_global_timer_stop,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_GLOBAL_TIMER => dispatch_json::dispatch(
-      timers::op_global_timer,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_NOW => {
-      dispatch_json::dispatch(performance::op_now, state, control, zero_copy)
-    }
-    OP_PERMISSIONS => dispatch_json::dispatch(
-      permissions::op_permissions,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_REVOKE_PERMISSION => dispatch_json::dispatch(
-      permissions::op_revoke_permission,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_CREATE_WORKER => dispatch_json::dispatch(
-      workers::op_create_worker,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_HOST_GET_WORKER_CLOSED => dispatch_json::dispatch(
-      workers::op_host_get_worker_closed,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_HOST_POST_MESSAGE => dispatch_json::dispatch(
-      workers::op_host_post_message,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_HOST_GET_MESSAGE => dispatch_json::dispatch(
-      workers::op_host_get_message,
-      state,
-      control,
-      zero_copy,
-    ),
-    // TODO: make sure these two ops are only accessible to appropriate Workers
-    OP_WORKER_POST_MESSAGE => dispatch_json::dispatch(
-      workers::op_worker_post_message,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_WORKER_GET_MESSAGE => dispatch_json::dispatch(
-      workers::op_worker_get_message,
-      state,
-      control,
-      zero_copy,
-    ),
-    OP_RUN => {
-      dispatch_json::dispatch(process::op_run, state, control, zero_copy)
-    }
-    OP_RUN_STATUS => {
-      dispatch_json::dispatch(process::op_run_status, state, control, zero_copy)
-    }
-    OP_KILL => {
-      dispatch_json::dispatch(process::op_kill, state, control, zero_copy)
-    }
     OP_FLATBUFFER => dispatch_flatbuffers::dispatch(state, control, zero_copy),
     _ => panic!("bad op_id"),
   };
diff --git a/cli/ops/net.rs b/cli/ops/net.rs
index 650127fad..5ce562492 100644
--- a/cli/ops/net.rs
+++ b/cli/ops/net.rs
@@ -1,12 +1,15 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{Deserialize, JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::*;
 use crate::deno_error;
+use crate::msg;
 use crate::resolve_addr::resolve_addr;
 use crate::resources;
 use crate::resources::Resource;
 use crate::state::ThreadSafeState;
 use crate::tokio_util;
 use deno::*;
+use flatbuffers::FlatBufferBuilder;
 use futures::Future;
 use std;
 use std::convert::From;
@@ -15,18 +18,15 @@ use tokio;
 use tokio::net::TcpListener;
 use tokio::net::TcpStream;
 
-#[derive(Deserialize)]
-struct AcceptArgs {
-  rid: i32,
-}
-
 pub fn op_accept(
   _state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: AcceptArgs = serde_json::from_value(args)?;
-  let server_rid = args.rid as u32;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+  let inner = base.inner_as_accept().unwrap();
+  let server_rid = inner.rid();
 
   match resources::lookup(server_rid) {
     None => Err(deno_error::bad_resource()),
@@ -34,65 +34,55 @@ pub fn op_accept(
       let op = tokio_util::accept(server_resource)
         .map_err(ErrBox::from)
         .and_then(move |(tcp_stream, _socket_addr)| {
-          let tcp_stream_resource = resources::add_tcp_stream(tcp_stream);
-          futures::future::ok(json!({
-            "rid": tcp_stream_resource.rid
-          }))
+          new_conn(cmd_id, tcp_stream)
         });
-
-      Ok(JsonOp::Async(Box::new(op)))
+      if base.sync() {
+        let buf = op.wait()?;
+        Ok(Op::Sync(buf))
+      } else {
+        Ok(Op::Async(Box::new(op)))
+      }
     }
   }
 }
 
-#[derive(Deserialize)]
-struct DialArgs {
-  network: String,
-  address: String,
-}
-
 pub fn op_dial(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: DialArgs = serde_json::from_value(args)?;
-  let network = args.network;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+  let inner = base.inner_as_dial().unwrap();
+  let network = inner.network().unwrap();
   assert_eq!(network, "tcp"); // TODO Support others.
-  let address = args.address;
+  let address = inner.address().unwrap();
 
   state.check_net(&address)?;
 
-  let op = resolve_addr(&address).and_then(move |addr| {
-    TcpStream::connect(&addr).map_err(ErrBox::from).and_then(
-      move |tcp_stream| {
-        let tcp_stream_resource = resources::add_tcp_stream(tcp_stream);
-        futures::future::ok(json!({
-          "rid": tcp_stream_resource.rid
-        }))
-      },
-    )
+  let op = resolve_addr(address).and_then(move |addr| {
+    TcpStream::connect(&addr)
+      .map_err(ErrBox::from)
+      .and_then(move |tcp_stream| new_conn(cmd_id, tcp_stream))
   });
-
-  Ok(JsonOp::Async(Box::new(op)))
-}
-
-#[derive(Deserialize)]
-struct ShutdownArgs {
-  rid: i32,
-  how: i32,
+  if base.sync() {
+    let buf = op.wait()?;
+    Ok(Op::Sync(buf))
+  } else {
+    Ok(Op::Async(Box::new(op)))
+  }
 }
 
 pub fn op_shutdown(
   _state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: ShutdownArgs = serde_json::from_value(args)?;
-
-  let rid = args.rid;
-  let how = args.how;
-  match resources::lookup(rid as u32) {
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let inner = base.inner_as_shutdown().unwrap();
+  let rid = inner.rid();
+  let how = inner.how();
+  match resources::lookup(rid) {
     None => Err(deno_error::bad_resource()),
     Some(mut resource) => {
       let shutdown_mode = match how {
@@ -100,36 +90,67 @@ pub fn op_shutdown(
         1 => Shutdown::Write,
         _ => unimplemented!(),
       };
-
-      // Use UFCS for disambiguation
-      Resource::shutdown(&mut resource, shutdown_mode)?;
-      Ok(JsonOp::Sync(json!({})))
+      blocking(base.sync(), move || {
+        // Use UFCS for disambiguation
+        Resource::shutdown(&mut resource, shutdown_mode)?;
+        Ok(empty_buf())
+      })
     }
   }
 }
 
-#[derive(Deserialize)]
-struct ListenArgs {
-  network: String,
-  address: String,
-}
-
 pub fn op_listen(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: ListenArgs = serde_json::from_value(args)?;
-
-  let network = args.network;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+  let inner = base.inner_as_listen().unwrap();
+  let network = inner.network().unwrap();
   assert_eq!(network, "tcp");
-  let address = args.address;
+  let address = inner.address().unwrap();
 
   state.check_net(&address)?;
 
-  let addr = resolve_addr(&address).wait()?;
+  let addr = resolve_addr(address).wait()?;
   let listener = TcpListener::bind(&addr)?;
   let resource = resources::add_tcp_listener(listener);
 
-  Ok(JsonOp::Sync(json!(resource.rid)))
+  let builder = &mut FlatBufferBuilder::new();
+  let inner =
+    msg::ListenRes::create(builder, &msg::ListenResArgs { rid: resource.rid });
+  let response_buf = serialize_response(
+    cmd_id,
+    builder,
+    msg::BaseArgs {
+      inner: Some(inner.as_union_value()),
+      inner_type: msg::Any::ListenRes,
+      ..Default::default()
+    },
+  );
+  ok_buf(response_buf)
+}
+
+fn new_conn(cmd_id: u32, tcp_stream: TcpStream) -> Result<Buf, ErrBox> {
+  let tcp_stream_resource = resources::add_tcp_stream(tcp_stream);
+  // TODO forward socket_addr to client.
+
+  let builder = &mut FlatBufferBuilder::new();
+  let inner = msg::NewConn::create(
+    builder,
+    &msg::NewConnArgs {
+      rid: tcp_stream_resource.rid,
+      ..Default::default()
+    },
+  );
+  Ok(serialize_response(
+    cmd_id,
+    builder,
+    msg::BaseArgs {
+      inner: Some(inner.as_union_value()),
+      inner_type: msg::Any::NewConn,
+      ..Default::default()
+    },
+  ))
 }
diff --git a/cli/ops/os.rs b/cli/ops/os.rs
index afb87539f..53ef63c60 100644
--- a/cli/ops/os.rs
+++ b/cli/ops/os.rs
@@ -1,11 +1,15 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+use super::dispatch_flatbuffers::serialize_response;
 use super::dispatch_json::{Deserialize, JsonOp, Value};
+use super::utils::*;
 use crate::ansi;
 use crate::fs as deno_fs;
+use crate::msg;
 use crate::state::ThreadSafeState;
 use crate::version;
 use atty;
 use deno::*;
+use flatbuffers::FlatBufferBuilder;
 use log;
 use std::collections::HashMap;
 use std::env;
@@ -13,38 +17,97 @@ use url::Url;
 
 pub fn op_start(
   state: &ThreadSafeState,
-  _args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  Ok(JsonOp::Sync(json!({
-    "cwd": deno_fs::normalize_path(&env::current_dir().unwrap()),
-    "pid": std::process::id(),
-    "argv": state.argv,
-    "mainModule": state.main_module().map(|x| x.as_str().to_string()),
-    "debugFlag": state
-      .flags
-      .log_level
-      .map_or(false, |l| l == log::Level::Debug),
-    "versionFlag": state.flags.version,
-    "v8Version": version::v8(),
-    "denoVersion": version::DENO,
-    "noColor": !ansi::use_color(),
-    "xevalDelim": state.flags.xeval_delim.clone(),
-  })))
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let mut builder = FlatBufferBuilder::new();
+
+  let state = state;
+  let argv = state.argv.iter().map(String::as_str).collect::<Vec<_>>();
+  let argv_off = builder.create_vector_of_strings(argv.as_slice());
+
+  let cwd_path = env::current_dir().unwrap();
+  let cwd_off =
+    builder.create_string(deno_fs::normalize_path(cwd_path.as_ref()).as_ref());
+
+  let v8_version = version::v8();
+  let v8_version_off = builder.create_string(v8_version);
+
+  let deno_version = version::DENO;
+  let deno_version_off = builder.create_string(deno_version);
+
+  let main_module = state
+    .main_module()
+    .map(|m| builder.create_string(&m.to_string()));
+
+  let xeval_delim = state
+    .flags
+    .xeval_delim
+    .clone()
+    .map(|m| builder.create_string(&m));
+
+  let debug_flag = state
+    .flags
+    .log_level
+    .map_or(false, |l| l == log::Level::Debug);
+
+  let inner = msg::StartRes::create(
+    &mut builder,
+    &msg::StartResArgs {
+      cwd: Some(cwd_off),
+      pid: std::process::id(),
+      argv: Some(argv_off),
+      main_module,
+      debug_flag,
+      version_flag: state.flags.version,
+      v8_version: Some(v8_version_off),
+      deno_version: Some(deno_version_off),
+      no_color: !ansi::use_color(),
+      xeval_delim,
+      ..Default::default()
+    },
+  );
+
+  ok_buf(serialize_response(
+    base.cmd_id(),
+    &mut builder,
+    msg::BaseArgs {
+      inner_type: msg::Any::StartRes,
+      inner: Some(inner.as_union_value()),
+      ..Default::default()
+    },
+  ))
 }
 
 pub fn op_home_dir(
   state: &ThreadSafeState,
-  _args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+
   state.check_env()?;
+
+  let builder = &mut FlatBufferBuilder::new();
   let path = dirs::home_dir()
     .unwrap_or_default()
     .into_os_string()
     .into_string()
     .unwrap_or_default();
-  Ok(JsonOp::Sync(json!(path)))
+  let path = Some(builder.create_string(&path));
+  let inner = msg::HomeDirRes::create(builder, &msg::HomeDirResArgs { path });
+
+  ok_buf(serialize_response(
+    cmd_id,
+    builder,
+    msg::BaseArgs {
+      inner: Some(inner.as_union_value()),
+      inner_type: msg::Any::HomeDirRes,
+      ..Default::default()
+    },
+  ))
 }
 
 pub fn op_exec_path(
@@ -61,21 +124,18 @@ pub fn op_exec_path(
   Ok(JsonOp::Sync(json!(path)))
 }
 
-#[derive(Deserialize)]
-struct SetEnv {
-  key: String,
-  value: String,
-}
-
 pub fn op_set_env(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: SetEnv = serde_json::from_value(args)?;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let inner = base.inner_as_set_env().unwrap();
+  let key = inner.key().unwrap();
+  let value = inner.value().unwrap();
   state.check_env()?;
-  env::set_var(args.key, args.value);
-  Ok(JsonOp::Sync(json!({})))
+  env::set_var(key, value);
+  ok_buf(empty_buf())
 }
 
 pub fn op_env(
diff --git a/cli/ops/performance.rs b/cli/ops/performance.rs
index 090fc3323..94f6dbc38 100644
--- a/cli/ops/performance.rs
+++ b/cli/ops/performance.rs
@@ -1,7 +1,10 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::*;
+use crate::msg;
 use crate::state::ThreadSafeState;
 use deno::*;
+use flatbuffers::FlatBufferBuilder;
 
 // Returns a milliseconds and nanoseconds subsec
 // since the start time of the deno runtime.
@@ -9,9 +12,10 @@ use deno::*;
 // nanoseconds are rounded on 2ms.
 pub fn op_now(
   state: &ThreadSafeState,
-  _args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
   let seconds = state.start_time.elapsed().as_secs();
   let mut subsec_nanos = state.start_time.elapsed().subsec_nanos();
   let reduced_time_precision = 2_000_000; // 2ms in nanoseconds
@@ -23,8 +27,22 @@ pub fn op_now(
     subsec_nanos -= subsec_nanos % reduced_time_precision
   }
 
-  Ok(JsonOp::Sync(json!({
-    "seconds": seconds,
-    "subsecNanos": subsec_nanos,
-  })))
+  let builder = &mut FlatBufferBuilder::new();
+  let inner = msg::NowRes::create(
+    builder,
+    &msg::NowResArgs {
+      seconds,
+      subsec_nanos,
+    },
+  );
+
+  ok_buf(serialize_response(
+    base.cmd_id(),
+    builder,
+    msg::BaseArgs {
+      inner: Some(inner.as_union_value()),
+      inner_type: msg::Any::NowRes,
+      ..Default::default()
+    },
+  ))
 }
diff --git a/cli/ops/permissions.rs b/cli/ops/permissions.rs
index 5d14f39be..6249581fb 100644
--- a/cli/ops/permissions.rs
+++ b/cli/ops/permissions.rs
@@ -1,35 +1,50 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{Deserialize, JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::*;
+use crate::msg;
 use crate::state::ThreadSafeState;
 use deno::*;
+use flatbuffers::FlatBufferBuilder;
 
 pub fn op_permissions(
   state: &ThreadSafeState,
-  _args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  Ok(JsonOp::Sync(json!({
-    "run": state.permissions.allows_run(),
-    "read": state.permissions.allows_read(),
-    "write": state.permissions.allows_write(),
-    "net": state.permissions.allows_net(),
-    "env": state.permissions.allows_env(),
-    "hrtime": state.permissions.allows_hrtime(),
-  })))
-}
-
-#[derive(Deserialize)]
-struct RevokePermissionArgs {
-  permission: String,
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+  let builder = &mut FlatBufferBuilder::new();
+  let inner = msg::PermissionsRes::create(
+    builder,
+    &msg::PermissionsResArgs {
+      run: state.permissions.allows_run(),
+      read: state.permissions.allows_read(),
+      write: state.permissions.allows_write(),
+      net: state.permissions.allows_net(),
+      env: state.permissions.allows_env(),
+      hrtime: state.permissions.allows_hrtime(),
+    },
+  );
+  let response_buf = serialize_response(
+    cmd_id,
+    builder,
+    msg::BaseArgs {
+      inner: Some(inner.as_union_value()),
+      inner_type: msg::Any::PermissionsRes,
+      ..Default::default()
+    },
+  );
+  ok_buf(response_buf)
 }
 
 pub fn op_revoke_permission(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: RevokePermissionArgs = serde_json::from_value(args)?;
-  let permission = args.permission.as_ref();
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let inner = base.inner_as_permission_revoke().unwrap();
+  let permission = inner.permission().unwrap();
   match permission {
     "run" => state.permissions.revoke_run(),
     "read" => state.permissions.revoke_read(),
@@ -39,6 +54,5 @@ pub fn op_revoke_permission(
     "hrtime" => state.permissions.revoke_hrtime(),
     _ => Ok(()),
   }?;
-
-  Ok(JsonOp::Sync(json!({})))
+  ok_buf(empty_buf())
 }
diff --git a/cli/ops/process.rs b/cli/ops/process.rs
index 8dff53c6e..d7b326d14 100644
--- a/cli/ops/process.rs
+++ b/cli/ops/process.rs
@@ -1,9 +1,13 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{Deserialize, JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::*;
+use crate::deno_error;
+use crate::msg;
 use crate::resources;
 use crate::signal::kill;
 use crate::state::ThreadSafeState;
 use deno::*;
+use flatbuffers::FlatBufferBuilder;
 use futures;
 use futures::Future;
 use std;
@@ -14,72 +18,63 @@ use tokio_process::CommandExt;
 #[cfg(unix)]
 use std::os::unix::process::ExitStatusExt;
 
-fn subprocess_stdio_map(s: &str) -> std::process::Stdio {
-  match s {
-    "inherit" => std::process::Stdio::inherit(),
-    "piped" => std::process::Stdio::piped(),
-    "null" => std::process::Stdio::null(),
-    _ => unreachable!(),
+fn subprocess_stdio_map(v: msg::ProcessStdio) -> std::process::Stdio {
+  match v {
+    msg::ProcessStdio::Inherit => std::process::Stdio::inherit(),
+    msg::ProcessStdio::Piped => std::process::Stdio::piped(),
+    msg::ProcessStdio::Null => std::process::Stdio::null(),
   }
 }
 
-#[derive(Deserialize)]
-#[serde(rename_all = "camelCase")]
-struct RunArgs {
-  args: Vec<String>,
-  cwd: Option<String>,
-  env: Vec<(String, String)>,
-  stdin: String,
-  stdout: String,
-  stderr: String,
-  stdin_rid: u32,
-  stdout_rid: u32,
-  stderr_rid: u32,
-}
-
 pub fn op_run(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let run_args: RunArgs = serde_json::from_value(args)?;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  if !base.sync() {
+    return Err(deno_error::no_async_support());
+  }
+  let cmd_id = base.cmd_id();
 
   state.check_run()?;
 
-  let args = run_args.args;
-  let env = run_args.env;
-  let cwd = run_args.cwd;
+  assert!(data.is_none());
+  let inner = base.inner_as_run().unwrap();
+  let args = inner.args().unwrap();
+  let env = inner.env().unwrap();
+  let cwd = inner.cwd();
 
-  let mut c = Command::new(args.get(0).unwrap());
+  let mut c = Command::new(args.get(0));
   (1..args.len()).for_each(|i| {
-    let arg = args.get(i).unwrap();
+    let arg = args.get(i);
     c.arg(arg);
   });
   cwd.map(|d| c.current_dir(d));
-  for (key, value) in &env {
-    c.env(key, value);
-  }
+  (0..env.len()).for_each(|i| {
+    let entry = env.get(i);
+    c.env(entry.key().unwrap(), entry.value().unwrap());
+  });
 
   // TODO: make this work with other resources, eg. sockets
-  let stdin_rid = run_args.stdin_rid;
+  let stdin_rid = inner.stdin_rid();
   if stdin_rid > 0 {
     c.stdin(resources::get_file(stdin_rid)?);
   } else {
-    c.stdin(subprocess_stdio_map(run_args.stdin.as_ref()));
+    c.stdin(subprocess_stdio_map(inner.stdin()));
   }
 
-  let stdout_rid = run_args.stdout_rid;
+  let stdout_rid = inner.stdout_rid();
   if stdout_rid > 0 {
     c.stdout(resources::get_file(stdout_rid)?);
   } else {
-    c.stdout(subprocess_stdio_map(run_args.stdout.as_ref()));
+    c.stdout(subprocess_stdio_map(inner.stdout()));
   }
 
-  let stderr_rid = run_args.stderr_rid;
+  let stderr_rid = inner.stderr_rid();
   if stderr_rid > 0 {
     c.stderr(resources::get_file(stderr_rid)?);
   } else {
-    c.stderr(subprocess_stdio_map(run_args.stderr.as_ref()));
+    c.stderr(subprocess_stdio_map(inner.stderr()));
   }
 
   // Spawn the command.
@@ -88,28 +83,44 @@ pub fn op_run(
   let pid = child.id();
   let resources = resources::add_child(child);
 
-  Ok(JsonOp::Sync(json!({
-    "rid": resources.child_rid,
-    "pid": pid,
-    "stdinRid": resources.stdin_rid,
-    "stdoutRid": resources.stdout_rid,
-    "stderrRid": resources.stderr_rid,
-  })))
-}
+  let mut res_args = msg::RunResArgs {
+    rid: resources.child_rid,
+    pid,
+    ..Default::default()
+  };
 
-#[derive(Deserialize)]
-#[serde(rename_all = "camelCase")]
-struct RunStatusArgs {
-  rid: i32,
+  if let Some(stdin_rid) = resources.stdin_rid {
+    res_args.stdin_rid = stdin_rid;
+  }
+  if let Some(stdout_rid) = resources.stdout_rid {
+    res_args.stdout_rid = stdout_rid;
+  }
+  if let Some(stderr_rid) = resources.stderr_rid {
+    res_args.stderr_rid = stderr_rid;
+  }
+
+  let builder = &mut FlatBufferBuilder::new();
+  let inner = msg::RunRes::create(builder, &res_args);
+  Ok(Op::Sync(serialize_response(
+    cmd_id,
+    builder,
+    msg::BaseArgs {
+      inner: Some(inner.as_union_value()),
+      inner_type: msg::Any::RunRes,
+      ..Default::default()
+    },
+  )))
 }
 
 pub fn op_run_status(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: RunStatusArgs = serde_json::from_value(args)?;
-  let rid = args.rid as u32;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+  let inner = base.inner_as_run_status().unwrap();
+  let rid = inner.rid();
 
   state.check_run()?;
 
@@ -128,30 +139,44 @@ pub fn op_run_status(
       .expect("Should have either an exit code or a signal.");
     let got_signal = signal.is_some();
 
-    futures::future::ok(json!({
-      "gotSignal": got_signal,
-       "exitCode": code.unwrap_or(-1),
-       "exitSignal": signal.unwrap_or(-1),
-    }))
+    let builder = &mut FlatBufferBuilder::new();
+    let inner = msg::RunStatusRes::create(
+      builder,
+      &msg::RunStatusResArgs {
+        got_signal,
+        exit_code: code.unwrap_or(-1),
+        exit_signal: signal.unwrap_or(-1),
+      },
+    );
+    Ok(serialize_response(
+      cmd_id,
+      builder,
+      msg::BaseArgs {
+        inner: Some(inner.as_union_value()),
+        inner_type: msg::Any::RunStatusRes,
+        ..Default::default()
+      },
+    ))
   });
-
-  Ok(JsonOp::Async(Box::new(future)))
-}
-
-#[derive(Deserialize)]
-struct KillArgs {
-  pid: i32,
-  signo: i32,
+  if base.sync() {
+    let buf = future.wait()?;
+    Ok(Op::Sync(buf))
+  } else {
+    Ok(Op::Async(Box::new(future)))
+  }
 }
 
 pub fn op_kill(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
   state.check_run()?;
 
-  let args: KillArgs = serde_json::from_value(args)?;
-  kill(args.pid, args.signo)?;
-  Ok(JsonOp::Sync(json!({})))
+  assert!(data.is_none());
+  let inner = base.inner_as_kill().unwrap();
+  let pid = inner.pid();
+  let signo = inner.signo();
+  kill(pid, signo)?;
+  ok_buf(empty_buf())
 }
diff --git a/cli/ops/random.rs b/cli/ops/random.rs
index 7470eab40..0c302a080 100644
--- a/cli/ops/random.rs
+++ b/cli/ops/random.rs
@@ -1,5 +1,6 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{JsonOp, Value};
+use super::utils::*;
+use crate::msg;
 use crate::state::ThreadSafeState;
 use deno::*;
 use rand::thread_rng;
@@ -7,18 +8,16 @@ use rand::Rng;
 
 pub fn op_get_random_values(
   state: &ThreadSafeState,
-  _args: Value,
-  zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  assert!(zero_copy.is_some());
-
+  _base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
   if let Some(ref seeded_rng) = state.seeded_rng {
     let mut rng = seeded_rng.lock().unwrap();
-    rng.fill(&mut zero_copy.unwrap()[..]);
+    rng.fill(&mut data.unwrap()[..]);
   } else {
     let mut rng = thread_rng();
-    rng.fill(&mut zero_copy.unwrap()[..]);
+    rng.fill(&mut data.unwrap()[..]);
   }
 
-  Ok(JsonOp::Sync(json!({})))
+  ok_buf(empty_buf())
 }
diff --git a/cli/ops/repl.rs b/cli/ops/repl.rs
index 7ab7509de..affe78739 100644
--- a/cli/ops/repl.rs
+++ b/cli/ops/repl.rs
@@ -1,50 +1,78 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{blocking_json, Deserialize, JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::blocking;
+use super::utils::ok_buf;
+use super::utils::CliOpResult;
+use crate::msg;
 use crate::repl;
 use crate::resources;
 use crate::state::ThreadSafeState;
 use deno::*;
-
-#[derive(Deserialize)]
-#[serde(rename_all = "camelCase")]
-struct ReplStartArgs {
-  history_file: String,
-}
+use flatbuffers::FlatBufferBuilder;
 
 pub fn op_repl_start(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: ReplStartArgs = serde_json::from_value(args)?;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let inner = base.inner_as_repl_start().unwrap();
+  let cmd_id = base.cmd_id();
+  let history_file = String::from(inner.history_file().unwrap());
 
-  debug!("op_repl_start {}", args.history_file);
-  let history_path = repl::history_path(&state.dir, &args.history_file);
+  debug!("op_repl_start {}", history_file);
+  let history_path = repl::history_path(&state.dir, &history_file);
   let repl = repl::Repl::new(history_path);
   let resource = resources::add_repl(repl);
 
-  Ok(JsonOp::Sync(json!(resource.rid)))
-}
-
-#[derive(Deserialize)]
-struct ReplReadlineArgs {
-  rid: i32,
-  prompt: String,
+  let builder = &mut FlatBufferBuilder::new();
+  let inner = msg::ReplStartRes::create(
+    builder,
+    &msg::ReplStartResArgs { rid: resource.rid },
+  );
+  ok_buf(serialize_response(
+    cmd_id,
+    builder,
+    msg::BaseArgs {
+      inner: Some(inner.as_union_value()),
+      inner_type: msg::Any::ReplStartRes,
+      ..Default::default()
+    },
+  ))
 }
 
 pub fn op_repl_readline(
   _state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: ReplReadlineArgs = serde_json::from_value(args)?;
-  let rid = args.rid;
-  let prompt = args.prompt;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let inner = base.inner_as_repl_readline().unwrap();
+  let cmd_id = base.cmd_id();
+  let rid = inner.rid();
+  let prompt = inner.prompt().unwrap().to_owned();
   debug!("op_repl_readline {} {}", rid, prompt);
 
-  blocking_json(false, move || {
-    let repl = resources::get_repl(rid as u32)?;
+  blocking(base.sync(), move || {
+    let repl = resources::get_repl(rid)?;
     let line = repl.lock().unwrap().readline(&prompt)?;
-    Ok(json!(line))
+
+    let builder = &mut FlatBufferBuilder::new();
+    let line_off = builder.create_string(&line);
+    let inner = msg::ReplReadlineRes::create(
+      builder,
+      &msg::ReplReadlineResArgs {
+        line: Some(line_off),
+      },
+    );
+    Ok(serialize_response(
+      cmd_id,
+      builder,
+      msg::BaseArgs {
+        inner: Some(inner.as_union_value()),
+        inner_type: msg::Any::ReplReadlineRes,
+        ..Default::default()
+      },
+    ))
   })
 }
diff --git a/cli/ops/resources.rs b/cli/ops/resources.rs
index dafd01d08..975d94490 100644
--- a/cli/ops/resources.rs
+++ b/cli/ops/resources.rs
@@ -1,14 +1,54 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::ok_buf;
+use super::utils::CliOpResult;
+use crate::msg;
 use crate::resources::table_entries;
 use crate::state::ThreadSafeState;
 use deno::*;
+use flatbuffers::FlatBufferBuilder;
 
 pub fn op_resources(
   _state: &ThreadSafeState,
-  _args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+
+  let builder = &mut FlatBufferBuilder::new();
   let serialized_resources = table_entries();
-  Ok(JsonOp::Sync(json!(serialized_resources)))
+
+  let res: Vec<_> = serialized_resources
+    .iter()
+    .map(|(key, value)| {
+      let repr = builder.create_string(value);
+
+      msg::Resource::create(
+        builder,
+        &msg::ResourceArgs {
+          rid: *key,
+          repr: Some(repr),
+        },
+      )
+    })
+    .collect();
+
+  let resources = builder.create_vector(&res);
+  let inner = msg::ResourcesRes::create(
+    builder,
+    &msg::ResourcesResArgs {
+      resources: Some(resources),
+    },
+  );
+
+  ok_buf(serialize_response(
+    cmd_id,
+    builder,
+    msg::BaseArgs {
+      inner: Some(inner.as_union_value()),
+      inner_type: msg::Any::ResourcesRes,
+      ..Default::default()
+    },
+  ))
 }
diff --git a/cli/ops/timers.rs b/cli/ops/timers.rs
index 46217a188..550d91f2c 100644
--- a/cli/ops/timers.rs
+++ b/cli/ops/timers.rs
@@ -1,7 +1,12 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{Deserialize, JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::empty_buf;
+use super::utils::CliOpResult;
+use crate::deno_error;
+use crate::msg;
 use crate::state::ThreadSafeState;
 use deno::*;
+use flatbuffers::FlatBufferBuilder;
 use futures::Future;
 use std;
 use std::time::Duration;
@@ -9,34 +14,50 @@ use std::time::Instant;
 
 pub fn op_global_timer_stop(
   state: &ThreadSafeState,
-  _args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  if !base.sync() {
+    return Err(deno_error::no_async_support());
+  }
+  assert!(data.is_none());
   let state = state;
   let mut t = state.global_timer.lock().unwrap();
   t.cancel();
-  Ok(JsonOp::Sync(json!({})))
-}
-
-#[derive(Deserialize)]
-struct GlobalTimerArgs {
-  timeout: u64,
+  Ok(Op::Sync(empty_buf()))
 }
 
 pub fn op_global_timer(
   state: &ThreadSafeState,
-  args: Value,
-  _zero_copy: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: GlobalTimerArgs = serde_json::from_value(args)?;
-  let val = args.timeout;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  if base.sync() {
+    return Err(deno_error::no_sync_support());
+  }
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+  let inner = base.inner_as_global_timer().unwrap();
+  let val = inner.timeout();
+  assert!(val >= 0);
 
   let state = state;
   let mut t = state.global_timer.lock().unwrap();
   let deadline = Instant::now() + Duration::from_millis(val as u64);
-  let f = t
-    .new_timeout(deadline)
-    .then(move |_| futures::future::ok(json!({})));
+  let f = t.new_timeout(deadline);
 
-  Ok(JsonOp::Async(Box::new(f)))
+  Ok(Op::Async(Box::new(f.then(move |_| {
+    let builder = &mut FlatBufferBuilder::new();
+    let inner =
+      msg::GlobalTimerRes::create(builder, &msg::GlobalTimerResArgs {});
+    Ok(serialize_response(
+      cmd_id,
+      builder,
+      msg::BaseArgs {
+        inner: Some(inner.as_union_value()),
+        inner_type: msg::Any::GlobalTimerRes,
+        ..Default::default()
+      },
+    ))
+  }))))
 }
diff --git a/cli/ops/workers.rs b/cli/ops/workers.rs
index 4eeecd068..1eb11420f 100644
--- a/cli/ops/workers.rs
+++ b/cli/ops/workers.rs
@@ -1,12 +1,17 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use super::dispatch_json::{Deserialize, JsonOp, Value};
+use super::dispatch_flatbuffers::serialize_response;
+use super::utils::ok_buf;
+use super::utils::CliOpResult;
+use crate::deno_error;
 use crate::deno_error::DenoError;
 use crate::deno_error::ErrorKind;
+use crate::msg;
 use crate::resources;
 use crate::startup_data;
 use crate::state::ThreadSafeState;
 use crate::worker::Worker;
 use deno::*;
+use flatbuffers::FlatBufferBuilder;
 use futures;
 use futures::Async;
 use futures::Future;
@@ -34,32 +39,48 @@ impl Future for GetMessageFuture {
 /// Get message from host as guest worker
 pub fn op_worker_get_message(
   state: &ThreadSafeState,
-  _args: Value,
-  _data: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  if base.sync() {
+    return Err(deno_error::no_sync_support());
+  }
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+
   let op = GetMessageFuture {
     state: state.clone(),
   };
-
-  let op = op
-    .map_err(move |_| -> ErrBox { unimplemented!() })
-    .and_then(move |maybe_buf| {
-      debug!("op_worker_get_message");
-
-      futures::future::ok(json!({
-        "data": maybe_buf.map(|buf| buf.to_owned())
-      }))
-    });
-
-  Ok(JsonOp::Async(Box::new(op)))
+  let op = op.map_err(move |_| -> ErrBox { unimplemented!() });
+  let op = op.and_then(move |maybe_buf| -> Result<Buf, ErrBox> {
+    debug!("op_worker_get_message");
+    let builder = &mut FlatBufferBuilder::new();
+
+    let data = maybe_buf.as_ref().map(|buf| builder.create_vector(buf));
+    let inner = msg::WorkerGetMessageRes::create(
+      builder,
+      &msg::WorkerGetMessageResArgs { data },
+    );
+    Ok(serialize_response(
+      cmd_id,
+      builder,
+      msg::BaseArgs {
+        inner: Some(inner.as_union_value()),
+        inner_type: msg::Any::WorkerGetMessageRes,
+        ..Default::default()
+      },
+    ))
+  });
+  Ok(Op::Async(Box::new(op)))
 }
 
 /// Post message to host as guest worker
 pub fn op_worker_post_message(
   state: &ThreadSafeState,
-  _args: Value,
+  base: &msg::Base<'_>,
   data: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
+) -> CliOpResult {
+  let cmd_id = base.cmd_id();
   let d = Vec::from(data.unwrap().as_ref()).into_boxed_slice();
 
   let tx = {
@@ -69,34 +90,33 @@ pub fn op_worker_post_message(
   tx.send(d)
     .wait()
     .map_err(|e| DenoError::new(ErrorKind::Other, e.to_string()))?;
-
-  Ok(JsonOp::Sync(json!({})))
-}
-
-#[derive(Deserialize)]
-#[serde(rename_all = "camelCase")]
-struct CreateWorkerArgs {
-  specifier: String,
-  include_deno_namespace: bool,
-  has_source_code: bool,
-  source_code: String,
+  let builder = &mut FlatBufferBuilder::new();
+
+  ok_buf(serialize_response(
+    cmd_id,
+    builder,
+    msg::BaseArgs {
+      ..Default::default()
+    },
+  ))
 }
 
 /// Create worker as the host
 pub fn op_create_worker(
   state: &ThreadSafeState,
-  args: Value,
-  _data: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: CreateWorkerArgs = serde_json::from_value(args)?;
-
-  let specifier = args.specifier.as_ref();
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+  let inner = base.inner_as_create_worker().unwrap();
+  let specifier = inner.specifier().unwrap();
   // Only include deno namespace if requested AND current worker
   // has included namespace (to avoid escalation).
   let include_deno_namespace =
-    args.include_deno_namespace && state.include_deno_namespace;
-  let has_source_code = args.has_source_code;
-  let source_code = args.source_code;
+    inner.include_deno_namespace() && state.include_deno_namespace;
+  let has_source_code = inner.has_source_code();
+  let source_code = inner.source_code().unwrap();
 
   let parent_state = state.clone();
 
@@ -130,13 +150,24 @@ pub fn op_create_worker(
   let exec_cb = move |worker: Worker| {
     let mut workers_tl = parent_state.workers.lock().unwrap();
     workers_tl.insert(rid, worker.shared());
-    json!(rid)
+    let builder = &mut FlatBufferBuilder::new();
+    let msg_inner =
+      msg::CreateWorkerRes::create(builder, &msg::CreateWorkerResArgs { rid });
+    serialize_response(
+      cmd_id,
+      builder,
+      msg::BaseArgs {
+        inner: Some(msg_inner.as_union_value()),
+        inner_type: msg::Any::CreateWorkerRes,
+        ..Default::default()
+      },
+    )
   };
 
   // Has provided source code, execute immediately.
   if has_source_code {
     worker.execute(&source_code).unwrap();
-    return Ok(JsonOp::Sync(exec_cb(worker)));
+    return ok_buf(exec_cb(worker));
   }
 
   let op = worker
@@ -144,23 +175,22 @@ pub fn op_create_worker(
     .and_then(move |()| Ok(exec_cb(worker)));
 
   let result = op.wait()?;
-  Ok(JsonOp::Sync(result))
-}
-
-#[derive(Deserialize)]
-struct HostGetWorkerClosedArgs {
-  rid: i32,
+  Ok(Op::Sync(result))
 }
 
 /// Return when the worker closes
 pub fn op_host_get_worker_closed(
   state: &ThreadSafeState,
-  args: Value,
-  _data: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: HostGetWorkerClosedArgs = serde_json::from_value(args)?;
-
-  let rid = args.rid as u32;
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  if base.sync() {
+    return Err(deno_error::no_sync_support());
+  }
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+  let inner = base.inner_as_host_get_worker_closed().unwrap();
+  let rid = inner.rid();
   let state = state.clone();
 
   let shared_worker_future = {
@@ -169,58 +199,79 @@ pub fn op_host_get_worker_closed(
     worker.clone()
   };
 
-  let op = Box::new(
-    shared_worker_future.then(move |_result| futures::future::ok(json!({}))),
-  );
-
-  Ok(JsonOp::Async(Box::new(op)))
-}
-
-#[derive(Deserialize)]
-struct HostGetMessageArgs {
-  rid: i32,
+  let op = Box::new(shared_worker_future.then(move |_result| {
+    let builder = &mut FlatBufferBuilder::new();
+
+    Ok(serialize_response(
+      cmd_id,
+      builder,
+      msg::BaseArgs {
+        ..Default::default()
+      },
+    ))
+  }));
+  Ok(Op::Async(Box::new(op)))
 }
 
 /// Get message from guest worker as host
 pub fn op_host_get_message(
   _state: &ThreadSafeState,
-  args: Value,
-  _data: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: HostGetMessageArgs = serde_json::from_value(args)?;
-
-  let rid = args.rid as u32;
-  let op = resources::get_message_from_worker(rid)
-    .map_err(move |_| -> ErrBox { unimplemented!() })
-    .and_then(move |maybe_buf| {
-      futures::future::ok(json!({
-        "data": maybe_buf.map(|buf| buf.to_owned())
-      }))
-    });
-
-  Ok(JsonOp::Async(Box::new(op)))
-}
-
-#[derive(Deserialize)]
-struct HostPostMessageArgs {
-  rid: i32,
+  base: &msg::Base<'_>,
+  data: Option<PinnedBuf>,
+) -> CliOpResult {
+  if base.sync() {
+    return Err(deno_error::no_sync_support());
+  }
+  assert!(data.is_none());
+  let cmd_id = base.cmd_id();
+  let inner = base.inner_as_host_get_message().unwrap();
+  let rid = inner.rid();
+
+  let op = resources::get_message_from_worker(rid);
+  let op = op.map_err(move |_| -> ErrBox { unimplemented!() });
+  let op = op.and_then(move |maybe_buf| -> Result<Buf, ErrBox> {
+    let builder = &mut FlatBufferBuilder::new();
+
+    let data = maybe_buf.as_ref().map(|buf| builder.create_vector(buf));
+    let msg_inner = msg::HostGetMessageRes::create(
+      builder,
+      &msg::HostGetMessageResArgs { data },
+    );
+    Ok(serialize_response(
+      cmd_id,
+      builder,
+      msg::BaseArgs {
+        inner: Some(msg_inner.as_union_value()),
+        inner_type: msg::Any::HostGetMessageRes,
+        ..Default::default()
+      },
+    ))
+  });
+  Ok(Op::Async(Box::new(op)))
 }
 
 /// Post message to guest worker as host
 pub fn op_host_post_message(
   _state: &ThreadSafeState,
-  args: Value,
+  base: &msg::Base<'_>,
   data: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let args: HostPostMessageArgs = serde_json::from_value(args)?;
-
-  let rid = args.rid as u32;
+) -> CliOpResult {
+  let cmd_id = base.cmd_id();
+  let inner = base.inner_as_host_post_message().unwrap();
+  let rid = inner.rid();
 
   let d = Vec::from(data.unwrap().as_ref()).into_boxed_slice();
 
   resources::post_message_to_worker(rid, d)
     .wait()
     .map_err(|e| DenoError::new(ErrorKind::Other, e.to_string()))?;
-
-  Ok(JsonOp::Sync(json!({})))
+  let builder = &mut FlatBufferBuilder::new();
+
+  ok_buf(serialize_response(
+    cmd_id,
+    builder,
+    msg::BaseArgs {
+      ..Default::default()
+    },
+  ))
 }
diff --git a/js/compiler.ts b/js/compiler.ts
index 5399d59ad..7519c5115 100644
--- a/js/compiler.ts
+++ b/js/compiler.ts
@@ -7,11 +7,9 @@ import { Console } from "./console";
 import { core } from "./core";
 import { Diagnostic, fromTypeScriptDiagnostic } from "./diagnostics";
 import { cwd } from "./dir";
-import * as dispatch from "./dispatch";
-import { sendSync } from "./dispatch_json";
-import { msg } from "./dispatch_flatbuffers";
+import { sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
 import * as os from "./os";
-import { TextEncoder } from "./text_encoding";
+import { TextDecoder, TextEncoder } from "./text_encoding";
 import { getMappedModuleName, parseTypeDirectives } from "./type_directives";
 import { assert, notImplemented } from "./util";
 import * as util from "./util";
@@ -123,15 +121,35 @@ interface EmitResult {
 
 /** Ops to Rust to resolve and fetch a modules meta data. */
 function fetchSourceFile(specifier: string, referrer: string): SourceFile {
-  util.log("compiler.fetchSourceFile", { specifier, referrer });
-  const res = sendSync(dispatch.OP_FETCH_SOURCE_FILE, {
-    specifier,
-    referrer
-  });
-
+  util.log("fetchSourceFile", { specifier, referrer });
+  // Send FetchSourceFile message
+  const builder = flatbuffers.createBuilder();
+  const specifier_ = builder.createString(specifier);
+  const referrer_ = builder.createString(referrer);
+  const inner = msg.FetchSourceFile.createFetchSourceFile(
+    builder,
+    specifier_,
+    referrer_
+  );
+  const baseRes = sendSync(builder, msg.Any.FetchSourceFile, inner);
+  assert(baseRes != null);
+  assert(
+    msg.Any.FetchSourceFileRes === baseRes!.innerType(),
+    `base.innerType() unexpectedly is ${baseRes!.innerType()}`
+  );
+  const fetchSourceFileRes = new msg.FetchSourceFileRes();
+  assert(baseRes!.inner(fetchSourceFileRes) != null);
+  const dataArray = fetchSourceFileRes.dataArray();
+  const decoder = new TextDecoder();
+  const sourceCode = dataArray ? decoder.decode(dataArray) : undefined;
+  // flatbuffers returns `null` for an empty value, this does not fit well with
+  // idiomatic TypeScript under strict null checks, so converting to `undefined`
   return {
-    ...res,
-    typeDirectives: parseTypeDirectives(res.sourceCode)
+    moduleName: fetchSourceFileRes.moduleName() || undefined,
+    filename: fetchSourceFileRes.filename() || undefined,
+    mediaType: fetchSourceFileRes.mediaType(),
+    sourceCode,
+    typeDirectives: parseTypeDirectives(sourceCode)
   };
 }
 
@@ -153,7 +171,19 @@ function humanFileSize(bytes: number): string {
 
 /** Ops to rest for caching source map and compiled js */
 function cache(extension: string, moduleId: string, contents: string): void {
-  sendSync(dispatch.OP_CACHE, { extension, moduleId, contents });
+  util.log("cache", extension, moduleId);
+  const builder = flatbuffers.createBuilder();
+  const extension_ = builder.createString(extension);
+  const moduleId_ = builder.createString(moduleId);
+  const contents_ = builder.createString(contents);
+  const inner = msg.Cache.createCache(
+    builder,
+    extension_,
+    moduleId_,
+    contents_
+  );
+  const baseRes = sendSync(builder, msg.Any.Cache, inner);
+  assert(baseRes == null);
 }
 
 const encoder = new TextEncoder();
diff --git a/js/dispatch.ts b/js/dispatch.ts
index 6c7551441..0c5c59553 100644
--- a/js/dispatch.ts
+++ b/js/dispatch.ts
@@ -12,40 +12,6 @@ export const OP_IS_TTY = 4;
 export const OP_ENV = 5;
 export const OP_EXEC_PATH = 6;
 export const OP_UTIME = 7;
-export const OP_SET_ENV = 8;
-export const OP_HOME_DIR = 9;
-export const OP_START = 10;
-export const OP_APPLY_SOURCE_MAP = 11;
-export const OP_FORMAT_ERROR = 12;
-export const OP_CACHE = 13;
-export const OP_FETCH_SOURCE_FILE = 14;
-export const OP_OPEN = 15;
-export const OP_CLOSE = 16;
-export const OP_SEEK = 17;
-export const OP_FETCH = 18;
-export const OP_METRICS = 19;
-export const OP_REPL_START = 20;
-export const OP_REPL_READLINE = 21;
-export const OP_ACCEPT = 22;
-export const OP_DIAL = 23;
-export const OP_SHUTDOWN = 24;
-export const OP_LISTEN = 25;
-export const OP_RESOURCES = 26;
-export const OP_GET_RANDOM_VALUES = 27;
-export const OP_GLOBAL_TIMER_STOP = 28;
-export const OP_GLOBAL_TIMER = 29;
-export const OP_NOW = 30;
-export const OP_PERMISSIONS = 31;
-export const OP_REVOKE_PERMISSION = 32;
-export const OP_CREATE_WORKER = 33;
-export const OP_HOST_GET_WORKER_CLOSED = 34;
-export const OP_HOST_POST_MESSAGE = 35;
-export const OP_HOST_GET_MESSAGE = 36;
-export const OP_WORKER_POST_MESSAGE = 37;
-export const OP_WORKER_GET_MESSAGE = 38;
-export const OP_RUN = 39;
-export const OP_RUN_STATUS = 40;
-export const OP_KILL = 41;
 
 export function asyncMsgFromRust(opId: number, ui8: Uint8Array): void {
   switch (opId) {
@@ -56,26 +22,10 @@ export function asyncMsgFromRust(opId: number, ui8: Uint8Array): void {
     case OP_READ:
       minimal.asyncMsgFromRust(opId, ui8);
       break;
-    case OP_EXIT:
-    case OP_IS_TTY:
-    case OP_ENV:
-    case OP_EXEC_PATH:
     case OP_UTIME:
-    case OP_OPEN:
-    case OP_SEEK:
-    case OP_FETCH:
-    case OP_REPL_START:
-    case OP_REPL_READLINE:
-    case OP_ACCEPT:
-    case OP_DIAL:
-    case OP_GLOBAL_TIMER:
-    case OP_HOST_GET_WORKER_CLOSED:
-    case OP_HOST_GET_MESSAGE:
-    case OP_WORKER_GET_MESSAGE:
-    case OP_RUN_STATUS:
       json.asyncMsgFromRust(opId, ui8);
       break;
     default:
-      throw Error("bad async opId");
+      throw Error("bad opId");
   }
 }
diff --git a/js/error_stack.ts b/js/error_stack.ts
index 7d41b9cf4..003717a72 100644
--- a/js/error_stack.ts
+++ b/js/error_stack.ts
@@ -1,8 +1,8 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 // Some of the code here is adapted directly from V8 and licensed under a BSD
 // style license available here: https://github.com/v8/v8/blob/24886f2d1c565287d33d71e4109a53bf0b54b75c/LICENSE.v8
-import * as dispatch from "./dispatch";
-import { sendSync } from "./dispatch_json";
+
+import { sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
 import { assert } from "./util";
 
 export interface Location {
@@ -17,6 +17,40 @@ export interface Location {
   column: number;
 }
 
+function req(
+  filename: string,
+  line: number,
+  column: number
+): [flatbuffers.Builder, msg.Any.ApplySourceMap, flatbuffers.Offset] {
+  const builder = flatbuffers.createBuilder();
+  const filename_ = builder.createString(filename);
+  const inner = msg.ApplySourceMap.createApplySourceMap(
+    builder,
+    filename_,
+    // On this side, line/column are 1 based, but in the source maps, they are
+    // 0 based, so we have to convert back and forth
+    line - 1,
+    column - 1
+  );
+  return [builder, msg.Any.ApplySourceMap, inner];
+}
+
+function res(baseRes: msg.Base | null): Location {
+  assert(baseRes != null);
+  assert(baseRes!.innerType() === msg.Any.ApplySourceMap);
+  const res = new msg.ApplySourceMap();
+  assert(baseRes!.inner(res) != null);
+  const filename = res.filename()!;
+  assert(filename != null);
+  return {
+    filename,
+    // On this side, line/column are 1 based, but in the source maps, they are
+    // 0 based, so we have to convert back and forth
+    line: res.line() + 1,
+    column: res.column() + 1
+  };
+}
+
 /** Given a current location in a module, lookup the source location and
  * return it.
  *
@@ -41,18 +75,7 @@ export interface Location {
  */
 export function applySourceMap(location: Location): Location {
   const { filename, line, column } = location;
-  // On this side, line/column are 1 based, but in the source maps, they are
-  // 0 based, so we have to convert back and forth
-  const res = sendSync(dispatch.OP_APPLY_SOURCE_MAP, {
-    filename,
-    line: line - 1,
-    column: column - 1
-  });
-  return {
-    filename: res.filename,
-    line: res.line + 1,
-    column: res.column + 1
-  };
+  return res(sendSync(...req(filename, line, column)));
 }
 
 /** Mutate the call site so that it returns the location, instead of its
diff --git a/js/fetch.ts b/js/fetch.ts
index 317239630..505da218c 100644
--- a/js/fetch.ts
+++ b/js/fetch.ts
@@ -1,5 +1,6 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 import { assert, createResolvable, notImplemented, isTypedArray } from "./util";
+import { sendAsync, msg, flatbuffers } from "./dispatch_flatbuffers";
 import * as domTypes from "./dom_types";
 import { TextDecoder, TextEncoder } from "./text_encoding";
 import { DenoBlob, bytesSymbol as blobBytesSymbol } from "./blob";
@@ -9,8 +10,6 @@ import { read, close } from "./files";
 import { Buffer } from "./buffer";
 import { FormData } from "./form_data";
 import { URLSearchParams } from "./url_search_params";
-import * as dispatch from "./dispatch";
-import { sendAsync } from "./dispatch_json";
 
 function getHeaderValueParams(value: string): Map<string, string> {
   const params = new Map();
@@ -321,35 +320,67 @@ export class Response implements domTypes.Response {
   }
 }
 
-interface FetchResponse {
-  bodyRid: number;
-  status: number;
-  headers: Array<[string, string]>;
-}
-
-async function sendFetchReq(
+function msgHttpRequest(
+  builder: flatbuffers.Builder,
   url: string,
-  method: string | null,
-  headers: domTypes.Headers | null,
-  body: ArrayBufferView | undefined
-): Promise<FetchResponse> {
-  let headerArray: Array<[string, string]> = [];
+  method: null | string,
+  headers: null | domTypes.Headers
+): flatbuffers.Offset {
+  const methodOffset = !method ? 0 : builder.createString(method);
+  let fieldsOffset: flatbuffers.Offset = 0;
+  const urlOffset = builder.createString(url);
   if (headers) {
-    headerArray = Array.from(headers.entries());
+    const kvOffsets: flatbuffers.Offset[] = [];
+    for (const [key, val] of headers.entries()) {
+      const keyOffset = builder.createString(key);
+      const valOffset = builder.createString(val);
+      kvOffsets.push(
+        msg.KeyValue.createKeyValue(builder, keyOffset, valOffset)
+      );
+    }
+    fieldsOffset = msg.HttpHeader.createFieldsVector(builder, kvOffsets);
+  } else {
   }
+  return msg.HttpHeader.createHttpHeader(
+    builder,
+    true,
+    methodOffset,
+    urlOffset,
+    0,
+    fieldsOffset
+  );
+}
 
-  let zeroCopy = undefined;
-  if (body) {
-    zeroCopy = new Uint8Array(body.buffer, body.byteOffset, body.byteLength);
+function deserializeHeaderFields(m: msg.HttpHeader): Array<[string, string]> {
+  const out: Array<[string, string]> = [];
+  for (let i = 0; i < m.fieldsLength(); i++) {
+    const item = m.fields(i)!;
+    out.push([item.key()!, item.value()!]);
   }
+  return out;
+}
 
-  const args = {
-    method,
-    url,
-    headers: headerArray
-  };
-
-  return (await sendAsync(dispatch.OP_FETCH, args, zeroCopy)) as FetchResponse;
+async function getFetchRes(
+  url: string,
+  method: string | null,
+  headers: domTypes.Headers | null,
+  body: ArrayBufferView | undefined
+): Promise<msg.FetchRes> {
+  // Send Fetch message
+  const builder = flatbuffers.createBuilder();
+  const headerOff = msgHttpRequest(builder, url, method, headers);
+  const resBase = await sendAsync(
+    builder,
+    msg.Any.Fetch,
+    msg.Fetch.createFetch(builder, headerOff),
+    body
+  );
+
+  // Decode FetchRes
+  assert(msg.Any.FetchRes === resBase.innerType());
+  const inner = new msg.FetchRes();
+  assert(resBase.inner(inner) != null);
+  return inner;
 }
 
 /** Fetch a resource from the network. */
@@ -417,13 +448,20 @@ export async function fetch(
   }
 
   while (remRedirectCount) {
-    const fetchResponse = await sendFetchReq(url, method, headers, body);
+    const inner = await getFetchRes(url, method, headers, body);
+
+    const header = inner.header()!;
+    const bodyRid = inner.bodyRid();
+    assert(!header.isRequest());
+    const status = header.status();
+
+    const headersList = deserializeHeaderFields(header);
 
     const response = new Response(
       url,
-      fetchResponse.status,
-      fetchResponse.headers,
-      fetchResponse.bodyRid,
+      status,
+      headersList,
+      bodyRid,
       redirected
     );
     if ([301, 302, 303, 307, 308].includes(response.status)) {
diff --git a/js/files.ts b/js/files.ts
index 4eff17aac..6f0e523c9 100644
--- a/js/files.ts
+++ b/js/files.ts
@@ -12,22 +12,37 @@ import {
 } from "./io";
 import { sendAsyncMinimal } from "./dispatch_minimal";
 import { assert } from "./util";
-import * as dispatch from "./dispatch";
-import {
-  sendSync as sendSyncJson,
-  sendAsync as sendAsyncJson
-} from "./dispatch_json";
-import { sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
+import { sendAsync, sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
 import { OP_READ, OP_WRITE } from "./dispatch";
 
+function reqOpen(
+  filename: string,
+  mode: OpenMode
+): [flatbuffers.Builder, msg.Any, flatbuffers.Offset] {
+  const builder = flatbuffers.createBuilder();
+  const filename_ = builder.createString(filename);
+  const mode_ = builder.createString(mode);
+  const inner = msg.Open.createOpen(builder, filename_, 0, mode_);
+  return [builder, msg.Any.Open, inner];
+}
+
+function resOpen(baseRes: null | msg.Base): File {
+  assert(baseRes != null);
+  assert(msg.Any.OpenRes === baseRes!.innerType());
+  const res = new msg.OpenRes();
+  assert(baseRes!.inner(res) != null);
+  const rid = res.rid();
+  // eslint-disable-next-line @typescript-eslint/no-use-before-define
+  return new File(rid);
+}
+
 /** Open a file and return an instance of the `File` object
  *  synchronously.
  *
  *       const file = Deno.openSync("/foo/bar.txt");
  */
 export function openSync(filename: string, mode: OpenMode = "r"): File {
-  const rid = sendSyncJson(dispatch.OP_OPEN, { filename, mode });
-  return new File(rid);
+  return resOpen(sendSync(...reqOpen(filename, mode)));
 }
 
 /** Open a file and return an instance of the `File` object.
@@ -40,8 +55,7 @@ export async function open(
   filename: string,
   mode: OpenMode = "r"
 ): Promise<File> {
-  const rid = await sendAsyncJson(dispatch.OP_OPEN, { filename, mode });
-  return new File(rid);
+  return resOpen(await sendAsync(...reqOpen(filename, mode)));
 }
 
 function reqRead(
@@ -151,13 +165,23 @@ export async function write(rid: number, p: Uint8Array): Promise<number> {
   }
 }
 
+function reqSeek(
+  rid: number,
+  offset: number,
+  whence: SeekMode
+): [flatbuffers.Builder, msg.Any, flatbuffers.Offset] {
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.Seek.createSeek(builder, rid, offset, whence);
+  return [builder, msg.Any.Seek, inner];
+}
+
 /** Seek a file ID synchronously to the given offset under mode given by `whence`.
  *
  *       const file = Deno.openSync("/foo/bar.txt");
  *       Deno.seekSync(file.rid, 0, 0);
  */
 export function seekSync(rid: number, offset: number, whence: SeekMode): void {
-  sendSyncJson(dispatch.OP_SEEK, { rid, offset, whence });
+  sendSync(...reqSeek(rid, offset, whence));
 }
 
 /** Seek a file ID to the given offset under mode given by `whence`.
@@ -172,12 +196,14 @@ export async function seek(
   offset: number,
   whence: SeekMode
 ): Promise<void> {
-  await sendAsyncJson(dispatch.OP_SEEK, { rid, offset, whence });
+  await sendAsync(...reqSeek(rid, offset, whence));
 }
 
 /** Close the file ID. */
 export function close(rid: number): void {
-  sendSyncJson(dispatch.OP_CLOSE, { rid });
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.Close.createClose(builder, rid);
+  sendSync(builder, msg.Any.Close, inner);
 }
 
 /** The Deno abstraction for reading and writing files. */
diff --git a/js/format_error.ts b/js/format_error.ts
index dde0f6a58..6670b05e2 100644
--- a/js/format_error.ts
+++ b/js/format_error.ts
@@ -1,9 +1,17 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import * as dispatch from "./dispatch";
-import { sendSync } from "./dispatch_json";
+import { sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
+import { assert } from "./util";
 
-// TODO(bartlomieju): move to `repl.ts`?
 export function formatError(errString: string): string {
-  const res = sendSync(dispatch.OP_FORMAT_ERROR, { error: errString });
-  return res.error;
+  const builder = flatbuffers.createBuilder();
+  const errString_ = builder.createString(errString);
+  const offset = msg.FormatError.createFormatError(builder, errString_);
+  const baseRes = sendSync(builder, msg.Any.FormatError, offset);
+  assert(baseRes != null);
+  assert(msg.Any.FormatErrorRes === baseRes!.innerType());
+  const formatErrorResMsg = new msg.FormatErrorRes();
+  assert(baseRes!.inner(formatErrorResMsg) != null);
+  const formattedError = formatErrorResMsg.error();
+  assert(formatError != null);
+  return formattedError!;
 }
diff --git a/js/get_random_values.ts b/js/get_random_values.ts
index 154e77f75..d5c0828c5 100644
--- a/js/get_random_values.ts
+++ b/js/get_random_values.ts
@@ -1,8 +1,15 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import * as dispatch from "./dispatch";
-import { sendSync } from "./dispatch_json";
+import { sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
 import { assert } from "./util";
 
+function req(
+  typedArray: ArrayBufferView
+): [flatbuffers.Builder, msg.Any, flatbuffers.Offset, ArrayBufferView] {
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.GetRandomValues.createGetRandomValues(builder);
+  return [builder, msg.Any.GetRandomValues, inner, typedArray];
+}
+
 /** Synchronously collects cryptographically secure random values. The
  * underlying CSPRNG in use is Rust's `rand::rngs::ThreadRng`.
  *
@@ -21,11 +28,6 @@ export function getRandomValues<
 >(typedArray: T): T {
   assert(typedArray !== null, "Input must not be null");
   assert(typedArray.length <= 65536, "Input must not be longer than 65536");
-  const ui8 = new Uint8Array(
-    typedArray.buffer,
-    typedArray.byteOffset,
-    typedArray.byteLength
-  );
-  sendSync(dispatch.OP_GET_RANDOM_VALUES, {}, ui8);
+  sendSync(...req(typedArray as ArrayBufferView));
   return typedArray;
 }
diff --git a/js/main.ts b/js/main.ts
index 25e27b69f..769f522a6 100644
--- a/js/main.ts
+++ b/js/main.ts
@@ -22,12 +22,12 @@ export default function denoMain(
   preserveDenoNamespace: boolean = true,
   name?: string
 ): void {
-  const s = os.start(preserveDenoNamespace, name);
+  const startResMsg = os.start(preserveDenoNamespace, name);
 
-  setVersions(s.denoVersion, s.v8Version);
+  setVersions(startResMsg.denoVersion()!, startResMsg.v8Version()!);
 
   // handle `--version`
-  if (s.versionFlag) {
+  if (startResMsg.versionFlag()) {
     console.log("deno:", deno.version.deno);
     console.log("v8:", deno.version.v8);
     console.log("typescript:", deno.version.typescript);
@@ -36,22 +36,24 @@ export default function denoMain(
 
   setPrepareStackTrace(Error);
 
-  if (s.mainModule) {
-    assert(s.mainModule.length > 0);
-    setLocation(s.mainModule);
+  const mainModule = startResMsg.mainModule();
+  if (mainModule) {
+    assert(mainModule.length > 0);
+    setLocation(mainModule);
   }
 
-  log("cwd", s.cwd);
+  const cwd = startResMsg.cwd();
+  log("cwd", cwd);
 
-  for (let i = 1; i < s.argv.length; i++) {
-    args.push(s.argv[i]);
+  for (let i = 1; i < startResMsg.argvLength(); i++) {
+    args.push(startResMsg.argv(i));
   }
   log("args", args);
   Object.freeze(args);
 
   if (window["_xevalWrapper"] !== undefined) {
-    xevalMain(window["_xevalWrapper"] as XevalFunc, s.xevalDelim);
-  } else if (!s.mainModule) {
+    xevalMain(window["_xevalWrapper"] as XevalFunc, startResMsg.xevalDelim());
+  } else if (!mainModule) {
     replLoop();
   }
 }
diff --git a/js/metrics.ts b/js/metrics.ts
index 48e3102e5..e93e9528c 100644
--- a/js/metrics.ts
+++ b/js/metrics.ts
@@ -1,6 +1,6 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import * as dispatch from "./dispatch";
-import { sendSync } from "./dispatch_json";
+import { assert } from "./util";
+import { sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
 
 export interface Metrics {
   opsDispatched: number;
@@ -10,6 +10,27 @@ export interface Metrics {
   bytesReceived: number;
 }
 
+function req(): [flatbuffers.Builder, msg.Any, flatbuffers.Offset] {
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.Metrics.createMetrics(builder);
+  return [builder, msg.Any.Metrics, inner];
+}
+
+function res(baseRes: null | msg.Base): Metrics {
+  assert(baseRes !== null);
+  assert(msg.Any.MetricsRes === baseRes!.innerType());
+  const res = new msg.MetricsRes();
+  assert(baseRes!.inner(res) !== null);
+
+  return {
+    opsDispatched: res.opsDispatched().toFloat64(),
+    opsCompleted: res.opsCompleted().toFloat64(),
+    bytesSentControl: res.bytesSentControl().toFloat64(),
+    bytesSentData: res.bytesSentData().toFloat64(),
+    bytesReceived: res.bytesReceived().toFloat64()
+  };
+}
+
 /** Receive metrics from the privileged side of Deno.
  *
  *      > console.table(Deno.metrics())
@@ -24,5 +45,5 @@ export interface Metrics {
  *      └──────────────────┴────────┘
  */
 export function metrics(): Metrics {
-  return sendSync(dispatch.OP_METRICS);
+  return res(sendSync(...req()));
 }
diff --git a/js/net.ts b/js/net.ts
index b478ae613..9c3bfbba5 100644
--- a/js/net.ts
+++ b/js/net.ts
@@ -1,9 +1,8 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 import { EOF, Reader, Writer, Closer } from "./io";
-import { notImplemented } from "./util";
+import { assert, notImplemented } from "./util";
+import { sendSync, sendAsync, msg, flatbuffers } from "./dispatch_flatbuffers";
 import { read, write, close } from "./files";
-import * as dispatch from "./dispatch";
-import { sendSync, sendAsync } from "./dispatch_json";
 
 export type Network = "tcp";
 // TODO support other types:
@@ -37,7 +36,10 @@ enum ShutdownMode {
 }
 
 function shutdown(rid: number, how: ShutdownMode): void {
-  sendSync(dispatch.OP_SHUTDOWN, { rid, how });
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.Shutdown.createShutdown(builder, rid, how);
+  const baseRes = sendSync(builder, msg.Any.Shutdown, inner);
+  assert(baseRes == null);
 }
 
 class ConnImpl implements Conn {
@@ -78,9 +80,14 @@ class ListenerImpl implements Listener {
   constructor(readonly rid: number) {}
 
   async accept(): Promise<Conn> {
-    const res = await sendAsync(dispatch.OP_ACCEPT, { rid: this.rid });
-    // TODO(bartlomieju): add remoteAddr and localAddr on Rust side
-    return new ConnImpl(res.rid, res.remoteAddr!, res.localAddr!);
+    const builder = flatbuffers.createBuilder();
+    const inner = msg.Accept.createAccept(builder, this.rid);
+    const baseRes = await sendAsync(builder, msg.Any.Accept, inner);
+    assert(baseRes != null);
+    assert(msg.Any.NewConn === baseRes!.innerType());
+    const res = new msg.NewConn();
+    assert(baseRes!.inner(res) != null);
+    return new ConnImpl(res.rid(), res.remoteAddr()!, res.localAddr()!);
   }
 
   close(): void {
@@ -136,8 +143,16 @@ export interface Conn extends Reader, Writer, Closer {
  * See `dial()` for a description of the network and address parameters.
  */
 export function listen(network: Network, address: string): Listener {
-  const rid = sendSync(dispatch.OP_LISTEN, { network, address });
-  return new ListenerImpl(rid);
+  const builder = flatbuffers.createBuilder();
+  const network_ = builder.createString(network);
+  const address_ = builder.createString(address);
+  const inner = msg.Listen.createListen(builder, network_, address_);
+  const baseRes = sendSync(builder, msg.Any.Listen, inner);
+  assert(baseRes != null);
+  assert(msg.Any.ListenRes === baseRes!.innerType());
+  const res = new msg.ListenRes();
+  assert(baseRes!.inner(res) != null);
+  return new ListenerImpl(res.rid());
 }
 
 /** Dial connects to the address on the named network.
@@ -168,9 +183,16 @@ export function listen(network: Network, address: string): Listener {
  *     dial("tcp", ":80")
  */
 export async function dial(network: Network, address: string): Promise<Conn> {
-  const res = await sendAsync(dispatch.OP_DIAL, { network, address });
-  // TODO(bartlomieju): add remoteAddr and localAddr on Rust side
-  return new ConnImpl(res.rid, res.remoteAddr!, res.localAddr!);
+  const builder = flatbuffers.createBuilder();
+  const network_ = builder.createString(network);
+  const address_ = builder.createString(address);
+  const inner = msg.Dial.createDial(builder, network_, address_);
+  const baseRes = await sendAsync(builder, msg.Any.Dial, inner);
+  assert(baseRes != null);
+  assert(msg.Any.NewConn === baseRes!.innerType());
+  const res = new msg.NewConn();
+  assert(baseRes!.inner(res) != null);
+  return new ConnImpl(res.rid(), res.remoteAddr()!, res.localAddr()!);
 }
 
 /** **RESERVED** */
diff --git a/js/os.ts b/js/os.ts
index c44c27825..f8938ab70 100644
--- a/js/os.ts
+++ b/js/os.ts
@@ -1,7 +1,8 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 import { core } from "./core";
 import * as dispatch from "./dispatch";
-import { sendSync } from "./dispatch_json";
+import { sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
+import * as dispatchJson from "./dispatch_json";
 import { assert } from "./util";
 import * as util from "./util";
 import { window } from "./window";
@@ -23,17 +24,21 @@ function setGlobals(pid_: number, noColor_: boolean): void {
  *       console.log(Deno.isTTY().stdout);
  */
 export function isTTY(): { stdin: boolean; stdout: boolean; stderr: boolean } {
-  return sendSync(dispatch.OP_IS_TTY);
+  return dispatchJson.sendSync(dispatch.OP_IS_TTY);
 }
 
 /** Exit the Deno process with optional exit code. */
 export function exit(code = 0): never {
-  sendSync(dispatch.OP_EXIT, { code });
+  dispatchJson.sendSync(dispatch.OP_EXIT, { code });
   return util.unreachable();
 }
 
 function setEnv(key: string, value: string): void {
-  sendSync(dispatch.OP_SET_ENV, { key, value });
+  const builder = flatbuffers.createBuilder();
+  const key_ = builder.createString(key);
+  const value_ = builder.createString(value);
+  const inner = msg.SetEnv.createSetEnv(builder, key_, value_);
+  sendSync(builder, msg.Any.SetEnv, inner);
 }
 
 /** Returns a snapshot of the environment variables at invocation. Mutating a
@@ -48,7 +53,7 @@ function setEnv(key: string, value: string): void {
  *       console.log(myEnv.TEST_VAR == newEnv.TEST_VAR);
  */
 export function env(): { [index: string]: string } {
-  const env = sendSync(dispatch.OP_ENV);
+  const env = dispatchJson.sendSync(dispatch.OP_ENV);
   return new Proxy(env, {
     set(obj, prop: string, value: string): boolean {
       setEnv(prop, value);
@@ -57,35 +62,35 @@ export function env(): { [index: string]: string } {
   });
 }
 
-interface Start {
-  cwd: string;
-  pid: number;
-  argv: string[];
-  mainModule: string; // Absolute URL.
-  debugFlag: boolean;
-  depsFlag: boolean;
-  typesFlag: boolean;
-  versionFlag: boolean;
-  denoVersion: string;
-  v8Version: string;
-  noColor: boolean;
-  xevalDelim: string;
+/** Send to the privileged side that we have setup and are ready. */
+function sendStart(): msg.StartRes {
+  const builder = flatbuffers.createBuilder();
+  const startOffset = msg.Start.createStart(builder, 0 /* unused */);
+  const baseRes = sendSync(builder, msg.Any.Start, startOffset);
+  assert(baseRes != null);
+  assert(msg.Any.StartRes === baseRes!.innerType());
+  const startResMsg = new msg.StartRes();
+  assert(baseRes!.inner(startResMsg) != null);
+  return startResMsg;
 }
 
 // This function bootstraps an environment within Deno, it is shared both by
 // the runtime and the compiler environments.
 // @internal
-export function start(preserveDenoNamespace = true, source?: string): Start {
+export function start(
+  preserveDenoNamespace = true,
+  source?: string
+): msg.StartRes {
   core.setAsyncHandler(dispatch.asyncMsgFromRust);
 
   // First we send an empty `Start` message to let the privileged side know we
   // are ready. The response should be a `StartRes` message containing the CLI
   // args and other info.
-  const s = sendSync(dispatch.OP_START);
+  const startResMsg = sendStart();
 
-  util.setLogDebug(s.debugFlag, source);
+  util.setLogDebug(startResMsg.debugFlag(), source);
 
-  setGlobals(s.pid, s.noColor);
+  setGlobals(startResMsg.pid(), startResMsg.noColor());
 
   if (preserveDenoNamespace) {
     util.immutableDefine(window, "Deno", window.Deno);
@@ -100,7 +105,7 @@ export function start(preserveDenoNamespace = true, source?: string): Start {
     assert(window.Deno === undefined);
   }
 
-  return s;
+  return startResMsg;
 }
 
 /**
@@ -108,10 +113,18 @@ export function start(preserveDenoNamespace = true, source?: string): Start {
  * Requires the `--allow-env` flag.
  */
 export function homeDir(): string {
-  const path = sendSync(dispatch.OP_HOME_DIR);
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.HomeDir.createHomeDir(builder);
+  const baseRes = sendSync(builder, msg.Any.HomeDir, inner)!;
+  assert(msg.Any.HomeDirRes === baseRes.innerType());
+  const res = new msg.HomeDirRes();
+  assert(baseRes.inner(res) != null);
+  const path = res.path();
+
   if (!path) {
     throw new Error("Could not get home directory.");
   }
+
   return path;
 }
 
@@ -120,5 +133,5 @@ export function homeDir(): string {
  * Requires the `--allow-env` flag.
  */
 export function execPath(): string {
-  return sendSync(dispatch.OP_EXEC_PATH);
+  return dispatchJson.sendSync(dispatch.OP_EXEC_PATH);
 }
diff --git a/js/performance.ts b/js/performance.ts
index d2f339c46..7aaa7ae45 100644
--- a/js/performance.ts
+++ b/js/performance.ts
@@ -1,11 +1,6 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import * as dispatch from "./dispatch";
-import { sendSync } from "./dispatch_json";
-
-interface NowResponse {
-  seconds: number;
-  subsecNanos: number;
-}
+import { sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
+import { assert } from "./util";
 
 export class Performance {
   /** Returns a current time from Deno's start in milliseconds.
@@ -16,7 +11,12 @@ export class Performance {
    *       console.log(`${t} ms since start!`);
    */
   now(): number {
-    const res = sendSync(dispatch.OP_NOW) as NowResponse;
-    return res.seconds * 1e3 + res.subsecNanos / 1e6;
+    const builder = flatbuffers.createBuilder();
+    const inner = msg.Now.createNow(builder);
+    const baseRes = sendSync(builder, msg.Any.Now, inner)!;
+    assert(msg.Any.NowRes === baseRes.innerType());
+    const res = new msg.NowRes();
+    assert(baseRes.inner(res) != null);
+    return res.seconds().toFloat64() * 1e3 + res.subsecNanos() / 1e6;
   }
 }
diff --git a/js/permissions.ts b/js/permissions.ts
index bc969f3a8..822ae8cbd 100644
--- a/js/permissions.ts
+++ b/js/permissions.ts
@@ -1,6 +1,6 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import * as dispatch from "./dispatch";
-import { sendSync } from "./dispatch_json";
+import { sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
+import { assert } from "./util";
 
 /** Permissions as granted by the caller */
 export interface Permissions {
@@ -15,6 +15,23 @@ export interface Permissions {
 
 export type Permission = keyof Permissions;
 
+function getReq(): [flatbuffers.Builder, msg.Any, flatbuffers.Offset] {
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.Permissions.createPermissions(builder);
+  return [builder, msg.Any.Permissions, inner];
+}
+
+function createPermissions(inner: msg.PermissionsRes): Permissions {
+  return {
+    read: inner.read(),
+    write: inner.write(),
+    net: inner.net(),
+    env: inner.env(),
+    run: inner.run(),
+    hrtime: inner.hrtime()
+  };
+}
+
 /** Inspect granted permissions for the current program.
  *
  *       if (Deno.permissions().read) {
@@ -23,7 +40,24 @@ export type Permission = keyof Permissions;
  *       }
  */
 export function permissions(): Permissions {
-  return sendSync(dispatch.OP_PERMISSIONS) as Permissions;
+  const baseRes = sendSync(...getReq())!;
+  assert(msg.Any.PermissionsRes === baseRes.innerType());
+  const res = new msg.PermissionsRes();
+  assert(baseRes.inner(res) != null);
+  // TypeScript cannot track assertion above, therefore not null assertion
+  return createPermissions(res);
+}
+
+function revokeReq(
+  permission: string
+): [flatbuffers.Builder, msg.Any, flatbuffers.Offset] {
+  const builder = flatbuffers.createBuilder();
+  const permission_ = builder.createString(permission);
+  const inner = msg.PermissionRevoke.createPermissionRevoke(
+    builder,
+    permission_
+  );
+  return [builder, msg.Any.PermissionRevoke, inner];
 }
 
 /** Revoke a permission. When the permission was already revoked nothing changes
@@ -35,5 +69,5 @@ export function permissions(): Permissions {
  *       Deno.readFile("example.test"); // -> error or permission prompt
  */
 export function revokePermission(permission: Permission): void {
-  sendSync(dispatch.OP_REVOKE_PERMISSION, { permission });
+  sendSync(...revokeReq(permission));
 }
diff --git a/js/process.ts b/js/process.ts
index dd4f70103..b2b6d4734 100644
--- a/js/process.ts
+++ b/js/process.ts
@@ -1,6 +1,6 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import { sendSync, sendAsync } from "./dispatch_json";
-import * as dispatch from "./dispatch";
+import { sendSync, sendAsync, msg, flatbuffers } from "./dispatch_flatbuffers";
+
 import { File, close } from "./files";
 import { ReadCloser, WriteCloser } from "./io";
 import { readAll } from "./buffer";
@@ -31,22 +31,21 @@ export interface RunOptions {
   stdin?: ProcessStdio | number;
 }
 
-interface RunStatusResponse {
-  gotSignal: boolean;
-  exitCode: number;
-  exitSignal: number;
-}
-
 async function runStatus(rid: number): Promise<ProcessStatus> {
-  const res = (await sendAsync(dispatch.OP_RUN_STATUS, {
-    rid
-  })) as RunStatusResponse;
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.RunStatus.createRunStatus(builder, rid);
 
-  if (res.gotSignal) {
-    const signal = res.exitSignal;
+  const baseRes = await sendAsync(builder, msg.Any.RunStatus, inner);
+  assert(baseRes != null);
+  assert(msg.Any.RunStatusRes === baseRes!.innerType());
+  const res = new msg.RunStatusRes();
+  assert(baseRes!.inner(res) != null);
+
+  if (res.gotSignal()) {
+    const signal = res.exitSignal();
     return { signal, success: false };
   } else {
-    const code = res.exitCode;
+    const code = res.exitCode();
     return { code, success: code === 0 };
   }
 }
@@ -57,7 +56,9 @@ async function runStatus(rid: number): Promise<ProcessStatus> {
  * Requires the `--allow-run` flag.
  */
 export function kill(pid: number, signo: number): void {
-  sendSync(dispatch.OP_KILL, { pid, signo });
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.Kill.createKill(builder, pid, signo);
+  sendSync(builder, msg.Any.Kill, inner);
 }
 
 export class Process {
@@ -68,20 +69,20 @@ export class Process {
   readonly stderr?: ReadCloser;
 
   // @internal
-  constructor(res: RunResponse) {
-    this.rid = res.rid;
-    this.pid = res.pid;
+  constructor(res: msg.RunRes) {
+    this.rid = res.rid();
+    this.pid = res.pid();
 
-    if (res.stdinRid && res.stdinRid > 0) {
-      this.stdin = new File(res.stdinRid);
+    if (res.stdinRid() > 0) {
+      this.stdin = new File(res.stdinRid());
     }
 
-    if (res.stdoutRid && res.stdoutRid > 0) {
-      this.stdout = new File(res.stdoutRid);
+    if (res.stdoutRid() > 0) {
+      this.stdout = new File(res.stdoutRid());
     }
 
-    if (res.stderrRid && res.stderrRid > 0) {
-      this.stderr = new File(res.stderrRid);
+    if (res.stderrRid() > 0) {
+      this.stderr = new File(res.stderrRid());
     }
   }
 
@@ -134,13 +135,14 @@ export interface ProcessStatus {
   signal?: number; // TODO: Make this a string, e.g. 'SIGTERM'.
 }
 
-// TODO: this method is only used to validate proper option, probably can be renamed
-function stdioMap(s: string): string {
+function stdioMap(s: ProcessStdio): msg.ProcessStdio {
   switch (s) {
     case "inherit":
+      return msg.ProcessStdio.Inherit;
     case "piped":
+      return msg.ProcessStdio.Piped;
     case "null":
-      return s;
+      return msg.ProcessStdio.Null;
     default:
       return unreachable();
   }
@@ -150,13 +152,6 @@ function isRid(arg: unknown): arg is number {
   return !isNaN(arg as number);
 }
 
-interface RunResponse {
-  rid: number;
-  pid: number;
-  stdinRid: number | null;
-  stdoutRid: number | null;
-  stderrRid: number | null;
-}
 /**
  * Spawns new subprocess.
  *
@@ -171,56 +166,71 @@ interface RunResponse {
  * they can be set to either `ProcessStdio` or `rid` of open file.
  */
 export function run(opt: RunOptions): Process {
-  assert(opt.args.length > 0);
-  let env: Array<[string, string]> = [];
+  const builder = flatbuffers.createBuilder();
+  const argsOffset = msg.Run.createArgsVector(
+    builder,
+    opt.args.map((a): number => builder.createString(a))
+  );
+  const cwdOffset = opt.cwd == null ? 0 : builder.createString(opt.cwd);
+  const kvOffset: flatbuffers.Offset[] = [];
   if (opt.env) {
-    env = Array.from(Object.entries(opt.env));
+    for (const [key, val] of Object.entries(opt.env)) {
+      const keyOffset = builder.createString(key);
+      const valOffset = builder.createString(String(val));
+      kvOffset.push(msg.KeyValue.createKeyValue(builder, keyOffset, valOffset));
+    }
   }
+  const envOffset = msg.Run.createEnvVector(builder, kvOffset);
 
-  let stdin = stdioMap("inherit");
-  let stdout = stdioMap("inherit");
-  let stderr = stdioMap("inherit");
-  let stdinRid = 0;
-  let stdoutRid = 0;
-  let stderrRid = 0;
+  let stdInOffset = stdioMap("inherit");
+  let stdOutOffset = stdioMap("inherit");
+  let stdErrOffset = stdioMap("inherit");
+  let stdinRidOffset = 0;
+  let stdoutRidOffset = 0;
+  let stderrRidOffset = 0;
 
   if (opt.stdin) {
     if (isRid(opt.stdin)) {
-      stdinRid = opt.stdin;
+      stdinRidOffset = opt.stdin;
     } else {
-      stdin = stdioMap(opt.stdin);
+      stdInOffset = stdioMap(opt.stdin);
     }
   }
 
   if (opt.stdout) {
     if (isRid(opt.stdout)) {
-      stdoutRid = opt.stdout;
+      stdoutRidOffset = opt.stdout;
     } else {
-      stdout = stdioMap(opt.stdout);
+      stdOutOffset = stdioMap(opt.stdout);
     }
   }
 
   if (opt.stderr) {
     if (isRid(opt.stderr)) {
-      stderrRid = opt.stderr;
+      stderrRidOffset = opt.stderr;
     } else {
-      stderr = stdioMap(opt.stderr);
+      stdErrOffset = stdioMap(opt.stderr);
     }
   }
 
-  const req = {
-    args: opt.args.map(String),
-    cwd: opt.cwd,
-    env,
-    stdin,
-    stdout,
-    stderr,
-    stdinRid,
-    stdoutRid,
-    stderrRid
-  };
+  const inner = msg.Run.createRun(
+    builder,
+    argsOffset,
+    cwdOffset,
+    envOffset,
+    stdInOffset,
+    stdOutOffset,
+    stdErrOffset,
+    stdinRidOffset,
+    stdoutRidOffset,
+    stderrRidOffset
+  );
+  const baseRes = sendSync(builder, msg.Any.Run, inner);
+  assert(baseRes != null);
+  assert(msg.Any.RunRes === baseRes!.innerType());
+  const res = new msg.RunRes();
+  assert(baseRes!.inner(res) != null);
 
-  const res = sendSync(dispatch.OP_RUN, req) as RunResponse;
   return new Process(res);
 }
 
diff --git a/js/repl.ts b/js/repl.ts
index ac6700657..c971e4420 100644
--- a/js/repl.ts
+++ b/js/repl.ts
@@ -1,12 +1,12 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import { assert } from "./util";
 import { close } from "./files";
+import { sendSync, sendAsync, msg, flatbuffers } from "./dispatch_flatbuffers";
 import { exit } from "./os";
 import { window } from "./window";
 import { core } from "./core";
 import { formatError } from "./format_error";
 import { stringifyArgs } from "./console";
-import * as dispatch from "./dispatch";
-import { sendSync, sendAsync } from "./dispatch_json";
 
 /**
  * REPL logging.
@@ -43,12 +43,34 @@ const replCommands = {
 };
 
 function startRepl(historyFile: string): number {
-  return sendSync(dispatch.OP_REPL_START, { historyFile });
+  const builder = flatbuffers.createBuilder();
+  const historyFile_ = builder.createString(historyFile);
+  const inner = msg.ReplStart.createReplStart(builder, historyFile_);
+
+  const baseRes = sendSync(builder, msg.Any.ReplStart, inner);
+  assert(baseRes != null);
+  assert(msg.Any.ReplStartRes === baseRes!.innerType());
+  const innerRes = new msg.ReplStartRes();
+  assert(baseRes!.inner(innerRes) != null);
+  const rid = innerRes.rid();
+  return rid;
 }
 
 // @internal
 export async function readline(rid: number, prompt: string): Promise<string> {
-  return sendAsync(dispatch.OP_REPL_READLINE, { rid, prompt });
+  const builder = flatbuffers.createBuilder();
+  const prompt_ = builder.createString(prompt);
+  const inner = msg.ReplReadline.createReplReadline(builder, rid, prompt_);
+
+  const baseRes = await sendAsync(builder, msg.Any.ReplReadline, inner);
+
+  assert(baseRes != null);
+  assert(msg.Any.ReplReadlineRes === baseRes!.innerType());
+  const innerRes = new msg.ReplReadlineRes();
+  assert(baseRes!.inner(innerRes) != null);
+  const line = innerRes.line();
+  assert(line !== null);
+  return line || "";
 }
 
 // Error messages that allow users to continue input
diff --git a/js/resources.ts b/js/resources.ts
index 6e2ec202b..49093fab1 100644
--- a/js/resources.ts
+++ b/js/resources.ts
@@ -1,6 +1,6 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import * as dispatch from "./dispatch";
-import { sendSync } from "./dispatch_json";
+import { assert } from "./util";
+import { sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
 
 export interface ResourceMap {
   [rid: number]: string;
@@ -10,10 +10,20 @@ export interface ResourceMap {
  * representation.
  */
 export function resources(): ResourceMap {
-  const res = sendSync(dispatch.OP_RESOURCES) as Array<[number, string]>;
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.Resource.createResource(builder, 0, 0);
+  const baseRes = sendSync(builder, msg.Any.Resources, inner);
+  assert(baseRes !== null);
+  assert(msg.Any.ResourcesRes === baseRes!.innerType());
+  const res = new msg.ResourcesRes();
+  assert(baseRes!.inner(res) !== null);
+
   const resources: ResourceMap = {};
-  for (const resourceTuple of res) {
-    resources[resourceTuple[0]] = resourceTuple[1];
+
+  for (let i = 0; i < res.resourcesLength(); i++) {
+    const item = res.resources(i)!;
+    resources[item.rid()!] = item.repr()!;
   }
+
   return resources;
 }
diff --git a/js/timers.ts b/js/timers.ts
index 079e779c4..cb0fd531c 100644
--- a/js/timers.ts
+++ b/js/timers.ts
@@ -1,8 +1,7 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 import { assert } from "./util";
+import { sendAsync, sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
 import { window } from "./window";
-import * as dispatch from "./dispatch";
-import { sendSync, sendAsync } from "./dispatch_json";
 
 interface Timer {
   id: number;
@@ -38,8 +37,11 @@ function getTime(): number {
 }
 
 function clearGlobalTimeout(): void {
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.GlobalTimerStop.createGlobalTimerStop(builder);
   globalTimeoutDue = null;
-  sendSync(dispatch.OP_GLOBAL_TIMER_STOP);
+  let res = sendSync(builder, msg.Any.GlobalTimerStop, inner);
+  assert(res == null);
 }
 
 async function setGlobalTimeout(due: number, now: number): Promise<void> {
@@ -50,8 +52,12 @@ async function setGlobalTimeout(due: number, now: number): Promise<void> {
   assert(timeout >= 0);
 
   // Send message to the backend.
+  const builder = flatbuffers.createBuilder();
+  msg.GlobalTimer.startGlobalTimer(builder);
+  msg.GlobalTimer.addTimeout(builder, timeout);
+  const inner = msg.GlobalTimer.endGlobalTimer(builder);
   globalTimeoutDue = due;
-  await sendAsync(dispatch.OP_GLOBAL_TIMER, { timeout });
+  await sendAsync(builder, msg.Any.GlobalTimer, inner);
   // eslint-disable-next-line @typescript-eslint/no-use-before-define
   fireTimers();
 }
diff --git a/js/workers.ts b/js/workers.ts
index 7bcbe6279..e59e853c5 100644
--- a/js/workers.ts
+++ b/js/workers.ts
@@ -1,8 +1,7 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 /* eslint-disable @typescript-eslint/no-explicit-any */
-import * as dispatch from "./dispatch";
-import { sendAsync, sendSync } from "./dispatch_json";
-import { log } from "./util";
+import { sendAsync, sendSync, msg, flatbuffers } from "./dispatch_flatbuffers";
+import { assert, log } from "./util";
 import { TextDecoder, TextEncoder } from "./text_encoding";
 import { window } from "./window";
 import { blobURLMap } from "./url";
@@ -27,28 +26,61 @@ function createWorker(
   hasSourceCode: boolean,
   sourceCode: Uint8Array
 ): number {
-  return sendSync(dispatch.OP_CREATE_WORKER, {
-    specifier,
+  const builder = flatbuffers.createBuilder();
+  const specifier_ = builder.createString(specifier);
+  const sourceCode_ = builder.createString(sourceCode);
+  const inner = msg.CreateWorker.createCreateWorker(
+    builder,
+    specifier_,
     includeDenoNamespace,
     hasSourceCode,
-    sourceCode: new TextDecoder().decode(sourceCode)
-  });
+    sourceCode_
+  );
+  const baseRes = sendSync(builder, msg.Any.CreateWorker, inner);
+  assert(baseRes != null);
+  assert(
+    msg.Any.CreateWorkerRes === baseRes!.innerType(),
+    `base.innerType() unexpectedly is ${baseRes!.innerType()}`
+  );
+  const res = new msg.CreateWorkerRes();
+  assert(baseRes!.inner(res) != null);
+  return res.rid();
 }
 
 async function hostGetWorkerClosed(rid: number): Promise<void> {
-  await sendAsync(dispatch.OP_HOST_GET_WORKER_CLOSED, { rid });
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.HostGetWorkerClosed.createHostGetWorkerClosed(builder, rid);
+  await sendAsync(builder, msg.Any.HostGetWorkerClosed, inner);
 }
 
 function hostPostMessage(rid: number, data: any): void {
   const dataIntArray = encodeMessage(data);
-  sendSync(dispatch.OP_HOST_POST_MESSAGE, { rid }, dataIntArray);
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.HostPostMessage.createHostPostMessage(builder, rid);
+  const baseRes = sendSync(
+    builder,
+    msg.Any.HostPostMessage,
+    inner,
+    dataIntArray
+  );
+  assert(baseRes != null);
 }
 
 async function hostGetMessage(rid: number): Promise<any> {
-  const res = await sendAsync(dispatch.OP_HOST_GET_MESSAGE, { rid });
-
-  if (res.data != null) {
-    return decodeMessage(new Uint8Array(res.data));
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.HostGetMessage.createHostGetMessage(builder, rid);
+  const baseRes = await sendAsync(builder, msg.Any.HostGetMessage, inner);
+  assert(baseRes != null);
+  assert(
+    msg.Any.HostGetMessageRes === baseRes!.innerType(),
+    `base.innerType() unexpectedly is ${baseRes!.innerType()}`
+  );
+  const res = new msg.HostGetMessageRes();
+  assert(baseRes!.inner(res) != null);
+
+  const dataArray = res.dataArray();
+  if (dataArray != null) {
+    return decodeMessage(dataArray);
   } else {
     return null;
   }
@@ -59,15 +91,36 @@ export let onmessage: (e: { data: any }) => void = (): void => {};
 
 export function postMessage(data: any): void {
   const dataIntArray = encodeMessage(data);
-  sendSync(dispatch.OP_WORKER_POST_MESSAGE, {}, dataIntArray);
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.WorkerPostMessage.createWorkerPostMessage(builder);
+  const baseRes = sendSync(
+    builder,
+    msg.Any.WorkerPostMessage,
+    inner,
+    dataIntArray
+  );
+  assert(baseRes != null);
 }
 
 export async function getMessage(): Promise<any> {
   log("getMessage");
-  const res = await sendAsync(dispatch.OP_WORKER_GET_MESSAGE);
-
-  if (res.data != null) {
-    return decodeMessage(new Uint8Array(res.data));
+  const builder = flatbuffers.createBuilder();
+  const inner = msg.WorkerGetMessage.createWorkerGetMessage(
+    builder,
+    0 /* unused */
+  );
+  const baseRes = await sendAsync(builder, msg.Any.WorkerGetMessage, inner);
+  assert(baseRes != null);
+  assert(
+    msg.Any.WorkerGetMessageRes === baseRes!.innerType(),
+    `base.innerType() unexpectedly is ${baseRes!.innerType()}`
+  );
+  const res = new msg.WorkerGetMessageRes();
+  assert(baseRes!.inner(res) != null);
+
+  const dataArray = res.dataArray();
+  if (dataArray != null) {
+    return decodeMessage(dataArray);
   } else {
     return null;
   }
diff --git a/tests/error_004_missing_module.ts.out b/tests/error_004_missing_module.ts.out
index e8d672739..cb0f3bc5a 100644
--- a/tests/error_004_missing_module.ts.out
+++ b/tests/error_004_missing_module.ts.out
@@ -1,12 +1,12 @@
 [WILDCARD]error: Uncaught NotFound: Cannot resolve module "[WILDCARD]/bad-module.ts"
-[WILDCARD] js/dispatch_json.ts:[WILDCARD]
+[WILDCARD] js/dispatch_flatbuffers.ts:[WILDCARD]
     at DenoError (js/errors.ts:[WILDCARD])
-    at toDenoError (js/dispatch_json.ts:[WILDCARD])
-    at sendSync$1 (js/dispatch_json.ts:[WILDCARD])
+    at maybeError (js/dispatch_flatbuffers.ts:[WILDCARD])
+    at maybeThrowError (js/dispatch_flatbuffers.ts:[WILDCARD])
+    at sendSync (js/dispatch_flatbuffers.ts:[WILDCARD])
     at fetchSourceFile (js/compiler.ts:[WILDCARD])
     at _resolveModule (js/compiler.ts:[WILDCARD])
     at js/compiler.ts:[WILDCARD]
     at resolveModuleNames (js/compiler.ts:[WILDCARD])
     at resolveModuleNamesWorker ([WILDCARD]typescript.js:[WILDCARD])
     at resolveModuleNamesReusingOldState ([WILDCARD]typescript.js:[WILDCARD])
-    at processImportedModules ([WILDCARD]typescript.js:[WILDCARD])
diff --git a/tests/error_005_missing_dynamic_import.ts.out b/tests/error_005_missing_dynamic_import.ts.out
index 2f39dc853..fbc25f701 100644
--- a/tests/error_005_missing_dynamic_import.ts.out
+++ b/tests/error_005_missing_dynamic_import.ts.out
@@ -1,11 +1,11 @@
 [WILDCARD]error: Uncaught NotFound: Cannot resolve module "[WILDCARD]/bad-module.ts"
-[WILDCARD] js/dispatch_json.ts:[WILDCARD]
+[WILDCARD] js/dispatch_flatbuffers.ts:[WILDCARD]
     at DenoError (js/errors.ts:[WILDCARD])
-    at toDenoError (js/dispatch_json.ts:[WILDCARD])
-    at sendSync$1 (js/dispatch_json.ts:[WILDCARD])
+    at maybeError (js/dispatch_flatbuffers.ts:[WILDCARD])
+    at maybeThrowError (js/dispatch_flatbuffers.ts:[WILDCARD])
+    at sendSync (js/dispatch_flatbuffers.ts:[WILDCARD])
     at fetchSourceFile (js/compiler.ts:[WILDCARD])
     at _resolveModule (js/compiler.ts:[WILDCARD])
     at js/compiler.ts:[WILDCARD]
     at resolveModuleNamesWorker ([WILDCARD])
     at resolveModuleNamesReusingOldState ([WILDCARD]typescript.js:[WILDCARD])
-    at processImportedModules ([WILDCARD]typescript.js:[WILDCARD])
diff --git a/tests/error_006_import_ext_failure.ts.out b/tests/error_006_import_ext_failure.ts.out
index b381fa96d..cb7ccee85 100644
--- a/tests/error_006_import_ext_failure.ts.out
+++ b/tests/error_006_import_ext_failure.ts.out
@@ -1,11 +1,11 @@
 [WILDCARD]error: Uncaught NotFound: Cannot resolve module "[WILDCARD]/non-existent"
-[WILDCARD] js/dispatch_json.ts:[WILDCARD]
+[WILDCARD] js/dispatch_flatbuffers.ts:[WILDCARD]
     at DenoError (js/errors.ts:[WILDCARD])
-    at toDenoError (js/dispatch_json.ts:[WILDCARD])
-    at sendSync$1 (js/dispatch_json.ts:[WILDCARD])
+    at maybeError (js/dispatch_flatbuffers.ts:[WILDCARD])
+    at maybeThrowError (js/dispatch_flatbuffers.ts:[WILDCARD])
+    at sendSync (js/dispatch_flatbuffers.ts:[WILDCARD])
     at fetchSourceFile (js/compiler.ts:[WILDCARD])
     at _resolveModule (js/compiler.ts:[WILDCARD])
     at js/compiler.ts:[WILDCARD]
     at resolveModuleNamesWorker ([WILDCARD])
     at resolveModuleNamesReusingOldState ([WILDCARD]typescript.js:[WILDCARD])
-    at processImportedModules ([WILDCARD]typescript.js:[WILDCARD])
diff --git a/tests/error_011_bad_module_specifier.ts.out b/tests/error_011_bad_module_specifier.ts.out
index 1d8e8c97e..1590f4e15 100644
--- a/tests/error_011_bad_module_specifier.ts.out
+++ b/tests/error_011_bad_module_specifier.ts.out
@@ -1,11 +1,12 @@
 [WILDCARD]error: Uncaught ImportPrefixMissing: relative import path "bad-module.ts" not prefixed with / or ./ or ../
-[WILDCARD] js/dispatch_json.ts:[WILDCARD]
+[WILDCARD] js/dispatch_flatbuffers.ts:[WILDCARD]
     at DenoError (js/errors.ts:[WILDCARD])
-    at toDenoError (js/dispatch_json.ts:[WILDCARD])
-    at sendSync$1 (js/dispatch_json.ts:[WILDCARD])
+    at maybeError (js/dispatch_flatbuffers.ts:[WILDCARD])
+    at maybeThrowError (js/dispatch_flatbuffers.ts:[WILDCARD])
+    at sendSync (js/dispatch_flatbuffers.ts:[WILDCARD])
     at fetchSourceFile (js/compiler.ts:[WILDCARD])
     at _resolveModule (js/compiler.ts:[WILDCARD])
     at js/compiler.ts:[WILDCARD]
-    at resolveModuleNamesWorker ([WILDCARD])
+    at resolveModuleNames (js/compiler.ts:[WILDCARD])
+    at resolveModuleNamesWorker ([WILDCARD]typescript.js:[WILDCARD])
     at resolveModuleNamesReusingOldState ([WILDCARD]typescript.js:[WILDCARD])
-    at processImportedModules ([WILDCARD]typescript.js:[WILDCARD])
diff --git a/tests/error_012_bad_dynamic_import_specifier.ts.out b/tests/error_012_bad_dynamic_import_specifier.ts.out
index 1d8e8c97e..ec5cba6f7 100644
--- a/tests/error_012_bad_dynamic_import_specifier.ts.out
+++ b/tests/error_012_bad_dynamic_import_specifier.ts.out
@@ -1,11 +1,12 @@
 [WILDCARD]error: Uncaught ImportPrefixMissing: relative import path "bad-module.ts" not prefixed with / or ./ or ../
-[WILDCARD] js/dispatch_json.ts:[WILDCARD]
+[WILDCARD] js/dispatch_flatbuffers.ts:[WILDCARD]
     at DenoError (js/errors.ts:[WILDCARD])
-    at toDenoError (js/dispatch_json.ts:[WILDCARD])
-    at sendSync$1 (js/dispatch_json.ts:[WILDCARD])
+    at maybeError (js/dispatch_flatbuffers.ts:[WILDCARD])
+    at maybeThrowError (js/dispatch_flatbuffers.ts:[WILDCARD])
+    at sendSync (js/dispatch_flatbuffers.ts:[WILDCARD])
     at fetchSourceFile (js/compiler.ts:[WILDCARD])
     at _resolveModule (js/compiler.ts:[WILDCARD])
     at js/compiler.ts:[WILDCARD]
+    at resolveModuleNames (js/compiler.ts:[WILDCARD])
     at resolveModuleNamesWorker ([WILDCARD])
     at resolveModuleNamesReusingOldState ([WILDCARD]typescript.js:[WILDCARD])
-    at processImportedModules ([WILDCARD]typescript.js:[WILDCARD])