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.

17 files changed, 924 insertions, 728 deletions

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()
+    },
+  ))
 }