Adds basic File I/O and FD table.

Adds deno.stdin, deno.stdout, deno.stderr, deno.open(), deno.write(),
deno.read(), deno.Reader, deno.Writer, deno.copy().

Fixes #721. tests/cat.ts works.

12 files changed, 553 insertions, 2 deletions

diff --git a/BUILD.gn b/BUILD.gn
index b901b1764..e573b7504 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -54,6 +54,8 @@ main_extern = [
   "$rust_build:tempfile",
   "$rust_build:rand",
   "$rust_build:tokio",
+  "$rust_build:tokio_io",
+  "$rust_build:tokio_fs",
   "$rust_build:tokio_executor",
   "$rust_build:tokio_threadpool",
   "$rust_build:url",
@@ -73,6 +75,8 @@ ts_sources = [
   "js/dom_types.ts",
   "js/errors.ts",
   "js/fetch.ts",
+  "js/files.ts",
+  "js/io.ts",
   "js/global-eval.ts",
   "js/globals.ts",
   "js/libdeno.ts",
diff --git a/js/deno.ts b/js/deno.ts
index 92ba5301d..44fba6164 100644
--- a/js/deno.ts
+++ b/js/deno.ts
@@ -2,6 +2,8 @@
 // Public deno module.
 /// <amd-module name="deno"/>
 export { env, exit } from "./os";
+export { File, open, stdin, stdout, stderr, read, write, close } from "./files";
+export { copy, Reader, Writer } from "./io";
 export { mkdirSync, mkdir } from "./mkdir";
 export { makeTempDirSync, makeTempDir } from "./make_temp_dir";
 export { removeSync, remove, removeAllSync, removeAll } from "./remove";
diff --git a/js/files.ts b/js/files.ts
new file mode 100644
index 000000000..d22f1b390
--- /dev/null
+++ b/js/files.ts
@@ -0,0 +1,89 @@
+// Copyright 2018 the Deno authors. All rights reserved. MIT license.
+
+import { Reader, Writer, Closer, ReadResult } from "./io";
+import * as dispatch from "./dispatch";
+import * as fbs from "gen/msg_generated";
+import { assert } from "./util";
+import { flatbuffers } from "flatbuffers";
+
+export class File implements Reader, Writer, Closer {
+  constructor(readonly fd: number) {}
+
+  write(p: ArrayBufferView): Promise<number> {
+    return write(this.fd, p);
+  }
+
+  read(p: ArrayBufferView): Promise<ReadResult> {
+    return read(this.fd, p);
+  }
+
+  close(): void {
+    return close(this.fd);
+  }
+}
+
+export const stdin = new File(0);
+export const stdout = new File(1);
+export const stderr = new File(2);
+
+// TODO This is just a placeholder - not final API.
+export type OpenMode = "r" | "w" | "w+" | "x";
+
+export function create(filename: string): Promise<File> {
+  return open(filename, "x");
+}
+
+export async function open(
+  filename: string,
+  mode: OpenMode = "r"
+): Promise<File> {
+  const builder = new flatbuffers.Builder();
+  const filename_ = builder.createString(filename);
+  fbs.Open.startOpen(builder);
+  fbs.Open.addFilename(builder, filename_);
+  const msg = fbs.Open.endOpen(builder);
+  const baseRes = await dispatch.sendAsync(builder, fbs.Any.Open, msg);
+  assert(baseRes != null);
+  assert(fbs.Any.OpenRes === baseRes!.msgType());
+  const res = new fbs.OpenRes();
+  assert(baseRes!.msg(res) != null);
+  const fd = res.fd();
+  return new File(fd);
+}
+
+export async function read(
+  fd: number,
+  p: ArrayBufferView
+): Promise<ReadResult> {
+  const builder = new flatbuffers.Builder();
+  fbs.Read.startRead(builder);
+  fbs.Read.addFd(builder, fd);
+  const msg = fbs.Read.endRead(builder);
+  const baseRes = await dispatch.sendAsync(builder, fbs.Any.Read, msg, p);
+  assert(baseRes != null);
+  assert(fbs.Any.ReadRes === baseRes!.msgType());
+  const res = new fbs.ReadRes();
+  assert(baseRes!.msg(res) != null);
+  return { nread: res.nread(), eof: res.eof() };
+}
+
+export async function write(fd: number, p: ArrayBufferView): Promise<number> {
+  const builder = new flatbuffers.Builder();
+  fbs.Write.startWrite(builder);
+  fbs.Write.addFd(builder, fd);
+  const msg = fbs.Write.endWrite(builder);
+  const baseRes = await dispatch.sendAsync(builder, fbs.Any.Write, msg, p);
+  assert(baseRes != null);
+  assert(fbs.Any.WriteRes === baseRes!.msgType());
+  const res = new fbs.WriteRes();
+  assert(baseRes!.msg(res) != null);
+  return res.nbyte();
+}
+
+export function close(fd: number): void {
+  const builder = new flatbuffers.Builder();
+  fbs.Close.startClose(builder);
+  fbs.Close.addFd(builder, fd);
+  const msg = fbs.Close.endClose(builder);
+  dispatch.sendSync(builder, fbs.Any.Close, msg);
+}
diff --git a/js/files_test.ts b/js/files_test.ts
new file mode 100644
index 000000000..82af10aa2
--- /dev/null
+++ b/js/files_test.ts
@@ -0,0 +1,20 @@
+// Copyright 2018 the Deno authors. All rights reserved. MIT license.
+
+import * as deno from "deno";
+import { test, assert, assertEqual } from "./test_util.ts";
+
+test(function filesStdioFileDescriptors() {
+  assertEqual(deno.stdin.fd, 0);
+  assertEqual(deno.stdout.fd, 1);
+  assertEqual(deno.stderr.fd, 2);
+});
+
+test(async function filesCopyToStdout() {
+  const filename = "package.json";
+  const file = await deno.open(filename);
+  assert(file.fd > 2);
+  const bytesWritten = await deno.copy(deno.stdout, file);
+  const fileSize = deno.statSync(filename).len;
+  assertEqual(bytesWritten, fileSize);
+  console.log("bytes written", bytesWritten);
+});
diff --git a/js/io.ts b/js/io.ts
new file mode 100644
index 000000000..710722f42
--- /dev/null
+++ b/js/io.ts
@@ -0,0 +1,114 @@
+// Interfaces 100% copied from Go.
+// Documentation liberally lifted from them too.
+// Thank you! We love Go!
+
+// The bytes read during an I/O call and a boolean indicating EOF.
+export interface ReadResult {
+  nread: number;
+  eof: boolean;
+}
+
+// Reader is the interface that wraps the basic read() method.
+// https://golang.org/pkg/io/#Reader
+export interface Reader {
+  // read() reads up to p.byteLength bytes into p. It returns the number of
+  // bytes read (0 <= n <= p.byteLength) and any error encountered. Even if
+  // read() returns n < p.byteLength, it may use all of p as scratch space
+  // during the call. If some data is available but not p.byteLength bytes,
+  // read() conventionally returns what is available instead of waiting for
+  // more.
+  //
+  // When read() encounters an error or end-of-file condition after successfully
+  // reading n > 0 bytes, it returns the number of bytes read. It may return the
+  // (non-nil) error from the same call or return the error (and n == 0) from a
+  // subsequent call. An instance of this general case is that a Reader
+  // returning a non-zero number of bytes at the end of the input stream may
+  // return either err == EOF or err == nil. The next read() should return 0,
+  // EOF.
+  //
+  // Callers should always process the n > 0 bytes returned before considering
+  // the EOF. Doing so correctly handles I/O errors that happen after reading
+  // some bytes and also both of the allowed EOF behaviors.
+  //
+  // Implementations of read() are discouraged from returning a zero byte count
+  // with a nil error, except when p.byteLength == 0. Callers should treat a
+  // return of 0 and nil as indicating that nothing happened; in particular it
+  // does not indicate EOF.
+  //
+  // Implementations must not retain p.
+  read(p: ArrayBufferView): Promise<ReadResult>;
+}
+
+// Writer is the interface that wraps the basic write() method.
+// https://golang.org/pkg/io/#Writer
+export interface Writer {
+  // write() writes p.byteLength bytes from p to the underlying data stream. It
+  // returns the number of bytes written from p (0 <= n <= p.byteLength) and any
+  // error encountered that caused the write to stop early. write() must return
+  // a non-nil error if it returns n < p.byteLength. write() must not modify the
+  // slice data, even temporarily.
+  //
+  // Implementations must not retain p.
+  write(p: ArrayBufferView): Promise<number>;
+}
+
+// https://golang.org/pkg/io/#Closer
+export interface Closer {
+  // The behavior of Close after the first call is undefined. Specific
+  // implementations may document their own behavior.
+  close(): void;
+}
+
+// https://golang.org/pkg/io/#Seeker
+export interface Seeker {
+  // Seek sets the offset for the next read() or write() to offset, interpreted
+  // according to whence: SeekStart means relative to the start of the file,
+  // SeekCurrent means relative to the current offset, and SeekEnd means
+  // relative to the end. Seek returns the new offset relative to the start of
+  // the file and an error, if any.
+  //
+  // Seeking to an offset before the start of the file is an error. Seeking to
+  // any positive offset is legal, but the behavior of subsequent I/O operations
+  // on the underlying object is implementation-dependent.
+  seek(offset: number, whence: number): Promise<void>;
+}
+
+// https://golang.org/pkg/io/#ReadCloser
+export interface ReaderCloser extends Reader, Closer {}
+
+// https://golang.org/pkg/io/#WriteCloser
+export interface WriteCloser extends Writer, Closer {}
+
+// https://golang.org/pkg/io/#ReadSeeker
+export interface ReadSeeker extends Reader, Seeker {}
+
+// https://golang.org/pkg/io/#WriteSeeker
+export interface WriteSeeker extends Writer, Seeker {}
+
+// https://golang.org/pkg/io/#ReadWriteCloser
+export interface ReadWriteCloser extends Reader, Writer, Closer {}
+
+// https://golang.org/pkg/io/#ReadWriteSeeker
+export interface ReadWriteSeeker extends Reader, Writer, Seeker {}
+
+// copy() copies from src to dst until either EOF is reached on src or an error
+// occurs. It returns the number of bytes copied and the first error encountered
+// while copying, if any.
+//
+// Because copy() is defined to read from src until EOF, it does not treat an
+// EOF from read() as an error to be reported.
+//
+// https://golang.org/pkg/io/#Copy
+export async function copy(dst: Writer, src: Reader): Promise<number> {
+  let n = 0;
+  const b = new Uint8Array(1024);
+  let gotEOF = false;
+  while (gotEOF === false) {
+    const result = await src.read(b);
+    if (result.eof) {
+      gotEOF = true;
+    }
+    n += await dst.write(b.subarray(0, result.nread));
+  }
+  return n;
+}
diff --git a/js/unit_tests.ts b/js/unit_tests.ts
index 578a65c6d..3a1fdd9d1 100644
--- a/js/unit_tests.ts
+++ b/js/unit_tests.ts
@@ -5,6 +5,7 @@ import "./compiler_test.ts";
 import "./console_test.ts";
 import "./fetch_test.ts";
 import "./os_test.ts";
+import "./files_test.ts";
 import "./read_file_test.ts";
 import "./write_file_test.ts";
 import "./mkdir_test.ts";
diff --git a/src/errors.rs b/src/errors.rs
index 1bedf8d40..872f3492e 100644
--- a/src/errors.rs
+++ b/src/errors.rs
@@ -15,15 +15,22 @@ pub struct DenoError {
 
 #[derive(Debug)]
 enum Repr {
-  // Simple(ErrorKind),
+  Simple(ErrorKind, String),
   IoErr(io::Error),
   UrlErr(url::ParseError),
   HyperErr(hyper::Error),
 }
 
+pub fn new(kind: ErrorKind, msg: String) -> DenoError {
+  DenoError {
+    repr: Repr::Simple(kind, msg),
+  }
+}
+
 impl DenoError {
   pub fn kind(&self) -> ErrorKind {
     match self.repr {
+      Repr::Simple(kind, ref _msg) => kind,
       // Repr::Simple(kind) => kind,
       Repr::IoErr(ref err) => {
         use std::io::ErrorKind::*;
@@ -87,10 +94,10 @@ impl DenoError {
 impl fmt::Display for DenoError {
   fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
     match self.repr {
+      Repr::Simple(_kind, ref _msg) => panic!("todo"),
       Repr::IoErr(ref err) => err.fmt(f),
       Repr::UrlErr(ref err) => err.fmt(f),
       Repr::HyperErr(ref err) => err.fmt(f),
-      // Repr::Simple(..) => Ok(()),
     }
   }
 }
@@ -98,6 +105,7 @@ impl fmt::Display for DenoError {
 impl std::error::Error for DenoError {
   fn description(&self) -> &str {
     match self.repr {
+      Repr::Simple(_kind, ref msg) => msg.as_str(),
       Repr::IoErr(ref err) => err.description(),
       Repr::UrlErr(ref err) => err.description(),
       Repr::HyperErr(ref err) => err.description(),
@@ -107,6 +115,7 @@ impl std::error::Error for DenoError {
 
   fn cause(&self) -> Option<&std::error::Error> {
     match self.repr {
+      Repr::Simple(_kind, ref _msg) => None,
       Repr::IoErr(ref err) => Some(err),
       Repr::UrlErr(ref err) => Some(err),
       Repr::HyperErr(ref err) => Some(err),
diff --git a/src/files.rs b/src/files.rs
new file mode 100644
index 000000000..64160bb84
--- /dev/null
+++ b/src/files.rs
@@ -0,0 +1,119 @@
+// Copyright 2018 the Deno authors. All rights reserved. MIT license.
+
+use futures;
+use futures::Poll;
+use std;
+use std::collections::HashMap;
+use std::io::Error;
+use std::io::{Read, Write};
+use std::sync::atomic::AtomicIsize;
+use std::sync::atomic::Ordering;
+use std::sync::Mutex;
+use tokio;
+use tokio::io::{AsyncRead, AsyncWrite};
+
+// These store Deno's file descriptors. These are not necessarally the operating
+// system ones.
+type FdTable = HashMap<i32, Repr>;
+
+lazy_static! {
+  // Starts at 3 because stdio is [0-2].
+  static ref NEXT_FD: AtomicIsize = AtomicIsize::new(3);
+  static ref FD_TABLE: Mutex<FdTable> = Mutex::new({
+    let mut m = HashMap::new();
+    // TODO Load these lazily during lookup?
+    m.insert(0, Repr::Stdin(tokio::io::stdin()));
+    m.insert(1, Repr::Stdout(tokio::io::stdout()));
+    m.insert(2, Repr::Stderr(tokio::io::stderr()));
+    m
+  });
+}
+
+// Internal representation of DFile.
+enum Repr {
+  Stdin(tokio::io::Stdin),
+  Stdout(tokio::io::Stdout),
+  Stderr(tokio::io::Stderr),
+  FsFile(tokio::fs::File),
+}
+
+// Abstract async file interface.
+// fd does not necessarally correspond to an OS fd.
+// Ideally in unix, if DFile represents an OS fd, it will be the same.
+pub struct DFile {
+  pub fd: i32,
+}
+
+impl Read for DFile {
+  fn read(&mut self, _buf: &mut [u8]) -> std::io::Result<usize> {
+    unimplemented!();
+  }
+}
+
+impl AsyncRead for DFile {
+  fn poll_read(&mut self, buf: &mut [u8]) -> Poll<usize, Error> {
+    let mut table = FD_TABLE.lock().unwrap();
+    let maybe_repr = table.get_mut(&self.fd);
+    match maybe_repr {
+      None => panic!("bad fd"),
+      Some(repr) => match repr {
+        Repr::FsFile(ref mut f) => f.poll_read(buf),
+        Repr::Stdin(ref mut f) => f.poll_read(buf),
+        Repr::Stdout(_) | Repr::Stderr(_) => {
+          panic!("Cannot read from stdout/stderr")
+        }
+      },
+    }
+  }
+}
+
+impl Write for DFile {
+  fn write(&mut self, _buf: &[u8]) -> std::io::Result<usize> {
+    unimplemented!()
+  }
+
+  fn flush(&mut self) -> std::io::Result<()> {
+    unimplemented!()
+  }
+}
+
+impl AsyncWrite for DFile {
+  fn poll_write(&mut self, buf: &[u8]) -> Poll<usize, Error> {
+    let mut table = FD_TABLE.lock().unwrap();
+    let maybe_repr = table.get_mut(&self.fd);
+    match maybe_repr {
+      None => panic!("bad fd"),
+      Some(repr) => match repr {
+        Repr::FsFile(ref mut f) => f.poll_write(buf),
+        Repr::Stdout(ref mut f) => f.poll_write(buf),
+        Repr::Stderr(ref mut f) => f.poll_write(buf),
+        Repr::Stdin(_) => panic!("Cannot write to stdin"),
+      },
+    }
+  }
+
+  fn shutdown(&mut self) -> futures::Poll<(), std::io::Error> {
+    unimplemented!()
+  }
+}
+
+fn new_fd() -> i32 {
+  // TODO If on unix, just extract the real FD of fs_file.
+  // let fd = AsRawFd::as_raw_fd(fs_file.std());
+  let next_fd = NEXT_FD.fetch_add(1, Ordering::SeqCst);
+  next_fd as i32
+}
+
+pub fn add_fs_file(fs_file: tokio::fs::File) -> DFile {
+  let fd = new_fd();
+  let mut tg = FD_TABLE.lock().unwrap();
+  match tg.insert(fd, Repr::FsFile(fs_file)) {
+    Some(_) => panic!("There is already a file with that fd"),
+    None => DFile { fd },
+  }
+}
+
+pub fn lookup(fd: i32) -> Option<DFile> {
+  let table = FD_TABLE.lock().unwrap();
+  table.get(&fd).map(|_| DFile { fd })
+}
diff --git a/src/handlers.rs b/src/handlers.rs
index 62bdabb61..b1ef67d94 100644
--- a/src/handlers.rs
+++ b/src/handlers.rs
@@ -1,5 +1,6 @@
 // Copyright 2018 the Deno authors. All rights reserved. MIT license.
 
+use errors;
 use errors::DenoError;
 use errors::DenoResult;
 use fs as deno_fs;
@@ -8,6 +9,7 @@ use isolate::IsolateState;
 use isolate::Op;
 use msg;
 
+use files;
 use flatbuffers::FlatBufferBuilder;
 use futures;
 use futures::future::poll_fn;
@@ -26,7 +28,10 @@ use std::path::PathBuf;
 use std::sync::Arc;
 use std::time::UNIX_EPOCH;
 use std::time::{Duration, Instant};
+use tokio;
 use tokio::timer::Delay;
+use tokio_io::AsyncRead;
+use tokio_io::AsyncWrite;
 use tokio_threadpool;
 
 type OpResult = DenoResult<Buf>;
@@ -62,6 +67,9 @@ pub fn msg_from_js(
     msg::Any::TimerClear => handle_timer_clear,
     msg::Any::MakeTempDir => handle_make_temp_dir,
     msg::Any::Mkdir => handle_mkdir,
+    msg::Any::Open => handle_open,
+    msg::Any::Read => handle_read,
+    msg::Any::Write => handle_write,
     msg::Any::Remove => handle_remove,
     msg::Any::ReadFile => handle_read_file,
     msg::Any::Rename => handle_rename,
@@ -551,6 +559,129 @@ fn handle_mkdir(
   })
 }
 
+fn handle_open(
+  _state: Arc<IsolateState>,
+  base: &msg::Base,
+  data: &'static mut [u8],
+) -> Box<Op> {
+  assert_eq!(data.len(), 0);
+  let cmd_id = base.cmd_id();
+  let msg = base.msg_as_open().unwrap();
+  let filename = PathBuf::from(msg.filename().unwrap());
+  // TODO let perm = msg.perm();
+
+  let op = tokio::fs::File::open(filename)
+    .map_err(|err| DenoError::from(err))
+    .and_then(move |fs_file| -> OpResult {
+      let dfile = files::add_fs_file(fs_file);
+      let builder = &mut FlatBufferBuilder::new();
+      let msg = msg::OpenRes::create(
+        builder,
+        &msg::OpenResArgs {
+          fd: dfile.fd,
+          ..Default::default()
+        },
+      );
+      Ok(serialize_response(
+        cmd_id,
+        builder,
+        msg::BaseArgs {
+          msg: Some(msg.as_union_value()),
+          msg_type: msg::Any::OpenRes,
+          ..Default::default()
+        },
+      ))
+    });
+  Box::new(op)
+}
+
+fn handle_read(
+  _state: Arc<IsolateState>,
+  base: &msg::Base,
+  data: &'static mut [u8],
+) -> Box<Op> {
+  let cmd_id = base.cmd_id();
+  let msg = base.msg_as_read().unwrap();
+  let fd = msg.fd();
+
+  match files::lookup(fd) {
+    None => odd_future(errors::new(
+      errors::ErrorKind::BadFileDescriptor,
+      String::from("Bad File Descriptor"),
+    )),
+    Some(mut dfile) => {
+      let op = futures::future::poll_fn(move || {
+        let poll = dfile.poll_read(data);
+        poll
+      }).map_err(|err| DenoError::from(err))
+      .and_then(move |nread: usize| {
+        let builder = &mut FlatBufferBuilder::new();
+        let msg = msg::ReadRes::create(
+          builder,
+          &msg::ReadResArgs {
+            nread: nread as u32,
+            eof: nread == 0,
+            ..Default::default()
+          },
+        );
+        Ok(serialize_response(
+          cmd_id,
+          builder,
+          msg::BaseArgs {
+            msg: Some(msg.as_union_value()),
+            msg_type: msg::Any::ReadRes,
+            ..Default::default()
+          },
+        ))
+      });
+      Box::new(op)
+    }
+  }
+}
+
+fn handle_write(
+  _state: Arc<IsolateState>,
+  base: &msg::Base,
+  data: &'static mut [u8],
+) -> Box<Op> {
+  let cmd_id = base.cmd_id();
+  let msg = base.msg_as_write().unwrap();
+  let fd = msg.fd();
+
+  match files::lookup(fd) {
+    None => odd_future(errors::new(
+      errors::ErrorKind::BadFileDescriptor,
+      String::from("Bad File Descriptor"),
+    )),
+    Some(mut dfile) => {
+      let op = futures::future::poll_fn(move || {
+        let poll = dfile.poll_write(data);
+        poll
+      }).map_err(|err| DenoError::from(err))
+      .and_then(move |bytes_written: usize| {
+        let builder = &mut FlatBufferBuilder::new();
+        let msg = msg::WriteRes::create(
+          builder,
+          &msg::WriteResArgs {
+            nbyte: bytes_written as u32,
+            ..Default::default()
+          },
+        );
+        Ok(serialize_response(
+          cmd_id,
+          builder,
+          msg::BaseArgs {
+            msg: Some(msg.as_union_value()),
+            msg_type: msg::Any::WriteRes,
+            ..Default::default()
+          },
+        ))
+      });
+      Box::new(op)
+    }
+  }
+}
+
 fn handle_remove(
   state: Arc<IsolateState>,
   base: &msg::Base,
diff --git a/src/main.rs b/src/main.rs
index cc762f1ae..01be538e1 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -8,6 +8,8 @@ extern crate rand;
 extern crate tempfile;
 extern crate tokio;
 extern crate tokio_executor;
+extern crate tokio_fs;
+extern crate tokio_io;
 extern crate tokio_threadpool;
 extern crate url;
 #[macro_use]
@@ -21,6 +23,7 @@ extern crate ring;
 
 mod deno_dir;
 mod errors;
+mod files;
 mod flags;
 mod fs;
 pub mod handlers;
diff --git a/src/msg.fbs b/src/msg.fbs
index 0d78395ea..7f42cd637 100644
--- a/src/msg.fbs
+++ b/src/msg.fbs
@@ -27,6 +27,13 @@ union Any {
   Stat,
   StatRes,
   SetEnv,
+  Open,
+  OpenRes,
+  Read,
+  ReadRes,
+  Write,
+  WriteRes,
+  Close,
 }
 
 enum ErrorKind: byte {
@@ -53,6 +60,8 @@ enum ErrorKind: byte {
   Other,
   UnexpectedEof,
 
+  BadFileDescriptor,
+
   // url errors
 
   EmptyHost,
@@ -199,6 +208,7 @@ table ReadFileRes {
 
 table WriteFile {
   filename: string;
+  data: [ubyte];
   perm: uint;
   // perm specified by https://godoc.org/os#FileMode
 }
@@ -237,4 +247,42 @@ table StatRes {
   has_mode: bool; // false on windows
 }
 
+table WriteFileSync {
+  filename: string;
+  data: [ubyte];
+  perm: uint;
+  // perm specified by https://godoc.org/os#FileMode
+}
+
+table Open {
+  filename: string;
+  perm: uint;
+}
+
+table OpenRes {
+  fd: int;
+}
+
+table Read {
+  fd: int;
+  // (ptr, len) is passed as second parameter to libdeno.send().
+}
+
+table ReadRes {
+  nread: uint;
+  eof: bool;
+}
+
+table Write {
+  fd: int;
+}
+
+table WriteRes {
+  nbyte: uint;
+}
+
+table Close {
+  fd: int;
+}
+
 root_type Base;
diff --git a/tests/cat.ts b/tests/cat.ts
new file mode 100644
index 000000000..bede0d432
--- /dev/null
+++ b/tests/cat.ts
@@ -0,0 +1,11 @@
+import { stdout, open, copy, args } from "deno";
+
+async function main() {
+  for (let i = 1; i < args.length; i++) {
+    let filename = args[i];
+    let file = await open(filename);
+    await copy(stdout, file);
+  }
+}
+
+main();