Move Add-on SDK source to toolkit/jetpack

6 files changed, 2310 insertions, 0 deletions

diff --git a/toolkit/jetpack/sdk/io/buffer.js b/toolkit/jetpack/sdk/io/buffer.js
new file mode 100644
index 000000000..5ea169402
--- /dev/null
+++ b/toolkit/jetpack/sdk/io/buffer.js
@@ -0,0 +1,351 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+'use strict';
+
+module.metadata = {
+  'stability': 'experimental'
+};
+
+/*
+ * Encodings supported by TextEncoder/Decoder:
+ * utf-8, utf-16le, utf-16be
+ * http://encoding.spec.whatwg.org/#interface-textencoder
+ *
+ * Node however supports the following encodings:
+ * ascii, utf-8, utf-16le, usc2, base64, hex
+ */
+
+const { Cu } = require('chrome');
+const { isNumber } = require('sdk/lang/type');
+const { TextEncoder, TextDecoder } = Cu.import('resource://gre/modules/commonjs/toolkit/loader.js', {});
+
+exports.TextEncoder = TextEncoder;
+exports.TextDecoder = TextDecoder;
+
+/**
+ * Use WeakMaps to work around Bug 929146, which prevents us from adding
+ * getters or values to typed arrays
+ * https://bugzilla.mozilla.org/show_bug.cgi?id=929146
+ */
+const parents = new WeakMap();
+const views = new WeakMap();
+
+function Buffer(subject, encoding /*, bufferLength */) {
+
+  // Allow invocation without `new` constructor
+  if (!(this instanceof Buffer))
+    return new Buffer(subject, encoding, arguments[2]);
+
+  var type = typeof(subject);
+
+  switch (type) {
+    case 'number':
+      // Create typed array of the given size if number.
+      try {
+        let buffer = new Uint8Array(subject > 0 ? Math.floor(subject) : 0);
+        return buffer;
+      } catch (e) {
+        if (/size and count too large/.test(e.message) ||
+            /invalid arguments/.test(e.message))
+          throw new RangeError('Could not instantiate buffer: size of buffer may be too large');
+        else
+          throw new Error('Could not instantiate buffer');
+      }
+      break;
+    case 'string':
+      // If string encode it and use buffer for the returned Uint8Array
+      // to create a local patched version that acts like node buffer.
+      encoding = encoding || 'utf8';
+      return new Uint8Array(new TextEncoder(encoding).encode(subject).buffer);
+    case 'object':
+      // This form of the constructor uses the form of
+      // new Uint8Array(buffer, offset, length);
+      // So we can instantiate a typed array within the constructor
+      // to inherit the appropriate properties, where both the
+      // `subject` and newly instantiated buffer share the same underlying
+      // data structure.
+      if (arguments.length === 3)
+        return new Uint8Array(subject, encoding, arguments[2]);
+      // If array or alike just make a copy with a local patched prototype.
+      else
+        return new Uint8Array(subject);
+    default:
+      throw new TypeError('must start with number, buffer, array or string');
+  }
+}
+exports.Buffer = Buffer;
+
+// Tests if `value` is a Buffer.
+Buffer.isBuffer = value => value instanceof Buffer
+
+// Returns true if the encoding is a valid encoding argument & false otherwise
+Buffer.isEncoding = function (encoding) {
+  if (!encoding) return false;
+  try {
+    new TextDecoder(encoding);
+  } catch(e) {
+    return false;
+  }
+  return true;
+}
+
+// Gives the actual byte length of a string. encoding defaults to 'utf8'.
+// This is not the same as String.prototype.length since that returns the
+// number of characters in a string.
+Buffer.byteLength = (value, encoding = 'utf8') =>
+  new TextEncoder(encoding).encode(value).byteLength
+
+// Direct copy of the nodejs's buffer implementation:
+// https://github.com/joyent/node/blob/b255f4c10a80343f9ce1cee56d0288361429e214/lib/buffer.js#L146-L177
+Buffer.concat = function(list, length) {
+  if (!Array.isArray(list))
+    throw new TypeError('Usage: Buffer.concat(list[, length])');
+
+  if (typeof length === 'undefined') {
+    length = 0;
+    for (var i = 0; i < list.length; i++)
+      length += list[i].length;
+  } else {
+    length = ~~length;
+  }
+
+  if (length < 0)
+    length = 0;
+
+  if (list.length === 0)
+    return new Buffer(0);
+  else if (list.length === 1)
+    return list[0];
+
+  if (length < 0)
+    throw new RangeError('length is not a positive number');
+
+  var buffer = new Buffer(length);
+  var pos = 0;
+  for (var i = 0; i < list.length; i++) {
+    var buf = list[i];
+    buf.copy(buffer, pos);
+    pos += buf.length;
+  }
+
+  return buffer;
+};
+
+// Node buffer is very much like Uint8Array although it has bunch of methods
+// that typically can be used in combination with `DataView` while preserving
+// access by index. Since in SDK each module has it's own set of bult-ins it
+// ok to patch ours to make it nodejs Buffer compatible.
+const Uint8ArraySet = Uint8Array.prototype.set
+Buffer.prototype = Uint8Array.prototype;
+Object.defineProperties(Buffer.prototype, {
+  parent: {
+    get: function() { return parents.get(this, undefined); }
+  },
+  view: {
+    get: function () {
+      let view = views.get(this, undefined);
+      if (view) return view;
+      view = new DataView(this.buffer);
+      views.set(this, view);
+      return view;
+    }
+  },
+  toString: {
+    value: function(encoding, start, end) {
+      encoding = !!encoding ? (encoding + '').toLowerCase() : 'utf8';
+      start = Math.max(0, ~~start);
+      end = Math.min(this.length, end === void(0) ? this.length : ~~end);
+      return new TextDecoder(encoding).decode(this.subarray(start, end));
+    }
+  },
+  toJSON: {
+    value: function() {
+      return { type: 'Buffer', data: Array.slice(this, 0) };
+    }
+  },
+  get: {
+    value: function(offset) {
+      return this[offset];
+    }
+  },
+  set: {
+    value: function(offset, value) { this[offset] = value; }
+  },
+  copy: {
+    value: function(target, offset, start, end) {
+      let length = this.length;
+      let targetLength = target.length;
+      offset = isNumber(offset) ? offset : 0;
+      start = isNumber(start) ? start : 0;
+
+      if (start < 0)
+        throw new RangeError('sourceStart is outside of valid range');
+      if (end < 0)
+        throw new RangeError('sourceEnd is outside of valid range');
+
+      // If sourceStart > sourceEnd, or targetStart > targetLength,
+      // zero bytes copied
+      if (start > end ||
+          offset > targetLength
+          )
+        return 0;
+
+      // If `end` is not defined, or if it is defined
+      // but would overflow `target`, redefine `end`
+      // so we can copy as much as we can
+      if (end - start > targetLength - offset ||
+          end == null) {
+        let remainingTarget = targetLength - offset;
+        let remainingSource = length - start;
+        if (remainingSource <= remainingTarget)
+          end = length;
+        else
+          end = start + remainingTarget;
+      }
+
+      Uint8ArraySet.call(target, this.subarray(start, end), offset);
+      return end - start;
+    }
+  },
+  slice: {
+    value: function(start, end) {
+      let length = this.length;
+      start = ~~start;
+      end = end != null ? end : length;
+
+      if (start < 0) {
+        start += length;
+        if (start < 0) start = 0;
+      } else if (start > length)
+        start = length;
+
+      if (end < 0) {
+        end += length;
+        if (end < 0) end = 0;
+      } else if (end > length)
+        end = length;
+
+      if (end < start)
+        end = start;
+
+      // This instantiation uses the new Uint8Array(buffer, offset, length) version
+      // of construction to share the same underling data structure
+      let buffer = new Buffer(this.buffer, start, end - start);
+
+      // If buffer has a value, assign its parent value to the
+      // buffer it shares its underlying structure with. If a slice of
+      // a slice, then use the root structure
+      if (buffer.length > 0)
+        parents.set(buffer, this.parent || this);
+
+      return buffer;
+    }
+  },
+  write: {
+    value: function(string, offset, length, encoding = 'utf8') {
+      // write(string, encoding);
+      if (typeof(offset) === 'string' && Number.isNaN(parseInt(offset))) {
+        [offset, length, encoding] = [0, null, offset];
+      }
+      // write(string, offset, encoding);
+      else if (typeof(length) === 'string')
+        [length, encoding] = [null, length];
+
+      if (offset < 0 || offset > this.length)
+        throw new RangeError('offset is outside of valid range');
+
+      offset = ~~offset;
+
+      // Clamp length if it would overflow buffer, or if its
+      // undefined
+      if (length == null || length + offset > this.length)
+        length = this.length - offset;
+
+      let buffer = new TextEncoder(encoding).encode(string);
+      let result = Math.min(buffer.length, length);
+      if (buffer.length !== length)
+        buffer = buffer.subarray(0, length);
+
+      Uint8ArraySet.call(this, buffer, offset);
+      return result;
+    }
+  },
+  fill: {
+    value: function fill(value, start, end) {
+      let length = this.length;
+      value = value || 0;
+      start = start || 0;
+      end = end || length;
+
+      if (typeof(value) === 'string')
+        value = value.charCodeAt(0);
+      if (typeof(value) !== 'number' || isNaN(value))
+        throw TypeError('value is not a number');
+      if (end < start)
+        throw new RangeError('end < start');
+
+      // Fill 0 bytes; we're done
+      if (end === start)
+        return 0;
+      if (length == 0)
+        return 0;
+
+      if (start < 0 || start >= length)
+        throw RangeError('start out of bounds');
+
+      if (end < 0 || end > length)
+        throw RangeError('end out of bounds');
+
+      let index = start;
+      while (index < end) this[index++] = value;
+    }
+  }
+});
+
+// Define nodejs Buffer's getter and setter functions that just proxy
+// to internal DataView's equivalent methods.
+
+// TODO do we need to check architecture to see if it's default big/little endian?
+[['readUInt16LE', 'getUint16', true],
+ ['readUInt16BE', 'getUint16', false],
+ ['readInt16LE', 'getInt16', true],
+ ['readInt16BE', 'getInt16', false],
+ ['readUInt32LE', 'getUint32', true],
+ ['readUInt32BE', 'getUint32', false],
+ ['readInt32LE', 'getInt32', true],
+ ['readInt32BE', 'getInt32', false],
+ ['readFloatLE', 'getFloat32', true],
+ ['readFloatBE', 'getFloat32', false],
+ ['readDoubleLE', 'getFloat64', true],
+ ['readDoubleBE', 'getFloat64', false],
+ ['readUInt8', 'getUint8'],
+ ['readInt8', 'getInt8']].forEach(([alias, name, littleEndian]) => {
+  Object.defineProperty(Buffer.prototype, alias, {
+    value: function(offset) {
+      return this.view[name](offset, littleEndian);
+    }
+  });
+});
+
+[['writeUInt16LE', 'setUint16', true],
+ ['writeUInt16BE', 'setUint16', false],
+ ['writeInt16LE', 'setInt16', true],
+ ['writeInt16BE', 'setInt16', false],
+ ['writeUInt32LE', 'setUint32', true],
+ ['writeUInt32BE', 'setUint32', false],
+ ['writeInt32LE', 'setInt32', true],
+ ['writeInt32BE', 'setInt32', false],
+ ['writeFloatLE', 'setFloat32', true],
+ ['writeFloatBE', 'setFloat32', false],
+ ['writeDoubleLE', 'setFloat64', true],
+ ['writeDoubleBE', 'setFloat64', false],
+ ['writeUInt8', 'setUint8'],
+ ['writeInt8', 'setInt8']].forEach(([alias, name, littleEndian]) => {
+  Object.defineProperty(Buffer.prototype, alias, {
+    value: function(value, offset) {
+      return this.view[name](offset, value, littleEndian);
+    }
+  });
+});
diff --git a/toolkit/jetpack/sdk/io/byte-streams.js b/toolkit/jetpack/sdk/io/byte-streams.js
new file mode 100644
index 000000000..6afab4369
--- /dev/null
+++ b/toolkit/jetpack/sdk/io/byte-streams.js
@@ -0,0 +1,104 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+module.metadata = {
+  "stability": "experimental"
+};
+
+exports.ByteReader = ByteReader;
+exports.ByteWriter = ByteWriter;
+
+const {Cc, Ci} = require("chrome");
+
+// This just controls the maximum number of bytes we read in at one time.
+const BUFFER_BYTE_LEN = 0x8000;
+
+function ByteReader(inputStream) {
+  const self = this;
+
+  let stream = Cc["@mozilla.org/binaryinputstream;1"].
+               createInstance(Ci.nsIBinaryInputStream);
+  stream.setInputStream(inputStream);
+
+  let manager = new StreamManager(this, stream);
+
+  this.read = function ByteReader_read(numBytes) {
+    manager.ensureOpened();
+    if (typeof(numBytes) !== "number")
+      numBytes = Infinity;
+
+    let data = "";
+    let read = 0;
+    try {
+      while (true) {
+        let avail = stream.available();
+        let toRead = Math.min(numBytes - read, avail, BUFFER_BYTE_LEN);
+        if (toRead <= 0)
+          break;
+        data += stream.readBytes(toRead);
+        read += toRead;
+      }
+    }
+    catch (err) {
+      throw new Error("Error reading from stream: " + err);
+    }
+
+    return data;
+  };
+}
+
+function ByteWriter(outputStream) {
+  const self = this;
+
+  let stream = Cc["@mozilla.org/binaryoutputstream;1"].
+               createInstance(Ci.nsIBinaryOutputStream);
+  stream.setOutputStream(outputStream);
+
+  let manager = new StreamManager(this, stream);
+
+  this.write = function ByteWriter_write(str) {
+    manager.ensureOpened();
+    try {
+      stream.writeBytes(str, str.length);
+    }
+    catch (err) {
+      throw new Error("Error writing to stream: " + err);
+    }
+  };
+}
+
+
+// This manages the lifetime of stream, a ByteReader or ByteWriter.  It defines
+// closed and close() on stream and registers an unload listener that closes
+// rawStream if it's still opened.  It also provides ensureOpened(), which
+// throws an exception if the stream is closed.
+function StreamManager(stream, rawStream) {
+  const self = this;
+  this.rawStream = rawStream;
+  this.opened = true;
+
+  stream.__defineGetter__("closed", function stream_closed() {
+    return !self.opened;
+  });
+
+  stream.close = function stream_close() {
+    self.ensureOpened();
+    self.unload();
+  };
+
+  require("../system/unload").ensure(this);
+}
+
+StreamManager.prototype = {
+  ensureOpened: function StreamManager_ensureOpened() {
+    if (!this.opened)
+      throw new Error("The stream is closed and cannot be used.");
+  },
+  unload: function StreamManager_unload() {
+    this.rawStream.close();
+    this.opened = false;
+  }
+};
diff --git a/toolkit/jetpack/sdk/io/file.js b/toolkit/jetpack/sdk/io/file.js
new file mode 100644
index 000000000..47467df87
--- /dev/null
+++ b/toolkit/jetpack/sdk/io/file.js
@@ -0,0 +1,196 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+module.metadata = {
+  "stability": "deprecated"
+};
+
+const {Cc,Ci,Cr} = require("chrome");
+const byteStreams = require("./byte-streams");
+const textStreams = require("./text-streams");
+
+// Flags passed when opening a file.  See nsprpub/pr/include/prio.h.
+const OPEN_FLAGS = {
+  RDONLY: parseInt("0x01"),
+  WRONLY: parseInt("0x02"),
+  CREATE_FILE: parseInt("0x08"),
+  APPEND: parseInt("0x10"),
+  TRUNCATE: parseInt("0x20"),
+  EXCL: parseInt("0x80")
+};
+
+var dirsvc = Cc["@mozilla.org/file/directory_service;1"]
+             .getService(Ci.nsIProperties);
+
+function MozFile(path) {
+  var file = Cc['@mozilla.org/file/local;1']
+             .createInstance(Ci.nsILocalFile);
+  file.initWithPath(path);
+  return file;
+}
+
+function ensureReadable(file) {
+  if (!file.isReadable())
+    throw new Error("path is not readable: " + file.path);
+}
+
+function ensureDir(file) {
+  ensureExists(file);
+  if (!file.isDirectory())
+    throw new Error("path is not a directory: " + file.path);
+}
+
+function ensureFile(file) {
+  ensureExists(file);
+  if (!file.isFile())
+    throw new Error("path is not a file: " + file.path);
+}
+
+function ensureExists(file) {
+  if (!file.exists())
+    throw friendlyError(Cr.NS_ERROR_FILE_NOT_FOUND, file.path);
+}
+
+function friendlyError(errOrResult, filename) {
+  var isResult = typeof(errOrResult) === "number";
+  var result = isResult ? errOrResult : errOrResult.result;
+  switch (result) {
+  case Cr.NS_ERROR_FILE_NOT_FOUND:
+    return new Error("path does not exist: " + filename);
+  }
+  return isResult ? new Error("XPCOM error code: " + errOrResult) : errOrResult;
+}
+
+exports.exists = function exists(filename) {
+  return MozFile(filename).exists();
+};
+
+exports.isFile = function isFile(filename) {
+  return MozFile(filename).isFile();
+};
+
+exports.read = function read(filename, mode) {
+  if (typeof(mode) !== "string")
+    mode = "";
+
+  // Ensure mode is read-only.
+  mode = /b/.test(mode) ? "b" : "";
+
+  var stream = exports.open(filename, mode);
+  try {
+    var str = stream.read();
+  }
+  finally {
+    stream.close();
+  }
+
+  return str;
+};
+
+exports.join = function join(base) {
+  if (arguments.length < 2)
+    throw new Error("need at least 2 args");
+  base = MozFile(base);
+  for (var i = 1; i < arguments.length; i++)
+    base.append(arguments[i]);
+  return base.path;
+};
+
+exports.dirname = function dirname(path) {
+  var parent = MozFile(path).parent;
+  return parent ? parent.path : "";
+};
+
+exports.basename = function basename(path) {
+  var leafName = MozFile(path).leafName;
+
+  // On Windows, leafName when the path is a volume letter and colon ("c:") is
+  // the path itself.  But such a path has no basename, so we want the empty
+  // string.
+  return leafName == path ? "" : leafName;
+};
+
+exports.list = function list(path) {
+  var file = MozFile(path);
+  ensureDir(file);
+  ensureReadable(file);
+
+  var entries = file.directoryEntries;
+  var entryNames = [];
+  while(entries.hasMoreElements()) {
+    var entry = entries.getNext();
+    entry.QueryInterface(Ci.nsIFile);
+    entryNames.push(entry.leafName);
+  }
+  return entryNames;
+};
+
+exports.open = function open(filename, mode) {
+  var file = MozFile(filename);
+  if (typeof(mode) !== "string")
+    mode = "";
+
+  // File opened for write only.
+  if (/w/.test(mode)) {
+    if (file.exists())
+      ensureFile(file);
+    var stream = Cc['@mozilla.org/network/file-output-stream;1'].
+                 createInstance(Ci.nsIFileOutputStream);
+    var openFlags = OPEN_FLAGS.WRONLY |
+                    OPEN_FLAGS.CREATE_FILE |
+                    OPEN_FLAGS.TRUNCATE;
+    var permFlags = 0o644; // u+rw go+r
+    try {
+      stream.init(file, openFlags, permFlags, 0);
+    }
+    catch (err) {
+      throw friendlyError(err, filename);
+    }
+    return /b/.test(mode) ?
+           new byteStreams.ByteWriter(stream) :
+           new textStreams.TextWriter(stream);
+  }
+
+  // File opened for read only, the default.
+  ensureFile(file);
+  stream = Cc['@mozilla.org/network/file-input-stream;1'].
+           createInstance(Ci.nsIFileInputStream);
+  try {
+    stream.init(file, OPEN_FLAGS.RDONLY, 0, 0);
+  }
+  catch (err) {
+    throw friendlyError(err, filename);
+  }
+  return /b/.test(mode) ?
+         new byteStreams.ByteReader(stream) :
+         new textStreams.TextReader(stream);
+};
+
+exports.remove = function remove(path) {
+  var file = MozFile(path);
+  ensureFile(file);
+  file.remove(false);
+};
+
+exports.mkpath = function mkpath(path) {
+  var file = MozFile(path);
+  if (!file.exists())
+    file.create(Ci.nsIFile.DIRECTORY_TYPE, 0o755); // u+rwx go+rx
+  else if (!file.isDirectory())
+    throw new Error("The path already exists and is not a directory: " + path);
+};
+
+exports.rmdir = function rmdir(path) {
+  var file = MozFile(path);
+  ensureDir(file);
+  try {
+    file.remove(false);
+  }
+  catch (err) {
+    // Bug 566950 explains why we're not catching a specific exception here.
+    throw new Error("The directory is not empty: " + path);
+  }
+};
diff --git a/toolkit/jetpack/sdk/io/fs.js b/toolkit/jetpack/sdk/io/fs.js
new file mode 100644
index 000000000..860a884a5
--- /dev/null
+++ b/toolkit/jetpack/sdk/io/fs.js
@@ -0,0 +1,984 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+module.metadata = {
+  "stability": "experimental"
+};
+
+const { Cc, Ci, CC } = require("chrome");
+
+const { setTimeout } = require("../timers");
+const { Stream, InputStream, OutputStream } = require("./stream");
+const { emit, on } = require("../event/core");
+const { Buffer } = require("./buffer");
+const { ns } = require("../core/namespace");
+const { Class } = require("../core/heritage");
+
+
+const nsILocalFile = CC("@mozilla.org/file/local;1", "nsILocalFile",
+                        "initWithPath");
+const FileOutputStream = CC("@mozilla.org/network/file-output-stream;1",
+                            "nsIFileOutputStream", "init");
+const FileInputStream = CC("@mozilla.org/network/file-input-stream;1",
+                           "nsIFileInputStream", "init");
+const BinaryInputStream = CC("@mozilla.org/binaryinputstream;1",
+                             "nsIBinaryInputStream", "setInputStream");
+const BinaryOutputStream = CC("@mozilla.org/binaryoutputstream;1",
+                              "nsIBinaryOutputStream", "setOutputStream");
+const StreamPump = CC("@mozilla.org/network/input-stream-pump;1",
+                      "nsIInputStreamPump", "init");
+
+const { createOutputTransport, createInputTransport } =
+  Cc["@mozilla.org/network/stream-transport-service;1"].
+  getService(Ci.nsIStreamTransportService);
+
+const { OPEN_UNBUFFERED } = Ci.nsITransport;
+
+
+const { REOPEN_ON_REWIND, DEFER_OPEN } = Ci.nsIFileInputStream;
+const { DIRECTORY_TYPE, NORMAL_FILE_TYPE } = Ci.nsIFile;
+const { NS_SEEK_SET, NS_SEEK_CUR, NS_SEEK_END } = Ci.nsISeekableStream;
+
+const FILE_PERMISSION = 0o666;
+const PR_UINT32_MAX = 0xfffffff;
+// Values taken from:
+// http://mxr.mozilla.org/mozilla-central/source/nsprpub/pr/include/prio.h#615
+const PR_RDONLY =       0x01;
+const PR_WRONLY =       0x02;
+const PR_RDWR =         0x04;
+const PR_CREATE_FILE =  0x08;
+const PR_APPEND =       0x10;
+const PR_TRUNCATE =     0x20;
+const PR_SYNC =         0x40;
+const PR_EXCL =         0x80;
+
+const FLAGS = {
+  "r":                  PR_RDONLY,
+  "r+":                 PR_RDWR,
+  "w":                  PR_CREATE_FILE | PR_TRUNCATE | PR_WRONLY,
+  "w+":                 PR_CREATE_FILE | PR_TRUNCATE | PR_RDWR,
+  "a":                  PR_APPEND | PR_CREATE_FILE | PR_WRONLY,
+  "a+":                 PR_APPEND | PR_CREATE_FILE | PR_RDWR
+};
+
+function accessor() {
+  let map = new WeakMap();
+  return function(fd, value) {
+    if (value === null) map.delete(fd);
+    if (value !== undefined) map.set(fd, value);
+    return map.get(fd);
+  }
+}
+
+var nsIFile = accessor();
+var nsIFileInputStream = accessor();
+var nsIFileOutputStream = accessor();
+var nsIBinaryInputStream = accessor();
+var nsIBinaryOutputStream = accessor();
+
+// Just a contstant object used to signal that all of the file
+// needs to be read.
+const ALL = new String("Read all of the file");
+
+function isWritable(mode) {
+  return !!(mode & PR_WRONLY || mode & PR_RDWR);
+}
+function isReadable(mode) {
+  return !!(mode & PR_RDONLY || mode & PR_RDWR);
+}
+
+function isString(value) {
+  return typeof(value) === "string";
+}
+function isFunction(value) {
+  return typeof(value) === "function";
+}
+
+function toArray(enumerator) {
+  let value = [];
+  while(enumerator.hasMoreElements())
+    value.push(enumerator.getNext())
+  return value
+}
+
+function getFileName(file) {
+  return file.QueryInterface(Ci.nsIFile).leafName;
+}
+
+
+function remove(path, recursive) {
+  let fd = new nsILocalFile(path)
+  if (fd.exists()) {
+    fd.remove(recursive || false);
+  }
+  else {
+    throw FSError("remove", "ENOENT", 34, path);
+  }
+}
+
+/**
+ * Utility function to convert either an octal number or string
+ * into an octal number
+ * 0777 => 0o777
+ * "0644" => 0o644
+ */
+function Mode(mode, fallback) {
+  return isString(mode) ? parseInt(mode, 8) : mode || fallback;
+}
+function Flags(flag) {
+  return !isString(flag) ? flag :
+         FLAGS[flag] || Error("Unknown file open flag: " + flag);
+}
+
+
+function FSError(op, code, errno, path, file, line) {
+  let error = Error(code + ", " + op + " " + path, file, line);
+  error.code = code;
+  error.path = path;
+  error.errno = errno;
+  return error;
+}
+
+const ReadStream = Class({
+  extends: InputStream,
+  initialize: function initialize(path, options) {
+    this.position = -1;
+    this.length = -1;
+    this.flags = "r";
+    this.mode = FILE_PERMISSION;
+    this.bufferSize = 64 * 1024;
+
+    options = options || {};
+
+    if ("flags" in options && options.flags)
+      this.flags = options.flags;
+    if ("bufferSize" in options && options.bufferSize)
+      this.bufferSize = options.bufferSize;
+    if ("length" in options && options.length)
+      this.length = options.length;
+    if ("position" in options && options.position !== undefined)
+      this.position = options.position;
+
+    let { flags, mode, position, length } = this;
+    let fd = isString(path) ? openSync(path, flags, mode) : path;
+    this.fd = fd;
+
+    let input = nsIFileInputStream(fd);
+    // Setting a stream position, unless it"s `-1` which means current position.
+    if (position >= 0)
+      input.QueryInterface(Ci.nsISeekableStream).seek(NS_SEEK_SET, position);
+    // We use `nsIStreamTransportService` service to transform blocking
+    // file input stream into a fully asynchronous stream that can be written
+    // without blocking the main thread.
+    let transport = createInputTransport(input, position, length, false);
+    // Open an input stream on a transport. We don"t pass flags to guarantee
+    // non-blocking stream semantics. Also we use defaults for segment size &
+    // count.
+    InputStream.prototype.initialize.call(this, {
+      asyncInputStream: transport.openInputStream(null, 0, 0)
+    });
+
+    // Close file descriptor on end and destroy the stream.
+    on(this, "end", _ => {
+      this.destroy();
+      emit(this, "close");
+    });
+
+    this.read();
+  },
+  destroy: function() {
+    closeSync(this.fd);
+    InputStream.prototype.destroy.call(this);
+  }
+});
+exports.ReadStream = ReadStream;
+exports.createReadStream = function createReadStream(path, options) {
+  return new ReadStream(path, options);
+};
+
+const WriteStream = Class({
+  extends: OutputStream,
+  initialize: function initialize(path, options) {
+    this.drainable = true;
+    this.flags = "w";
+    this.position = -1;
+    this.mode = FILE_PERMISSION;
+
+    options = options || {};
+
+    if ("flags" in options && options.flags)
+      this.flags = options.flags;
+    if ("mode" in options && options.mode)
+      this.mode = options.mode;
+    if ("position" in options && options.position !== undefined)
+      this.position = options.position;
+
+    let { position, flags, mode } = this;
+    // If pass was passed we create a file descriptor out of it. Otherwise
+    // we just use given file descriptor.
+    let fd = isString(path) ? openSync(path, flags, mode) : path;
+    this.fd = fd;
+
+    let output = nsIFileOutputStream(fd);
+    // Setting a stream position, unless it"s `-1` which means current position.
+    if (position >= 0)
+      output.QueryInterface(Ci.nsISeekableStream).seek(NS_SEEK_SET, position);
+    // We use `nsIStreamTransportService` service to transform blocking
+    // file output stream into a fully asynchronous stream that can be written
+    // without blocking the main thread.
+    let transport = createOutputTransport(output, position, -1, false);
+    // Open an output stream on a transport. We don"t pass flags to guarantee
+    // non-blocking stream semantics. Also we use defaults for segment size &
+    // count.
+    OutputStream.prototype.initialize.call(this, {
+      asyncOutputStream: transport.openOutputStream(OPEN_UNBUFFERED, 0, 0),
+      output: output
+    });
+
+    // For write streams "finish" basically means close.
+    on(this, "finish", _ => {
+       this.destroy();
+       emit(this, "close");
+    });
+  },
+  destroy: function() {
+    OutputStream.prototype.destroy.call(this);
+    closeSync(this.fd);
+  }
+});
+exports.WriteStream = WriteStream;
+exports.createWriteStream = function createWriteStream(path, options) {
+  return new WriteStream(path, options);
+};
+
+const Stats = Class({
+  initialize: function initialize(path) {
+    let file = new nsILocalFile(path);
+    if (!file.exists()) throw FSError("stat", "ENOENT", 34, path);
+    nsIFile(this, file);
+  },
+  isDirectory: function() {
+    return nsIFile(this).isDirectory();
+  },
+  isFile: function() {
+    return nsIFile(this).isFile();
+  },
+  isSymbolicLink: function() {
+    return nsIFile(this).isSymlink();
+  },
+  get mode() {
+    return nsIFile(this).permissions;
+  },
+  get size() {
+    return nsIFile(this).fileSize;
+  },
+  get mtime() {
+    return nsIFile(this).lastModifiedTime;
+  },
+  isBlockDevice: function() {
+    return nsIFile(this).isSpecial();
+  },
+  isCharacterDevice: function() {
+    return nsIFile(this).isSpecial();
+  },
+  isFIFO: function() {
+    return nsIFile(this).isSpecial();
+  },
+  isSocket: function() {
+    return nsIFile(this).isSpecial();
+  },
+  // non standard
+  get exists() {
+    return nsIFile(this).exists();
+  },
+  get hidden() {
+    return nsIFile(this).isHidden();
+  },
+  get writable() {
+    return nsIFile(this).isWritable();
+  },
+  get readable() {
+    return nsIFile(this).isReadable();
+  }
+});
+exports.Stats = Stats;
+
+const LStats = Class({
+  extends: Stats,
+  get size() {
+    return this.isSymbolicLink() ? nsIFile(this).fileSizeOfLink :
+                                   nsIFile(this).fileSize;
+  },
+  get mtime() {
+    return this.isSymbolicLink() ? nsIFile(this).lastModifiedTimeOfLink :
+                                   nsIFile(this).lastModifiedTime;
+  },
+  // non standard
+  get permissions() {
+    return this.isSymbolicLink() ? nsIFile(this).permissionsOfLink :
+                                   nsIFile(this).permissions;
+  }
+});
+
+const FStat = Class({
+  extends: Stats,
+  initialize: function initialize(fd) {
+    nsIFile(this, nsIFile(fd));
+  }
+});
+
+function noop() {}
+function Async(wrapped) {
+  return function (path, callback) {
+    let args = Array.slice(arguments);
+    callback = args.pop();
+    // If node is not given a callback argument
+    // it just does not calls it.
+    if (typeof(callback) !== "function") {
+      args.push(callback);
+      callback = noop;
+    }
+    setTimeout(function() {
+      try {
+        var result = wrapped.apply(this, args);
+        if (result === undefined) callback(null);
+        else callback(null, result);
+      } catch (error) {
+        callback(error);
+      }
+    }, 0);
+  }
+}
+
+
+/**
+ * Synchronous rename(2)
+ */
+function renameSync(oldPath, newPath) {
+  let source = new nsILocalFile(oldPath);
+  let target = new nsILocalFile(newPath);
+  if (!source.exists()) throw FSError("rename", "ENOENT", 34, oldPath);
+  return source.moveTo(target.parent, target.leafName);
+};
+exports.renameSync = renameSync;
+
+/**
+ * Asynchronous rename(2). No arguments other than a possible exception are
+ * given to the completion callback.
+ */
+var rename = Async(renameSync);
+exports.rename = rename;
+
+/**
+ * Test whether or not the given path exists by checking with the file system.
+ */
+function existsSync(path) {
+  return new nsILocalFile(path).exists();
+}
+exports.existsSync = existsSync;
+
+var exists = Async(existsSync);
+exports.exists = exists;
+
+/**
+ * Synchronous ftruncate(2).
+ */
+function truncateSync(path, length) {
+  let fd = openSync(path, "w");
+  ftruncateSync(fd, length);
+  closeSync(fd);
+}
+exports.truncateSync = truncateSync;
+
+/**
+ * Asynchronous ftruncate(2). No arguments other than a possible exception are
+ * given to the completion callback.
+ */
+function truncate(path, length, callback) {
+  open(path, "w", function(error, fd) {
+    if (error) return callback(error);
+    ftruncate(fd, length, function(error) {
+      if (error) {
+        closeSync(fd);
+        callback(error);
+      }
+      else {
+        close(fd, callback);
+      }
+    });
+  });
+}
+exports.truncate = truncate;
+
+function ftruncate(fd, length, callback) {
+  write(fd, new Buffer(length), 0, length, 0, function(error) {
+    callback(error);
+  });
+}
+exports.ftruncate = ftruncate;
+
+function ftruncateSync(fd, length = 0) {
+  writeSync(fd, new Buffer(length), 0, length, 0);
+}
+exports.ftruncateSync = ftruncateSync;
+
+function chownSync(path, uid, gid) {
+  throw Error("Not implemented yet!!");
+}
+exports.chownSync = chownSync;
+
+var chown = Async(chownSync);
+exports.chown = chown;
+
+function lchownSync(path, uid, gid) {
+  throw Error("Not implemented yet!!");
+}
+exports.lchownSync = chownSync;
+
+var lchown = Async(lchown);
+exports.lchown = lchown;
+
+/**
+ * Synchronous chmod(2).
+ */
+function chmodSync (path, mode) {
+  let file;
+  try {
+    file = new nsILocalFile(path);
+  } catch(e) {
+    throw FSError("chmod", "ENOENT", 34, path);
+  }
+
+  file.permissions = Mode(mode);
+}
+exports.chmodSync = chmodSync;
+/**
+ * Asynchronous chmod(2). No arguments other than a possible exception are
+ * given to the completion callback.
+ */
+var chmod = Async(chmodSync);
+exports.chmod = chmod;
+
+/**
+ * Synchronous chmod(2).
+ */
+function fchmodSync(fd, mode) {
+  throw Error("Not implemented yet!!");
+};
+exports.fchmodSync = fchmodSync;
+/**
+ * Asynchronous chmod(2). No arguments other than a possible exception are
+ * given to the completion callback.
+ */
+var fchmod = Async(fchmodSync);
+exports.fchmod = fchmod;
+
+
+/**
+ * Synchronous stat(2). Returns an instance of `fs.Stats`
+ */
+function statSync(path) {
+  return new Stats(path);
+};
+exports.statSync = statSync;
+
+/**
+ * Asynchronous stat(2). The callback gets two arguments (err, stats) where
+ * stats is a `fs.Stats` object. It looks like this:
+ */
+var stat = Async(statSync);
+exports.stat = stat;
+
+/**
+ * Synchronous lstat(2). Returns an instance of `fs.Stats`.
+ */
+function lstatSync(path) {
+  return new LStats(path);
+};
+exports.lstatSync = lstatSync;
+
+/**
+ * Asynchronous lstat(2). The callback gets two arguments (err, stats) where
+ * stats is a fs.Stats object. lstat() is identical to stat(), except that if
+ * path is a symbolic link, then the link itself is stat-ed, not the file that
+ * it refers to.
+ */
+var lstat = Async(lstatSync);
+exports.lstat = lstat;
+
+/**
+ * Synchronous fstat(2). Returns an instance of `fs.Stats`.
+ */
+function fstatSync(fd) {
+  return new FStat(fd);
+};
+exports.fstatSync = fstatSync;
+
+/**
+ * Asynchronous fstat(2). The callback gets two arguments (err, stats) where
+ * stats is a fs.Stats object.
+ */
+var fstat = Async(fstatSync);
+exports.fstat = fstat;
+
+/**
+ * Synchronous link(2).
+ */
+function linkSync(source, target) {
+  throw Error("Not implemented yet!!");
+};
+exports.linkSync = linkSync;
+
+/**
+ * Asynchronous link(2). No arguments other than a possible exception are given
+ * to the completion callback.
+ */
+var link = Async(linkSync);
+exports.link = link;
+
+/**
+ * Synchronous symlink(2).
+ */
+function symlinkSync(source, target) {
+  throw Error("Not implemented yet!!");
+};
+exports.symlinkSync = symlinkSync;
+
+/**
+ * Asynchronous symlink(2). No arguments other than a possible exception are
+ * given to the completion callback.
+ */
+var symlink = Async(symlinkSync);
+exports.symlink = symlink;
+
+/**
+ * Synchronous readlink(2). Returns the resolved path.
+ */
+function readlinkSync(path) {
+  return new nsILocalFile(path).target;
+};
+exports.readlinkSync = readlinkSync;
+
+/**
+ * Asynchronous readlink(2). The callback gets two arguments
+ * `(error, resolvedPath)`.
+ */
+var readlink = Async(readlinkSync);
+exports.readlink = readlink;
+
+/**
+ * Synchronous realpath(2). Returns the resolved path.
+ */
+function realpathSync(path) {
+  return new nsILocalFile(path).path;
+};
+exports.realpathSync = realpathSync;
+
+/**
+ * Asynchronous realpath(2). The callback gets two arguments
+ * `(err, resolvedPath)`.
+ */
+var realpath = Async(realpathSync);
+exports.realpath = realpath;
+
+/**
+ * Synchronous unlink(2).
+ */
+var unlinkSync = remove;
+exports.unlinkSync = unlinkSync;
+
+/**
+ * Asynchronous unlink(2). No arguments other than a possible exception are
+ * given to the completion callback.
+ */
+var unlink = Async(remove);
+exports.unlink = unlink;
+
+/**
+ * Synchronous rmdir(2).
+ */
+var rmdirSync = remove;
+exports.rmdirSync = rmdirSync;
+
+/**
+ * Asynchronous rmdir(2). No arguments other than a possible exception are
+ * given to the completion callback.
+ */
+var rmdir = Async(rmdirSync);
+exports.rmdir = rmdir;
+
+/**
+ * Synchronous mkdir(2).
+ */
+function mkdirSync(path, mode) {
+  try {
+    return nsILocalFile(path).create(DIRECTORY_TYPE, Mode(mode));
+  } catch (error) {
+    // Adjust exception thorw to match ones thrown by node.
+    if (error.name === "NS_ERROR_FILE_ALREADY_EXISTS") {
+      let { fileName, lineNumber } = error;
+      error = FSError("mkdir", "EEXIST", 47, path, fileName, lineNumber);
+    }
+    throw error;
+  }
+};
+exports.mkdirSync = mkdirSync;
+
+/**
+ * Asynchronous mkdir(2). No arguments other than a possible exception are
+ * given to the completion callback.
+ */
+var mkdir = Async(mkdirSync);
+exports.mkdir = mkdir;
+
+/**
+ * Synchronous readdir(3). Returns an array of filenames excluding `"."` and
+ * `".."`.
+ */
+function readdirSync(path) {
+  try {
+    return toArray(new nsILocalFile(path).directoryEntries).map(getFileName);
+  }
+  catch (error) {
+    // Adjust exception thorw to match ones thrown by node.
+    if (error.name === "NS_ERROR_FILE_TARGET_DOES_NOT_EXIST" ||
+        error.name === "NS_ERROR_FILE_NOT_FOUND")
+    {
+      let { fileName, lineNumber } = error;
+      error = FSError("readdir", "ENOENT", 34, path, fileName, lineNumber);
+    }
+    throw error;
+  }
+};
+exports.readdirSync = readdirSync;
+
+/**
+ * Asynchronous readdir(3). Reads the contents of a directory. The callback
+ * gets two arguments `(error, files)` where `files` is an array of the names
+ * of the files in the directory excluding `"."` and `".."`.
+ */
+var readdir = Async(readdirSync);
+exports.readdir = readdir;
+
+/**
+ * Synchronous close(2).
+ */
+ function closeSync(fd) {
+   let input = nsIFileInputStream(fd);
+   let output = nsIFileOutputStream(fd);
+
+   // Closing input stream and removing reference.
+   if (input) input.close();
+   // Closing output stream and removing reference.
+   if (output) output.close();
+
+   nsIFile(fd, null);
+   nsIFileInputStream(fd, null);
+   nsIFileOutputStream(fd, null);
+   nsIBinaryInputStream(fd, null);
+   nsIBinaryOutputStream(fd, null);
+};
+exports.closeSync = closeSync;
+/**
+ * Asynchronous close(2). No arguments other than a possible exception are
+ * given to the completion callback.
+ */
+var close = Async(closeSync);
+exports.close = close;
+
+/**
+ * Synchronous open(2).
+ */
+function openSync(aPath, aFlag, aMode) {
+  let [ fd, flags, mode, file ] =
+      [ { path: aPath }, Flags(aFlag), Mode(aMode), nsILocalFile(aPath) ];
+
+  nsIFile(fd, file);
+
+  // If trying to open file for just read that does not exists
+  // need to throw exception as node does.
+  if (!file.exists() && !isWritable(flags))
+    throw FSError("open", "ENOENT", 34, aPath);
+
+  // If we want to open file in read mode we initialize input stream.
+  if (isReadable(flags)) {
+    let input = FileInputStream(file, flags, mode, DEFER_OPEN);
+    nsIFileInputStream(fd, input);
+  }
+
+  // If we want to open file in write mode we initialize output stream for it.
+  if (isWritable(flags)) {
+    let output = FileOutputStream(file, flags, mode, DEFER_OPEN);
+    nsIFileOutputStream(fd, output);
+  }
+
+  return fd;
+}
+exports.openSync = openSync;
+/**
+ * Asynchronous file open. See open(2). Flags can be
+ * `"r", "r+", "w", "w+", "a"`, or `"a+"`. mode defaults to `0666`.
+ * The callback gets two arguments `(error, fd).
+ */
+var open = Async(openSync);
+exports.open = open;
+
+/**
+ * Synchronous version of buffer-based fs.write(). Returns the number of bytes
+ * written.
+ */
+function writeSync(fd, buffer, offset, length, position) {
+  if (length + offset > buffer.length) {
+    throw Error("Length is extends beyond buffer");
+  }
+  else if (length + offset !== buffer.length) {
+    buffer = buffer.slice(offset, offset + length);
+  }
+
+  let output = BinaryOutputStream(nsIFileOutputStream(fd));
+  nsIBinaryOutputStream(fd, output);
+  // We write content as a byte array as this will avoid any transcoding
+  // if content was a buffer.
+  output.writeByteArray(buffer.valueOf(), buffer.length);
+  output.flush();
+};
+exports.writeSync = writeSync;
+
+/**
+ * Write buffer to the file specified by fd.
+ *
+ * `offset` and `length` determine the part of the buffer to be written.
+ *
+ * `position` refers to the offset from the beginning of the file where this
+ * data should be written. If `position` is `null`, the data will be written
+ * at the current position. See pwrite(2).
+ *
+ * The callback will be given three arguments `(error, written, buffer)` where
+ * written specifies how many bytes were written into buffer.
+ *
+ * Note that it is unsafe to use `fs.write` multiple times on the same file
+ * without waiting for the callback.
+ */
+function write(fd, buffer, offset, length, position, callback) {
+  if (!Buffer.isBuffer(buffer)) {
+    // (fd, data, position, encoding, callback)
+    let encoding = null;
+    [ position, encoding, callback ] = Array.slice(arguments, 1);
+    buffer = new Buffer(String(buffer), encoding);
+    offset = 0;
+  } else if (length + offset > buffer.length) {
+    throw Error("Length is extends beyond buffer");
+  } else if (length + offset !== buffer.length) {
+    buffer = buffer.slice(offset, offset + length);
+  }
+
+  let writeStream = new WriteStream(fd, { position: position,
+                                          length: length });
+  writeStream.on("error", callback);
+  writeStream.write(buffer, function onEnd() {
+    writeStream.destroy();
+    if (callback)
+      callback(null, buffer.length, buffer);
+  });
+};
+exports.write = write;
+
+/**
+ * Synchronous version of string-based fs.read. Returns the number of
+ * bytes read.
+ */
+function readSync(fd, buffer, offset, length, position) {
+  let input = nsIFileInputStream(fd);
+  // Setting a stream position, unless it"s `-1` which means current position.
+  if (position >= 0)
+    input.QueryInterface(Ci.nsISeekableStream).seek(NS_SEEK_SET, position);
+  // We use `nsIStreamTransportService` service to transform blocking
+  // file input stream into a fully asynchronous stream that can be written
+  // without blocking the main thread.
+  let binaryInputStream = BinaryInputStream(input);
+  let count = length === ALL ? binaryInputStream.available() : length;
+  if (offset === 0) binaryInputStream.readArrayBuffer(count, buffer.buffer);
+  else {
+    let chunk = new Buffer(count);
+    binaryInputStream.readArrayBuffer(count, chunk.buffer);
+    chunk.copy(buffer, offset);
+  }
+
+  return buffer.slice(offset, offset + count);
+};
+exports.readSync = readSync;
+
+/**
+ * Read data from the file specified by `fd`.
+ *
+ * `buffer` is the buffer that the data will be written to.
+ * `offset` is offset within the buffer where writing will start.
+ *
+ * `length` is an integer specifying the number of bytes to read.
+ *
+ * `position` is an integer specifying where to begin reading from in the file.
+ * If `position` is `null`, data will be read from the current file position.
+ *
+ * The callback is given the three arguments, `(error, bytesRead, buffer)`.
+ */
+function read(fd, buffer, offset, length, position, callback) {
+  let bytesRead = 0;
+  let readStream = new ReadStream(fd, { position: position, length: length });
+  readStream.on("data", function onData(data) {
+      data.copy(buffer, offset + bytesRead);
+      bytesRead += data.length;
+  });
+  readStream.on("end", function onEnd() {
+    callback(null, bytesRead, buffer);
+    readStream.destroy();
+  });
+};
+exports.read = read;
+
+/**
+ * Asynchronously reads the entire contents of a file.
+ * The callback is passed two arguments `(error, data)`, where data is the
+ * contents of the file.
+ */
+function readFile(path, encoding, callback) {
+  if (isFunction(encoding)) {
+    callback = encoding
+    encoding = null
+  }
+
+  let buffer = null;
+  try {
+    let readStream = new ReadStream(path);
+    readStream.on("data", function(data) {
+      if (!buffer) buffer = data;
+      else buffer = Buffer.concat([buffer, data], 2);
+    });
+    readStream.on("error", function onError(error) {
+      callback(error);
+    });
+    readStream.on("end", function onEnd() {
+      // Note: Need to destroy before invoking a callback
+      // so that file descriptor is released.
+      readStream.destroy();
+      callback(null, buffer);
+    });
+  }
+  catch (error) {
+    setTimeout(callback, 0, error);
+  }
+};
+exports.readFile = readFile;
+
+/**
+ * Synchronous version of `fs.readFile`. Returns the contents of the path.
+ * If encoding is specified then this function returns a string.
+ * Otherwise it returns a buffer.
+ */
+function readFileSync(path, encoding) {
+  let fd = openSync(path, "r");
+  let size = fstatSync(fd).size;
+  let buffer = new Buffer(size);
+  try {
+    readSync(fd, buffer, 0, ALL, 0);
+  }
+  finally {
+    closeSync(fd);
+  }
+  return buffer;
+};
+exports.readFileSync = readFileSync;
+
+/**
+ * Asynchronously writes data to a file, replacing the file if it already
+ * exists. data can be a string or a buffer.
+ */
+function writeFile(path, content, encoding, callback) {
+  if (!isString(path))
+    throw new TypeError('path must be a string');
+
+  try {
+    if (isFunction(encoding)) {
+      callback = encoding
+      encoding = null
+    }
+    if (isString(content))
+      content = new Buffer(content, encoding);
+
+    let writeStream = new WriteStream(path);
+    let error = null;
+
+    writeStream.end(content, function() {
+      writeStream.destroy();
+      callback(error);
+    });
+
+    writeStream.on("error", function onError(reason) {
+      error = reason;
+      writeStream.destroy();
+    });
+  } catch (error) {
+    callback(error);
+  }
+};
+exports.writeFile = writeFile;
+
+/**
+ * The synchronous version of `fs.writeFile`.
+ */
+function writeFileSync(filename, data, encoding) {
+  // TODO: Implement this in bug 1148209 https://bugzilla.mozilla.org/show_bug.cgi?id=1148209
+  throw Error("Not implemented");
+};
+exports.writeFileSync = writeFileSync;
+
+
+function utimesSync(path, atime, mtime) {
+  throw Error("Not implemented");
+}
+exports.utimesSync = utimesSync;
+
+var utimes = Async(utimesSync);
+exports.utimes = utimes;
+
+function futimesSync(fd, atime, mtime, callback) {
+  throw Error("Not implemented");
+}
+exports.futimesSync = futimesSync;
+
+var futimes = Async(futimesSync);
+exports.futimes = futimes;
+
+function fsyncSync(fd, atime, mtime, callback) {
+  throw Error("Not implemented");
+}
+exports.fsyncSync = fsyncSync;
+
+var fsync = Async(fsyncSync);
+exports.fsync = fsync;
+
+
+/**
+ * Watch for changes on filename. The callback listener will be called each
+ * time the file is accessed.
+ *
+ * The second argument is optional. The options if provided should be an object
+ * containing two members a boolean, persistent, and interval, a polling value
+ * in milliseconds. The default is { persistent: true, interval: 0 }.
+ */
+function watchFile(path, options, listener) {
+  throw Error("Not implemented");
+};
+exports.watchFile = watchFile;
+
+
+function unwatchFile(path, listener) {
+  throw Error("Not implemented");
+}
+exports.unwatchFile = unwatchFile;
+
+function watch(path, options, listener) {
+  throw Error("Not implemented");
+}
+exports.watch = watch;
diff --git a/toolkit/jetpack/sdk/io/stream.js b/toolkit/jetpack/sdk/io/stream.js
new file mode 100644
index 000000000..0698b8e32
--- /dev/null
+++ b/toolkit/jetpack/sdk/io/stream.js
@@ -0,0 +1,440 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+module.metadata = {
+  "stability": "experimental"
+};
+
+const { CC, Cc, Ci, Cu, Cr, components } = require("chrome");
+const { EventTarget } = require("../event/target");
+const { emit } = require("../event/core");
+const { Buffer } = require("./buffer");
+const { Class } = require("../core/heritage");
+const { setTimeout } = require("../timers");
+
+
+const MultiplexInputStream = CC("@mozilla.org/io/multiplex-input-stream;1",
+                                "nsIMultiplexInputStream");
+const AsyncStreamCopier = CC("@mozilla.org/network/async-stream-copier;1",
+                             "nsIAsyncStreamCopier", "init");
+const StringInputStream = CC("@mozilla.org/io/string-input-stream;1",
+                             "nsIStringInputStream");
+const ArrayBufferInputStream = CC("@mozilla.org/io/arraybuffer-input-stream;1",
+                                  "nsIArrayBufferInputStream");
+
+const BinaryInputStream = CC("@mozilla.org/binaryinputstream;1",
+                             "nsIBinaryInputStream", "setInputStream");
+const InputStreamPump = CC("@mozilla.org/network/input-stream-pump;1",
+                           "nsIInputStreamPump", "init");
+
+const threadManager = Cc["@mozilla.org/thread-manager;1"].
+                      getService(Ci.nsIThreadManager);
+
+const eventTarget = Cc["@mozilla.org/network/stream-transport-service;1"].
+                    getService(Ci.nsIEventTarget);
+
+var isFunction = value => typeof(value) === "function"
+
+function accessor() {
+  let map = new WeakMap();
+  return function(target, value) {
+    if (value)
+      map.set(target, value);
+    return map.get(target);
+  }
+}
+
+const Stream = Class({
+  extends: EventTarget,
+  initialize: function() {
+    this.readable = false;
+    this.writable = false;
+    this.encoding = null;
+  },
+  setEncoding: function setEncoding(encoding) {
+    this.encoding = String(encoding).toUpperCase();
+  },
+  pipe: function pipe(target, options) {
+    let source = this;
+    function onData(chunk) {
+      if (target.writable) {
+        if (false === target.write(chunk))
+          source.pause();
+      }
+    }
+    function onDrain() {
+      if (source.readable)
+        source.resume();
+    }
+    function onEnd() {
+      target.end();
+    }
+    function onPause() {
+      source.pause();
+    }
+    function onResume() {
+      if (source.readable)
+        source.resume();
+    }
+
+    function cleanup() {
+      source.removeListener("data", onData);
+      target.removeListener("drain", onDrain);
+      source.removeListener("end", onEnd);
+
+      target.removeListener("pause", onPause);
+      target.removeListener("resume", onResume);
+
+      source.removeListener("end", cleanup);
+      source.removeListener("close", cleanup);
+
+      target.removeListener("end", cleanup);
+      target.removeListener("close", cleanup);
+    }
+
+    if (!options || options.end !== false)
+      target.on("end", onEnd);
+
+    source.on("data", onData);
+    target.on("drain", onDrain);
+    target.on("resume", onResume);
+    target.on("pause", onPause);
+
+    source.on("end", cleanup);
+    source.on("close", cleanup);
+
+    target.on("end", cleanup);
+    target.on("close", cleanup);
+
+    emit(target, "pipe", source);
+  },
+  pause: function pause() {
+    emit(this, "pause");
+  },
+  resume: function resume() {
+    emit(this, "resume");
+  },
+  destroySoon: function destroySoon() {
+    this.destroy();
+  }
+});
+exports.Stream = Stream;
+
+
+var nsIStreamListener = accessor();
+var nsIInputStreamPump = accessor();
+var nsIAsyncInputStream = accessor();
+var nsIBinaryInputStream = accessor();
+
+const StreamListener = Class({
+  initialize: function(stream) {
+    this.stream = stream;
+  },
+
+  // Next three methods are part of `nsIStreamListener` interface and are
+  // invoked by `nsIInputStreamPump.asyncRead`.
+  onDataAvailable: function(request, context, input, offset, count) {
+    let stream = this.stream;
+    let buffer = new ArrayBuffer(count);
+    nsIBinaryInputStream(stream).readArrayBuffer(count, buffer);
+    emit(stream, "data", new Buffer(buffer));
+  },
+
+  // Next two methods implement `nsIRequestObserver` interface and are invoked
+  // by `nsIInputStreamPump.asyncRead`.
+  onStartRequest: function() {},
+  // Called to signify the end of an asynchronous request. We only care to
+  // discover errors.
+  onStopRequest: function(request, context, status) {
+    let stream = this.stream;
+    stream.readable = false;
+    if (!components.isSuccessCode(status))
+      emit(stream, "error", status);
+    else
+      emit(stream, "end");
+  }
+});
+
+
+const InputStream = Class({
+  extends: Stream,
+  readable: false,
+  paused: false,
+  initialize: function initialize(options) {
+    let { asyncInputStream } = options;
+
+    this.readable = true;
+
+    let binaryInputStream = new BinaryInputStream(asyncInputStream);
+    let inputStreamPump = new InputStreamPump(asyncInputStream,
+                                              -1, -1, 0, 0, false);
+    let streamListener = new StreamListener(this);
+
+    nsIAsyncInputStream(this, asyncInputStream);
+    nsIInputStreamPump(this, inputStreamPump);
+    nsIBinaryInputStream(this, binaryInputStream);
+    nsIStreamListener(this, streamListener);
+
+    this.asyncInputStream = asyncInputStream;
+    this.inputStreamPump = inputStreamPump;
+    this.binaryInputStream = binaryInputStream;
+  },
+  get status() {
+    return nsIInputStreamPump(this).status;
+  },
+  read: function() {
+    nsIInputStreamPump(this).asyncRead(nsIStreamListener(this), null);
+  },
+  pause: function pause() {
+    this.paused = true;
+    nsIInputStreamPump(this).suspend();
+    emit(this, "paused");
+  },
+  resume: function resume() {
+    this.paused = false;
+    if (nsIInputStreamPump(this).isPending()) {
+        nsIInputStreamPump(this).resume();
+        emit(this, "resume");
+    }
+  },
+  close: function close() {
+    this.readable = false;
+    nsIInputStreamPump(this).cancel(Cr.NS_OK);
+    nsIBinaryInputStream(this).close();
+    nsIAsyncInputStream(this).close();
+  },
+  destroy: function destroy() {
+    this.close();
+
+    nsIInputStreamPump(this);
+    nsIAsyncInputStream(this);
+    nsIBinaryInputStream(this);
+    nsIStreamListener(this);
+  }
+});
+exports.InputStream = InputStream;
+
+
+
+var nsIRequestObserver = accessor();
+var nsIAsyncOutputStream = accessor();
+var nsIAsyncStreamCopier = accessor();
+var nsIMultiplexInputStream = accessor();
+
+const RequestObserver = Class({
+  initialize: function(stream) {
+    this.stream = stream;
+  },
+  // Method is part of `nsIRequestObserver` interface that is
+  // invoked by `nsIAsyncStreamCopier.asyncCopy`.
+  onStartRequest: function() {},
+  // Method is part of `nsIRequestObserver` interface that is
+  // invoked by `nsIAsyncStreamCopier.asyncCopy`.
+  onStopRequest: function(request, context, status) {
+    let stream = this.stream;
+    stream.drained = true;
+
+    // Remove copied chunk.
+    let multiplexInputStream = nsIMultiplexInputStream(stream);
+    multiplexInputStream.removeStream(0);
+
+    // If there was an error report.
+    if (!components.isSuccessCode(status))
+      emit(stream, "error", status);
+
+    // If there more chunks in queue then flush them.
+    else if (multiplexInputStream.count)
+      stream.flush();
+
+    // If stream is still writable notify that queue has drained.
+    else if (stream.writable)
+      emit(stream, "drain");
+
+    // If stream is no longer writable close it.
+    else {
+      nsIAsyncStreamCopier(stream).cancel(Cr.NS_OK);
+      nsIMultiplexInputStream(stream).close();
+      nsIAsyncOutputStream(stream).close();
+      nsIAsyncOutputStream(stream).flush();
+    }
+  }
+});
+
+const OutputStreamCallback = Class({
+  initialize: function(stream) {
+    this.stream = stream;
+  },
+  // Method is part of `nsIOutputStreamCallback` interface that
+  // is invoked by `nsIAsyncOutputStream.asyncWait`. It is registered
+  // with `WAIT_CLOSURE_ONLY` flag that overrides the default behavior,
+  // causing the `onOutputStreamReady` notification to be suppressed until
+  // the stream becomes closed.
+  onOutputStreamReady: function(nsIAsyncOutputStream) {
+    emit(this.stream, "finish");
+  }
+});
+
+const OutputStream = Class({
+  extends: Stream,
+  writable: false,
+  drained: true,
+  get bufferSize() {
+    let multiplexInputStream = nsIMultiplexInputStream(this);
+    return multiplexInputStream && multiplexInputStream.available();
+  },
+  initialize: function initialize(options) {
+    let { asyncOutputStream, output } = options;
+    this.writable = true;
+
+    // Ensure that `nsIAsyncOutputStream` was provided.
+    asyncOutputStream.QueryInterface(Ci.nsIAsyncOutputStream);
+
+    // Create a `nsIMultiplexInputStream` and `nsIAsyncStreamCopier`. Former
+    // is used to queue written data chunks that `asyncStreamCopier` will
+    // asynchronously drain into `asyncOutputStream`.
+    let multiplexInputStream = MultiplexInputStream();
+    let asyncStreamCopier = AsyncStreamCopier(multiplexInputStream,
+                                              output || asyncOutputStream,
+                                              eventTarget,
+                                              // nsIMultiplexInputStream
+                                              // implemnts .readSegments()
+                                              true,
+                                              // nsIOutputStream may or
+                                              // may not implemnet
+                                              // .writeSegments().
+                                              false,
+                                              // Use default buffer size.
+                                              null,
+                                              // Should not close an input.
+                                              false,
+                                              // Should not close an output.
+                                              false);
+
+    // Create `requestObserver` implementing `nsIRequestObserver` interface
+    // in the constructor that's gonna be reused across several flushes.
+    let requestObserver = RequestObserver(this);
+
+
+    // Create observer that implements `nsIOutputStreamCallback` and register
+    // using `WAIT_CLOSURE_ONLY` flag. That way it will be notfied once
+    // `nsIAsyncOutputStream` is closed.
+    asyncOutputStream.asyncWait(OutputStreamCallback(this),
+                                asyncOutputStream.WAIT_CLOSURE_ONLY,
+                                0,
+                                threadManager.currentThread);
+
+    nsIRequestObserver(this, requestObserver);
+    nsIAsyncOutputStream(this, asyncOutputStream);
+    nsIMultiplexInputStream(this, multiplexInputStream);
+    nsIAsyncStreamCopier(this, asyncStreamCopier);
+
+    this.asyncOutputStream = asyncOutputStream;
+    this.multiplexInputStream = multiplexInputStream;
+    this.asyncStreamCopier = asyncStreamCopier;
+  },
+  write: function write(content, encoding, callback) {
+    if (isFunction(encoding)) {
+      callback = encoding;
+      encoding = callback;
+    }
+
+    // If stream is not writable we throw an error.
+    if (!this.writable) throw Error("stream is not writable");
+
+    let chunk = null;
+
+    // If content is not a buffer then we create one out of it.
+    if (Buffer.isBuffer(content)) {
+      chunk = new ArrayBufferInputStream();
+      chunk.setData(content.buffer, 0, content.length);
+    }
+    else {
+      chunk = new StringInputStream();
+      chunk.setData(content, content.length);
+    }
+
+    if (callback)
+      this.once("drain", callback);
+
+    // Queue up chunk to be copied to output sync.
+    nsIMultiplexInputStream(this).appendStream(chunk);
+    this.flush();
+
+    return this.drained;
+  },
+  flush: function() {
+    if (this.drained) {
+      this.drained = false;
+      nsIAsyncStreamCopier(this).asyncCopy(nsIRequestObserver(this), null);
+    }
+  },
+  end: function end(content, encoding, callback) {
+    if (isFunction(content)) {
+      callback = content
+      content = callback
+    }
+    if (isFunction(encoding)) {
+      callback = encoding
+      encoding = callback
+    }
+
+    // Setting a listener to "finish" event if passed.
+    if (isFunction(callback))
+      this.once("finish", callback);
+
+
+    if (content)
+      this.write(content, encoding);
+    this.writable = false;
+
+    // Close `asyncOutputStream` only if output has drained. If it's
+    // not drained than `asyncStreamCopier` is busy writing, so let
+    // it finish. Note that since `this.writable` is false copier will
+    // close `asyncOutputStream` once output drains.
+    if (this.drained)
+      nsIAsyncOutputStream(this).close();
+  },
+  destroy: function destroy() {
+    nsIAsyncOutputStream(this).close();
+    nsIAsyncOutputStream(this);
+    nsIMultiplexInputStream(this);
+    nsIAsyncStreamCopier(this);
+    nsIRequestObserver(this);
+  }
+});
+exports.OutputStream = OutputStream;
+
+const DuplexStream = Class({
+  extends: Stream,
+  implements: [InputStream, OutputStream],
+  allowHalfOpen: true,
+  initialize: function initialize(options) {
+    options = options || {};
+    let { readable, writable, allowHalfOpen } = options;
+
+    InputStream.prototype.initialize.call(this, options);
+    OutputStream.prototype.initialize.call(this, options);
+
+    if (readable === false)
+      this.readable = false;
+
+    if (writable === false)
+      this.writable = false;
+
+    if (allowHalfOpen === false)
+      this.allowHalfOpen = false;
+
+    // If in a half open state and it's disabled enforce end.
+    this.once("end", () => {
+      if (!this.allowHalfOpen && (!this.readable || !this.writable))
+        this.end();
+    });
+  },
+  destroy: function destroy(error) {
+    InputStream.prototype.destroy.call(this);
+    OutputStream.prototype.destroy.call(this);
+  }
+});
+exports.DuplexStream = DuplexStream;
diff --git a/toolkit/jetpack/sdk/io/text-streams.js b/toolkit/jetpack/sdk/io/text-streams.js
new file mode 100644
index 000000000..ed4ec4972
--- /dev/null
+++ b/toolkit/jetpack/sdk/io/text-streams.js
@@ -0,0 +1,235 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+module.metadata = {
+  "stability": "experimental"
+};
+
+const { Cc, Ci, Cu, components } = require("chrome");
+const { ensure } = require("../system/unload");
+const { NetUtil } = Cu.import("resource://gre/modules/NetUtil.jsm", {});
+
+// NetUtil.asyncCopy() uses this buffer length, and since we call it, for best
+// performance we use it, too.
+const BUFFER_BYTE_LEN = 0x8000;
+const PR_UINT32_MAX = 0xffffffff;
+const DEFAULT_CHARSET = "UTF-8";
+
+
+/**
+ * An input stream that reads text from a backing stream using a given text
+ * encoding.
+ *
+ * @param inputStream
+ *        The stream is backed by this nsIInputStream.  It must already be
+ *        opened.
+ * @param charset
+ *        Text in inputStream is expected to be in this character encoding.  If
+ *        not given, "UTF-8" is assumed.  See nsICharsetConverterManager.idl for
+ *        documentation on how to determine other valid values for this.
+ */
+function TextReader(inputStream, charset) {
+  charset = checkCharset(charset);
+
+  let stream = Cc["@mozilla.org/intl/converter-input-stream;1"].
+               createInstance(Ci.nsIConverterInputStream);
+  stream.init(inputStream, charset, BUFFER_BYTE_LEN,
+              Ci.nsIConverterInputStream.DEFAULT_REPLACEMENT_CHARACTER);
+
+  let manager = new StreamManager(this, stream);
+
+  /**
+   * Reads a string from the stream.  If the stream is closed, an exception is
+   * thrown.
+   *
+   * @param  numChars
+   *         The number of characters to read.  If not given, the remainder of
+   *         the stream is read.
+   * @return The string read.  If the stream is already at EOS, returns the
+   *         empty string.
+   */
+  this.read = function TextReader_read(numChars) {
+    manager.ensureOpened();
+
+    let readAll = false;
+    if (typeof(numChars) === "number")
+      numChars = Math.max(numChars, 0);
+    else
+      readAll = true;
+
+    let str = "";
+    let totalRead = 0;
+    let chunkRead = 1;
+
+    // Read in numChars or until EOS, whichever comes first.  Note that the
+    // units here are characters, not bytes.
+    while (true) {
+      let chunk = {};
+      let toRead = readAll ?
+                   PR_UINT32_MAX :
+                   Math.min(numChars - totalRead, PR_UINT32_MAX);
+      if (toRead <= 0 || chunkRead <= 0)
+        break;
+
+      // The converter stream reads in at most BUFFER_BYTE_LEN bytes in a call
+      // to readString, enough to fill its byte buffer.  chunkRead will be the
+      // number of characters encoded by the bytes in that buffer.
+      chunkRead = stream.readString(toRead, chunk);
+      str += chunk.value;
+      totalRead += chunkRead;
+    }
+
+    return str;
+  };
+}
+exports.TextReader = TextReader;
+
+/**
+ * A buffered output stream that writes text to a backing stream using a given
+ * text encoding.
+ *
+ * @param outputStream
+ *        The stream is backed by this nsIOutputStream.  It must already be
+ *        opened.
+ * @param charset
+ *        Text will be written to outputStream using this character encoding.
+ *        If not given, "UTF-8" is assumed.  See nsICharsetConverterManager.idl
+ *        for documentation on how to determine other valid values for this.
+ */
+function TextWriter(outputStream, charset) {
+  charset = checkCharset(charset);
+
+  let stream = outputStream;
+
+  // Buffer outputStream if it's not already.
+  let ioUtils = Cc["@mozilla.org/io-util;1"].getService(Ci.nsIIOUtil);
+  if (!ioUtils.outputStreamIsBuffered(outputStream)) {
+    stream = Cc["@mozilla.org/network/buffered-output-stream;1"].
+             createInstance(Ci.nsIBufferedOutputStream);
+    stream.init(outputStream, BUFFER_BYTE_LEN);
+  }
+
+  // I'd like to use nsIConverterOutputStream.  But NetUtil.asyncCopy(), which
+  // we use below in writeAsync(), naturally expects its sink to be an instance
+  // of nsIOutputStream, which nsIConverterOutputStream's only implementation is
+  // not.  So we use uconv and manually convert all strings before writing to
+  // outputStream.
+  let uconv = Cc["@mozilla.org/intl/scriptableunicodeconverter"].
+              createInstance(Ci.nsIScriptableUnicodeConverter);
+  uconv.charset = charset;
+
+  let manager = new StreamManager(this, stream);
+
+  /**
+   * Flushes the backing stream's buffer.
+   */
+  this.flush = function TextWriter_flush() {
+    manager.ensureOpened();
+    stream.flush();
+  };
+
+  /**
+   * Writes a string to the stream.  If the stream is closed, an exception is
+   * thrown.
+   *
+   * @param str
+   *        The string to write.
+   */
+  this.write = function TextWriter_write(str) {
+    manager.ensureOpened();
+    let istream = uconv.convertToInputStream(str);
+    let len = istream.available();
+    while (len > 0) {
+      stream.writeFrom(istream, len);
+      len = istream.available();
+    }
+    istream.close();
+  };
+
+  /**
+   * Writes a string on a background thread.  After the write completes, the
+   * backing stream's buffer is flushed, and both the stream and the backing
+   * stream are closed, also on the background thread.  If the stream is already
+   * closed, an exception is thrown immediately.
+   *
+   * @param str
+   *        The string to write.
+   * @param callback
+   *        An optional function.  If given, it's called as callback(error) when
+   *        the write completes.  error is an Error object or undefined if there
+   *        was no error.  Inside callback, |this| is the stream object.
+   */
+  this.writeAsync = function TextWriter_writeAsync(str, callback) {
+    manager.ensureOpened();
+    let istream = uconv.convertToInputStream(str);
+    NetUtil.asyncCopy(istream, stream, (result) => {
+        let err = components.isSuccessCode(result) ? undefined :
+        new Error("An error occured while writing to the stream: " + result);
+      if (err)
+        console.error(err);
+
+      // asyncCopy() closes its output (and input) stream.
+      manager.opened = false;
+
+      if (typeof(callback) === "function") {
+        try {
+          callback.call(this, err);
+        }
+        catch (exc) {
+          console.exception(exc);
+        }
+      }
+    });
+  };
+}
+exports.TextWriter = TextWriter;
+
+// This manages the lifetime of stream, a TextReader or TextWriter.  It defines
+// closed and close() on stream and registers an unload listener that closes
+// rawStream if it's still opened.  It also provides ensureOpened(), which
+// throws an exception if the stream is closed.
+function StreamManager(stream, rawStream) {
+  this.rawStream = rawStream;
+  this.opened = true;
+
+  /**
+   * True iff the stream is closed.
+   */
+  stream.__defineGetter__("closed", () => !this.opened);
+
+  /**
+   * Closes both the stream and its backing stream.  If the stream is already
+   * closed, an exception is thrown.  For TextWriters, this first flushes the
+   * backing stream's buffer.
+   */
+  stream.close = () => {
+    this.ensureOpened();
+    this.unload();
+  };
+
+  ensure(this);
+}
+
+StreamManager.prototype = {
+  ensureOpened: function StreamManager_ensureOpened() {
+    if (!this.opened)
+      throw new Error("The stream is closed and cannot be used.");
+  },
+  unload: function StreamManager_unload() {
+    // TextWriter.writeAsync() causes rawStream to close and therefore sets
+    // opened to false, so check that we're still opened.
+    if (this.opened) {
+      // Calling close() on both an nsIUnicharInputStream and
+      // nsIBufferedOutputStream closes their backing streams.  It also forces
+      // nsIOutputStreams to flush first.
+      this.rawStream.close();
+      this.opened = false;
+    }
+  }
+};
+
+function checkCharset(charset) {
+  return typeof(charset) === "string" ? charset : DEFAULT_CHARSET;
+}