Implement Mojo message codec in JavaScript

mojo/public/bindings/js/codec.js

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+define("codec", function() {

[Aaron Boodman, 2013/11/18 18:34:48]

According to the AMD web page, it is encouraged to leave the modules anonymous
and to let their URLs define them.

I was curious what your thoughts on this were and if you plan to change it
later, once URL loading is in place.

[abarth-chromium, 2013/11/18 19:13:20]

Yep.
I've fixed this now that we can find the modules on disk.

+
+  // Memory -------------------------------------------------------------------
+
+  function store8(memory, pointer, val) {
+    memory[pointer] = val;
+  }
+
+  function store16(memory, pointer, val) {
+    memory[pointer + 0] = val >>  0;
+    memory[pointer + 1] = val >>  8;
+  }
+
+  function store32(memory, pointer, val) {
+    memory[pointer + 0] = val >>  0;
+    memory[pointer + 1] = val >>  8;
+    memory[pointer + 2] = val >> 16;
+    memory[pointer + 3] = val >> 24;
+  }
+
+  function store64(memory, pointer, val) {
+    store32(memory, pointer, val);
+    var hi = (val / 0x10000) | 0;

[Aaron Boodman, 2013/11/18 18:34:48]

high :)

[abarth-chromium, 2013/11/18 19:13:20]

Fixed.  :)

+    store32(memory, pointer + 4, hi);
+  }
+
+  function load8(memory, pointer) {
+    return memory[pointer];
+  }
+
+  function load16(memory, pointer) {
+    return (memory[pointer + 0] <<  0) +
+           (memory[pointer + 1] <<  8);
+  }
+
+  function load32(memory, pointer) {
+    return (memory[pointer + 0] <<  0) +
+           (memory[pointer + 1] <<  8) +
+           (memory[pointer + 2] << 16) +
+           (memory[pointer + 3] << 24);
+  }
+
+  function load64(memory, pointer) {
+    var lo = load32(memory, pointer);
+    var hi = load32(memory, pointer + 4);
+    return lo + hi * 0x10000;

[abarth-chromium, 2013/11/18 19:13:20]

Fixed here too.

+  }
+
+  // Buffer -------------------------------------------------------------------
+
+  function Buffer(size) {
+    this.memory = new Uint8Array(size);
+    this.next = 0;
+  }
+
+  Buffer.prototype.alloc = function(size) {
+    var pointer = this.next;
+    this.next += size;
+    if (this.next > this.memory.length)
+      this.grow(1.5 * (this.memory.length + size));

[Aaron Boodman, 2013/11/18 18:34:48]

Make the rounding explicit here, just so that readers don't have to trace
through grow() to make sure fractional values work.

[abarth-chromium, 2013/11/18 19:13:20]

Done.

+    return pointer;
+  };
+
+  Buffer.prototype.grow = function(size) {
+    var newMemory = new Uint8Array(size);
+    var oldMemory = this.memory;
+    for (var i = 0; i < oldMemory.length; ++i)
+      newMemory[i] = oldMemory[i];
+    this.memory = newMemory;
+  };
+
+  // Constants ----------------------------------------------------------------
+
+  var kArrayHeaderSize = 8;
+  var kStructHeaderSize = 8;
+  var kMessageHeaderSize = 8;
+
+  // Decoder ------------------------------------------------------------------
+
+  function Decoder(memory, handles, base) {
+    this.memory = memory;
+    this.handles = handles;
+    this.base = base;
+    this.next = base;
+  }
+
+  Decoder.prototype.skip = function(offset) {
+    this.next += offset;
+  };
+
+  Decoder.prototype.read8 = function() {
+    var result = load8(this.memory, this.next);
+    this.next += 1;
+    return result;
+  };
+
+  Decoder.prototype.read32 = function() {
+    var result = load32(this.memory, this.next);
+    this.next += 4;
+    return result;
+  };
+
+  Decoder.prototype.read64 = function() {
+    var result = load64(this.memory, this.next);
+    this.next += 8;
+    return result;
+  };
+
+  Decoder.prototype.decodePointer = function() {
+    // TODO(abarth): To correctly decode a pointer, we need to know the real
+    // base address of the array buffer.
+    var offsetPointer = this.next;
+    var offset = this.read64();
+    if (!offset)
+      return 0;
+    return offsetPointer + offset;
+  };
+
+  Decoder.prototype.decodeAndCreateDecoder = function() {
+    return new Decoder(this.memory, this.handles, this.decodePointer());
+  };
+
+  Decoder.prototype.decodeHandle = function() {
+    return this.handles[this.read32()];
+  };
+
+  Decoder.prototype.decodeString = function() {
+    // TODO(abarth): We should really support UTF-8. We might want to
+    // jump out of the VM to decode the string directly from the array
+    // buffer using v8::String::NewFromUtf8.
+    var numberOfBytes = this.read32();
+    var numberOfElements = this.read32();
+    var val = new Array(numberOfElements);
+    var memory = this.memory;
+    var base = this.next;
+    for (var i = 0; i < numberOfElements; ++i) {
+      val[i] = String.fromCharCode(memory[base + i] & 0x7F);
+    }
+    this.next += numberOfElements;
+    return val.join('');
+  };
+
+  Decoder.prototype.decodeArray = function(cls) {
+    var numberOfBytes = this.read32();
+    var numberOfElements = this.read32();
+    var val = new Array(numberOfElements);
+    for (var i = 0; i < numberOfElements; ++i) {
+      val[i] = cls.decode(this);
+    }
+    return val;
+  };
+
+  Decoder.prototype.decodeStructPointer = function(cls) {
+    return cls.decode(this.decodeAndCreateDecoder());
+  };
+
+  Decoder.prototype.decodeArrayPointer = function(cls) {
+    return this.decodeAndCreateDecoder().decodeArray(cls);
+  };
+
+  Decoder.prototype.decodeStringPointer = function() {
+    return this.decodeAndCreateDecoder().decodeString();
+  };
+
+  // Encoder ------------------------------------------------------------------
+
+  function Encoder(buffer, handles, base) {
+    this.buffer = buffer;
+    this.handles = handles;
+    this.base = base;
+    this.next = base;
+  }
+
+  Encoder.prototype.skip = function(offset) {
+    this.next += offset;
+  };
+
+  Encoder.prototype.write8 = function(val) {
+    store8(this.buffer.memory, this.next, val);
+    this.next += 1;
+  };
+
+  Encoder.prototype.write32 = function(val) {
+    store32(this.buffer.memory, this.next, val);
+    this.next += 4;
+  };
+
+  Encoder.prototype.write64 = function(val) {
+    store64(this.buffer.memory, this.next, val);
+    this.next += 8;
+  };
+
+  Encoder.prototype.encodePointer = function(pointer) {
+    if (!pointer)
+      return this.write64(0);
+    // TODO(abarth): To correctly encode a pointer, we need to know the real
+    // base address of the array buffer.
+    var offset = pointer - this.next;
+    this.write64(offset);
+  };
+
+  Encoder.prototype.createAndEncodeEncoder = function(size) {
+    var pointer = this.buffer.alloc(size);
+    this.encodePointer(pointer);
+    return new Encoder(this.buffer, this.handles, pointer);
+  };
+
+  Encoder.prototype.encodeHandle = function(handle) {
+    this.handles.push(handle);
+    this.write32(this.handles.length - 1);
+  };
+
+  Encoder.prototype.encodeString = function(val) {
+    var numberOfElements = val.length;
+    var numberOfBytes = kArrayHeaderSize + numberOfElements;
+    this.write32(numberOfBytes);
+    this.write32(numberOfElements);
+    // TODO(abarth): We should really support UTF-8. We might want to
+    // jump out of the VM to encode the string directly from the array
+    // buffer using v8::String::WriteUtf8.
+    var memory = this.buffer.memory;
+    var base = this.next;
+    var len = val.length;
+    for (var i = 0; i < len; ++i) {
+      memory[base + i] = val.charCodeAt(i) & 0x7F;
+    }
+    this.next += len;
+  };
+
+  Encoder.prototype.encodeArray = function(cls, val) {
+    var numberOfElements = val.length;
+    var numberOfBytes = kArrayHeaderSize + cls.encodedSize * numberOfElements;
+    this.write32(numberOfBytes);
+    this.write32(numberOfElements);
+    for (var i = 0; i < numberOfElements; ++i) {
+      cls.encode(this, val[i]);
+    }
+  };
+
+  Encoder.prototype.encodeStructPointer = function(cls, val) {
+    var encoder = this.createAndEncodeEncoder(cls.encodedSize);
+    cls.encode(encoder, val);
+  };
+
+  Encoder.prototype.encodeArrayPointer = function(cls, val) {
+    var encodedSize = kArrayHeaderSize + cls.encodedSize * val.length;
+    var encoder = this.createAndEncodeEncoder(encodedSize);
+    encoder.encodeArray(cls, val);
+  };
+
+  Encoder.prototype.encodeStringPointer = function(val) {
+    // TODO(abarth): This won't be right once we support UTF-8.
+    var encodedSize = kArrayHeaderSize + val.length;
+    var encoder = this.createAndEncodeEncoder(encodedSize);
+    encoder.encodeString(val);
+  };
+
+  // Message ------------------------------------------------------------------
+
+  function Message(memory, handles) {
+    this.memory = memory;
+    this.handles = handles;
+  }
+
+  // MessageBuilder -----------------------------------------------------------
+
+  function MessageBuilder(messageName, payloadSize) {
+    var numberOfBytes = kMessageHeaderSize + payloadSize;
+    this.buffer = new Buffer(numberOfBytes);
+    this.handles = [];
+    var encoder = this.createEncoder(kMessageHeaderSize);
+    encoder.write32(numberOfBytes);
+    encoder.write32(messageName);
+  }
+
+  MessageBuilder.prototype.createEncoder = function(size) {
+    var pointer = this.buffer.alloc(size);
+    return new Encoder(this.buffer, this.handles, pointer);
+  }
+
+  MessageBuilder.prototype.encodeStruct = function(cls, val) {
+    cls.encode(this.createEncoder(cls.encodedSize), val);
+  };
+
+  MessageBuilder.prototype.finish = function() {
+    var message = new Message(this.buffer.memory, this.handles);
+    this.buffer = null;
+    this.handles = null;
+    this.encoder = null;
+    return message;
+  };
+
+  // MessageReader ------------------------------------------------------------
+
+  function MessageReader(message) {
+    this.decoder = new Decoder(message.memory, message.handles, 0);
+    this.payloadSize = this.decoder.read32() - kMessageHeaderSize;
+    this.messageName = this.decoder.read32();
+  }
+
+  MessageReader.prototype.decodeStruct = function(cls) {
+    return cls.decode(this.decoder);
+  };
+
+  // Built-in types -----------------------------------------------------------
+
+  function Uint8() {
+  }
+
+  Uint8.encodedSize = 1;
+
+  Uint8.decode = function(decoder) {
+    return decoder.read8();
+  };
+
+  Uint8.encode = function(encoder, val) {
+    encoder.write8(val);
+  };
+
+  function Uint16() {
+  }
+
+  Uint16.encodedSize = 2;
+
+  Uint16.decode = function(decoder) {
+    return decoder.read16();
+  };
+
+  Uint16.encode = function(encoder, val) {
+    encoder.write16(val);
+  };
+
+  function Uint32() {
+  }
+
+  Uint32.encodedSize = 4;
+
+  Uint32.decode = function(decoder) {
+    return decoder.read32();
+  };
+
+  Uint32.encode = function(encoder, val) {
+    encoder.write32(val);
+  };
+
+  function Uint64() {
+  };
+
+  Uint64.encodedSize = 8;
+
+  Uint64.decode = function(decoder) {
+    return decoder.read64();
+  };
+
+  Uint64.encode = function(encoder, val) {
+    encoder.write64(val);
+  };
+
+  function PointerTo(cls) {
+    this.cls = cls;
+  };
+
+  PointerTo.prototype.encodedSize = 8;
+
+  PointerTo.prototype.decode = function(decoder) {
+    return this.cls.decode(decoder.decodeAndCreateDecoder());
+  };
+
+  PointerTo.prototype.encode = function(encoder, val) {
+    var objectEncoder = encoder.createAndEncodeEncoder(this.cls.encodedSize);
+    this.cls.encode(objectEncoder, val);
+  };
+
+  function Handle() {
+  }
+
+  Handle.encodedSize = 4;
+
+  Handle.decode = function(decoder) {
+    return decoder.decodeHandle();
+  };
+
+  Handle.encode = function(encoder, val) {
+    encoder.encodeHandle(val);
+  };
+
+  var exports = {};
+  exports.load32 = load32;
+  exports.MessageBuilder = MessageBuilder;
+  exports.MessageReader = MessageReader;
+  exports.kArrayHeaderSize = kArrayHeaderSize;
+  exports.kStructHeaderSize = kStructHeaderSize;
+  exports.kMessageHeaderSize = kMessageHeaderSize;
+  exports.Uint8 = Uint8;
+  exports.Uint16 = Uint16;
+  exports.Uint32 = Uint32;
+  exports.Uint64 = Uint64;
+  exports.PointerTo = PointerTo;
+  exports.Handle = Handle;
+  return exports;
+});