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.
+
+// Memory ---------------------------------------------------------------------
+
+function store8(memory, ptr, val) {

[Aaron Boodman, 2013/11/13 19:32:36]

What is intended to be the public API out of all these identifiers?The rest of
them should be hidden in a closure.

[abarth-chromium, 2013/11/13 19:41:51]

Definitely!  I was hoping we'd have a module system by the time I got this
working so I could just use that to control visibility.

+  memory[ptr] = val;
+}
+
+function load8(memory, ptr, val) {
+  return memory[ptr];
+}
+
+function store16(memory, ptr, val) {
+  memory[ptr + 0] = val >>  0;
+  memory[ptr + 1] = val >>  8;
+}
+
+function load16(memory, ptr, val) {
+  return memory[ptr + 0] <<  0 +
+         memory[ptr + 1] <<  8;
+}
+
+function store32(memory, ptr, val) {
+  memory[ptr + 0] = val >>  0;
+  memory[ptr + 1] = val >>  8;
+  memory[ptr + 2] = val >> 16;
+  memory[ptr + 3] = val >> 24;
+}
+
+function load32(memory, ptr, val) {
+  return memory[ptr + 0] <<  0 +
+         memory[ptr + 1] <<  8 +
+         memory[ptr + 2] << 16 +
+         memory[ptr + 3] << 24;
+}
+
+function store64(memory, ptr, val) {
+  memory[ptr + 0] = val >>  0;
+  memory[ptr + 1] = val >>  8;
+  memory[ptr + 2] = val >> 16;
+  memory[ptr + 3] = val >> 24;
+  memory[ptr + 4] = val >> 32;
+  memory[ptr + 5] = val >> 40;
+  memory[ptr + 6] = val >> 48;
+  memory[ptr + 7] = val >> 56;
+}
+
+function load64(memory, ptr, val) {
+  return memory[ptr + 0] <<  0 +
+         memory[ptr + 1] <<  8 +
+         memory[ptr + 2] << 16 +
+         memory[ptr + 3] << 24 +
+         memory[ptr + 4] << 32 +
+         memory[ptr + 5] << 40 +
+         memory[ptr + 6] << 48 +
+         memory[ptr + 7] << 56;
+}
+
+function align(size) {
+  var kAlignment = 8;
+  return size + (kAlignment - (size % kAlignment)) % kAlignment;

[Aaron Boodman, 2013/11/13 19:32:36]

I think the "% kAlignment" at the end is unnecessary?

[abarth-chromium, 2013/11/13 19:41:51]

I haven't found any callers for this function, so I'm just going to delete it
until needed.

+}
+
+// Serialization --------------------------------------------------------------
+
+function encodePointer(memory, ptr, offsetPtr) {

[Aaron Boodman, 2013/11/13 19:32:36]

Weird to use both 'ptr' and 'pointer'. Google style would be to use 'pointer'
everywhere.

[abarth-chromium, 2013/11/13 19:41:51]

Ok.  I was thinking about switching to addr, but we can use pointer.

+  if (!ptr) {
+    store64(memory, offsetPtr, 0);
+    return;
+  }
+  var offset = ptr - offsetPtr;
+  store64(memory, offsetPtr, offset);
+}
+
+function decodePointer(memory, offsetPtr) {
+  var offset = load64(memory, offsetPtr);
+  if (!offset)
+    return 0;
+  return offsetPtr + offset;
+}
+
+function encodeHandle(memory, handlePtr, handles) {
+  handles.push(load32(memory, handlePtr));
+  store32(memory, handlePtr, handles.length - 1);
+}
+
+function decodeHandle(memory, handlePtr, handles) {
+  var index = load32(memory, handlePtr);
+  store32(memory, handlePtr, handles[index]);
+}
+
+// Record ---------------------------------------------------------------------
+
+function Record(memory, ptr) {
+  this.memory = memory;
+  this.base = ptr;
+  this.next = ptr;
+}
+
+Record.prototype.advance = function(offset) {
+  this.next += offset;
+}
+
+Record.prototype.readPtr = function() {
+  var ptr = decodePointer(this.memory, this.next);
+  this.next += 8;
+  return ptr;
+}
+
+Record.prototype.writePtr = function(ptr) {
+  encodePointer(this.memory, ptr, this.next);
+  this.next += 8;
+}
+
+Record.prototype.readRecord = function() {
+  return new Record(this.memory, this.readPtr());
+}
+
+Record.prototype.readString = function(len) {
+  // 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.

[Aaron Boodman, 2013/11/13 19:32:36]

There are javascript implementations of utf8! I wrote one once!

[abarth-chromium, 2013/11/13 19:41:51]

Link?  :)

I'd like to start with a pure JS implementation and optimize as indicated.

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

I believe that there is one I wrote internally as one of my first projects at
Google. I thought we open sourced it, but I can't find it. Will research
tomorrow when I'm in the office -- no vpn here.

+  var result = "";
+  var memory = this.memory;
+  var base = this.next;
+  for (var i = 0; i < len; ++i) {
+    result += String.fromCharCode(memory[base + i] & 0x7F);
+  }
+  this.next += len;
+  return result;
+}
+
+Record.prototype.read8 = function() {
+  var result = load8(this.memory, this.next);
+  this.next += 1;
+  return result;
+}
+
+Record.prototype.read32 = function() {
+  var result = load32(this.memory, this.next);
+  this.next += 4;
+  return result;
+}
+
+Record.prototype.read64 = function() {
+  var result = load64(this.memory, this.next);
+  this.next += 8;
+  return result;
+}
+
+Record.prototype.write8 = function(val) {
+  store8(this.memory, this.next, val);
+  this.next += 1;
+}
+
+Record.prototype.write32 = function(val) {
+  var after = this.next + 4;
+  store32(this.memory, this.next, val);
+  this.next += 4;
+};
+
+Record.prototype.write64 = function(val) {
+  store64(this.memory, this.next, val);
+  this.next += 8;
+};
+
+// Buffer ---------------------------------------------------------------------
+
+function Buffer(size) {
+  this.memory = new Uint8Array(size);
+  this.nextAllocation = 0;
+}
+
+Buffer.prototype.alloc = function(size) {
+  var ptr = this.nextAllocation;
+  this.nextAllocation += size;
+  if (this.nextAllocation > this.memory.length)
+    throw "Buffer full.";
+  return new Record(this.memory, ptr);
+};
+
+// Fields ---------------------------------------------------------------------
+
+var kArrayHeaderSize = 8;
+var kStructHeaderSize = 8;
+
+function encodeArray(record, class, val) {
+  var numberOfElements = val.length;
+  record.write32(kArrayHeaderSize + class.encodedSize * numberOfElements);
+  record.write32(numberOfElements);
+  for (var i = 0; i < numberOfElements; ++i) {
+    class.encode(record, val[i]);
+  }
+  // TODO(abarth): We should sanity check that everthing fits.
+}
+
+function decodeArray(record, class) {
+  var numberOfBytes = record.read32();
+  var numberOfElements = record.read32();
+  var val = [];
+  for (var i = 0; i < numberOfElements; ++i) {
+    val.push(class.decode(record));
+  }
+  // TODO(abarth): We should sanity check that everthing fits.
+  return val;
+}
+
+function decodeString(record) {
+  var numberOfBytes = record.read32();
+  var numberOfElements = record.read32();
+  return record.readString(numberOfElements);
+}
+
+// Message --------------------------------------------------------------------
+
+var kMessageHeaderSize = 8;
+
+function Message() {
+  this.memory = null;
+  this.handles = [];
+}
+
+Message.prototype.dispose = function() {
+  var len = this.handles.length;
+  for (var i = 0; i < len; ++i) {
+    mojo.core.close(this.handles[i]);
+    this.handles[i] = mojo.core.HANDLE_INVALID;
+  }
+};
+
+// MessageBuilder -------------------------------------------------------------
+
+function MessageBuilder(messageName, payloadSize) {
+  var buffer = new Buffer(kMessageHeaderSize + payloadSize);
+  var header = buffer.alloc(kMessageHeaderSize);
+  header.write32(buffer.length);
+  header.write32(messageName);
+
+  this.buffer = buffer;
+}
+
+MessageBuilder.prototype.takeBuffer = function() {
+  var buffer = this.buffer;
+  this.buffer = null;
+  return buffer;
+};
+
+// Basic types ----------------------------------------------------------------
+
+function Uint8() {
+}
+
+Uint8.encodedSize = 1;
+
+Uint8.decode = function(record) {
+  return record.read8();
+};
+
+Uint8.encode = function(record, val) {
+  record.write8(val);
+};
+
+function Ptr(class) {
+  this.class = class;
+};
+
+Ptr.prototype.encodedSize = 8;
+
+Ptr.prototype.decode = function(record) {
+  return class.decode(record.readRecord());
+};
+
+Ptr.prototype.encode = function(record, val) {
+  // TODO(abarth): Where does |buffer| come from?
+  objectRecord = buffer.alloc(class.encodedSize);
+  class.encode(objectRecord, val);
+  record.writePtr(objectRecord.base);
+};
+
+function Handle() {
+}
+
+// TOOD(abarth): Implement handles.
+
+// "Generated" code ===========================================================
+
+function Bar() {
+  this.alpha = 0;
+  this.beta = 0;
+  this.gamma = 0;
+}
+
+Bar.encodedSize = kStructHeaderSize + 8;
+
+Bar.decode = function(record) {
+  var val = new Bar();
+  // TODO(abarth): We need to support optional fields.
+  record.advance(kStructHeaderSize);
+  val.alpha = record.read8();
+  val.beta = record.read8();
+  val.gamma = record.read8();
+  record.advance(5);
+  return val;
+};
+
+Bar.encode = function(record, val) {
+  record.write32(Bar.encodedSize);
+  record.write32(3);
+  record.write8(val.alpha);
+  record.write8(val.beta);
+  record.write8(val.gamma);
+  record.advance(5);
+};
+
+  // int32_t x_;
+  // int32_t y_;
+  // uint8_t a_ : 1;
+  // uint8_t b_ : 1;
+  // uint8_t c_ : 1;
+  // uint8_t _pad0_[7];
+  // mojo::internal::StructPointer<Bar> bar_;
+  // mojo::internal::ArrayPointer<uint8_t> data_;
+  // mojo::internal::ArrayPointer<Bar*> extra_bars_;
+  // mojo::internal::StringPointer name_;
+  // mojo::internal::ArrayPointer<mojo::Handle> files_;
+
+function Foo() {
+  this.x = 0;
+  this.y = 0;
+  this.a = 0;
+  this.b = 0;
+  this.c = 0;
+  this.bar = null;
+  this.data = null;
+  this.extra_bars = null;
+  this.name = null;
+  this.files = null;
+}
+
+Foo.encodedSize = 64;
+
+Foo.decode = function(record) {
+  var val = new Foo();
+  // TODO(abarth): We need to support optional fields.
+  record.advance(kStructHeaderSize);
+  val.x = record.read32();
+  val.y = record.read32();
+  var packed = record.read8();
+  val.a = (packed >> 0) & 1;
+  val.b = (packed >> 1) & 1;
+  val.c = (packed >> 2) & 1;
+  record.advance(7);
+  val.bar = Bar.decode(record.readRecord());
+  val.data = decodeArray(record.readRecord(), Uint8);
+  val.extra_bars = decodeArray(record.readRecord(), new Ptr(Bar));
+  val.name = decodeString(record.readRecord());
+  val.files = decodeArray(record.readRecord(), Handle);
+}
+
+Foo.encode = function(record, val) {
+  record.write32(Foo.encodedSize);
+  record.write32(10);
+  record.write32(val.x);
+  record.write32(val.y);
+  var packed = (val.a & 1) << 0 |
+               (val.b & 1) << 1 |
+               (val.c & 1) << 2;
+  record.write8(packed);
+  record.advance(7);
+
+  // TODO(abarth): Where does buffer come from?
+  var barRecord = buffer.alloc(Bar.encodedSize);
+  Bar.encode(barRecord, val.bar);
+  record.writePtr(barRecord.base);
+
+  var dataRecord = buffer.alloc(Uint8.encodedSize);
+  encodeArray(dataRecord, Uint8, this.data);
+  record.writePtr(dataRecord.base);
+
+  var extra_barsClass = new Ptr(Bar);
+  var extra_barsRecord = buffer.alloc(extra_barsClass.encodedSize);
+  encodeArray(dataRecord, extra_barsClass, this.data);
+  record.writePtr(extra_barsRecord.base);
+
+  // TODO(abarth): We'll need something fancier here to support UTF-8.
+  var nameLength = val.name.length;
+  nameRecord = buffer.alloc(nameLength);
+  encodeString(nameRecord, val.name);
+  record.writePtr(nameRecord.base);
+
+  // TODO(abarth): We need to be able to encode handles.
+};