msgpack

node-msgpack is an addon for NodeJS that provides an API for serializing and de-serializing JavaScript objects using the MessagePack library. The performance of this addon compared to the native JSON object isn't too bad, and the space required for serialized data is far less than JSON.

Performance

node-msgpack is currently slower than the built-in JSON.stringify() and JSON.parse() methods. In recent versions of node.js, the JSON functions have been heavily optimized. node-msgpack is still more compact, and we are currently working performance improvements. Testing shows that, over 500k iterations, msgpack.pack() is about 5x slower than JSON.stringify(), and msgpack.unpack() is about 3.5x slower than JSON.parse().
Old performance numbers are below.
The following tests were performed with 500,000 instances of the JavaScript object {'abcdef' : 1, 'qqq' : 13, '19' : [1, 2, 3, 4]}:

* `JSON.stringify()` 7.17 seconds
* `JSON.parse(JSON.stringify())` 22.18 seconds
* `msgpack.pack()` 5.80 seconds
* `msgpack.unpack(msgpack.pack())` 8.62 seconds

Note that node-msgpack produces and consumes Buffer objects, and a such does not incur encoding/decoding overhead when performing I/O with native strings.

Usage

This module provides two methods: pack(), which consumes a JavaScript object and produces a node Buffer object; and unpack(), which consumes a node Buffer object and produces a JavaScript object. Packing of all native JavaScript types (undefined, boolean, numbers, strings, arrays and objects) is supported, as is the node Buffer type.
The below code snippet packs and then unpacks a JavaScript object, verifying the resulting object at the end using assert.deepEqual().

var assert = require('assert');
var msgpack = require('msgpack');

var o = {"a" : 1, "b" : 2, "c" : [1, 2, 3]};
var b = msgpack.pack(o);
var oo = msgpack.unpack(b);

assert.deepEqual(oo, o);

As a convenience, a higher level streaming API is provided in the msgpack.Stream class, which can be constructed around a net.Stream instance. This object emits msg events when an object has been received.

var msgpack = require('msgpack');

// ... get a net.Stream instance, s, from somewhere

var ms = new msgpack.Stream(s);
ms.addListener('msg', function(m) {
    sys.debug('received message: ' + sys.inspect(m));
});

Type Mapping

The JavaScript type system does not map cleanly on to the MsgPack type system, though it's pretty close.
When packing, JavaScript values are mapped to MsgPack types as follows

* `undefined` and `null` values map to `MSGPACK_OBJECT_NIL`
* `boolean` values map to `MSGPACK_OBJECT_BOOLEAN`
* `number` values map differently depending on their value
   * Floating point values map to `MSGPACK_OBJECT_DOUBLE`
   * Positive values map to `MSGPACK_OBJECT_POSITIVE_INTEGER`
   * Negative values map to `MSGPACK_OBJECT_NEGATIVE_INTEGER`
* `string` values map to `MSGPACK_OBJECT_RAW`; all strings are serialized
  with UTF-8 encoding
* Array values (as defined by `Array.isArray()`) map to
  `MSGPACK_OBJECT_ARRAY`; each element in the array is packed individually
  the rules in this list
* NodeJS Buffer values map to `MSGPACK_OBJECT_RAW`
* Everything else maps to `MSGPACK_OBJECT_MAP`, where we iterate over
  the object's properties and pack them and their values as per the
  mappings in this list

When unpacking, MsgPack types are mapped to JavaScript values as follows

* `MSGPACK_OBJECT_NIL` values map to the `null` value
* `MSGPACK_OBJECT_BOOLEAN` values map to `boolean` values
* `MSGPACK_OBJECT_POSITIVE_INTEGER`, `MSGPACK_OBJECT_NEGATIVE_INTEGER` and
  `MSGPACK_OBJECT_DOUBLE` values map to `number` values
* `MSGPACK_OBJECT_ARRAY` values map to arrays; each object in the array is
   packed individually using the rules in this list
* `MSGPACK_OBJECT_RAW` values are mapped to `string` values; these values are
   unpacked using either UTF-8 or ASCII encoding, depending on the contents
   of the raw buffer
* `MSGPACK_OBJECT_MAP` values are mapped to JavaScript objects; keys and
   values are unpacked individually using the rules in this list

Strings are particularly problematic here, as it's difficult to get hints down into the packing and unpacking codepaths about how to interpret a particular string or MSGPACK_OBJECT_RAW. If you have strict requirements about the encoding of your strings, it's recommended that you populate a Buffer object yourself (e.g. using Buffer.write()) and pack that buffer rather than the string. This will ensure that you can control what gets packed.
When unpacking, things are trickier as there is no way to know the encoding used when a string was packed. There is an an open ticket for the MsgPack format to address this.

Command Line Utilities

As a convenience and for debugging, bin/json2msgpack and bin/msgpack2json are provided to convert JSON data to and from MessagePack data, reading from stdin and writing to stdout.

% echo '[1, 2, 3]' | ./bin/json2msgpack | xxd -
0000000: 9301 0203                                ....
% echo '[1, 2, 3]' | ./bin/json2msgpack | ./bin/msgpack2json 
[1,2,3]

Building, Installation, Testing

There are two ways to install msgpack.

NPM

npm install msgpack

This should build and install msgpack for you. Then just require('msgpack').

Manually

You will need node-gyp:

npm install -g node-gyp

Then from the root of the msgpack repo, you can run:

node-gyp rebuild

NOTE:

node-gyp attempts to contact the Internet and download the target version
of node.js source and store it locally.  This will only happen once for
each time it sees a new node.js version.  If you're on a host with no
direct Internet access, you may need to shuffle this source over from
another box or sneaker net.  Good luck!

Testing

To run all tests use:

./run_tests

To run a specific test:

./run_tests test/lib/msgpack.js

NOTE:

Tests are based on a modified version of
nodeunit (https://github.com/godsflaw/nodeunit).
Follow ./run_tests instructions if you run into problems.

Benchmarks

To run benchmarks:

./run_tests test/benchmark/benchmark.js