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 is quite good, and the space required for serialized data is far less than JSON.

Performance

node-msgpack outperforms the built-in JSON.stringify() and JSON.parse() methods handily. 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 and installation

There are two ways to install msgpack.

npm

	npm install msgpack

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

Manually

Use make to build the add-on, then manually copy build/default/mpBindings.node and lib/msgpack.js it to wherever your node.js installation will look for it (or add the build directory to your $NODE_PATH).

% ls
LICENSE  Makefile  README.md  deps/  src/  tags  test.js
% make

The MessagePack library on which this depends is packaged with node-msgpack and will be built as part of this process.

Note: MessagePack may fail to build if you do not have a modern version of gcc in your $PATH. On Mac OS X Snow Leopard (10.5.x), you may have to use gcc-4.2, which should come with your box but is not used by default.

% make CC=gcc-4.2 CXX=gcc-4.2