MessagePack for JavaScript/ECMA-262

This is a JavaScript/ECMA-262 implementation of MessagePack, an efficient binary serilization format:

https://msgpack.org/

This library is a universal JavaScript, which suppors both browsers and NodeJS. In addition, because it is implemented in TypeScript, type definition files (d.ts) are bundled in the distribution.

Synopsis

import { deepStrictEqual } from "assert";
import { encode, decode } from "@msgpack/msgpack";

const object = {
  nil: null,
  integer: 1,
  float: Math.PI,
  string: "Hello, world!",
  binary: Uint8Array.from([1, 2, 3]),
  array: [10, 20, 30],
  map: { foo: "bar" },
  timestampExt: new Date(),
};

const encoded: Uint8Array = encode(object);

deepStrictEqual(decode(encoded), object);

Install

This library is publised as @msgpack/msgpack in npmjs.com.

npm install @msgpack/msgpack

API

encode(data: unknown, options?: EncodeOptions): Uint8Array

It encodes data and returns a byte array as Uint8Array.

decode(buffer: ArrayLike<number>, options?: DecodeOptions): unknown

It decodes buffer encoded as MessagePack, and returns a decoded object as uknown.

buffer must be an array of bytes, which is typically Uint8Array.

DecodeOptions

Name	Type	Default
extensionCodec	ExtensionCodec	ExtensinCodec.defaultCodec
maxStrLength	number	4_294_967_295 (UINT32_MAX)
maxBinLength	number	4_294_967_295 (UINT32_MAX)
maxArrayLength	number	4_294_967_295 (UINT32_MAX)
maxMapLength	number	4_294_967_295 (UINT32_MAX)
maxExtLength	number	4_294_967_295 (UINT32_MAX)

You can use max${Type}Length to limit the length of each type decoded.

decodeAsync(stream: AsyncIterable<ArrayLike<number>> | ReadableStream<ArrayLike<number>>, options?: DecodeAsyncOptions): Promise<unknown>

It decodes stream in an async iterable of byte arrays, and returns decoded object as uknown type, wrapped in Promise. This function works asyncronously.

DecodeAsyncOptions is the same as DecodeOptions for decode().

This function is designed to work with whatwg fetch() like this:

import { decodeAsync } from "@msgpack/msgpack";

const MSGPACK_TYPE = "application/x-msgpack";

const response = await fetch(url);
const contentType = response.headers.get("Content-Type");
if (contentType && contentType.startsWith(MSGPACK_TYPE) && response.body != null) {
  const object = await decodeAsync(response.body);
  // do something with object
} else { /* handle errors */ }

decodeArrayStream(stream: AsyncIterable< ArrayLike<number>> | ReadableStream<ArrayLike<number>>, options?: DecodeAsyncOptions): AsyncIterable<unknown>

It is alike to decodeAsync(), but only accepts an array of items as the input stream, and emits the decoded item one by one.

It throws errors when the input is not an array.

decodeStream(stream: AsyncIterable<ArrayLike<number>> | ReadableStream<ArrayLike<number>>, options?: DecodeAsyncOptions): AsyncIterable<unknown>

It is like to decodeAsync() and decodeArrayStream(), but the input stream consists of independent MessagePack items.

In other words, it decodes an unlimited stream and emits an item one by one.

Extension Types

To handle MessagePack Extension Types, this library provides ExtensionCodec class.

Here is an example to setup custom extension types that handles Map and Set classes in TypeScript:

import { encode, decode, ExtensionCodec } from "@msgpack/msgpack";

const extensionCodec = new ExtensionCodec();

// Set<T>
const SET_EXT_TYPE = 0 // Any in 0-127
extensionCodec.register({
  type: SET_EXT_TYPE,
  encode: (object: unknown): Uint8Array | null => {
    if (object instanceof Set) {
      return encode([...object]);
    } else {
      return null;
    }
  },
  decode: (data: Uint8Array) => {
    const array = decode(data) as Array<unknown>;
    return new Set(array);
  },
});

// Map<T>
const MAP_EXT_TYPE = 1; // Any in 0-127
extensionCodec.register({
  type: 1,
  encode: (object: unknown): Uint8Array => {
    if (object instanceof Map) {
      return encode([...object]);
    } else {
      return null;
    }
  },
  decode: (data: Uint8Array) => {
    const array = decode(data) as Array<[unknown, unknown]>;
    return new Map(array);
  },
});

// and later
import { encode, decode } from "@msgpack/msgpack";

const encoded = = encode([new Set<any>(), new Map<any, any>()], { extensionCodec });
const decoded = decode(encoded, { extensionCodec });

Not that extension types for custom objects must be [0, 127], while [-1, -128] is reserved for MessagePack itself.

Handling BigInt with ExtensionCodec

This library does not handle BigInt by default, but you can handle it with ExtensionCodec like this:

import { deepStrictEqual } from "assert";
import { encode, decode, ExtensionCodec } from "@msgpack/msgpack";

const BIGINT_EXT_TYPE = 0; // Any in 0-127
const extensionCodec = new ExtensionCodec();
extensionCodec.register({
  type: BIGINT_EXT_TYPE,
  encode: (input: unknown) => {
    if (typeof input === "bigint") {
      return encode(input.toString());
    } else {
      return null;
    }
  },
  decode: (data: Uint8Array) => {
    return BigInt(decode(data));
  },
});

const value = BigInt(Number.MAX_SAFE_INTEGER) + BigInt(1);
const encoded: = encode(value, { extensionCodec });
deepStrictEqual(decode(encoded, { extensionCodec }), value);

The temporal module as timestamp extensions

There is a proposal for a new date/time representations in JavaScript:

• https://github.com/tc39/proposal-temporal

This library maps Date to the MessagePack timestamp extension by default, but you can re-map the temporal module (or @std-proposal/temporal ponyfill) to the timestamp extension like this:

import { Instant } from "@std-proposal/temporal";
import { deepStrictEqual } from "assert";
import {
  encode,
  decode,
  ExtensionCodec,
  EXT_TIMESTAMP,
  encodeTimeSpecToTimestamp,
  decodeTimestampToTimeSpec,
} from "@msgpack/msgpack";

const extensionCodec = new ExtensionCodec();
extensionCodec.register({
  type: EXT_TIMESTAMP, // override the default behavior!
  encode: (input: any) => {
    if (input instanceof Instant) {
      const sec = input.seconds;
      const nsec = Number(input.nanoseconds - BigInt(sec) * BigInt(1e9));
      return encodeTimeSpecToTimestamp({ sec, nsec });
    } else {
      return null;
    }
  },
  decode: (data: Uint8Array) => {
    const timeSpec = decodeTimestampToTimeSpec(data);
    const sec = BigInt(timeSpec.sec);
    const nsec = BigInt(timeSpec.nsec);
    return Instant.fromEpochNanoseconds(sec * BigInt(1e9) + nsec);
  },
});

const instant = Instant.fromEpochMilliseconds(Date.now());
const encoded = encode(instant, { extensionCodec });
const decoded = decode(encoded, { extensionCodec });
deepStrictEqual(decoded, instant);

This will be default once the temporal module is standardizied, which is not a near-future, though.

MessagePack Specification

This library is compatible with the "August 2017" revision of MessagePack specification at the point where timestamp ext was added.

The specification is here:

https://github.com/msgpack/msgpack

MessagePack Mapping Table

The following table shows how JavaScript values are mapped to MessagePack formats and vice versa.

Source Value	MessagePack Format	Value Decoded
null, undefined	nil format family	null (*1)
boolean (true, false)	bool format family	boolean (true, false)
number (53-bit int)	int format family	number (53-bit int)
number (64-bit float)	float format family	number (64-bit float)
string	str format family	string
ArrayBufferView	bin format family	Uint8Array (*2)
Array	array format family	Array
Object	map format family	Object (*3)
Date	timestamp ext format family	Date (*4)

• *1 Both null and undefined are mapped to nil (0xC0) type, and are decoded into null
• *2 Any ArrayBufferViews including NodeJS's Buffer are mapped to bin family, and are decoded into Uint8Array
• *3 In handling Object, it is regarded as Record<string, unknown> in terms of TypeScript
• *4 MessagePack timestamps may have nanoseconds, which will lost when it is decoded into JavaScript Date. This behavior can be overrided by registering -1 for the extension codec.

Prerequsites

This is a universal JavaScript library that supports major browsers and NodeJS.

ECMA-262

• ES5 language features
• ES2018 standard library, including:
  • Typed arrays (ES2015)
  • Async iterations (ES2018)
  • Features added in ES2015-ES2018

ES2018 standard library used in this library can be polyfilled. For example, core-js is used as polyfills to run tests on IE11, which has only ES5 language features.

NodeJS

NodeJS v10 is required, but NodeJS v12 or later is recommended because it includes the V8 feature of Improving DataView performance in V8.

Benchmark

Benchmark on NodeJS/v12.3.1

operation	op	ms	op/s
buf = Buffer.from(JSON.stringify(obj));	497600	5000	99520
buf = JSON.stringify(obj);	969500	5000	193900
obj = JSON.parse(buf);	345300	5000	69060
buf = require("msgpack-lite").encode(obj);	369100	5000	73820
obj = require("msgpack-lite").decode(buf);	278900	5000	55780
buf = require("@msgpack/msgpack").encode(obj);	556900	5000	111380
obj = require("@msgpack/msgpack").decode(buf);	502200	5000	100440

Note that Buffer.from() for JSON.stringify() is added to emulate I/O where a JavaScript string must be converted into a byte array encoded in UTF-8, whereas MessagePack's encode() returns a byte array.

Distrubition

The NPM package distributed in npmjs.com includes both ES2015+ and ES5 files:

• /dist is compiled into ES2015+
• /dist.es5 is compiled into ES5 and bundled to singile file

If you use NodeJS and/or webpack, their module resolvers use the suitable one automatically.

Maintenance

Testing

test matrix:

• WebAssembly availability
  • WASM=force / WASM=never
• TypeScript targets
  • target=es2019 / target=es5
• JavaScript engines
  • NodeJS, borwsers (Chrome, Firefox, Safari, IE11)

See test:* in package.json and .travis.yml for details.

Relase Engineering

# run tests on NodeJS, Chrome, and Firefox
make test-all

# edit the changelog
code CHANGELOG.md

# bump version
npm version patch|minor|major

# run the publishing task
make publish

Updating Dependencies

npm run update-dependencies

Big Thanks

Cross-browser Testing Platform and Open Source <3 Provided by Sauce Labs.

License

Copyright 2019 The MessagePack community.

This software uses the ISC license:

https://opensource.org/licenses/ISC

See LICENSE for details.