pbf

A low-level, ultra-lightweight (2.9KB gzipped) protocol buffers implementation in JavaScript for browsers and Node.

Designed to be a building block for writing a customized, lazy decoder for a stable protobuf schema. If you need an all-purpose protobuf JS library that does most of the work for you, take a look at protocol-buffers.

Install

Node and Browserify:

npm install pbf

Making a browser build:

npm install
npm run build-dev # pbf-dev.js (development build)
npm run build-min # pbf.js (minified production build)

Example

Reading

var pbf = new Pbf(buffer),
    name, version, layerName;

pbf.readFields(function(tag) {
    if (tag === 1) name = pbf.readString();
    else if (tag === 2) version = pbf.readVarint();
    else if (tag === 3) {
        pbf.readMessage(function(tag) {
            if (tag === 1) layerName = pbf.readString();
        });
    }
});

Writing

var pbf = new Pbf();

pbf.writeStringField(1, 'Hello world');
pbf.writeVarintField(2, 300);

var layer = new Pbf();
layer.writeStringField(1, 'foobar');

pbf.writeMessage(3, layer);

var buffer = pbf.finish();

API

Create a Protobuf object, optionally given a Buffer as input data (or Uint8Array in browsers):

var pbf = Protobuf(/*Buffer or Uint8Array*/ buf);

Protobuf object properties:

pbf.length; // length of the underlying buffer
pbf.pos; // current offset for reading or writing

Reading

Read a sequence of fields:

pbf.readFields(function (tag) {
    if (tag === 1) pbf.readVarint();
    else if (tag === 2) pbf.readString();
    else ...
});

It optionally accepts an object that will be passed to the reading function for easier construction of decoded data, and also passes the Protobuf object as a third argument:

var result = pbf.readFields(callback, {})

function callback(tag, result, pbf) {
    if (tag === 1) result.id = pbf.readVarint();
}

To read an embedded message, use pbf.readMessage(fn[, obj]) (in the same way as read).

Read values:

var value = pbf.readVarint();
var packed = pbf.readPacked('UInt32');

For lazy or partial decoding, simply save the position instead of reading a value, then later set it back to the saved value and read:

var fooPos = -1;
pbf.readFields(function (tag) {
    if (tag === 1) fooPos = pbf.pos;
});
...
pbf.pos = fooPos;
pbf.readMessage(readFoo);

Basic reading methods:

• readVarint()
• readSVarint()
• readFixed32()
• readFixed64()
• readSFixed32()
• readSFixed64()
• readBoolean()
• readFloat()
• readDouble()
• readString()
• readBytes()
• readPacked(type)
• skip(value)

Writing

Write values:

pbf.writeVarint(123);
pbf.writeString("Hello world");

Field writing methods:

• writeVarintField(tag, val)
• writeSVarintField(tag, val)
• writeFixed32Field(tag, val)
• writeFixed64Field(tag, val)
• writeSFixed32Field(tag, val)
• writeSFixed64Field(tag, val)
• writeBooleanField(tag, val)
• writeFloatField(tag, val)
• writeDoubleField(tag, val)
• writeStringField(tag, val)
• writeBytesField(tag, buffer)
• writePacked(tag, type, items)
• writeMessage(tag, pbf)

Scalar writing methods:

• writeVarint(val)
• writeSVarint(val)
• writeSFixed32(val)
• writeSFixed64(val)
• writeFloat(val)
• writeDouble(val)
• writeString(val)
• writeBytes(buffer)

Misc methods:

• realloc(minBytes) - pad the underlying buffer size to accommodate the given number of bytes; note that the size increases exponentially, so it won't necessarily equal the size of data written
• finish() - make the current buffer ready for reading and return the data as a buffer slice
• destroy() - dispose the buffer

For an example of a real-world usage of the library, see vector-tile-js.

Changelog

1.1.2 (Dec 26 2014)

Brings tons of improvements and fixes over the previous version (0.0.2). Basically makes the library complete.

Improvements

• Improved performance of both reading and writing.
• Made the browser build 3 times smaller.
• Added convenience readFields and readMessage methods for a much easier reading API.
• Added reading methods: readFloat, readBoolean, readSFixed32, readSFixed64.
• Added writing methods: writeUInt64, writeSFixed32, writeSFixed64.
• Improved readDouble and readString to use native Buffer methods under Node.
• Improved readString and writeString to use HTML5 TextEncoder and TextDecoder where available.
• Made Pbf buffer argument optional.
• Added extensive docs and examples in the readme.
• Added an extensive test suite that brings test coverage up to 100%.

Breaking API changes

• Renamed readBuffer/writeBuffer to readBytes/writeBytes.
• Renamed readUInt32/writeUInt32 to readFixed32/writeFixed32, etc.
• Renamed writeTaggedVarint to writeVarintField, etc.
• Changed writePacked signature from (type, tag, items) to (tag, type, items).

Bugfixes

• Fixed readVarint to handle varints bigger than 6 bytes.
• Fixed readSVarint to handle number bigger than 2^30.
• Fixed writeVarint failing on some integers.
• Fixed writeVarint not throwing an error on numbers that are too big.
• Fixed readUInt64 always failing.
• Fixed writing to an empty buffer always failing.