length-prefixed-buffers

encode and decode an array of buffers as a single varint length-prefixed binary blob

• for encoding, turns an array of buffers into a single buffer
• for decoding, turns a single buffer into an array of buffers

Works in nodejs and the browser and does not pull in a Buffer implementation when compiled for the browser:

$ browserify example/u8.js | wc -c
4815
$ browserify -p tinyify example/u8.js | gzip | wc -c
756

example

use nodejs buffers:

var lpb = require('length-prefixed-buffers')

var buffers = [
  Buffer.from('abc'),
  Buffer.from('defgh'),
  Buffer.from('ijk')
]
var encoded = Buffer.alloc(lpb.length(buffers))
lpb.encode(encoded, buffers)

console.log('encoded:', encoded)
console.log('decoded:', lpb.decode(encoded))

or Uint8arrays:

var lpb = require('length-prefixed-buffers')

var buffers = [
  Uint8Array.from([97,98,99]),
  Uint8Array.from([100,101,102,103,104]),
  Uint8Array.from([105,106,107])
]
var encoded = new Uint8Array(lpb.length(buffers))
lpb.encode(encoded, buffers)

console.log('encoded:', encoded)
console.log('decoded:', lpb.decode(encoded))

or use from() which takes an array and constructs a collection of the appropriate type based on the first buffer in the array:

var lpb = require('length-prefixed-buffers')

var encoded = lpb.from([
  Uint8Array.from([97,98,99]),
  Uint8Array.from([100,101,102,103,104]),
  Uint8Array.from([105,106,107])
])
console.log('encoded:', encoded) // encoded is a Uint8Array
console.log('decoded:', lpb.decode(encoded))

In this example encoded is a Uint8Array but if from() were passed an array of Buffers then encoded would be a Buffer.

api

var { encode, decode, length, from } = require('length-prefixed-buffers')
var encode = require('length-prefixed-buffers/encode')
var decode = require('length-prefixed-buffers/decode')
var length = require('length-prefixed-buffers/length')
var from = require('length-prefixed-buffers/from')

Each of these except from() has a variant where the initial count of buffers is not included:

var { encode, decode, length, from } = require('length-prefixed-buffers/without-count')
var encode = require('length-prefixed-buffers/without-count/encode')
var decode = require('length-prefixed-buffers/without-count/decode')
var length = require('length-prefixed-buffers/without-count/length')

encode(out, buffers, offset=0)

Write the data from buffers, an array of Buffers or Uint8Arrays into out starting at the index offset. Returns out.

The number of bytes written is stored in encode.bytes (similar to the varint api).

var buffers = decode(src, offset=0)

Reconstruct an array of buffers from src, a Buffer or Uint8Array starting at offset.

The buffers are constructed using subarray() so if you mutate them you will mutate src.

The types of buffers are the same as the type of src.

The number of bytes read is stored in decode.bytes (similar to the varint api).

var nbytes = length(buffers)

Return the number of bytes nbytes that are required to store the array buffers.

var encoded = from(buffers)

Allocate a buffer encoded for an array of buffers.

This is a convenience method that uses length and encode() to construct an encoded buffer.

install

npm install length-prefixed-buffers

license

bsd