it-length-prefixed

Streaming length prefixed buffers with async iterables

Table of contents

• Install
  • Browser <script> tag
• Usage
• API
  • encode(source, [opts])
  • encode.single(chunk, [opts])
  • decode(source, [opts])
  • decode.fromReader(reader, [opts])
• Contribute
• API Docs
• License
• Contribution

Install

$ npm i it-length-prefixed

Browser <script> tag

Loading this module through a script tag will make it's exports available as ItLengthPrefixed in the global namespace.

<script src="https://unpkg.com/it-length-prefixed/dist/index.min.js"></script>

Usage

import { pipe } from 'it-pipe'
import * as lp from 'it-length-prefixed'

const encoded = []

// encode
await pipe(
  [uint8ArrayFromString('hello world')],
  (source) => lp.encode(source),
  async source => {
    for await (const chunk of source) {
      encoded.push(chunk.slice()) // (.slice converts Uint8ArrayList to Uint8Array)
    }
  }
)

console.log(encoded)
// => [Buffer <0b 68 65 6c 6c 6f 20 77 6f 72 6c 64>]

const decoded = []

// decode
await pipe(
  encoded, // e.g. from above
  (source) => lp.decode(source),
  async source => {
    for await (const chunk of source) {
      decoded.push(chunk.slice()) // (.slice converts Uint8ArrayList to Uint8Array)
    }
  }
)

console.log(decoded)
// => [Buffer <68 65 6c 6c 6f 20 77 6f 72 6c 64>]

API

import {
  encode, decode
} from 'it-length-prefixed'

import {
  encode
} from 'it-length-prefixed/encode'

import {
  decode,
  MAX_LENGTH_LENGTH,
  MAX_DATA_LENGTH
} from 'it-length-prefixed/decode'

encode(source, [opts])

• source: Iterable<Uint8ArrayList | Uint8Array> | AsyncIterable<Uint8ArrayList | Uint8Array> source to read bytes from
• opts: Object, optional
  • lengthEncoder: Function: A function that encodes the length that will prefix each message. By default this is a varint encoder. It is passed a value to encode, an (optional) target buffer to write to and an (optional) offset to start writing from. The function should encode the value into the target (or alloc a new Buffer if not specified), set the lengthEncoder.bytes value (the number of bytes written) and return the target.

Returns Generator or AsyncGenerator that yields Uint8ArrayList objects. All messages will be prefixed with a length, determined by the lengthEncoder function.

encode.single(chunk, [opts])

• chunk: Buffer|Uint8ArrayList chunk to encode
• opts: Object, optional
  • lengthEncoder: Function: See description above. Note that this encoder will not be passed a target or offset and so will need to allocate a buffer to write to.

Returns a Uint8ArrayList containing the encoded chunk.

decode(source, [opts])

• source: Iterable<Uint8ArrayList | Uint8Array> | AsyncIterable<Uint8ArrayList | Uint8Array> source to read bytes from
• opts: Object, optional
  • maxLengthLength: If provided, will not decode messages whose length section exceeds the size specified, if omitted will use the default of 147 bytes.
  • maxDataLength: If provided, will not decode messages whose data section exceeds the size specified, if omitted will use the default of 4MB.
  • onLength(len: Number): Called for every length prefix that is decoded from the stream
  • onData(data: Uint8ArrayList): Called for every chunk of data that is decoded from the stream
  • lengthDecoder: Function: A function that decodes the length that prefixes each message. By default this is a varint decoder. It is passed some data to decode which is a Uint8ArrayList. The function should decode the length, set the lengthDecoder.bytes value (the number of bytes read) and return the length. If the length cannot be decoded, the function should throw a RangeError.

Returns Generator or AsyncGenerator that yields Uint8ArrayList objects.

decode.fromReader(reader, [opts])

Behaves like decode except it only reads the exact number of bytes needed for each message in reader.

• reader: Reader: An it-reader
• opts: Object, optional
  • maxLengthLength: If provided, will not decode messages whose length section exceeds the size specified, if omitted will use the default of 147 bytes.
  • maxDataLength: If provided, will not decode messages whose data section exceeds the size specified, if omitted will use the default of 4MB.
  • onData(data: Uint8ArrayList): Called for every chunk of data that is decoded from the stream
  • lengthEncoder: Function: See description above.

Returns Generator or AsyncGenerator that yields Uint8ArrayList objects.

Contribute

PRs and issues gladly accepted! Check out the issues.

API Docs

• https://alanshaw.github.io/it-length-prefixed

License

Licensed under either of

• Apache 2.0, (LICENSE-APACHE / http://www.apache.org/licenses/LICENSE-2.0)
• MIT (LICENSE-MIT / http://opensource.org/licenses/MIT)

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.