it-length-prefixed

it-length-prefixed

Streaming length prefixed buffers with async iterators

Install

npm install it-length-prefixed

Usage

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

const encoded = []

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

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
  lp.decode(),
  async source => {
    for await (const chunk of source) {
      decoded.push(chunk.slice()) // (.slice converts BufferList to Buffer)
    }
  }
)

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,
  MIN_POOL_SIZE,
  DEFAULT_POOL_SIZE
} from 'it-length-prefixed/encode'

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

encode([opts])

• opts: Object, optional
  • poolSize: 10 * 1024: Buffer pool size to allocate up front
  • minPoolSize: 8: The minimum size the pool can be before it is re-allocated. Note: it is important this value is greater than the maximum value that can be encoded by the lengthEncoder (see the next option). Since encoded lengths are written into a buffer pool, there needs to be enough space to hold the encoded value.
  • 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.
    • The following additional length encoders are available:
      • int32BE - const { int32BEEncode } = require('it-length-prefixed')

Returns a transform that yields BufferList objects. All messages will be prefixed with a length, determined by the lengthEncoder function.

encode.single(chunk, [opts])

• chunk: Buffer|BufferList 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 BufferList containing the encoded chunk.

decode([opts])

• 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: BufferList): 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 BufferList. 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.
    • The following additional length decoders are available:
      • int32BE - const { int32BEDecode } = require('it-length-prefixed')

Returns a transform that yields BufferList 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: BufferList): Called for every chunk of data that is decoded from the stream
  • lengthEncoder: Function: See description above.

Returns a transform that yields BufferList objects.

Contribute

PRs and issues gladly accepted! Check out the issues.

License

MIT © 2016 Friedel Ziegelmayer

Changelog

6.0.1 (2022-01-13)

Bug Fixes

• emit uint8arrays (#19) (a6c59df)