torrent-piece/index.js

Torrent piece abstraction

/*! torrent-piece. MIT License. WebTorrent LLC <https://webtorrent.io/opensource> */
import { concat } from 'uint8-util'

const BLOCK_LENGTH = 1 << 14

export default class Piece {
  constructor (length) {
    this.length = length
    this.missing = length
    this.sources = null

    this._chunks = Math.ceil(length / BLOCK_LENGTH)
    this._remainder = (length % BLOCK_LENGTH) || BLOCK_LENGTH
    this._buffered = 0
    this._buffer = null
    this._cancellations = null
    this._reservations = 0
    this._flushed = false
  }

  chunkLength (i) {
    return i === this._chunks - 1 ? this._remainder : BLOCK_LENGTH
  }

  chunkLengthRemaining (i) {
    return this.length - (i * BLOCK_LENGTH)
  }

  chunkOffset (i) {
    return i * BLOCK_LENGTH
  }

  reserve () {
    if (!this.init()) return -1
    if (this._cancellations.length) return this._cancellations.pop()
    if (this._reservations < this._chunks) return this._reservations++
    return -1
  }

  reserveRemaining () {
    if (!this.init()) return -1
    if (this._cancellations.length || this._reservations < this._chunks) {
      let min = this._reservations
      while (this._cancellations.length) {
        min = Math.min(min, this._cancellations.pop())
      }
      this._reservations = this._chunks
      return min
    }
    return -1
  }

  cancel (i) {
    if (!this.init()) return
    this._cancellations.push(i)
  }

  cancelRemaining (i) {
    if (!this.init()) return
    this._reservations = i
  }

  get (i) {
    if (!this.init()) return null
    return this._buffer[i]
  }

  set (i, data, source) {
    if (!this.init()) return false
    const len = data.length
    const blocks = Math.ceil(len / BLOCK_LENGTH)
    for (let j = 0; j < blocks; j++) {
      if (!this._buffer[i + j]) {
        const offset = j * BLOCK_LENGTH
        const splitData = data.subarray(offset, offset + BLOCK_LENGTH)
        this._buffered++
        this._buffer[i + j] = splitData
        this.missing -= splitData.length
        if (!this.sources.includes(source)) {
          this.sources.push(source)
        }
      }
    }
    return this._buffered === this._chunks
  }

  flush () {
    if (!this._buffer || this._chunks !== this._buffered) return null
    const buffer = concat(this._buffer, this.length)
    this._buffer = null
    this._cancellations = null
    this.sources = null
    this._flushed = true
    return buffer
  }

  init () {
    if (this._flushed) return false
    if (this._buffer) return true
    this._buffer = new Array(this._chunks)
    this._cancellations = []
    this.sources = []
    return true
  }
}

Piece.BLOCK_LENGTH = BLOCK_LENGTH