incoming.js

const {
  Transform
} = require('readable-stream')

const FIN         = 0x80
const RSV1        = 0x40
const RSV2        = 0x20
const RSV3        = 0x10
const RSV_ALL     = RSV1 | RSV2 | RSV3
const OPCODE      = 0x0f
const MASKED      = 0x80
const LENGTH      = 0x7f
const LENGTH_EXT1 = 0x7e
const LENGTH_EXT2 = 0x7f


class Incoming extends Transform {

  constructor(options) {
    super(options)

    this.header = null
    this.inHeader = true
    this.needsHeadBase = true
    this.needsHeadExtended = false

    this.rawHead = []

    // TODO: move this.headLength to headBytesRead
    this.totalBytesRead = 0
    this.payloadBytesRead = 0
    this.payloadBytesToRead = 0
  }

  _cache(chunk) {
    this.rawHead.push(chunk)

    return Buffer.concat(this.rawHead)
  }

  _transform(chunk, encoding, done) {
    var header = this.header = this.header || {}

    if (this.inHeader) {
      chunk = this._cache(chunk)

      // buffer until we have two bytes to parse
      // and to calculated total head byte length
      if (chunk.length >= 2 && this.needsHeadBase) {
        if (RSV_ALL & chunk[0]) {
          this.emit('error', new Error('RSV flag should not be set.'))

          return
        }

        header.final = !!(FIN & chunk[0])
        header.masked = !!(MASKED & chunk[1])
        header.opcode = OPCODE & chunk[0]
        this.length = LENGTH & chunk[1]

        this.headLength = 2
        if (header.masked) {
          this.headLength += 4
        }
        if (this.length === LENGTH_EXT1) {
          this.headLength += 2
        }
        if (this.length === LENGTH_EXT2) {
          this.headLength += 8
        }
        this.totalBytesRead += 2

        this.needsHeadBase = false
        this.needsHeadExtended = true
      }

      // buffer until we have all required head bytes and parse
      if (chunk.length >= this.headLength && this.needsHeadExtended) {
        header.length = this.length
        if (header.masked) {
          header.masking = chunk.slice(this.headLength - 4)
        }
        switch (this.length) {
          case LENGTH_EXT1:
            header.length = chunk.readUInt16BE(2, 2)
            break
          case LENGTH_EXT2:
            if (chunk.readUInt32BE(2, 4)) {
              this.emit('error', new Error('Payload length is too big.'))

              return
            }
            header.length = chunk.readUInt32BE(6, 4)
            break
        }
        this.totalBytesRead += chunk.length
        this.payloadBytesToRead += header.length

        this.inHeader = false
        this.needsHeadExtended = false

        this.emit('header', header)
      }

      // if we are finished with head bytes slice payload if in head length
      // else set chunk to null to avoid being consumed by stream
      if (!this.needsHeadBase && !this.needsHeadExtended) {
        chunk = chunk.slice(this.headLength)
      }
    }

    if (!this.inHeader) {
      // if we have more chunk then we need to read we probably got two frames
      // glued to each other. In this case we will flush them away.
      if (chunk.length > this.payloadBytesToRead) {
        this.emit('flush', chunk.slice(this.payloadBytesToRead))

        chunk = chunk.slice(0, this.payloadBytesToRead)
      }

      // unmask the payload
      if (header.masked) {
        for (var i = 0; i < chunk.length; i++) {
          chunk[i] = chunk[i] ^ header.masking[(i + this.payloadBytesRead) % 4]
        }
      }

      this.push(chunk)

      // update all counters
      this.totalBytesRead += chunk.length
      this.payloadBytesRead += chunk.length
      this.payloadBytesToRead -= chunk.length

      if (!this.payloadBytesToRead) {
        this.push(null)
      }
    }

    done()
  }

}

module.exports = Incoming