block-stream.js

// write data to it, and it'll emit data in 512 byte blocks.
// if you .end() or .flush(), it'll emit whatever it's got,
// padded with nulls to 512 bytes.

module.exports = BlockStream

var Stream = require("stream").Stream
  , inherits = require("inherits")
  , assert = require("assert").ok
  , debug = process.env.DEBUG ? console.error : function () {}

function BlockStream (size, opt) {
  this.writable = this.readable = true
  this._opt = opt || {}
  this._chunkSize = size || 512
  this._offset = 0
  this._buffer = []
  this._bufferLength = 0
  if (this._opt.nopad) this._zeroes = false
  else {
    this._zeroes = new Buffer(this._chunkSize)
    for (var i = 0; i < this._chunkSize; i ++) {
      this._zeroes[i] = 0
    }
  }
}

inherits(BlockStream, Stream)

BlockStream.prototype.write = function (c) {
  // debug("   BS write", c)
  if (this._ended) throw new Error("BlockStream: write after end")
  if (c && !Buffer.isBuffer(c)) c = new Buffer(c + "")
  if (c.length) {
    this._buffer.push(c)
    this._bufferLength += c.length
  }
  // debug("pushed onto buffer", this._bufferLength)
  if (this._bufferLength >= this._chunkSize) {
    if (this._paused) {
      // debug("   BS paused, return false, need drain")
      this._needDrain = true
      return false
    }
    this._emitChunk()
  }
  return true
}

BlockStream.prototype.pause = function () {
  // debug("   BS pausing")
  this._paused = true
}

BlockStream.prototype.resume = function () {
  // debug("   BS resume")
  this._paused = false
  return this._emitChunk()
}

BlockStream.prototype.end = function (chunk) {
  // debug("end", chunk)
  if (typeof chunk === "function") cb = chunk, chunk = null
  if (chunk) this.write(chunk)
  this._ended = true
  this.flush()
}

BlockStream.prototype.flush = function () {
  this._emitChunk(true)
}

BlockStream.prototype._emitChunk = function (flush) {
  // debug("emitChunk flush=%j emitting=%j paused=%j", flush, this._emitting, this._paused)

  // emit a <chunkSize> chunk
  if (flush && this._zeroes) {
    // debug("    BS push zeroes", this._bufferLength)
    // push a chunk of zeroes
    var padBytes = (this._bufferLength % this._chunkSize)
    if (padBytes !== 0) padBytes = this._chunkSize - padBytes
    if (padBytes > 0) {
      // debug("padBytes", padBytes, this._zeroes.slice(0, padBytes))
      this._buffer.push(this._zeroes.slice(0, padBytes))
      this._bufferLength += padBytes
      // debug(this._buffer[this._buffer.length - 1].length, this._bufferLength)
    }
  }

  if (this._emitting || this._paused) return
  this._emitting = true

  // debug("    BS entering loops")
  var bufferIndex = 0
  while (this._bufferLength >= this._chunkSize &&
         (flush || !this._paused)) {
    // debug("     BS data emission loop", this._bufferLength)

    var out
      , outOffset = 0
      , outHas = this._chunkSize

    while (outHas > 0 && (flush || !this._paused) ) {
      // debug("    BS data inner emit loop", this._bufferLength)
      var cur = this._buffer[bufferIndex]
        , curHas = cur.length - this._offset
      // debug("cur=", cur)
      // debug("curHas=%j", curHas)
      // If it's not big enough to fill the whole thing, then we'll need
      // to copy multiple buffers into one.  However, if it is big enough,
      // then just slice out the part we want, to save unnecessary copying.
      // Also, need to copy if we've already done some copying, since buffers
      // can't be joined like cons strings.
      if (out || curHas < outHas) {
        out = out || new Buffer(this._chunkSize)
        cur.copy(out, outOffset,
                 this._offset, this._offset + Math.min(curHas, outHas))
      } else if (cur.length === outHas && this._offset === 0) {
        // shortcut -- cur is exactly long enough, and no offset.
        out = cur
      } else {
        // slice out the piece of cur that we need.
        out = cur.slice(this._offset, this._offset + outHas)
      }

      if (curHas > outHas) {
        // means that the current buffer couldn't be completely output
        // update this._offset to reflect how much WAS written
        this._offset += outHas
        outHas = 0
      } else {
        // output the entire current chunk.
        // toss it away
        outHas -= curHas
        outOffset += curHas
        bufferIndex ++
        this._offset = 0
      }
    }

    this._bufferLength -= this._chunkSize
    assert(out.length === this._chunkSize)
    // debug("emitting data", out)
    // debug("   BS emitting, paused=%j", this._paused, this._bufferLength)
    this.emit("data", out)
    out = null
  }
  // debug("    BS out of loops", this._bufferLength)

  // whatever is left, it's not enough to fill up a block, or we're paused
  this._buffer = this._buffer.slice(bufferIndex)
  if (this._paused) {
    // debug("    BS paused, leaving", this._bufferLength)
    this._needsDrain = true
    this._emitting = false
    return
  }

  // if flushing, and not using null-padding, then need to emit the last
  // chunk(s) sitting in the queue.  We know that it's not enough to
  // fill up a whole block, because otherwise it would have been emitted
  // above, but there may be some offset.
  var l = this._buffer.length
  if (flush && !this._zeroes && l) {
    if (l === 1) {
      if (this._offset) {
        this.emit("data", this._buffer[0].slice(this._offset))
      } else {
        this.emit("data", this._buffer[0])
      }
    } else {
      var outHas = this._bufferLength
        , out = new Buffer(outHas)
        , outOffset = 0
      for (var i = 0; i < l; i ++) {
        var cur = this._buffer[i]
          , curHas = cur.length - this._offset
        cur.copy(out, outOffset, this._offset)
        this._offset = 0
        outOffset += curHas
        this._bufferLength -= curHas
      }
      this.emit("data", out)
    }
    // truncate
    this._buffer.length = 0
    this._bufferLength = 0
    this._offset = 0
  }

  // now either drained or ended
  // debug("either draining, or ended", this._bufferLength, this._ended)
  // means that we've flushed out all that we can so far.
  if (this._needDrain) {
    // debug("emitting drain", this._bufferLength)
    this._needDrain = false
    this.emit("drain")
  }

  if ((this._bufferLength === 0) && this._ended && !this._endEmitted) {
    // debug("emitting end", this._bufferLength)
    this._endEmitted = true
    this.emit("end")
  }

  this._emitting = false

  // debug("    BS no longer emitting", flush, this._paused, this._emitting, this._bufferLength, this._chunkSize)
}