reading length-prefixed streams

gistfile1.coffee

class StreamReader  
  constructor: (@callback) ->
    
  read: (buffer) ->
    unless @buffer? 
      if this.initialize(buffer)
        @partial = null
        @partialLength = 0
      else
        return
    
    toRead = @buffer.length - @read
    toRead = buffer.length if toRead > buffer.length
    buffer.copy(@buffer, @read, 0, toRead)
    @read += toRead
    
    if @read == @buffer.length
      @callback(new Buffer(@buffer))
      @buffer = null
      if toRead < buffer.length
        this.read(buffer.slice(toRead))

  initialize: (buffer) ->
    if @partial?
      if @partialLength + buffer.length >= 4
        buffer.copy(@partial, @partialLength, 0, 4 - @partialLength)
        @buffer = new Buffer(@partial.readInt32LE(0))
        @partial.copy(@buffer, 0, 0, @partialLength)
        @read = @partialLength
        return true

      buffer.copy(@partial, @partialLength, 0, buffer.length)
      @partialLength += buffer.length
      return false
      
    if buffer.length < 4
      @partial = new Buffer(4)  #todo: reduce allocation/fragementation
      buffer.copy(@partial)
      @partialLength = buffer.length
      return false

    @buffer = new Buffer(buffer.readInt32LE(0))
    @read = 0
    return true
      
  debug: ->
    console.log("partial is ", @partial)
    console.log("partial length is %d", @partialLength)
    console.log("buffer is ", @buffer)
      
exports.StreamReader = StreamReader