How long is the message boundary in node.js?

Question

How can I detect the message boundary in node.js? The client sends messages with along their length: length + data .

socket.on(data) receives all data in one line. But, I need to receive only 2 bytes first then x bytes data.

Answer 1

tcp sockets are just byte streams, there's no message boundary, you need to count the bytes consumed and compare this number to the one from the preamble.

here's a bit of code that does what you need. it's written in CoffeeScript, and uses 32-bit int for message size, so you'll have to adjust a bit.

  remaining = 0
  input = undefined

  msgsize = 0
  msbuf = new Buffer 4
  msneeded = 4

  sock.on 'data', (bytes) =>

    start = 0
    end = bytes.length

    while start < bytes.length

      if remaining == 0
        msavail = (Math.min 4, bytes.length - start)
        bytes.copy msbuf, msbuf.length - msneeded, start, start + msavail
        msneeded -= msavail
        continue if msneeded > 0
        msneeded = 4
        remaining = msgsize = msbuf.readUInt32LE 0
        start += 4
        input = new Buffer msgsize

      end = (Math.min start + remaining, bytes.length)
      bytes.copy input, msgsize - remaining, start, end
      remaining -= (end - start)
      start = end

      @emit 'data', input if 0 == remaining