Socket read() call returning before timeout.

Question

I have a couple of applications which use the following basic socket reading approach:
Socket socket = new Socket("192.168.0.1", 54321);
socket.setSoTimeout (5000);
InputStream stream = socket.getInputStream();
byte[] data = new byte[232];
boolean done = false;
while (!done) {
    int res= stream.read(data);
    if (res < data.length) {
        System.err.println ("Error reading packet data - not enough data received: "+ res);
    // process and output the data
try { stream.close(); } catch (Exception e) {}
try { socket.close(); } catch (Exception e) {}The problem I am having is that sometimes read(byte[]) returns a before the full array's worth of data has been read, and before a timeout has occurred. I never get a SocketTimeoutException, but I do get my debugging output. I have recorded the network traffic with a packet sniffer (Wireshark), and what I am seeing is that in the instances where the read returns prematurely, it stops at the end of a TCP packet. The rest of the data is in another packet that arrives shortly afterwords (~1.5 ms or less).
I know that with normal (file) input streams, read can return whenever it wants regardless of how many bytes were read, however I was under the impression that network streams are supposed to block until all the data arrives (or a timeout occurs, if set). Is this incorrect?

Answer 1

djpeaco wrote:
I know that with normal (file) input streams, read can return whenever it wants regardless of how many bytes were readThat's correct and that's exactly the reason you see the behavior you see.
however I was under the impression that network streams are supposed to block until all the data arrives (or a timeout occurs, if set).Why? Why do you think that network streams behave differently in this regard?
Why shouldn't it give you the data as soon as it's available, when every other stream works this way?
Is this incorrect?Yes, you must assume that the streams of a socket follow the general InputStream/OutputStream contract and that includes possibly returning from read() before the full array is filled.