Managing stream between java server and c client

Question

Hi all
I'm working on a client/server application.
Client have been written in C
Server is in Java.
The client connect to the server, send a message (unknown size) and wait a response from the server.
The server on connection start a new thread. This thread try to read data from the socket, using a BufferedInputStream :
BufferedInputStream in = new BufferedInputStream(socket.getInputStream());
As far as I dont know the size of the incoming message, i use the folowing algorythme to read data :
    byte[] bytesLus = new byte[1000];
    byte[] tmpBytesLus;
    byte[] tousLesBytes;int nb;
    i = 0;
    tousLesBytes = new byte[0];
    Log.trace(sourceTag,"Lecture des premiers octets");
    nb=in.read(bytesLus,0,bytesLus.length);
    Log.trace(sourceTag,nb+"octets lus");
    while (nb>0){                                                     
        tmpBytesLus = new byte[i+nb];
        System.arraycopy(tousLesBytes,0,tmpBytesLus,0,tousLesBytes.length);
        System.arraycopy(bytesLus,0,tmpBytesLus,tousLesBytes.length,nb);
        tousLesBytes = tmpBytesLus;
        i = i+nb;
        bytesLus = new byte[1000];
        Log.trace(sourceTag,"nb octets lus : " + i);
        if (in.available()>0)
            nb=in.read(bytesLus,0,bytesLus.length);
        else
            nb=0;
This seemed (but only seemed - i will explain it later) to work fine :
the client send a 6300 bytes sized msg. Server receive it, treat it and send response back. and this at each try.
But when i change the log level of the server from TRACE to ERROR (wich have on consequence to accelerate the instruction Log.trace( ... ) the server doesn't work so fine !
On first try, everything is ok, but on second, client send the same 6300 bytes msg, but server consider receiving only 3000 !
After debbuging, i found why :
the reason is the use of :
if (in.available()>0)
If you are reading faster than the writer, there is a moment where the stream is in a blocking state for the reader. and in.available return the number of bytes you can read before blocking...
So my server consider that it reached the end of the message....
So, after this long introduction, here my question :
What is the best way to detect the end of a stream ?
Should I send a special character on the stream and decode it on server ?
Thank's for your advice.
Olivier

Answer 1

Generally, there are n ways of making sure an entire message of unknown size is recieved:
1. Include some kind of validation criteria at the beginning of the message : checksum, bytecount, etc.
2. Format the message such that the server can tell when the end is reached (subject to "line noise" problems)
3. Enable two-way communication between the client and server, so they can work it out as they go.
4. Use a pre-established protocol that handles all this for you
5. Close the stream after writing if you only have one message.
6. etc etc etc.