Ross,
Thanks a lot - you were correct about what was
happening. Your comments were very helpful.
Mark
On Fri, 25 Sep 1998, Ross Mark wrote:
> When programming sockets for TCP it's
> important that you never assume that writes and
> reads will send or receive everything in one go.
> Java seem to take care of the writes but in most other
> languages like C and Perl you have to handle partial writes
> yourself within a loop.
>
> Client reads return the number of bytes that are currently
> available. As soon as the first byte of data arrives the client
> is ready to read. It may take many packets at the network
> level for the entire message to be transferred or the server may
> implement its writes one byte at a time. If the client
> is able to read faster than the packets are arriving then the
> data will be seen in chunks. If the client is slower than the
> network then you may be able to read the entire packet in
> one go.
>
> Some system like Java will hide what is happening a the
> network level but typically thing to remember are:
> 1. If writes return the number of bytes written always check
> the value and write out what is remanding.
> 2. Never assume that entire packets will returned by a single
> read even if during testing this is always the case.
> 3. If reads can be interrupted then check the error and restart
> the read.
>
> For your problem of only reading one byte it may be a case
> that the server is writing Strings one byte at atime. Not very
> efficient but there nothing illegal about it. Putting your client
> into a loop until all the data is available should fix your problem.
>
> When it comes to network programming learn to
> use a monitoring tool like snoop or tcpdump. Even
> truss or strace may help show what is happening.
>
> Hope this helps
>
> Ross Mark
>
> PS Anyone know how to do decent quoting within MS outlook?
> ie '>' around the original message.
> -----Original Message-----
> From: [EMAIL PROTECTED] [SMTP:[EMAIL PROTECTED]]
> Sent: Friday, September 25, 1998 7:28 AM
> To: [EMAIL PROTECTED]
> Subject: socket problems
>
>
> This problem may have nothing to do with java on linux, but
> I thought i might ask and see if anyone knows what is
> happening. I am having many problems with sockets in java and I'm not
> sure whether I'm missing something or if something else is
> wrong.
>
> I have a java server and a C client.
>
> First, the server's DataOutputStream.writeBytes() method seems to be
> doing something else in addition to writing bytes to client. I infer
> this because the client's "read" function never returns
> more than 1 reflecting only 1 byte is being read even though
> the server is sending 2 bytes.
>
> ***
> -- JAVA method called in server --
> clientsocket_out.writeBytes("OK");
>
> -- C client function called --
> n = read(sockfd, recvline, 15); (n is 1 and recvline
> is "O", but n should be 2 and recvline should be "OK")
>
> ***
>
> If I use clientsocket_out.write(buf) where buf is a byte
> array and buf.length is 2, the C "read" function works just
> fine. In this case n is 2 reflecting that 2 bytes were read and
> recvline contains the 2 bytes sent by the server.
>
> Anyone have any idea why this is?
>
> Also, no matter what I do, I can't seem to pass more than
> 1460 bytes to a DataOutputStream (Socket) using the write
> method. Lets say I have byte buffer[]=new byte[30000] and
> I call the method clientsocket_out.write(buf), I expect that
> write will write 30000 bytes to the dos, but instead the client
> reports that only 1460 bytes have been read. Is this because of
> TCP MTU or some other limitation?
>
> Thanks,
>
> Mark
>
