TCP stream relay [closed] - linux

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Closed 10 years ago.
I have two program communicating with TCP/IP.
this works fine.
program A opens a TCP socket.
program B connects to this socket.
program B gives data to program A.
everything works very fine.
but when i put a relay between A and B
and just pass the byte stream, something goes wrong.
program C opens two TCP socket(socket1, socket2).
program B connects to this socket(socket1).
program A connects to this socket(socket2).
program C relays TCP strem from B to A with following code.
(this is based on linux)
char buf[BUFSIZE];
while(1){
// recv a packet segment
if( my_recv(socket1, buf, BUFSIZE) <= 0 ){
return 0;
}
if( send(socket2, buf, BUFSIZE, MSG_NOSIGNAL) != BUFSIZE ){
return 0;
}
}
my_recv is a wrapper for recv to guarantee it will recv
request size.
int my_recv(int sd, char* p, unsigned int len){
// recv a packet segment
unsigned int ssize=0;
int d;
while(ssize < len){
if( (d=recv( sd, p+ssize, len - ssize, 0))<=0){
return -1;
}
ssize += d;
}
return ssize;
}
this works fine for first time.
but after few seconds, everything is messed up.
I have debugged program A and B.
there is nothing wrong with them.
they send and recv in correct order but it seems
that relay gives false data...
some advise would be appreciated.
thank you in advance.

Answer 1

You are assuming each read fills the buffer. You have to use the count returned by the recv() call as the length argument to the send() call.
while ((count = recv(fd, buffer, sizeof buffer, 0)) > 0)
send(fd, buffer, count, 0);