Question

The server that Im working on (which is a Unix C multi-threaded non-block socket server) need to receive a file from a client and broadcast it to all the other clients connected to the server.

Everything is working at the exception that Im having a hard time to determine when a file is done transferring… since Im using non-block socket Im having the issue that sometimes during the file transfer recv return -1 (which I was assuming was the end of the file) then the next pass more bytes comes in.

I try to hack the whole thing putting “END” at the end of the stream. However, sometimes when multiple files are sent in a row the “END” is part of the same recv buffer as the beginning of the next file. Or even worst, sometimes I end up with a buffer that finish with EN and the next pass the D comes in.

What would be the best approach to avoid the situations mentioned above, I don’t really want that each time I receive some bytes from the socket loop the whole accumulated buffer to check if “END” is part of it then cut appropriately… Im sure there’s a better solution to this right?

Thanks in advance!

Answer 1

The most simpe case EJP is referring to, the case where you take the closing of the socket by the other end as end-of-file, could look like the following:

{
  ssize_t sizeRead = 0;

  while (sizeRead = recv(...)) {
    if (0 > sizeRead) { /* recv() failed */
      if ((EGAGAIN == errno) ¦¦ (EWOULDBLOCK == errno)) { /* retry the recv() on those two kinds of error */
        usleep(1) /* optional */
        continue;
      }
      else
        break;
    }

    ... /* process the data read ... */
  }

  if (0 > sizeRead) {
    /* There had been an error during recv() */
  }
}