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From: putnam@peanuts.nosc.mil (Mike Putnam)
Newsgroups: comp.unix.questions
Subject: socket connection dropping characters
Message-ID: <2125@nosc.NOSC.MIL>
Date: 12 Apr 90 20:59:33 GMT
Sender: nobody@nosc.NOSC.MIL
Reply-To: putnam@peanuts.nosc.mil (Mike Putnam)
Distribution: usa
Organization: Naval Ocean Systems Center, San Diego
Lines: 58
X-Local-Date: 12 Apr 90 13:59:33 PDT

Being new to the world of interprocess communications I wrote two simple test 
programs on an Apollo workstation running Apollo's version of BSD4.3. The
first program, the server, opens a stream socket and waits for a connection.  
The second program, the client, connects to the server and goes into an 
infinite loop sending a string using the write command.  The server reads the 
message and prints it to standard output.  Unfortunately after about twenty or 
so writes by the client the server begins to drop characters. Below is the
program fragments that do the actual reading and writing after the connection
has been made:

Server
*********************************
   do {
      FD_ZERO(&ready);
      FD_SET(sock,&ready);
      to.tv_sec = 5;
      if (select (sock + 1, &ready,0, 0, &to) < 0) {
         perror ("select");
         continue;
      }
      if (FD_ISSET(sock, &ready)) {
         msgsock = accept(sock, (struct sockaddr *)0, (int *)0);
         if (msgsock == -1)
            perror("accept");
         else do {   
            bzero(buf, sizeof(buf));
            if ((rval = read(msgsock, buf, sizeof(buf))) <0)
               perror("reading stream message");
            else if (rval == 0)   
               printf("ending connection\n");
            else
               printf ("-->%s\n",buf);
              /* write(msgsock,OK,sizeof(OK));*/
         } while (rval > 0);
         close(msgsock);
      } else
         printf("do something else\n");
   } while (TRUE);


Client
*********************************
   do {
     if (write(sock, DATA, sizeof(DATA)) < 0) {
        perror("writing on stream socket");
        close (sock);
     } 
   } while (TRUE);

I assume the server is not reading as fast as the client is writing. Is there
a simple way avoid the loss of characters passing through the connection?  

                                            Mike Putnam
                                            Naval Ocean Systems Center
                                            San Diego, CA 
                                       
                                                  Internet: putnam@nosc.mil
                                                  UUCP: sdcsvax!noscvax!putnam