sockets/i6d_ucase_sv.c

This is sockets/i6d_ucase_sv.c (Listing 59-3, page 1208), an example from the book, The Linux Programming Interface.

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Cover of The Linux Programming Interface

+/* i6d_ucase_sv.c
+
+   A server that receives datagrams, converts their contents to uppercase, and
+   then returns them to the senders.
+
+   See also i6d_ucase_cl.c.
+*/
 #include "i6d_ucase.h"
 
 int
 main(int argc, char *argv[])
 {
     struct sockaddr_in6 svaddr, claddr;
     int sfd, j;
     ssize_t numBytes;
     socklen_t len;
     char buf[BUF_SIZE];
     char claddrStr[INET6_ADDRSTRLEN];
 
+    /* Create a datagram socket bound to an address in the IPv6 domain */
+
     sfd = socket(AF_INET6, SOCK_DGRAM, 0);
     if (sfd == -1)
         errExit("socket");
 
     memset(&svaddr, 0, sizeof(struct sockaddr_in6));
     svaddr.sin6_family = AF_INET6;
     svaddr.sin6_addr = in6addr_any;                     /* Wildcard address */
     svaddr.sin6_port = htons(PORT_NUM);
 
     if (bind(sfd, (struct sockaddr *) &svaddr,
                 sizeof(struct sockaddr_in6)) == -1)
         errExit("bind");
 
     /* Receive messages, convert to uppercase, and return to client */
 
     for (;;) {
         len = sizeof(struct sockaddr_in6);
         numBytes = recvfrom(sfd, buf, BUF_SIZE, 0,
                             (struct sockaddr *) &claddr, &len);
         if (numBytes == -1)
             errExit("recvfrom");
 
+        /* Display address of client that sent the message */
+
         if (inet_ntop(AF_INET6, &claddr.sin6_addr, claddrStr,
                     INET6_ADDRSTRLEN) == NULL)
             printf("Couldn't convert client address to string\n");
         else
             printf("Server received %ld bytes from (%s, %u)\n",
                     (long) numBytes, claddrStr, ntohs(claddr.sin6_port));
 
         for (j = 0; j < numBytes; j++)
             buf[j] = toupper((unsigned char) buf[j]);
 
         if (sendto(sfd, buf, numBytes, 0, (struct sockaddr *) &claddr, len) !=
                 numBytes)
             fatal("sendto");
     }
 }

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