sockets/id_echo_sv.c

+/* id_echo_sv.c
+
+   This program implements a daemon that provides the UDP "echo" service. It
+   reads datagrams and then sends copies back to the originating address.
+
+   NOTE: this program must be run under a root login, in order to allow the
+   "echo" port (7) to be bound. Alternatively, for test purposes, you can edit
+   id_echo.h and replace the SERVICE name with a suitable unreserved port
+   number (e.g., "51000"), and make a corresponding change in the client.
+
+   See also id_echo_cl.c.
+*/
 #include <syslog.h>
 #include "id_echo.h"
 #include "become_daemon.h"
 
 int
 main(int argc, char *argv[])
 {
     int sfd;
     ssize_t numRead;
     socklen_t len;
     struct sockaddr_storage claddr;
     char buf[BUF_SIZE];
     char addrStr[IS_ADDR_STR_LEN];
 
     if (becomeDaemon(0) == -1)
         errExit("becomeDaemon");
 
     sfd = inetBind(SERVICE, SOCK_DGRAM, NULL);
     if (sfd == -1) {
         syslog(LOG_ERR, "Could not create server socket (%s)", strerror(errno));
         exit(EXIT_FAILURE);
     }
 
     /* Receive datagrams and return copies to senders */
 
     for (;;) {
         len = sizeof(struct sockaddr_storage);
         numRead = recvfrom(sfd, buf, BUF_SIZE, 0,
                            (struct sockaddr *) &claddr, &len);
         if (numRead == -1)
             errExit("recvfrom");
 
         if (sendto(sfd, buf, numRead, 0, (struct sockaddr *) &claddr, len)
                         != numRead)
             syslog(LOG_WARNING, "Error echoing response to %s (%s)",
                     inetAddressStr((struct sockaddr *) &claddr, len,
                                    addrStr, IS_ADDR_STR_LEN),
                     strerror(errno));
     }
 }