sockets/is_seqnum_sv.c

+/* is_seqnum_sv.c
+
+   A simple Internet stream socket server. Our service is to provide
+   unique sequence numbers to clients.
+
+   Usage:  is_seqnum_sv [init-seq-num]
+                        (default = 0)
+
+   See also is_seqnum_cl.c.
+*/
 #define _BSD_SOURCE             /* To get definitions of NI_MAXHOST and
                                    NI_MAXSERV from <netdb.h> */
 #include <netdb.h>
 #include "is_seqnum.h"
 
 #define BACKLOG 50
 
 int
 main(int argc, char *argv[])
 {
     uint32_t seqNum;
     char reqLenStr[INT_LEN];            /* Length of requested sequence */
     char seqNumStr[INT_LEN];            /* Start of granted sequence */
     struct sockaddr_storage claddr;
     int lfd, cfd, optval, reqLen;
     socklen_t addrlen;
     struct addrinfo hints;
     struct addrinfo *result, *rp;
 #define ADDRSTRLEN (NI_MAXHOST + NI_MAXSERV + 10)
     char addrStr[ADDRSTRLEN];
     char host[NI_MAXHOST];
     char service[NI_MAXSERV];
 
     if (argc > 1 && strcmp(argv[1], "--help") == 0)
         usageErr("%s [init-seq-num]\n", argv[0]);
 
     seqNum = (argc > 1) ? getInt(argv[1], 0, "init-seq-num") : 0;
 
+    /* Ignore the SIGPIPE signal, so that we find out about broken connection
+       errors via a failure from write(). */
+
     if (signal(SIGPIPE, SIG_IGN) == SIG_ERR)    errExit("signal");
 
     /* Call getaddrinfo() to obtain a list of addresses that
        we can try binding to */
 
     memset(&hints, 0, sizeof(struct addrinfo));
     hints.ai_canonname = NULL;
     hints.ai_addr = NULL;
     hints.ai_next = NULL;
     hints.ai_socktype = SOCK_STREAM;
     hints.ai_family = AF_UNSPEC;        /* Allows IPv4 or IPv6 */
     hints.ai_flags = AI_PASSIVE | AI_NUMERICSERV;
                         /* Wildcard IP address; service name is numeric */
 
     if (getaddrinfo(NULL, PORT_NUM, &hints, &result) != 0)
         errExit("getaddrinfo");
 
     /* Walk through returned list until we find an address structure
        that can be used to successfully create and bind a socket */
 
     optval = 1;
     for (rp = result; rp != NULL; rp = rp->ai_next) {
         lfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
         if (lfd == -1)
             continue;                   /* On error, try next address */
 
         if (setsockopt(lfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval))
                 == -1)
              errExit("setsockopt");
 
         if (bind(lfd, rp->ai_addr, rp->ai_addrlen) == 0)
             break;                      /* Success */
 
         /* bind() failed: close this socket and try next address */
 
         close(lfd);
     }
 
     if (rp == NULL)
         fatal("Could not bind socket to any address");
 
     if (listen(lfd, BACKLOG) == -1)
         errExit("listen");
 
     freeaddrinfo(result);
 
     for (;;) {                  /* Handle clients iteratively */
 
         /* Accept a client connection, obtaining client's address */
 
         addrlen = sizeof(struct sockaddr_storage);
         cfd = accept(lfd, (struct sockaddr *) &claddr, &addrlen);
         if (cfd == -1) {
             errMsg("accept");
             continue;
         }
 
         if (getnameinfo((struct sockaddr *) &claddr, addrlen,
                     host, NI_MAXHOST, service, NI_MAXSERV, 0) == 0)
             snprintf(addrStr, ADDRSTRLEN, "(%s, %s)", host, service);
         else
             snprintf(addrStr, ADDRSTRLEN, "(?UNKNOWN?)");
         printf("Connection from %s\n", addrStr);
 
         /* Read client request, send sequence number back */
 
         if (readLine(cfd, reqLenStr, INT_LEN) <= 0) {
             close(cfd);
             continue;                   /* Failed read; skip request */
         }
 
         reqLen = atoi(reqLenStr);
         if (reqLen <= 0) {              /* Watch for misbehaving clients */
             close(cfd);
             continue;                   /* Bad request; skip it */
         }
 
         snprintf(seqNumStr, INT_LEN, "%d\n", seqNum);
         if (write(cfd, seqNumStr, strlen(seqNumStr)) != strlen(seqNumStr))
             fprintf(stderr, "Error on write");
 
         seqNum += reqLen;               /* Update sequence number */
 
         if (close(cfd) == -1)           /* Close connection */
             errMsg("close");
     }
 }