UDP server Code

Code Example:

The following programs demonstrate the use of getaddrinfo(), gai_strerror(), freeaddrinfo(), and  getnameinfo().  The programs are an echo server and client for UDP datagrams.

服务器端程序：

 ###Server program

        #include <sys/types.h>
        #include <stdio.h>
        #include <stdlib.h>
        #include <unistd.h>
        #include <string.h>
        #include <sys/socket.h>
        #include <netdb.h>

        #define BUF_SIZE 500

        int
        main(int argc, char *argv[])
        {
            struct addrinfo hints;
            struct addrinfo *result, *rp;
            int sfd, s;
            struct sockaddr_storage peer_addr;
            socklen_t peer_addr_len;
            ssize_t nread;
            char buf[BUF_SIZE];

            if (argc != ) {
                fprintf(stderr, "Usage: %s port\n", argv[]);
                exit(EXIT_FAILURE);
            }

            memset(&hints, , sizeof(struct addrinfo));
            hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
            hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
            hints.ai_flags = AI_PASSIVE;    /* For wildcard IP address */
            hints.ai_protocol = ;          /* Any protocol */
            hints.ai_canonname = NULL;
            hints.ai_addr = NULL;
            hints.ai_next = NULL;

            s = getaddrinfo(NULL, argv[], &hints, &result);
            if (s != ) {
                fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
                exit(EXIT_FAILURE);
            }

            /* getaddrinfo() returns a list of address structures.
               Try each address until we successfully bind(2).
               If socket(2) (or bind(2)) fails, we (close the socket
               and) try the next address. */

            for (rp = result; rp != NULL; rp = rp->ai_next) {
                sfd = socket(rp->ai_family, rp->ai_socktype,
                        rp->ai_protocol);
                if (sfd == -)
                    continue;

                if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == )
                    break;                  /* Success */

                close(sfd);
            }

            if (rp == NULL) {               /* No address succeeded */
                fprintf(stderr, "Could not bind\n");
                exit(EXIT_FAILURE);
            }

            freeaddrinfo(result);           /* No longer needed */

            /* Read datagrams and echo them back to sender */

            for (;;) {
                peer_addr_len = sizeof(struct sockaddr_storage);
                nread = recvfrom(sfd, buf, BUF_SIZE, ,
                        (struct sockaddr *) &peer_addr, &peer_addr_len);
                if (nread == -)
                    continue;               /* Ignore failed request */

                char host[NI_MAXHOST], service[NI_MAXSERV];

                s = getnameinfo((struct sockaddr *) &peer_addr,
                                peer_addr_len, host, NI_MAXHOST,
                                service, NI_MAXSERV, NI_NUMERICSERV);
                if (s == )
                    printf("Received %zd bytes from %s:%s\n",
                            nread, host, service);
                else
                    fprintf(stderr, "getnameinfo: %s\n", gai_strerror(s));

                if (sendto(sfd, buf, nread, ,
                            (struct sockaddr *) &peer_addr,
                            peer_addr_len) != nread)
                    fprintf(stderr, "Error sending response\n");
            }
        }

客户端程序：

  ###Client program

        #include <sys/types.h>
        #include <sys/socket.h>
        #include <netdb.h>
        #include <stdio.h>
        #include <stdlib.h>
        #include <unistd.h>
        #include <string.h>

        #define BUF_SIZE 500

        int
        main(int argc, char *argv[])
        {
            struct addrinfo hints;
            struct addrinfo *result, *rp;
            int sfd, s, j;
            size_t len;
            ssize_t nread;
            char buf[BUF_SIZE];

            if (argc < ) {
                fprintf(stderr, "Usage: %s host port msg...\n", argv[]);
                exit(EXIT_FAILURE);
            }

            /* Obtain address(es) matching host/port */

            memset(&hints, , sizeof(struct addrinfo));
            hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
            hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
            hints.ai_flags = ;
            hints.ai_protocol = ;          /* Any protocol */

            s = getaddrinfo(argv[], argv[], &hints, &result);
            if (s != ) {
                fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
                exit(EXIT_FAILURE);
            }

            /* getaddrinfo() returns a list of address structures.
               Try each address until we successfully connect(2).
               If socket(2) (or connect(2)) fails, we (close the socket
               and) try the next address. */

            for (rp = result; rp != NULL; rp = rp->ai_next) {
                sfd = socket(rp->ai_family, rp->ai_socktype,
                             rp->ai_protocol);
                if (sfd == -)
                    continue;

                if (connect(sfd, rp->ai_addr, rp->ai_addrlen) != -)
                    break;                  /* Success */

                close(sfd);
            }

            if (rp == NULL) {               /* No address succeeded */
                fprintf(stderr, "Could not connect\n");
                exit(EXIT_FAILURE);
            }

            freeaddrinfo(result);           /* No longer needed */

            /* Send remaining command-line arguments as separate
               datagrams, and read responses from server */

            for (j = ; j < argc; j++) {
                len = strlen(argv[j]) + ;
                        /* +1 for terminating null byte */

                if (len +  > BUF_SIZE) {
                    fprintf(stderr,
                            "Ignoring long message in argument %d\n", j);
                    continue;
                }

                if (write(sfd, argv[j], len) != len) {
                    fprintf(stderr, "partial/failed write\n");
                    exit(EXIT_FAILURE);
                }

                nread = read(sfd, buf, BUF_SIZE);
                if (nread == -) {
                    perror("read");
                    exit(EXIT_FAILURE);
                }

                printf("Received %zd bytes: %s\n", nread, buf);
            }

            exit(EXIT_SUCCESS);
        }

Come from url: http://man7.org/linux/man-pages/man3/getaddrinfo.3.html