1 ###Server program
 2 
 3        #include <sys/types.h>
 4        #include <stdio.h>
 5        #include <stdlib.h>
 6        #include <unistd.h>
 7        #include <string.h>
 8        #include <sys/socket.h>
 9        #include <netdb.h>
10 
11        #define BUF_SIZE 500
12 
13        int
14        main(int argc, char *argv[])
15        {
16            struct addrinfo hints;
17            struct addrinfo *result, *rp;
18            int sfd, s;
19            struct sockaddr_storage peer_addr;
20            socklen_t peer_addr_len;
21            ssize_t nread;
22            char buf[BUF_SIZE];
23 
24            if (argc != 2) {
25                fprintf(stderr, "Usage: %s port\n", argv[0]);
26                exit(EXIT_FAILURE);
27            }
28 
29            memset(&hints, 0, sizeof(struct addrinfo));
30            hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
31            hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
32            hints.ai_flags = AI_PASSIVE;    /* For wildcard IP address */
33            hints.ai_protocol = 0;          /* Any protocol */
34            hints.ai_canonname = NULL;
35            hints.ai_addr = NULL;
36            hints.ai_next = NULL;
37 
38            s = getaddrinfo(NULL, argv[1], &hints, &result);
39            if (s != 0) {
40                fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
41                exit(EXIT_FAILURE);
42            }
43 
44            /* getaddrinfo() returns a list of address structures.
45               Try each address until we successfully bind(2).
46               If socket(2) (or bind(2)) fails, we (close the socket
47               and) try the next address. */
48 
49            for (rp = result; rp != NULL; rp = rp->ai_next) {
50                sfd = socket(rp->ai_family, rp->ai_socktype,
51                        rp->ai_protocol);
52                if (sfd == -1)
53                    continue;
54 
55                if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0)
56                    break;                  /* Success */
57 
58                close(sfd);
59            }
60 
61            if (rp == NULL) {               /* No address succeeded */
62                fprintf(stderr, "Could not bind\n");
63                exit(EXIT_FAILURE);
64            }
65 
66            freeaddrinfo(result);           /* No longer needed */
67 
68            /* Read datagrams and echo them back to sender */
69 
70            for (;;) {
71                peer_addr_len = sizeof(struct sockaddr_storage);
72                nread = recvfrom(sfd, buf, BUF_SIZE, 0,
73                        (struct sockaddr *) &peer_addr, &peer_addr_len);
74                if (nread == -1)
75                    continue;               /* Ignore failed request */
76 
77                char host[NI_MAXHOST], service[NI_MAXSERV];
78 
79                s = getnameinfo((struct sockaddr *) &peer_addr,
80                                peer_addr_len, host, NI_MAXHOST,
81                                service, NI_MAXSERV, NI_NUMERICSERV);
82                if (s == 0)
83                    printf("Received %zd bytes from %s:%s\n",
84                            nread, host, service);
85                else
86                    fprintf(stderr, "getnameinfo: %s\n", gai_strerror(s));
87 
88                if (sendto(sfd, buf, nread, 0,
89                            (struct sockaddr *) &peer_addr,
90                            peer_addr_len) != nread)
91                    fprintf(stderr, "Error sending response\n");
92            }
93        }

 1  ###Client program
 2 
 3        #include <sys/types.h>
 4        #include <sys/socket.h>
 5        #include <netdb.h>
 6        #include <stdio.h>
 7        #include <stdlib.h>
 8        #include <unistd.h>
 9        #include <string.h>
10 
11        #define BUF_SIZE 500
12 
13        int
14        main(int argc, char *argv[])
15        {
16            struct addrinfo hints;
17            struct addrinfo *result, *rp;
18            int sfd, s, j;
19            size_t len;
20            ssize_t nread;
21            char buf[BUF_SIZE];
22 
23            if (argc < 3) {
24                fprintf(stderr, "Usage: %s host port msg...\n", argv[0]);
25                exit(EXIT_FAILURE);
26            }
27 
28            /* Obtain address(es) matching host/port */
29 
30            memset(&hints, 0, sizeof(struct addrinfo));
31            hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
32            hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
33            hints.ai_flags = 0;
34            hints.ai_protocol = 0;          /* Any protocol */
35 
36            s = getaddrinfo(argv[1], argv[2], &hints, &result);
37            if (s != 0) {
38                fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
39                exit(EXIT_FAILURE);
40            }
41 
42            /* getaddrinfo() returns a list of address structures.
43               Try each address until we successfully connect(2).
44               If socket(2) (or connect(2)) fails, we (close the socket
45               and) try the next address. */
46 
47            for (rp = result; rp != NULL; rp = rp->ai_next) {
48                sfd = socket(rp->ai_family, rp->ai_socktype,
49                             rp->ai_protocol);
50                if (sfd == -1)
51                    continue;
52 
53                if (connect(sfd, rp->ai_addr, rp->ai_addrlen) != -1)
54                    break;                  /* Success */
55 
56                close(sfd);
57            }
58 
59            if (rp == NULL) {               /* No address succeeded */
60                fprintf(stderr, "Could not connect\n");
61                exit(EXIT_FAILURE);
62            }
63 
64            freeaddrinfo(result);           /* No longer needed */
65 
66            /* Send remaining command-line arguments as separate
67               datagrams, and read responses from server */
68 
69            for (j = 3; j < argc; j++) {
70                len = strlen(argv[j]) + 1;
71                        /* +1 for terminating null byte */
72 
73                if (len + 1 > BUF_SIZE) {
74                    fprintf(stderr,
75                            "Ignoring long message in argument %d\n", j);
76                    continue;
77                }
78 
79                if (write(sfd, argv[j], len) != len) {
80                    fprintf(stderr, "partial/failed write\n");
81                    exit(EXIT_FAILURE);
82                }
83 
84                nread = read(sfd, buf, BUF_SIZE);
85                if (nread == -1) {
86                    perror("read");
87                    exit(EXIT_FAILURE);
88                }
89 
90                printf("Received %zd bytes: %s\n", nread, buf);
91            }
92 
93            exit(EXIT_SUCCESS);
94        }