The two following program examples illustrate how a streams connection in the Internet domain is initialized by the client and accepted by the server:
The example programs are only valid for the communications domain AF_INET. If they are modified according to the information in the sections "Socket addressing" and "Creating a socket", they are also valid for the AF_INET6 domain.
Example 1: Initialization of a streams connection by the client
This program creates a socket and initializes a connection with the socket passed in the command line. A message is sent over the connection. The socket is then closed and the connection shut down.
The program call is: programname hostname portnumber
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#define DATA "Half a league, half a league . . ."
int main(int argc, char **argv)
{
int sock;
struct sockaddr_in server;
struct hostent *hp;
/* Create socket. */
sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock < 0) {
perror("opening stream socket");
exit(1);
}
/* Connection setup using the specified name. */
server.sin_family = AF_INET;
hp = gethostbyname(argv[1]);
if (hp == 0) {
fprintf(stderr, "%s: unknown host\n", argv[1]);
exit(2);
}
memcpy((char *)&server.sin_addr, (char *)hp->h_addr, hp->h_length);
server.sin_port = htons(atoi(argv[2]));
if (connect(sock, (struct sockaddr *)&server, sizeof server ) < 0) {
perror("connecting stream socket");
exit(1);
}
if (send(sock, DATA, sizeof DATA, 0) < 0)
perror("writing on stream socket");
close(sock);
exit(0);
}
Example 2: Acceptance of the streams connection by the server
This program creates a socket and then goes into an endless loop. With each loop run, it accepts a connection and sends messages. If the connection is interrupted or a termination message is passed, the program accepts a new connection. As this program runs in an endless loop, the socket is never explicitly closed. However, all sockets are closed automatically if a process is terminated or reaches its normal termination.
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#define TRUE 1
#define TESTPORT 2222
int main(int argc, char **argv)
{
int sock, length;
struct sockaddr_in server, client;
int msgsock;
char buf[1024];
int rval;
/* Create socket. */
sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock < 0) {
perror("opening stream socket");
exit(1);
}
/* The socket name is assigned a name using wildcards. */
server.sin_family = AF_INET;
server.sin_addr.s_addr = htonl(INADDR_ANY);
server.sin_port = htons(TESTPORT);
if (bind(sock, (struct sockaddr *)&server, sizeof server ) < 0) {
perror("binding stream socket");
exit(1);
}
/* Find and output the appropriate port number. */
length = sizeof server;
if (getsockname(sock, (struct sockaddr *)&server, &length) < 0) {
perror("getting socket name");
exit(1);
}
printf("Socket port #%d\n", ntohs(server.sin_port));
/* Start acceptance of connection requests. */
listen(sock, 5);
do {
length = sizeof client;
msgsock = accept(sock, (struct sockaddr *)&client,&length);
if (msgsock == -1) {
perror("accept");
} else do {
memset(buf, 0, sizeof buf );
if ((rval = recv(msgsock, buf, 1024, 0)) < 0) {
perror("reading stream message");
} else if (rval == 0) {
printf("Ending connection\n");
} else {
printf("-->%s\n", buf);
}
} while (rval > 0);
close(msgsock);
} while (TRUE);
/* NOTREACHED */
exit(0);
}