a stream socket server & client demo

client.c

/*
** client.c -- a stream socket client demo
*/

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

#include <arpa/inet.h>

#define PORT "3490" // the port client will be connecting to 

#define MAXDATASIZE 100 // max number of bytes we can get at once 

// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }

    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(int argc, char *argv[])
{
    int sockfd, numbytes;  
    char buf[MAXDATASIZE];
    struct addrinfo hints, *servinfo, *p;
    int rv;
    char s[INET6_ADDRSTRLEN];

    if (argc != 2) {
        fprintf(stderr,"usage: client hostname\n");
        exit(1);
    }

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;

    if ((rv = getaddrinfo(argv[1], PORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }

    // loop through all the results and connect to the first we can
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1) {
            perror("client: socket");
            continue;
        }

        if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
            close(sockfd);
            perror("client: connect");
            continue;
        }

        break;
    }

    if (p == NULL) {
        fprintf(stderr, "client: failed to connect\n");
        return 2;
    }

    inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr),
            s, sizeof s);
    printf("client: connecting to %s\n", s);

    freeaddrinfo(servinfo); // all done with this structure

    if ((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1) {
        perror("recv");
        exit(1);
    }

    buf[numbytes] = '\0';

    printf("client: received '%s'\n",buf);

    close(sockfd);

    return 0;
}

server.c

/*
** server.c -- a stream socket server demo
*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <signal.h>

#define PORT "3490"  // the port users will be connecting to

#define BACKLOG 10	 // how many pending connections queue will hold

void sigchld_handler(int s)
{
	while(waitpid(-1, NULL, WNOHANG) > 0);
}

// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
	if (sa->sa_family == AF_INET) {
		return &(((struct sockaddr_in*)sa)->sin_addr);
	}

	return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(void)
{
	int sockfd, new_fd;  // listen on sock_fd, new connection on new_fd
	struct addrinfo hints, *servinfo, *p;
	struct sockaddr_storage their_addr; // connector's address information
	socklen_t sin_size;
	struct sigaction sa;
	int yes=1;
	char s[INET6_ADDRSTRLEN];
	int rv;

	memset(&hints, 0, sizeof hints);
	hints.ai_family = AF_UNSPEC;
	hints.ai_socktype = SOCK_STREAM;
	hints.ai_flags = AI_PASSIVE; // use my IP

	if ((rv = getaddrinfo(NULL, PORT, &hints, &servinfo)) != 0) {
		fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
		return 1;
	}

	// loop through all the results and bind to the first we can
	for(p = servinfo; p != NULL; p = p->ai_next) {
		if ((sockfd = socket(p->ai_family, p->ai_socktype,
				p->ai_protocol)) == -1) {
			perror("server: socket");
			continue;
		}

		if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes,
				sizeof(int)) == -1) {
			perror("setsockopt");
			exit(1);
		}

		if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
			close(sockfd);
			perror("server: bind");
			continue;
		}

		break;
	}

	if (p == NULL)  {
		fprintf(stderr, "server: failed to bind\n");
		return 2;
	}

	freeaddrinfo(servinfo); // all done with this structure

	if (listen(sockfd, BACKLOG) == -1) {
		perror("listen");
		exit(1);
	}

	sa.sa_handler = sigchld_handler; // reap all dead processes
	sigemptyset(&sa.sa_mask);
	sa.sa_flags = SA_RESTART;
	if (sigaction(SIGCHLD, &sa, NULL) == -1) {
		perror("sigaction");
		exit(1);
	}

	printf("server: waiting for connections...\n");

	while(1) {  // main accept() loop
		sin_size = sizeof their_addr;
		new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
		if (new_fd == -1) {
			perror("accept");
			continue;
		}

		inet_ntop(their_addr.ss_family,
			get_in_addr((struct sockaddr *)&their_addr),
			s, sizeof s);
		printf("server: got connection from %s\n", s);

		if (!fork()) { // this is the child process
			close(sockfd); // child doesn't need the listener
			if (send(new_fd, "Hello, world!", 13, 0) == -1)
				perror("send");
			close(new_fd);
			exit(0);
		}
		close(new_fd);  // parent doesn't need this
	}

	return 0;
}