Network-Programming-in-C/examples/tcp_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) {
	
	// waitpid() might overwrite errno, so we save and restore it:

	int saved_errno = errno;

	while (waitpid(-1, NULL, WNOHANG) > 0);

	errno = saved_errno;
}


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

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

		break;
	}

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

	if( p == NULL ){
		fprintf(stderr, "server: failed to bind\n");
		exit(1);
	}

	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;
}