multi_server.c

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

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

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

	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);
	}

	printf("server: waiting for connections...\n");
	sin_size = sizeof their_addr;

	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);
	}

	while(1){
		new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
		if (new_fd == -1) {
	//		perror("accept");
			return;
		}
	
		inet_ntop(their_addr.sin_family,(struct sockaddr *)&their_addr.sin_addr,s, sizeof s);	
		printf("server: got connection from %s port: %d\n", s,their_addr.sin_port);

		if (!fork()) { // this is the child process
			close(sockfd); // child doesn't need the listener
			if ((numbytes = recv(new_fd, buf, 256, 0)) == -1) {	
				perror("recv");
				exit(1);
			}else  if (numbytes == 0) {
				// connection closed
				printf("Client socket %s hung up\n",s );
			}else{
				printf("received:%s",buf);
				if (send(new_fd, buf, numbytes, 0) == -1) {	
					perror("send");
				}
			}
			printf("Client socket %s closed\n",s );
		}
		close(new_fd); // parent doesn't need this
	}
	close(sockfd); // listen socket
	return 0;
}