/*
** tcp_server_multi.c -- a multi-threaded tcp server
*/

#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 <arpa/inet.h>
#include <sys/wait.h>
#include <signal.h>

#define MYPORT 3490	// the port users will be connecting to

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

// since we are forking, we need to take care of child processes
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 sockaddr_in my_addr;	// my address information
	struct sockaddr_in their_addr; // connector's address information
	socklen_t sin_size;
	struct sigaction sa;
	int yes=1;
	
	// create a tcp socket to listen on
	if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
		perror("socket");
		exit(1);
	}

	// specify that the address is to be reused: useful if the server is stopped 
	// and immediately restarted before the port has been reclaimed by the kernel
	if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
		perror("setsockopt");
		exit(1);
	}
	
	my_addr.sin_family = AF_INET;		 // host byte order
	my_addr.sin_port = htons(MYPORT);	 // short, network byte order
	my_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP
	memset(my_addr.sin_zero, '\0', sizeof my_addr.sin_zero);

	// bind the socket to MYPORT
	if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof my_addr) == -1) {
		perror("bind");
		exit(1);
	}

	// listen on the socket for connections
	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);
	}

	while(1) {  // main accept() loop
		sin_size = sizeof their_addr;
		// accept connection from client
		if ((new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size)) == -1) {
			perror("accept");
			continue;
		}
		printf("tcp_server_multi: got connection from %s\n",inet_ntoa(their_addr.sin_addr));
		
		// everything in the following block happens simultaneously in the
		// child process, while the parent continues from the line after
		// the fork block
		if (!fork()) { // this is the child process
			close(sockfd); // child doesn't need the listener
			if (send(new_fd, "Hello, world!\n", 14, 0) == -1)
				perror("send");
			close(new_fd);
			exit(0);
		} // child ends here
		
		// parent continues here
		close(new_fd);  // parent doesn't need this
	}

	return 0;
}