/*
 ============================================================================
 Name        : W17_Telnet_listener.c
 Author      :
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 ** listener.c -- a datagram sockets "server" demo
 */
/*
 ** 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 "1955" // 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(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;
	}
	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;
}