mini_serv.c

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/select.h>

#include <fcntl.h> // TEST ONLY

int clients[FD_SETSIZE];
int serverSocket;

void putstr_fd(char *str, int fd) {
	write(fd, str, strlen(str));
}

void fatal_error() {
	putstr_fd("Fatal error\n", 2);
	exit(1);
}


void close_all() {
	close(serverSocket);
	for (size_t i = 0; i < FD_SETSIZE; i++) {
		if (clients[i] > 0)
			close(i);
	}
}

void send_all(int sender, char* buf, int len) {
	for (int i = 0; i < FD_SETSIZE; i++) {
		if (i != sender  && i != serverSocket && clients[i] != -1) {
			int total = 0;
			int bytesleft = len;
			int n;
			while(total < len) {
				n = send(i, buf+total, bytesleft, 0);
				if (n == -1) {
					close_all();
					fatal_error();
				}
				total += n;
				bytesleft -= n;
			}
		}
	}
}

int main(int argc, char **argv) {
	if (argc < 2) {
		putstr_fd("Wrong number of arguments", 2);
		exit(1);
	}
	memset(&clients, -1, sizeof(int) * FD_SETSIZE);
	fd_set sockets, readReady;
	FD_ZERO(&sockets);
	FD_ZERO(&readReady);
	serverSocket = socket(AF_INET, SOCK_STREAM, 0);
	if (serverSocket < 0)
		fatal_error();
	fcntl(serverSocket, F_SETFL, O_NONBLOCK); // TEST ONLY
	FD_SET(serverSocket, &sockets);
	struct sockaddr_in addr;
	socklen_t addr_size = sizeof(addr);
	memset(&addr, 0, addr_size);
	addr.sin_family = AF_INET;
	addr.sin_port = htons(atoi(argv[1]));
	addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
	if (bind(serverSocket, (const struct sockaddr *)&addr, addr_size) < 0) {
		close(serverSocket);
		fatal_error();
	}
	if (listen(serverSocket, SOMAXCONN) < 0) {
		close(serverSocket);
		fatal_error();
	}
	int maxFd = serverSocket;
	int currId = 0;
	while(1) {
		readReady = sockets;
		if (select(maxFd + 1, &readReady, NULL, NULL, NULL) < 0) { // check for write ready?
			close_all();
			fatal_error();
		}
		for(int fd = 0; fd <= maxFd; fd++) {
			if (FD_ISSET(fd, &readReady)) {
				if (fd == serverSocket) {
					int newFd = accept(serverSocket, (struct sockaddr *)&addr, &addr_size);
					if (newFd < 0) {
						close_all();
						fatal_error();
					}
					fcntl(newFd, F_SETFL, O_NONBLOCK); // TEST ONLY
					FD_SET(newFd, &sockets);
					maxFd = maxFd > newFd ? maxFd : newFd;	
					clients[newFd] = currId;
					char buf[33];
					int len = sprintf(buf, "server: client %d just arrived\n", currId);
					send_all(newFd, buf, len);
					++currId;
				} else {
					char message[65536]; // max MTU
					int res = recv(fd, message, 65536, 0);
					message[res] = 0;
					if (res < 0) {
						close_all();
						fatal_error();
					}
					if (res == 0) {
						char buf[30];
						int len = sprintf(buf, "server: client %d just left\n", clients[fd]);
						send_all(fd, buf, len);
						FD_CLR(fd, &sockets);
						close(fd);
						clients[fd] = -1;
					} else {
						char *end;
						int offset = 0;
						while (message[offset]) {
							end = strstr(&message[offset], "\n");
							if (end)
								*end = 0;
							else
								end = &message[offset] + strlen(&message[offset]);				
							char buf[end - &message[offset] + 14];	
							int len = sprintf(buf, "client %d: %s\n", clients[fd], &message[offset]);
							send_all(fd, buf, len);
							offset += end - &message[offset] + 1;
						}
					}
				}
			}
		}
	}
	close_all();
}