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//Simple TCP Chat Server
//Taken from:
//Using select() for I/O multiplexing
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
#include <termios.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
//Port we're listening on
#define PORT 2020
int main(int argc, char *argv[]) {
fd_set master; //master file descriptor list
fd_set read_fds; //temporary file descriptor list for select()
struct sockaddr_in serveraddr; //server address
struct sockaddr_in clientaddr; //client address
int fdmax; //maximum file descriptor number
int listener; //listening socket descriptor
int newfd; //newly accept()ed socket descriptor
char buf[1024]; //buffer for client data
int nbytes;
int yes = 1; //for setsockopt() SO_REUSEADDR, below
unsigned int addrlen;
int i, j;
//clear the master and temporary file descriptor sets
//get a socket for listening on
if((listener = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("Server-socket() error lol!");
exit(1); //just exit lol!
printf("Server-socket() is OK...\n");
//"address already in use" error message
if(setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
perror("Server-setsockopt() error lol!");
printf("Server-setsockopt() is OK...\n");
serveraddr.sin_family = AF_INET;
serveraddr.sin_addr.s_addr = INADDR_ANY;
serveraddr.sin_port = htons(PORT);
memset(&(serveraddr.sin_zero), '\0', 8);
if(bind(listener, (struct sockaddr *)&serveraddr, sizeof(serveraddr)) == -1) {
perror("Server-bind() error lol!");
printf("Server-bind() is OK...\n");
if(listen(listener, 10) == -1) {
perror("Server-listen() error lol!");
printf("Server-listen() is OK...\n");
//add the listener to the master set
FD_SET(listener, &master);
//keep track of the biggest file descriptor
fdmax = listener; //so far, it's this one
for(;;) {
//copy it
read_fds = master;
if(select(fdmax+1, &read_fds, NULL, NULL, NULL) == -1) {
perror("Server-select() error lol!");
//printf("Server-select() is OK...\n");
//run through the existing connections looking for data to be read
for(i = 0; i <= fdmax; i++) {
if(FD_ISSET(i, &read_fds)) {
//we got one...
if(i == listener) {
//handle new connections
addrlen = sizeof(clientaddr);
if((newfd = accept(listener, (struct sockaddr *)&clientaddr, &addrlen)) == -1) {
perror("Server-accept() error lol!");
} else {
printf("Server-accept() is OK...\n");
FD_SET(newfd, &master); //add to master set
if(newfd > fdmax) {
//keep track of the maximum
fdmax = newfd;
printf("New connection from %s on socket %d\n", inet_ntoa(clientaddr.sin_addr), newfd);
} else {
//handle data from a client
if((nbytes = recv(i, buf, sizeof(buf), 0)) <= 0) {
//got error or connection closed by client
if(nbytes == 0)
//connection closed
printf("socket %d hung up\n", i);
perror("recv() error lol!");
//close it...
//remove from master set
FD_CLR(i, &master);
} else {
//we got some data from a client
printf("Socket %d sent %d bytes\n",i,nbytes);
for(j = 0; j <= fdmax; j++) {
//send to everyone!
if(FD_ISSET(j, &master)) {
//except the listener and ourselves
if(j != listener && j != i) {
if(send(j, buf, nbytes, 0) == -1)
perror("send() error lol!");
printf("\tForwarded %d bytes to socket %d\n",nbytes,j);
return 0;
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