Chapter 12: Networks
Echo Server
How sockets are used for server processes differs slightly from how they are used in clients. The follow-
ing sample program demonstrates how a simple echo server can be implemented:#include<stdio.h>
#include<netinet/in.h>
#include<sys/types.h>
#include<string.h>int main() {
char* echo_host = "192.168.1.20";
int echo_port = 7777;
int sockfd;
struct sockaddr_in *server=
(struct sockaddr_in*)malloc(sizeof(struct sockaddr_in));/* Set own address */
server->sin_family = AF_INET;
server->sin_port = htons(echo_port); // Note network byte order!
server->sin_addr.s_addr = inet_addr(echo_host);/* Create a socket */
sockfd = socket(AF_INET, SOCK_STREAM, 0);/* Bind to an address */
if (bind(sockfd, (struct sockaddr*)server, sizeof(*server))) {
printf("bind failed\n");
}/* Enable server mode of socket */
listen(sockfd, SOMAXCONN);/* ...and wait for incoming data */
int clientfd;
struct sockaddr_in* client =
(struct sockaddr_in*)malloc(sizeof(struct sockaddr_in));
int client_size = sizeof(*client);
char* buf = (char*)malloc(1000);
int bytes;printf("Wait for connection to port %u\n", echo_port);/* Accept a connection request */
clientfd = accept(sockfd, (struct sockaddr*)client, &client_size);
printf("Connected to %s:%u\n\n", inet_ntoa(client->sin_addr),
ntohs(client->sin_port));
printf("Numeric: %u\n", ntohl(client->sin_addr.s_addr));while(1) { /* Endless loop */
/* Receive transmitted data */
bytes = read(clientfd, (void*)buf, 1000);
if (bytes <= 0) {
close(clientfd);
printf("Connection closed.\n");
exit(0);
}