In this article I will show you how to write a simple TCP echo server.
The echo server is the simpliest server you can develop, it waits for data from a client and then sends the same data to the client.
/*+————————————————————–+
| tcp.server.c – description |
| ——————- |
| begin : 05/08/2010 20.00 |
| copyright : (C) 2010 xAppSoftware |
| author : Luigi D'Andrea |
| email : gg1 ( at ) xappsoftware dot com |
| compiling : gcc -o tcp.server tcp.server.c |
| |
| Latest version on http://www.xappsoftware.com |
+————————————————————–+
| udp client-server may be redistributed and modified under |
| certain conditions. This software is distributed on an |
| "AS IS" basis WITHOUT WARRANTY OF ANY KIND, either express or|
| implied. See the file License.txt for details. |
+————————————————————–+*/
/*+————————————————————–+
| SYSTEM INCLUDES |
+————————————————————–+*/
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
/*+————————————————————–+
| PROTOTYPES |
+————————————————————–+*/
int main(int argc, char **argv);
void Usage(char **argv);
Blablablabla.
Finally the main function…..
/*+————————————————————–+
| Function name : main |
| Parameters : The port number |
| Description : The simple TCP echo server |
+————————————————————–+*/
int main(int argc, char **argv)
{
int serv_fd, clnt_fd;
struct sockaddr_in serv_addr;
char c;
First of all I check for the command line arguments, the echo server shall know the port on which it must wait for a connection. Normally on Unix systems port from 0 to 2048 are reserved so use a port number greater than 2048.
{
Usage(argv);
exit(EXIT_FAILURE);
}
I create a socket, if the socket() call fails then the program exits.
/* create socket*/
serv_fd = socket(AF_INET, SOCK_STREAM, 0);
if(serv_fd==-1)
{
perror("Error while opening socket");
exit(EXIT_FAILURE);
}
Preparing the server address where I want to receive data.
/* prepare for bind*/
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(atoi(argv[1]));
serv_addr.sin_addr.s_addr = INADDR_ANY;
Binding the address
/* bind*/
bind(serv_fd, (struct sockaddr *) &serv_addr, sizeof(serv_addr));
/* listen only 1 queue*/
Prepare for listening, only 1 client per time. If you want to accept more client you shall change the 2nd parameter of the listen() call.
listen(serv_fd, 1);
/* accept only 1 client*/
Waiting for a connection
clnt_fd = accept(serv_fd, NULL, NULL);
The following lines will echo data received from the client to the client itself.
/* read and write until ^D (from client)*/
while (read(clnt_fd, &c, 1)) /* read from client*/
{
write(clnt_fd, &c, 1); /* write to client*/
}
Release the sockets and exit.
/* close connection from client and stop echo server*/
close(clnt_fd);
close(serv_fd);
return 0;
}
void Usage(char **argv)
{
printf("Usage: %s <port_number>\n", argv[0]);
return;
}
In a next article the client.
Gg1