echo_server.c

#include <sys/socket.h>       /*  socket definitions        */
#include <sys/types.h>        /*  socket types              */
#include <arpa/inet.h>        /*  inet (3) funtions         */
#include <unistd.h>           /*  misc. UNIX functions      */
 
#include "helper.h"           /*  our own helper functions  */
 
#include <stdlib.h>
#include <stdio.h>
 
 
/*  Global constants  */
 
#define ECHO_PORT          (2002)
#define MAX_LINE           (1000)
 
 
int main(int argc, char *argv[]) {
    int       list_s;                /*  listening socket          */
    int       conn_s;                /*  connection socket         */
    short int port;                  /*  port number               */
    struct    sockaddr_in servaddr;  /*  socket address structure  */
    char      buffer[MAX_LINE];      /*  character buffer          */
    char     *endptr;                /*  for strtol()              */
 
 
    /*  Get port number from the command line, and
        set to default port if no arguments were supplied  */
 
    if ( argc == 2 ) {
	port = strtol(argv[1], &endptr, 0);
	if ( *endptr ) {
	    fprintf(stderr, "ECHOSERV: Invalid port number.\n");
	    exit(EXIT_FAILURE);
	}
    }
    else if ( argc < 2 ) {
	port = ECHO_PORT;
    }
    else {
	fprintf(stderr, "ECHOSERV: Invalid arguments.\n");
	exit(EXIT_FAILURE);
    }
 
 
    /*  Create the listening socket  */
 
    if ( (list_s = socket(AF_INET, SOCK_STREAM, 0)) < 0 ) {
	fprintf(stderr, "ECHOSERV: Error creating listening socket.\n");
	exit(EXIT_FAILURE);
    }
 
 
    /*  Set all bytes in socket address structure to
        zero, and fill in the relevant data members   */
 
    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family      = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port        = htons(port);
 
 
    /*  Bind our socket addresss to the
	listening socket, and call listen()  */
 
    if ( bind(list_s, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0 ) {
	fprintf(stderr, "ECHOSERV: Error calling bind()\n");
	exit(EXIT_FAILURE);
    }
 
    if ( listen(list_s, LISTENQ) < 0 ) {
	fprintf(stderr, "ECHOSERV: Error calling listen()\n");
	exit(EXIT_FAILURE);
    }
 
 
    /*  Enter an infinite loop to respond
        to client requests and echo input  */
 
    while ( 1 ) {
 
	/*  Wait for a connection, then accept() it  */
 
	if ( (conn_s = accept(list_s, NULL, NULL) ) < 0 ) {
	    fprintf(stderr, "ECHOSERV: Error calling accept()\n");
	    exit(EXIT_FAILURE);
	}
 
 
	/*  Retrieve an input line from the connected socket
	    then simply write it back to the same socket.     */
 
	Readline(conn_s, buffer, MAX_LINE-1);
	Writeline(conn_s, buffer, strlen(buffer));
 
 
	/*  Close the connected socket  */
 
	if ( close(conn_s) < 0 ) {
	    fprintf(stderr, "ECHOSERV: Error calling close()\n");
	    exit(EXIT_FAILURE);
	}
    }
}