client.c

/* A simple client program for server.c

   To compile: gcc client.c -o client

   To run: start the server, then the client */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <unistd.h>

int main(int argc, char ** argv)
{
    int sockfd, portno, n;
    struct sockaddr_in serv_addr;
    struct hostent * server;

    char buffer[256];

    if (argc < 3)
    {
        fprintf(stderr, "usage %s hostname port\n", argv[0]);
        exit(0);
    }

    portno = atoi(argv[2]);


    /* Translate host name into peer's IP address ;
     * This is name translation service by the operating system
     */
    server = gethostbyname(argv[1]);

    if (server == NULL)
    {
        fprintf(stderr, "ERROR, no such host\n");
        exit(0);
    }

    /* Building data structures for socket */

    bzero((char *)&serv_addr, sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;

    bcopy(server->h_addr_list[0], (char *)&serv_addr.sin_addr.s_addr, server->h_length);

    serv_addr.sin_port = htons(portno);

    /* Create TCP socket -- active open
    * Preliminary steps: Setup: creation of active open socket
    */

    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    if (sockfd < 0)
    {
        perror("ERROR opening socket");
        exit(0);
    }

    if (connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
    {
        perror("ERROR connecting");
        exit(0);
    }

    /* Do processing
    */

    printf("Please enter the message: ");

    bzero(buffer, 256);

    fgets(buffer, 255, stdin);

    n = write(sockfd, buffer, strlen(buffer));

    if (n < 0)
    {
        perror("ERROR writing to socket");
        exit(0);
    }

    bzero(buffer, 256);

    n = read(sockfd, buffer, 255);

    if (n < 0)
    {
        perror("ERROR reading from socket");
        exit(0);
    }

    printf("%s\n", buffer);

    return 0;
}

server.c

/* A simple server in the internet domain using TCP
The port number is passed as an argument


 To compile: gcc server.c -o server
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>


int main(int argc, char **argv)
{
	int sockfd, newsockfd, portno;// clilen;
	char buffer[256];
	struct sockaddr_in serv_addr, cli_addr;
	socklen_t clilen;
	int n;

	if (argc < 2)
	{
		fprintf(stderr,"ERROR, no port provided\n");
		exit(1);
	}

	 /* Create TCP socket */

	sockfd = socket(AF_INET, SOCK_STREAM, 0);

	if (sockfd < 0)
	{
		perror("ERROR opening socket");
		exit(1);
	}


	bzero((char *) &serv_addr, sizeof(serv_addr));

	portno = atoi(argv[1]);

	/* Create address we're going to listen on (given port number)
	 - converted to network byte order & any IP address for
	 this machine */

	serv_addr.sin_family = AF_INET;
	serv_addr.sin_addr.s_addr = INADDR_ANY;
	serv_addr.sin_port = htons(portno);  // store in machine-neutral format

	 /* Bind address to the socket */

	if (bind(sockfd, (struct sockaddr *) &serv_addr,
			sizeof(serv_addr)) < 0)
	{
		perror("ERROR on binding");
		exit(1);
	}

	/* Listen on socket - means we're ready to accept connections -
	 incoming connection requests will be queued */

	listen(sockfd,5);

	clilen = sizeof(cli_addr);

	/* Accept a connection - block until a connection is ready to
	 be accepted. Get back a new file descriptor to communicate on. */

	newsockfd = accept(	sockfd, (struct sockaddr *) &cli_addr,
						&clilen);

	if (newsockfd < 0)
	{
		perror("ERROR on accept");
		exit(1);
	}

	bzero(buffer,256);

	/* Read characters from the connection,
		then process */

	n = read(newsockfd,buffer,255);

	if (n < 0)
	{
		perror("ERROR reading from socket");
		exit(1);
	}

	printf("Here is the message: %s\n",buffer);

	n = write(newsockfd,"I got your message",18);

	if (n < 0)
	{
		perror("ERROR writing to socket");
		exit(1);
	}

	/* close socket */

	close(sockfd);

	return 0;
}