Two-way communication in TCP: server-client implementation

Question

I have written some code to establish a client and server. I have managed to get a one way communication from client to server. I have added the code below. Can someone please have a look and see it is the right way to do it? If this is good enough, how can I get two communication to work now?

Client:

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

#define PORT 3490
#define MAXSIZE 1024

int main(int argc, char *argv[])
{
    struct sockaddr_in server_info;
    struct hostent *he;
    int socket_fd,num;
    char buffer[1024];

    char buff[1024];

    if (argc != 2) {
        fprintf(stderr, "Usage: client hostname\n");
        exit(1);
    }

    if ((he = gethostbyname(argv[1]))==NULL) {
        fprintf(stderr, "Cannot get host name\n");
        exit(1);
    }

    if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0))== -1) {
        fprintf(stderr, "Socket Failure!!\n");
        exit(1);
    }

    memset(&server_info, 0, sizeof(server_info));
    server_info.sin_family = AF_INET;
    server_info.sin_port = htons(PORT);
    server_info.sin_addr = *((struct in_addr *)he->h_addr);
    if (connect(socket_fd, (struct sockaddr *)&server_info, sizeof(struct sockaddr))<0) {
        //fprintf(stderr, "Connection Failure\n");
        perror("connect");
        exit(1);
    }

    //buffer = "Hello World!! Lets have fun\n";
    //memset(buffer, 0 , sizeof(buffer));
    while(1) {
        fgets(buffer,MAXSIZE-1,stdin);
        if ((send(socket_fd,buffer, strlen(buffer),0))== -1) {
            fprintf(stderr, "Failure Sending Message\n");
            close(socket_fd);
            exit(1);
        }
        else {
            printf("Message being sent: %s\n",buffer);
        }
    }   

    /*if ((num = recv(socket_fd, buff, 1024,0))== -1) {
            //fprintf(stderr,"Error in receiving message!!\n");
            perror("recv");
            exit(1);
        }   
    //  num = recv(client_fd, buffer, sizeof(buffer),0);
    buff[num] = '\0';
    printf("Message received: %s\nNumber of bytes received: %d\n", buff,num);*/
    close(socket_fd);   

}

Server:

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

#define PORT 3490
#define BACKLOG 10

int main()
{
    struct sockaddr_in server;
    struct sockaddr_in dest;
    int status,socket_fd, client_fd,num;
    socklen_t size;

    char buffer[10241];
    char *buff;
//  memset(buffer,0,sizeof(buffer));
    int yes =1;



    if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0))== -1) {
        fprintf(stderr, "Socket failure!!\n");
        exit(1);
    }

    if (setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
        perror("setsockopt");
        exit(1);
    }
    memset(&server, 0, sizeof(server));
    memset(&dest,0,sizeof(dest));
    server.sin_family = AF_INET;
    server.sin_port = htons(PORT);
    server.sin_addr.s_addr = INADDR_ANY; 
    if ((bind(socket_fd, (struct sockaddr *)&server, sizeof(struct sockaddr )))== -1)    { //sizeof(struct sockaddr) 
        fprintf(stderr, "Binding Failure\n");
        exit(1);
    }

    if ((listen(socket_fd, BACKLOG))== -1){
        fprintf(stderr, "Listening Failure\n");
        exit(1);
    }

    while(1) {
        size = sizeof(struct sockaddr_in);  

        if ((client_fd = accept(socket_fd, (struct sockaddr *)&dest, &size))==-1) {
            //fprintf(stderr,"Accept Failure\n");
            perror("accept");
            exit(1);
        }
        printf("Server got connection from client %s\n", inet_ntoa(dest.sin_addr));
        //buffer = "Hello World!! I am networking!!\n";

        while(1) {
        if ((num = recv(client_fd, buffer, 10240,0))== -1) {
            //fprintf(stderr,"Error in receiving message!!\n");
            perror("recv");
            exit(1);
        }   
        else if (num == 0) {
            printf("Connection closed\n");
            return 0;
        }
    //  num = recv(client_fd, buffer, sizeof(buffer),0);
        buffer[num] = '\0';
        printf("Message received: %s\n", buffer);
        }

    /*  buff = "I am communicating with the client!!\n";

        if ((send(client_fd,buff, strlen(buff),0))== -1) {
        fprintf(stderr, "Failure Sending Message\n");
        close(client_fd);
        exit(1);
    }
    else {
        printf("Message being sent: %s\nNumber of bytes sent: %d\n",buff, strlen(buff));
    }*/

        close(client_fd);   
        close(socket_fd);   
        //return 0;
    }
    //close(client_fd); 
    return 0;
}

Answer 1

You can do a two way data transfer here. I have modified your code to show that. Now the server is echoing back to the client the same string which it has received. Now the client displays the same string, which it receives from the server. Pl. experiment with this.

client main loop

    while(1) {
        printf("Client: Enter Data for Server:\n");
        fgets(buffer,MAXSIZE-1,stdin);
        if ((send(socket_fd,buffer, strlen(buffer),0))== -1) {
                fprintf(stderr, "Failure Sending Message\n");
                close(socket_fd);
                exit(1);
        }
        else {
                printf("Client:Message being sent: %s\n",buffer);
                num = recv(socket_fd, buffer, sizeof(buffer),0);
                if ( num <= 0 )
                {
                        printf("Either Connection Closed or Error\n");
                        //Break from the While
                        break;
                }

                buff[num] = '\0';
                printf("Client:Message Received From Server -  %s\n",buffer);
           }
    }
    close(socket_fd);

}//End of main

Server main loop

    while(1) {

        size = sizeof(struct sockaddr_in);

        if ((client_fd = accept(socket_fd, (struct sockaddr *)&dest, &size))==-1 ) {
            perror("accept");
            exit(1);
        }
        printf("Server got connection from client %s\n", inet_ntoa(dest.sin_addr));

        while(1) {

                if ((num = recv(client_fd, buffer, 1024,0))== -1) {
                        perror("recv");
                        exit(1);
                }
                else if (num == 0) {
                        printf("Connection closed\n");
                        //So I can now wait for another client
                        break;
                }
                buffer[num] = '\0';
                printf("Server:Msg Received %s\n", buffer);
                if ((send(client_fd,buffer, strlen(buffer),0))== -1) 
                {
                     fprintf(stderr, "Failure Sending Message\n");
                     close(client_fd);
                     break;
                }

                printf("Server:Msg being sent: %s\nNumber of bytes sent: %d\n",b
                uffer, strlen(buffer));

        } //End of Inner While...
        //Close Connection Socket
        close(client_fd);
    } //Outer While

    close(socket_fd);
    return 0;
} //End of main