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Is is possible to implement a client / server program using the online compiler?

+5 votes
asked May 15 by Shawn Armstrong (310 points)

I thought about trying to get this client/server implementation to work using the online compilers. Using this program, I noticed the IP address changes every time you run. Which leads me to believe it's not really possible unless somebody can think of a witty work around?

1 Answer

+1 vote
answered May 21 by xDELLx (9,400 points)
selected Jun 12 by Shawn Armstrong
 
Best answer

https://onlinegdb.com/VjEji9cJH

The trick is to use loopback ip for both client & server.

when creating server socket, specify the loopback ip for binding(Line #131).

Also since i cant run client & server on seperate instances of onlineGDB, i created a client thread to run parallel to server(main) thread.

the placement of running of child thread is crucial as we have start cleint thread after server socket is bound & not yet listening.

As listen(& few other api,by default) socket calls are blocking & pause execution, i think its the best place to spawn a child thread.


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

#define MAX 80
#define PORT 9090
#define SA struct sockaddr
void func(int connfd)
{
    char buff[MAX];
    int n=0;
    // infinite loop for chat
    for (;;)
    {
        bzero(buff, MAX);

        // read the message from client and copy it in buffer
        read(connfd, buff, sizeof(buff));
        // print buffer which contains the client contents
        printf("I am Server || Msg from client ==>> %s\n", buff);
        bzero(buff, MAX);
        // copy server message in the buffer
        //while ((buff[n++] = getchar()) != '\n')
            ;
        sprintf(buff,"** got !! msg %d from Server **\n",n);
        // and send that buffer to client
        write(connfd, buff, sizeof(buff));

        // if msg contains "Exit" then server exit and chat ended.
        if (strncmp("exit", buff, 4) == 0) {
            printf("Server Exit...\n");
//            break;
        }
        sleep(2);
        n++;
    }
}

void client_func(int sockfd)
{
    char buff[MAX];
    int n=0;
    for (;;)
    {
        bzero(buff, sizeof(buff));
        //printf("Enter the string : ");
    n++;
    sprintf(buff,"Msg %d to server !!\n",n);
        write(sockfd, buff, sizeof(buff));
        bzero(buff, sizeof(buff));
        read(sockfd, buff, sizeof(buff));
        printf("I am Client || Msg From Server : %s\n", buff);

        if ((strncmp(buff, "exit", 4)) == 0) {
            printf("Client Exit...\n");
        }
    }
}

int create_client(void* arg){
int sockfd, connfd;
    struct sockaddr_in servaddr, cli;

    // socket create and verification
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd == -1) {
        printf("socket creation failed...\n");
        exit(0);
    }
    else
        printf("Socket successfully created..\n");
    bzero(&servaddr, sizeof(servaddr));

    // assign IP, PORT
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
    servaddr.sin_port = htons(PORT);

    // connect the client socket to server socket
    if (connect(sockfd, (SA*)&servaddr, sizeof(servaddr)) != 0) {
        printf("connection with the server failed...\n");
        exit(0);
    }
    else
        printf("connected to the server..\n");

    // function for chat
    client_func(sockfd);

    // close the socket
    
    close(sockfd);
    
    return 0;
    
}

// Driver function
int main()
{
    int sockfd, connfd, len;
    struct sockaddr_in servaddr, cli;
    thrd_t client_thrd_handle;

    // socket create and verification
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd == -1) {
        printf("socket creation failed...\n");
        exit(0);
    }
    else
        printf("Socket successfully created..\n");
    bzero(&servaddr, sizeof(servaddr));

    // assign IP, PORT
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
    servaddr.sin_port = htons(PORT);

    // Binding newly created socket to given IP and verification
    if ((bind(sockfd, (SA*)&servaddr, sizeof(servaddr))) != 0) {
        printf("socket bind failed...\n");
        exit(0);
    }
    else
        printf("Socket successfully binded..\n");

//creating client on sepearte thread
    thrd_create(&client_thrd_handle,create_client,NULL);

    // Now server is ready to listen and verification
    if ((listen(sockfd, 5)) != 0) {
        printf("Listen failed...\n");
        exit(0);
    }
    else
        printf("Server listening..\n");
    len = sizeof(cli);

    // Accept the data packet from client and verification
    connfd = accept(sockfd, (SA*)&cli, &len);
    if (connfd < 0) {
        printf("server accept failed...\n");
        exit(0);
    }
    else
        printf("server accept the client...\n");

 func(connfd);

    // After chatting close the socket
    close(sockfd);
    thrd_join(client_thrd_handle,NULL);
}

commented May 21 by xDELLx (9,400 points)
On second thoughts , i think running server & client of 2 separate threads would do the trick.
Irrespective of loop-back address, i thnik!!
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