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I googled and stack-overflowed a lot but didn't find any solution. I have a simple echo client-server program in which client sends a word and the server echoes it.

This is my server.c file:

#define PORT 4444
#define MAX_CONNESSIONI 100

int main ()
{
    int serverSocket, bindStatus;
    struct sockaddr_in serverAddress;
    int clientSocket;
    struct sockaddr_in newAddress;
    char buffer[1024];
    pid_t child;
    socklen_t addrSize;
    ssize_t nread;

    // Creazione della socket
    serverSocket = socket(AF_INET, SOCK_STREAM, 0);
    if (serverSocket == -1) {
        perror("[-]Errore durante la creazione della socket\n");
        exit(-1);
    }

    printf("[+]Echo-Server socket has been created\n");

    memset(&serverAddress, '\0', sizeof(serverAddress));

    // Riempimento dei campi della struct
    serverAddress.sin_family = AF_INET;
    serverAddress.sin_port = htons(PORT);
    serverAddress.sin_addr.s_addr = INADDR_ANY;

    // Binding della socket all'indirizzo specificato. Associa alla socket un indirizzo in modo da poter essere contattata dai client
    if (bind(serverSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress)) == -1) {
        perror("[-]Errore durante il binding\n");
        exit(1);
    }
    printf("[+]Bind to port %d\n", PORT);


    // Imposta la socket all'ascolto. I parametri sono il descrittore della socket e la massima lunghezza della coda di connessioni entranti
    if (listen(serverSocket, MAX_CONNESSIONI) != -1) {
        printf("Listening . . .\n\n");
    }
    else {
        perror("[-]Error during listening\n");
        exit(1);
    }


    while (1) {

        // Accettazione della connessione
        clientSocket = accept(serverSocket, (struct sockaddr*)&newAddress, &addrSize);
        if (clientSocket == -1) {
            exit(-1);
        }
        printf("%s:%d joined\n", inet_ntoa(newAddress.sin_addr), ntohs(newAddress.sin_port));

        child = fork();
        if (child == 0) {

            close(serverSocket);

            while (1) {

                // Ricezione del messaggio
                if ( (nread=recv(clientSocket, buffer, sizeof buffer - 1, 0)) <= 0) {
                    perror("[-]Error in receiving data from server\n");
                }
                else {
                    buffer[nread] = '\0';
                }


                if (strcmp(buffer, ":exit") == 0) {
                    printf("%s:%d left\n", inet_ntoa(newAddress.sin_addr), ntohs(newAddress.sin_port));
                    break;
                }
                else {
                    printf("%s:%d wrote: %s\n", inet_ntoa(newAddress.sin_addr), ntohs(newAddress.sin_port), buffer);
                    // Invio del messaggio
                    send(clientSocket, buffer, strlen(buffer), 0);
                    bzero(buffer, sizeof(buffer));
                }

            }

        }

    }

    close(clientSocket);

    return 0;
}

you can compile it using

gcc -o server.out server.c

and execute it using

./server.out

and this is my client.c file:

#define PORT 4444

int main ()
{
    int clientSocket;
    struct sockaddr_in serverAddress;
    char buffer[1024];
    ssize_t nread;

    // Creazione della socket
    clientSocket = socket(AF_INET, SOCK_STREAM, 0);
    if (clientSocket == -1) {
        perror("[-]Errore durante la creazione della socket\n");
        exit(-1);
    }
    printf("[+]Client socket has been created\n");


    memset(&serverAddress, '\0', sizeof(serverAddress));

    // Riempimento dei campi della struct
    serverAddress.sin_family = AF_INET;
    serverAddress.sin_port = htons(PORT);
    serverAddress.sin_addr.s_addr = INADDR_ANY;

    // Connessione
    if (connect(clientSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress)) == -1) {
        perror("Errore con la connessione\n");
        exit(-1);
    }
    printf("[+]Connected to Server\n");
    printf("[+]Use single-word and :exit to logout\n");

    while (1) {

        printf("> ");
        //fgets(buffer, 1024, stdin); Per ottenere una stringa con gli spazi
        fflush(stdin);
        scanf("%s", buffer);


        // Invio dei dati al server
        if (send(clientSocket, buffer, strlen(buffer), 0) == -1) {
            perror("Errore con l'invio");
            exit(1);
        }

        // Per uscire dalla connessione
        if(strcmp(buffer, ":exit") == 0) {
            close(clientSocket);
            printf("[-]Disconnected from Server\n");
            exit(0);
        }

        // Riceve i dati dal server
        if ( (nread=recv(clientSocket, buffer, sizeof buffer - 1, 0)) <= 0) {
            perror("[-]Error in receiving data from server\n");
        }
        else {
            buffer[nread] = '\0';
            printf("Server received: %s\n", buffer);
        }

    }

    close(clientSocket);

    return 0;
}

you can compile it using gcc -o client.out client.c and execute it using ./client.out

This works fine.

  • How can I edit so that I can execute the server on two different computers?

1 Answers1

1

Change INADDR_ANY to your server IP address.

serverAddress.sin_addr.s_addr = inet_addr("192.168.1.20");
Sasi V
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  • What if I can't know what it my server ip address? –  Feb 27 '20 at 11:06
  • You can not establish a connection without server IP. You must know where to connect. sockets are not intelligent enough to figure out the server ip it has to connect. – Sasi V Feb 27 '20 at 11:08
  • @Sasi I think you don't understend his question. He tolk about "server socket". You can bind your server socket to ALL available interfaces with `htonl (INADDR_ANY);` See : https://stackoverflow.com/questions/16508685/understanding-inaddr-any-for-socket-programming. It is not practice to use a fixe Ip adress because this is not well suited with DHCP mode ... – Landstalker Feb 27 '20 at 14:15
  • @Sasi you tolk about `serverAddress.sin_addr.s_addr = INADDR_ANY;` of **server.c** or **client.c** ? That of `client.c` is false because we must indicate the exact address of the server on which we want to establish the connection. – Landstalker Feb 28 '20 at 13:14
  • His question was about client. My answer was about client too. I said read his client program i.e client.c – Sasi V Feb 28 '20 at 21:43