Socket can't connect to server?

Question

linux

Server:

#include <iostream>
#include <sys/types.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <string.h>
#include <string>

using namespace std;

int main()
{
    // Create a socket
    int listening = socket(AF_INET, SOCK_STREAM, 0);
    if (listening == -1)
    {
        cerr << "Can't create a socket! Quitting" << endl;
        return -1;
    }

    // Bind the ip address and port to a socket
    sockaddr_in hint;
    hint.sin_family = AF_INET;
    hint.sin_port = htons(4444);
    inet_pton(AF_INET, "127.0.0.1", &hint.sin_addr);

    bind(listening, (sockaddr*)&hint, sizeof(hint));

    // Tell Winsock the socket is for listening
    listen(listening, SOMAXCONN);

    // Wait for a connection
    sockaddr_in client;
    socklen_t clientSize = sizeof(client);

    int clientSocket = accept(listening, (sockaddr*)&client, &clientSize);

    char host[NI_MAXHOST];      // Client's remote name
    char service[NI_MAXSERV];   // Service (i.e. port) the client is connect on

    memset(host, 0, NI_MAXHOST); // same as memset(host, 0, NI_MAXHOST);
    memset(service, 0, NI_MAXSERV);

    if (getnameinfo((sockaddr*)&client, sizeof(client), host, NI_MAXHOST, service, NI_MAXSERV, 0) == 0)
    {
        cout << host << " connected on port " << service << endl;
    }
    else
    {
        inet_ntop(AF_INET, &client.sin_addr, host, NI_MAXHOST);
        cout << host << " connected on port " << ntohs(client.sin_port) << endl;
    }

    // Close listening socket
    close(listening);

    // While loop: accept and echo message back to client
    char buf[4096];

    while (true)
    {
        memset(buf, 0, 4096);

        // Wait for client to send data
        int bytesReceived = recv(clientSocket, buf, 4096, 0);
        if (bytesReceived == -1)
        {
            cerr << "Error in recv(). Quitting" << endl;
            break;
        }

        if (bytesReceived == 0)
        {
            cout << "Client disconnected " << endl;
            break;
        }

        cout << string(buf, 0, bytesReceived) << endl;

        // Echo message back to client
        send(clientSocket, buf, bytesReceived + 1, 0);
    }

    // Close the socket
    close(clientSocket);

    return 0;
}

Customer:

#include <iostream>
#include <sys/types.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <string.h>
#include <string>

using namespace std;

int main()
{
    //	Create a socket
    int sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock == -1)
    {
        return 1;
    }

    //	Create a hint structure for the server we're connecting with
    int port = 4444;
    string ipAddress = "127.0.0.1";

    sockaddr_in hint;
    hint.sin_family = AF_INET;
    hint.sin_port = htons(port);
    inet_pton(AF_INET, ipAddress.c_str(), &hint.sin_addr);

    //	Connect to the server on the socket
    int connectRes = connect(sock, (sockaddr*)&hint, sizeof(hint));
    if (connectRes == -1)
    {
        return 1;
    }

    //	While loop:
    char buf[4096];
    string userInput;


    do {
        //		Enter lines of text
        cout << "> ";
        getline(cin, userInput);

        //		Send to server
        int sendRes = send(sock, userInput.c_str(), userInput.size() + 1, 0);
        if (sendRes == -1)
        {
            cout << "Could not send to server! Whoops!\r\n";
            continue;
        }

        //		Wait for response
        memset(buf, 0, 4096);
        int bytesReceived = recv(sock, buf, 4096, 0);
        if (bytesReceived == -1)
        {
            cout << "There was an error getting response from server\r\n";
        }
        else
        {
            //		Display response
            cout << "SERVER> " << string(buf, bytesReceived) << "\r\n";
        }
    } while(true);

    //	Close the socket
    close(sock);

    return 0;
}

If you specify the local IP 127.0.0.1 in the socket parameters, then everything works.
And when you try to connect to this server on another PC (IP is indicated), there is no connection.
What is the problem?
Thanks for the help!

Answer 1

at the very least, the problem is that you are only listening for connections on the loopback interface:
inet_pton(AF_INET, "127.0.0.1", &hint.sin_addr);
instead, specify the IP address of the interface on which you want the connection from the client to come.