C++ server unable to receive data from client / Winsock

Question

I am working on a simple client-server application. However, after client runs, i get the message error 10038 with the recv(), in the server side. The socket number descriptor retains the same value in both client and server, thus i think there is no a socket error. Any help would be appreciated.

client:

#ifndef UNICODE
#define UNICODE
#endif

#define WIN32_LEAN_AND_MEAN

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>

// Need to link with Ws2_32.lib.
#pragma comment(lib, "ws2_32.lib")

int wmain()
{
    // Initialize Winsock.
    WSADATA wsaData;
    int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != NO_ERROR) {
        printf("WSAStartup() failed with error: %d\n", iResult);
        return 1;
    }

    // Create a socket for connecting to server.
    SOCKET ConnectSocket;
    ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (ConnectSocket == INVALID_SOCKET) {
        printf("socket() failed with error: %ld\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }
    printf("Socket descriptor: %d\n",ConnectSocket);

    // The sockaddr_in structure specifies the address family,
    // IP address, and port of the server to be connected to.
    sockaddr_in Service;
    memset(&Service, 0, sizeof(Service));
    Service.sin_family = AF_INET;
    Service.sin_addr.s_addr = inet_addr("127.0.0.1");
    Service.sin_port = htons(27015);

    // Connect to server.
    iResult = connect(ConnectSocket, (SOCKADDR *) &Service, sizeof (Service));
    if (iResult == SOCKET_ERROR) {
        printf("connect() failed with error: %ld\n", WSAGetLastError());
        iResult = closesocket(ConnectSocket);
        if (iResult == SOCKET_ERROR)
            printf("closesocket() failed with error: %ld\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }
    printf("Connected to server.\n");

    // Message that has to be sent.
    char receiveBuffer[1000];
    char message[1000];

    printf("\nEnter message: ");
    gets_s(message);

    printf("Message you wrote is: %s\n", message);

    // Send a message.
    if (send(ConnectSocket, message, sizeof(message), 0) == SOCKET_ERROR)
    {
        printf("send() failed with error code: %d\n", WSAGetLastError());
    }

        printf("Message successfully sent to server.");

    // Receive a message. 
    if (recv(ConnectSocket, receiveBuffer, 1000, 0) == SOCKET_ERROR)
    {
       printf("recv() failed with error code: %d\n", WSAGetLastError());
       while(1);
    }

    printf("\nServer says:");
    printf(receiveBuffer,sizeof(receiveBuffer));

  while(1);

closesocket(ConnectSocket);
WSACleanup();

return 0;
}

server:

#ifndef UNICODE
#define UNICODE
#endif

#define WIN32_LEAN_AND_MEAN

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>

// Need to link with Ws2_32.lib
#pragma comment(lib, "ws2_32.lib")

int wmain()
{
    // Initialize Winsock.
    WSADATA wsaData;
    int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != NO_ERROR) {
        printf("WSAStartup() failed with error: %d\n", iResult);
        return 1;
    }

    // Create a socket for connecting to client.
    SOCKET ConnectSocket;
    ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (ConnectSocket == INVALID_SOCKET) {
        printf("socket() failed with error: %ld\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }
    printf("Socket descriptor: %d\n", ConnectSocket);

    // The sockaddr_in structure specifies the address family,
    // IP address, and port of the server to be connected to.
    sockaddr_in Service;
    memset(&Service, 0, sizeof(Service));
    Service.sin_family = AF_INET;
    Service.sin_addr.s_addr = inet_addr("127.0.0.1");
    Service.sin_port = htons(27015);

    //Bind.
    if (bind(ConnectSocket, (struct sockaddr *)&Service, sizeof(Service)) == SOCKET_ERROR)
    {
        printf("Bind failed with error code: %d\n" , WSAGetLastError());
    }
    printf("Bind done.\n");

    // Listen on the socket for a client.
    if (listen(ConnectSocket, 1) ==  SOCKET_ERROR)
    {
        printf ("listen() failed with error: %ld\n", WSAGetLastError() );
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }
    printf("listen() run successfully.\n");

    // Accept a connection from a client.
    SOCKET acceptSocket;
    acceptSocket = accept(ConnectSocket, NULL, NULL);
    if (acceptSocket == INVALID_SOCKET) {
        printf("accept() failed with error: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }
    else{
        printf("accept() run successfully.\n");
    }

    // No longer need server socket.
    closesocket(ConnectSocket);

    char receiveBuffer[1000];
    int recv_len;

    printf("\nWaiting for data...\n");
    fflush(stdout);

    // Receive a message.
    if (recv_len = recv(ConnectSocket, receiveBuffer, 1000, 0) == SOCKET_ERROR)
    {
        printf("Socket descriptor, after recv(): %d\n", ConnectSocket);
        printf("recv() failed with error code: %d\n", WSAGetLastError());
        while(1);
    }
    // Send a message.
    if (send(ConnectSocket, receiveBuffer, recv_len, 0) == SOCKET_ERROR)
    {
        printf("sendto() failed with error code: %d\n", WSAGetLastError());
        while(1);
    }
    else
        printf("\nMessage sent back to client.");
    while(1);

closesocket(ConnectSocket);
WSACleanup();

return 0;
}

I am a beginner at Winsock programming and any help would be appreciated.

Answer 1

Error 10038 is WSAENOTSOCK, which means you do not have a valid socket. On the server side, you are using the server socket (ConnectSocket) after you have closed it. To receive and send, you need to use the connected socket (acceptSocket) instead. Also, you need to close acceptSocket when you are done with it, do not close ConnectSocket a second time.