Why is my c++ Winsock server unable to receive data from the client?

Question

I tried to run a simple client and server program. Therin, I tried to send the server a message from the client and have the server echo that message back. The problem is that every time I do I get a 10057 error. I have no idea why.

Here is the Server code

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

#define MYBUFSIZE   128


void shutdown_close(SOCKET s)
{

    // Tell the operating system the socket is
    // about to be closed   
    shutdown(s, SD_BOTH); 

    // close the socket….
    closesocket(s); 
}

void shutdown_close_and_exit(SOCKET s)
{
    shutdown_close(s);
    exit(1);
}

void main(int argc, char *argv[])
{
    SOCKET srvr_socket;
    struct sockaddr_in srvr_addr;
    struct sockaddr_in clnt_addr; // Client address
    int addr_len = 0;
    WSADATA wsaData;
    char recv_buf[MYBUFSIZE];
    int recv_msg_len;
    short portnum;


    if (argc == 2)
    {
        portnum = atoi(argv[1]);
        printf("Setting port number to %d\n", portnum);

    } else
    {
        fprintf(stderr, "Usage: %s port_num_to_listen_at\n",
                argv[0]);
        exit(1);
    }

    // Init Winsock
    if (WSAStartup(MAKEWORD(2, 0), &wsaData) != 0)
    {
        fprintf(stderr, "Error: WSAStartup() failed");
        exit(1);
    }

    // Create UDP datagram socket for incoming connections
    if ((srvr_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: socket() failed with error %d\n", WSAGetLastError());
        shutdown_close_and_exit(srvr_socket);
    }

    // Construct local address structure
    memset(&srvr_addr, 0, sizeof(srvr_addr));
    srvr_addr.sin_family = AF_INET;
    srvr_addr.sin_addr.s_addr = inet_addr("127.0.0.1");  // Accept messages on any network interface.
    srvr_addr.sin_port = htons(portnum);     // Bind the port number specified on the command line.

    /* Bind to the local address */
    if (bind(srvr_socket, (struct sockaddr *) &srvr_addr, sizeof(srvr_addr)) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: socket() failed with error %d", WSAGetLastError());
        shutdown_close_and_exit(srvr_socket);
    }

    listen(srvr_socket, SOMAXCONN);

    // Loop forever
    for (;;)
    {
        // Set the size of the in-out parameter, where the client address
        // and port number will be stored by the OS
        addr_len = sizeof(clnt_addr);

        if(accept(srvr_socket,(SOCKADDR *) &srvr_addr, &addr_len) == SOCKET_ERROR)
        {
            fprintf(stderr, "Error: accept() failed with error %d\n", WSAGetLastError());
            shutdown_close_and_exit(srvr_socket);
        }

        // Receive message from client
        if ((recv_msg_len = recvfrom(srvr_socket, recv_buf, MYBUFSIZE, 0,
            (struct sockaddr *) &clnt_addr, &addr_len )) == SOCKET_ERROR) {

            fprintf(stderr, "Error: recvfrom() failed with error %d\n", WSAGetLastError());
            shutdown_close_and_exit(srvr_socket);
        } else {
            printf("Received message of size %d: %s\n from client %s:%d\n", 
                    recv_msg_len, recv_buf, inet_ntoa(clnt_addr.sin_addr),
                    ntohs(clnt_addr.sin_port));
        }


        // 'echo' message back to client
        if ((recv_msg_len = sendto(srvr_socket, recv_buf, recv_msg_len, 0,
            (struct sockaddr *) &clnt_addr, addr_len )) == SOCKET_ERROR) {

            fprintf(stderr, "Error: sendto() failed with error %d\n", WSAGetLastError());
            shutdown_close_and_exit(srvr_socket);
        } else {
            printf("Echo'd message %s to client %s:%d\n", 
                    recv_buf, inet_ntoa(clnt_addr.sin_addr),
                    ntohs(clnt_addr.sin_port));
        }
    }
}

and here is the client code:

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

#define BUFSIZE 128  /* Size of receive buffer */


void shutdown_close(SOCKET s)
{

    // Tell the operating system the socket is
    // about to be closed   
    shutdown(s, SD_BOTH); 

    // close the socket….
    closesocket(s); 
}

void shutdown_close_and_exit(SOCKET s)
{
    shutdown_close(s);
    exit(1);
}

void main(int argc, char *argv[])
{
    SOCKET servSock;
    struct sockaddr_in srvr_addr;
    struct sockaddr_in recv_addr;
    int addr_len = 0; 
    WSADATA wsaData;
    char mesg_buf[BUFSIZE];
    char *mesg_to_send;
    long server_IP;
    short portnum;


    if (argc == 4)
    {
        portnum = atoi(argv[1]);
        printf("Setting port number to %d\n", portnum);

        server_IP = inet_addr(argv[2]);
        printf("Target server IP address is %s\n", argv[2]);

        mesg_to_send = argv[3];

    } else
    {
        fprintf(stderr, "Usage: %s server_port_num server_IP_address message_to_send\n",
                argv[0]);
        exit(1);
    }

    // Init Winsock
    if (WSAStartup(MAKEWORD(2, 0), &wsaData) != 0)
    {
        fprintf(stderr, "Error: WSAStartup() failed with error %d\n", WSAGetLastError());
        exit(1);
    }

    // Create socket for incoming connections
    if ((servSock = socket(AF_INET,SOCK_STREAM, IPPROTO_TCP)) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: socket() failed with error %d\n", WSAGetLastError());
        shutdown_close_and_exit(servSock);
    }

    // Construct local address structure
    // with server address.  This is like
    // addressing the envelope of a letter.
    memset(&srvr_addr, 0, sizeof(srvr_addr));
    srvr_addr.sin_family = AF_INET;
    srvr_addr.sin_addr.s_addr = server_IP;
    srvr_addr.sin_port = htons(portnum);

    if ( connect(servSock, (SOCKADDR*) &srvr_addr, sizeof(srvr_addr)) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: connect() failed with error %d\n", WSAGetLastError());
        shutdown_close_and_exit(servSock);
    }

    // Set the size of the in-out parameter
    addr_len = sizeof(recv_addr);

    if (sendto(servSock, mesg_to_send, strlen(mesg_to_send) + 1, 0,
                (sockaddr *) &srvr_addr, addr_len) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: sendto() failed with error %d\n", WSAGetLastError());
        shutdown_close_and_exit(servSock);
    }

    printf("Send message %s to server at %s:%d\n", argv[3], argv[2], portnum);

    // Sleep 1 full second to allow message  to get to server and be sent back...
    Sleep(1000);

    addr_len = sizeof(recv_addr);

    if (recvfrom(servSock, mesg_buf, BUFSIZE, 0,
                (sockaddr *) &recv_addr, &addr_len) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: recvfrom() failed with error %d\n", WSAGetLastError());
        shutdown_close_and_exit(servSock);
    }

    printf("Received message %s from %s:%d\n", mesg_buf, 
            inet_ntoa(recv_addr.sin_addr), ntohs(recv_addr.sin_port));

    // close socket gracefully
    shutdown_close(servSock);

}

Can anyone see anything wrong with the code?

score 1 · Answer 1 · answered May 17 '13 at 09:08

1

You should use recv for SOCK_STREAM sockets, not recvfrom.

(But that's a huge pile of code and no obvious indication of where the failure is, so there could be other problems besides.)

answered May 17 '13 at 09:08

RichieHindle

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And `send()` instead of `sendto()`. – Remy Lebeau May 17 '13 at 16:56

score 1 · Answer 2 · answered May 17 '13 at 16:59

1

Use send() instead of sendto(), and recv() instead of recvfrom(). Also, you are passing the wrong sockaddr_in to accept() on the server side.

answered May 17 '13 at 16:59

Remy Lebeau

555,201
31
458
770

score 0 · Answer 3 · answered May 17 '13 at 17:24

I figured out what was wrong. My server was never establishing a connection because I never established a connection with the accept function. In other words I was accepting a connection but not remembering it. I should have created a socket for accepting connections and set it equal to accept function like so :

Socket acceptSocket;

...

AcceptSocket = accept(srvr_socket,(SOCKADDR *) &clnt_addr, &addr_len) ;

        if(AcceptSocket == INVALID_SOCKET)
        {
            fprintf(stderr, "Error: accept() failed with error %d\n", WSAGetLastError());
            shutdown_close_and_exit(srvr_socket);
        }

Also I should have used recv() and send() instead of sendto() and recvfrom() like RichieHindle mentioned because they are designed for UDP connectionless sockets and not TCP connected sockets

score 0 · Answer 4 · edited Aug 27 '15 at 16:18

My Initial code segment when I was receiving error 10057 from the recvfrom() is as follows:

if (listen(s, SOMAXCONN) == SOCKET_ERROR) {
printf("Error in Listening .. ErroR Code: %d \n", WSAGetLastError());
exit(EXIT_FAILURE);
}
else
printf("Listening\n");

//Accept and incoming connection
puts("Waiting for incoming connections...");

c = sizeof(struct sockaddr_in);
new_socket = accept(s, (struct sockaddr *)&client, &c);

if (new_socket == INVALID_SOCKET)
{
printf("accept failed with error code : %d", WSAGetLastError());
return 1;
}
else
puts("Connection accepted");
recv_size = recvfrom(s , client_msg, sizeof(client_msg), 0,
(SOCKADDR *)&recv_from, &addrlen);

I was trying to receive data from the client on the same socket that I was listening i.e. "s" rather than the new socket I got the client connection accepted i.e."new_socket ".

    After making the following changes:
recv_size = recvfrom(new_socket , client_msg, sizeof(client_msg), 0, (SOCKADDR 
*)&recv_from, &addrlen);

I could receive data from the client application perfectly.

Why is my c++ Winsock server unable to receive data from the client?

4 Answers4