Sockets program

I have to send data over the internet and I have a working windows sockets program that does it but after like sending a command about 50 times or so, the link goes bad and I cant send any more data. I think a buffer of some sort is filling up but I dont know how to empty it.


Thank you.

please post what you think is the offending code.

Is the other end reading the data off OK?

As Draco said, posting code is always useful when asking questions about it, preferably along with the error messages you're receiving.

Here is the server side of my sockets program.

Code:

---

// winsock for our network communication
#include <winsock2.h>
// stdio for I/O
#include <stdio.h>
#include <iostream.h>
#include <time.h>

// -----------------------------------------------------------------------------------
// startupServerForListening() - will return us a socket that is bound to the
// port we specify, and is listening for connections if all operations succeeded,
// and a -1 if startup failed.
int startupServerForListening(unsigned short port);

// -----------------------------------------------------------------------------------
// shutdownServer() - will take the socket we specify and shutdown the
// network utilities we started with startupServerForListening()
// Note: In order to function properly, the socket passed in MUST be the
// socket created by the startupServerForListening() function
void shutdownServer(int socket);

void main()
{


        // the socket my server will use for listening
        int serverSocket;

        // startup our server utilities with my handy function
        serverSocket = startupServerForListening(7654);

        // check for errors
        if (serverSocket == -1)
        {
                printf("Network Startup Failed!\nProgram Terminating\n");
                return;
        }

        // accept a client
        int clientSocket;
        clientSocket = accept(serverSocket, 0, 0);

        // check for errors
        if (clientSocket == SOCKET_ERROR)
        {
                printf("Accept Failed!\n");
        }

        int nBytes;
        // message size so we will know how much data we will send and receive
        #define MESSAGE_SIZE 2
        char inMessage[MESSAGE_SIZE];
        // receive at MAX sizeof(inMessage) bytes into inMessage from the client using clientSocket
        nBytes = recv(clientSocket, inMessage, sizeof(inMessage), 0);

        // check for errors
        if (nBytes == SOCKET_ERROR)
        {
                printf("Recv Failed!\n");
        }
        else
        {
                cout<<"Command received"<<endl;
                cout<<"Command is: "<<inMessage<<endl;
               
        }
        //and shutting down our network.
        if (inMessage[MESSAGE_SIZE] = 0)
        {
                // close our client socket
                closesocket(clientSocket);

                // and shutdown our network
                shutdownServer(serverSocket);

                printf("Press any key to continue ...\n");
                getchar();
        }
}

// -----------------------------------------------------------------------------------
// startupServerForListening() - a function to startup winsock, and open a socket for listening

int startupServerForListening(unsigned short port) {

        // the winsock data structure
        WSAData wsaData;

        // startup winsock
        if (WSAStartup(MAKEWORD(2, 2), &wsaData) == SOCKET_ERROR) {
                printf("Could Not Start Up Winsock!\n");
                return -1;
        }

        // create  socket
        int mySocket = socket(AF_INET, SOCK_STREAM, 0);

        // make sure nothing bad happened
        if (mySocket == SOCKET_ERROR) {
                printf("Error Opening Socket!\n");
                return -1;
        }

        // the address structure
        struct sockaddr_in server;

        // fill the address structure with appropriate data
        server.sin_family = AF_INET;
        server.sin_port = htons(port);
        server.sin_addr.s_addr = INADDR_ANY;

        // and now bind my socket
        if (bind(mySocket, (sockaddr*)&server, sizeof(server)) == SOCKET_ERROR) {
                printf("Bind Failed!\n");
                closesocket(mySocket);
                return -1;
        }

        // mark socket for listening
        if (listen(mySocket, 5) == SOCKET_ERROR) {
                printf("Listen Failed!\n");
                closesocket(mySocket);
                return -1;
        }

        printf("Server Started\n");

        return mySocket;
}

// -----------------------------------------------------------------------------------
// shutdownServer() - a function to shutdown a socket and clean up winsock

void shutdownServer(int socket) {
        // close our socket
        closesocket(socket);

        // shut down winsock
        WSACleanup();

        printf("Server Shutdown\n");
}

---

> #include <stdio.h>
> #include <iostream.h>
Choose C or C++, not some horrible mix
Like why call printf() and cout ?

> void main()
See avatar - void main bad, int main good

> nBytes = recv(clientSocket, inMessage, sizeof(inMessage), 0);
This doesn't append a \0 for you to make it a printable string

Code:

---

        nBytes = recv(clientSocket, inMessage, sizeof(inMessage)-1, 0);
        // check for errors
        if (nBytes == SOCKET_ERROR)
        {
                printf("Recv Failed!\n");
        }
        else
        {
                inMessage[nBytes] = '\0';  // make it a string
                cout<<"Command received"<<endl;
                cout<<"Command is: "<<inMessage<<endl;
               
        }

---

> if (inMessage[MESSAGE_SIZE] = 0)
1. this is an assignment, you meant comparison, which is ==
2. it is also an out of bounds access - the indices of an array run from 0 to N-1

>>This doesn't append a \0 for you to make it a printable string
.. and to highlight to the OP, one call to recv() doesn't guarantee you'll get one "string" of data, you might only get a partial string. Or, if the other end has sent two strings in succession, one call to recv() might get you:

• part of the first string only
• all of the first string
• all of the first string, plus part of the second
• all of the first string and all of the second
• an error

Your app should be able to cater for all of the above, calling recv() multiple times where appropriate, and manipulating the data buffer correctly.


(maybe your code does this, I haven't read it through)