Question

I’m having some strange things happen with my program, and I’m not sure what I should be doing. This is a pseudocode version of what my code looks like so far:

Server:

//Set up Server sockets

int maximum;

// Collect the maximum
cout << "\nEnter a Maximum:";
cin >> maximum;
cout << "\n";

int *array = new int[maximum + 1];

memset(array, 0, sizeof(array));

while(array[0] < anInt){

    //receive the array from the client
    if(recv(newsockfd, array, maximum, 0) < 0){
        perror("ERROR receiving from socket");
    }

    mathFunction(array);  //A function that alters the contents of array
    array[0]++;

    //If array[0] isn't too big
    if(array[0] < anInt){
        // Send the array to the client
        if(send(newsockfd, array, maximum, 0) < 0){
            perror("ERROR sending to socket");
        }
    }
}

Client:

//Set up Client sockets

//The maximum was already sent over earlier
int *array = new int[maximum + 1];

while(array[0] < anInt){

    //receive the array from the server
    if(recv(sockfd, array, maximum, 0) < 0){
        perror("ERROR receiving from socket");
    }

    mathFunction(array);  //A function that alters the contents of array
    array[0]++;

    if(send(sockfd, array, maximum, 0) < 0){
        perror("ERROR sending to socket");
    }
}

My problem is that I keep getting a “Connection reset by peer” error, which leads to a Segmentation Fault, crashing my program. Also, when playing around with the 3rd argument of the send/recv functions (currently set as maximum), my program acts differently. It will actually work perfectly if the user enters a maximum of 100, but anything more than that screws it up.

I know this is a long shot, but can anyone see something that I’m doing wrong?

Answer 1

First of all code that posted by you has a logical error:

Server first receive data from the client, do something with it and then send its result back to the client.

In the other side client also receive data from server, do something with it and then send it back to the server.

And that’s obviously a race condition, no one send data to other side to begin communication.

Beside that logical error you have some C++ errors:

1) memset(array, 0, sizeof(array)) only 0 initialize sizeof(int*) bytes from your array not entire array, since sizeof(array) is always sizeof(int*) if you want to 0 initialize entire array (and I think you want it) you should call:

memset(array, 0, (maximum + 1) * sizeof(int));

or even better:

std::fill( array, array + maximum + 1, 0 );

And in C++ it is much better to use classes like std::vector instead of raw pointers:

std::vector<int> array( maximum + 1 ); // automatically initialize to 0

2) Your array type is int* and send/recv count its input by byte, so if you want to send/recv entire array you must have something like:

send(sockfd, (char*)array, maximum * sizeof(int), 0);

3) You should check return value of send/recv, specially recv since it may recv less data in each call, for example you send 8K data and recv only receive first 1K and rest of it remain in the network buffer, so you should call it repeatedly until you read your buffer completely.