winsock select() function returning 0

Question

I am implementing a TFTP Client application in MFC. Below are two functions:

1) Connect to server function..

int TFTPClient::connectToServer() {

  cout << "Connecting to " << server_ip << " on port " << server_port <<  endl;

socket_descriptor = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

if (socket_descriptor == -1) {

    throw new ETFTPSocketCreate;

}

client_address.sin_family = AF_INET;
client_address.sin_port = htons(server_port);   //- taip pat turi buti ir serveryje!
client_address.sin_addr.s_addr = inet_addr(this->server_ip);

#ifdef WIN32
    //memset(client_address.sin_zero, 0, sizeof(client_address.sinzero);
    //- suvienodinam SOCKADDR_IN ir SOCKADDR strukturu dydzius
#endif

connection = connect(socket_descriptor, (const struct sockaddr  *)&client_address, sizeof(client_address));

if (connection != 0) {

    cout << "Unable to connect to an address\n";
    return -1;

}

DEBUGMSG("Successfully connected");

AfxMessageBox("Successfully connected");

return 1;

}

2) Wait for response...

int TFTPClient::waitForPacket(TFTP_Packet* packet, int timeout_ms) {

packet->clear();

fd_set fd_reader;         
timeval connection_timer; 

connection_timer.tv_sec = timeout_ms / 1000; // = 2
connection_timer.tv_usec = 0; 

FD_ZERO(&fd_reader);

FD_SET(socket_descriptor, &fd_reader);

int select_ready = select(socket_descriptor + 1, &fd_reader, NULL, NULL, &connection_timer);

if (select_ready == -1) {

#ifdef WIN32
    cout << "Error in select(), no: " << WSAGetLastError() << endl;
#else
    cout << "Error in select(): " << endl;
#endif

return TFTP_CLIENT_ERROR_SELECT;

} else if (select_ready == 0) {

    DEBUGMSG("Timeout");

    return TFTP_CLIENT_ERROR_TIMEOUT;

}



int receive_status;

receive_status = recv(socket_descriptor, (char*)packet->getData(), TFTP_PACKET_MAX_SIZE, 0);

if (receive_status == 0) {
    cout << "Connection was closed by server\n";
    return TFTP_CLIENT_ERROR_CONNECTION_CLOSED;
}

if (receive_status == SOCKET_ERROR) {
    DEBUGMSG("recv() error in waitForPackage()");
    return TFTP_CLIENT_ERROR_RECEIVE;
}



packet->setSize(receive_status);

return TFTP_CLIENT_ERROR_NO_ERROR;

}

The select function in function 2 returns 0 every time I run the application, which indicates a timeout. My question: Is there another way I can implement this whole function without using select()? or is this function necessary before I call recv? I am not sure why there is a timeout and I am aware that I only need to receive an ack from the server before sending the next data packet and loop until the file is fully transferred.

Answer 1

If you only have a single file descriptor to worry about and you want to wait indefinitely, don't bother with select. Just call recv, which will block until you get data.