Multiple connections from same host cause socket disconnection issues - c++

Question

I'm writting a C++ app for Linux. It uses sockets for TCP communication. I read data from remote hosts as follows (a bit simplified for this topic's needs):
Packet Connection::receiveRawData()
{
int length = recv(socketDescriptor, receiveBuffer, MAXBUF, 0);
if(length < 0)
{
std::cout << getConnectionDetails() << " - nothing to read.\n";
return Packet(); //Empty packet object (with no data)
}
else if(length == 0)
{
std::cout << getConnectionDetails() << " - disconnected suddenly!\n";
//Do something about this closed connection
}
return Packet(receiveBuffer, length);
}
getConnectionDetails() shows me adress and port number (like this: xx.xx.xx.xx:yy) so I would know that the message is about specific connection (since even if they're from same host they'll still have different port numbers). Couts are just for debuging purpose.
The thing is, it doesn't work quite well when I close one of the connections from the same host (ie. after making three different connection to the application, but all of them come from same machine). Only when I close them in reversed order (from newest to oldest) it works as expected - it shows "xx.xx.xx.xx:yy - disconnected suddenly!" in app's console. But when I try from oldest to newest, I keep getting "xx.xx.xx.xx:yy - nothing to read." for every connection, even though these connections should be closed!
What's going on? recv() is supposed to return 0 when remote host closed its connection, so why doesn't it happen when I close connection (from the remote host side) from oldest or even from the "middle" (neither oldest nor newest)?
It doesn't occur when I close connections from different machines (so that no machine makes more than one connection to the app) - order of these operations don't matter then, it just works fine as it should.
Edit: some more code so you can see how I set up connection sockets:
//Create "empty" socket object associated with the given port number
Connection::Connection(PortNumberFormat portNum)
: address(), port(portNum), socketDescriptor(socket(AF_INET, SOCK_STREAM, 0)), isConnected(false), isListening(false), isShuttingDown(false)
{
if(socketDescriptor < 0)
throw std::string("Fatal error: cannot create socket! The error was: " + std::string( strerror(errno) ));
}
//Create socket object using specified socket descriptor and mark it as connected to the server
//available on specified address and port
Connection::Connection(SocketDescriptor sock, char *addr, PortNumberFormat portNum)
: address(addr), port(portNum), socketDescriptor(sock), isConnected(true), isListening(false), isShuttingDown(false)
{
setTimeouts();
}
Connection::~Connection()
{
if(socketDescriptor < 0) return;
if(!isShuttingDown) signalShutdown();
close(socketDescriptor);
}
//Turn socket into listening mode by binding it to the specified port
void Connection::startListen()
{
if(isConnected || isListening || socketDescriptor < 0)
throw std::string("Socket can not be set as listening!");
struct sockaddr_in bindData;
int dummy = 1;
memset(&bindData, 0, sizeof(bindData));
bindData.sin_family = AF_INET;
bindData.sin_addr.s_addr = INADDR_ANY;
bindData.sin_port = htons(port);
setsockopt(socketDescriptor, SOL_SOCKET, SO_REUSEADDR, &dummy, sizeof(dummy)); //Release socket ASAP on closing
if(bind(socketDescriptor, (struct sockaddr*)&bindData, sizeof(bindData)) < 0)
throw std::string("Fatal error: cannot bind socket for listening! The error was: " + std::string( strerror(errno) ));
if(listen(socketDescriptor, MAXCONN) < 0)
throw std::string("Fatal error: cannot listen on bound socket! The error was: " + std::string( strerror(errno) ));
isListening = true;
}
//Get new Connection object that represents external client connection
//This method will block until client connects or the socket shutdown occurs
Connection Connection::getClientConnection()
{
if(!isListening || socketDescriptor < 0)
throw std::string("Can't get connection from non-listening socket!");
struct sockaddr_in clientData;
socklen_t len = sizeof(clientData);
SocketDescriptor clientSocket = accept(socketDescriptor, (struct sockaddr*)&clientData, &len);
if(isShuttingDown) //An shutdown occured
{
if(clientSocket < 0)
throw std::string("Information: listening connection is shutting down peacefully.");
//Else...
close(clientSocket); //Just to be extra sure
throw std::string("Warning: listening connection is shutting down. Client connection has been discarded.");
}
if(clientSocket < 0)
throw std::string("Fatal error: cannot open client connection socket! The error was: " + std::string( strerror(errno) ));
return Connection(clientSocket, inet_ntoa(clientData.sin_addr), ntohs(clientData.sin_port));
}
//Invalidates socket and prepares it to be closed
void Connection::signalShutdown()
{
if(socketDescriptor < 0) return;
isShuttingDown = true;
shutdown(socketDescriptor, SHUT_RDWR);
}
inline void Connection::setTimeouts()
{
struct timeval timeout;
timeout.tv_sec = 2;
timeout.tv_usec = 0;
if(setsockopt(socketDescriptor, SOL_SOCKET, SO_RCVTIMEO, (void*)&timeout, sizeof(timeout)) < 0
|| setsockopt(socketDescriptor, SOL_SOCKET, SO_SNDTIMEO, (void*)&timeout, sizeof(timeout)) < 0)
{
//Do something about it
}
}
std::string Connection::getConnectionDetails()
{
return std::string(address + ":" + std::to_string(port));
}
Listening connection is created using first constructor (port number only), then I call startListen() on it. Connections from hosts are returned to external code with getClientConnection() method (they are created using second constructor). Now these are our troublemakers.