Contents

Introduction
Architecture
On to WinSock
The Basics
Socket Types
Error Checking
The price you
pay...
Rock, Paper,
Scissor, Shoot!
How to use
the demo
A word on lag
Conclusion

Demo
Printable version

Error checking (yuck)

Error checking is very annoying, but it is necessary in a commercial game. Remember that commercial software should be fool-proof and that means a hell of a lot of error checking. How do I check for errors? Most WinSock functions return an int. As a general rule, it is good to say:


if (function(…) == SOCKET_ERROR)
{
  cout << "Error!\n";
  WSACleanup ();
  return;
}

Functions that create or accept sockets usually won't return SOCKET_ERROR, but will return INVALID_SOCKET.

That was basic error checking… Here is the hard part. After SOCKET_ERROR or INVALID_SOCKET, and application should call int WSAGetLastError ( void ). WSAGetLastError will return an error code.

WinSock error codes taken from WSAPI22.DOC:

WinSock code Berkeley equivalent Error Interpretation

WSAEINTR EINTR 10004 As in standard C

WSAEBADF EBADF 10009 As in standard C

WSAEACCES EACCES 10013 As in standard C

WSAEFAULT EFAULT 10014 As in standard C

WSAEINVAL EINVAL 10022 As in standard C

WSAEMFILE EMFILE 10024 As in standard C

WSAEWOULDBLOCK EWOULDBLOCK 10035 As in BSD

WSAEINPROGRESS EINPROGRESS 10036 This error is returned if any WinSock function is called while a blocking function is in progress.

WSAEALREADY EALREADY 10037 As in BSD

WSAENOTSOCK ENOTSOCK 10038 As in BSD

WSAEDESTADDRREQ EDESTADDRREQ 10039 As in BSD

WSAEMSGSIZE EMSGSIZE 10040 As in BSD

WSAEPROTOTYPE EPROTOTYPE 10041 As in BSD

WSAENOPROTOOPT ENOPROTOOPT 10042 As in BSD

WSAEPROTONOSUPPORT EPROTONOSUPPORT 10043 As in BSD

WSAESOCKTNOSUPPORT ESOCKTNOSUPPORT 10044 As in BSD

WSAEOPNOTSUPP EOPNOTSUPP 10045 As in BSD

WSAEPFNOSUPPORT EPFNOSUPPORT 10046 As in BSD

WSAEAFNOSUPPORT EAFNOSUPPORT 10047 As in BSD

WSAEADDRINUSE EADDRINUSE 10048 As in BSD

WSAEADDRNOTAVAIL EADDRNOTAVAIL 10049 As in BSD

WSAENETDOWN ENETDOWN 10050 As in BSD. This error may be reported at any time if the WinSock implementation detects an underlying failure.

WSAENETUNREACH
ENETUNREACH
10051 As in BSD

WSAENETRESET ENETRESET 10052 As in BSD

WSAECONNABORTED ECONNABORTED 10053
As in BSD

WSAECONNRESET ECONNRESET 10054 As in BSD

WSAENOBUFS ENOBUFS 10055 As in BSD

WSAEISCONN EISCONN 10056 As in BSD

WSAENOTCONN ENOTCONN 10057 As in BSD

WSAESHUTDOWN ESHUTDOWN 10058 As in BSD

WSAETOOMANYREFS ETOOMANYREFS 10059 As in BSD

WSAETIMEDOUT ETIMEDOUT 10060 As in BSD

WSAECONNREFUSED ECONNREFUSED 10061 As in BSD

WSAELOOP ELOOP 10062 As in BSD

WSAENAMETOOLONG ENAMETOOLONG 10063 As in BSD

WSAEHOSTDOWN EHOSTDOWN 10064 As in BSD

WSAEHOSTUNREACH EHOSTUNREACH 10065 As in BSD

Missing 10066 thru 10071

WSASYSNOTREADY 10091 Returned by WSAStartup() indicating that the network subsystem is unusable.

WSAVERNOTSUPPORTED 10092 Returned by WSAStartup() indicating that the WinSock DLL cannot support this app.

WSANOTINITIALISED 10093 Returned by any function except WSAStartup() indicating that a successful WSAStartup() has not yet been performed.

WSAEDISCON 100101 Returned by WSARecv(), WSARecvFrom() to indicate the remote party has initiated a graceful shutdown sequence.

Missing 10102 thru 10112

WSA_OPERATION_ABORTED * An overlapped operation has been canceled due to the closure of the socket, or the execution of the SIO_FLUSH command in WSAIoctl()

WSAHOST_NOT_FOUND HOST_NOT_FOUND 11001 As in BSD.

WSATRY_AGAIN TRY_AGAIN 11002 As in BSD

WSANO_RECOVERY NO_RECOVERY 11003 As in BSD

WSANO_DATA NO_DATA 11004 As in BSD

To find detailed descriptions of error codes, look at WSAPI22.DOC (Microsoft's WinSock 2.2 API reference). So our fool-proof version looks like this:


if (function(…) == SOCKET_ERROR)
{
  cout << "Error:\n";
  switch (WSAGetLastError ())
  {
    case …:
      cout << "this type of error happened!\n";
      break;
    case …
  }
  WSACleanup ();
  cout << "If this error happens again, sue Microsoft!\n";
  return;
}

I know it is a real pain in the neck to do all that error checking, but it is necessary.

Next : The price you pay for using asynchronous sockets