[libmicrohttpd] Sockets on Windows

[Michael Lenaghan]

Christian, the following code (from MHD_start_daemon_va) is wrong for Windows:

    socket_fd = SOCKET (PF_INET, SOCK_STREAM, 0);
  if (socket_fd < 0)
    {
#if HAVE_MESSAGES
      if ((options & MHD_USE_DEBUG) != 0)
        FPRINTF (stderr, "Call to socket failed: %s\n", STRERROR (errno));
#endif
      free (retVal);
      return NULL;
    }
  if (socket_fd >= FD_SETSIZE)
    {
#if HAVE_MESSAGES
      if ((options & MHD_USE_DEBUG) != 0)
        FPRINTF (stderr,
                 "Socket descriptor larger than FD_SETSIZE: %d > %d\n",
                 socket_fd,
                 FD_SETSIZE);

On Windows socket() returns a value of type SOCKET:

WINSOCK_API_LINKAGE
SOCKET
WSAAPI
socket(
    IN int af,
    IN int type,
    IN int protocol
    );

SOCKET isn't a signed int--it's a pointer-sized unsigned int:

typedef UINT_PTR        SOCKET;

Here's the description of UINT_PTR:

// The INT_PTR is guaranteed to be the same size as a pointer.  Its
// size with change with pointer size (32/64).  It should be used
// anywhere that a pointer is cast to an integer type. UINT_PTR is
// the unsigned variation.

fd_set is an array of these values:

typedef struct fd_set {
        u_int   fd_count;               /* how many are SET? */
        SOCKET  fd_array[FD_SETSIZE];   /* an array of SOCKETs */
} fd_set;

FD_SET() simply fills the next available slot in the array:

#define FD_SET(fd, set) do { \
    if (((fd_set FAR *)(set))->fd_count < FD_SETSIZE) \
        ((fd_set FAR *)(set))->fd_array[((fd_set FAR
*)(set))->fd_count++]=(fd);\
} while(0)

And select() ignores its first parameter.

So on Windows:

 * You should only test socket fds against INVALID_SOCKET

 * You shouldn't check socket fds against FD_SETSIZE

 * You should check the total number of sockets being select()ed
against FD_SETSIZE