socket: use INVALID_SOCKET

* Replace "fd = -1" with "fd = INVALID_SOCKET"
* Replace "fd < 0" with "fd == INVALID_SOCKET": SOCKET_T is unsigned on Windows

Bug found by Pavel Belikov ("Fragment N1"):
http://www.viva64.com/en/b/0414/#ID0ECDAE

Modules/_ssl.c

@@ -113,6 +113,10 @@ struct py_ssl_library_code {
 # define HAVE_ALPN
 #endif
 
+#ifndef INVALID_SOCKET /* MS defines this */
+#define INVALID_SOCKET (-1)
+#endif
+
 enum py_ssl_error {
     /* these mirror ssl.h */
     PY_SSL_ERROR_NONE,
@@ -1699,7 +1703,7 @@ PySSL_select(PySocketSockObject *s, int writing, _PyTime_t timeout)
     }
 
     /* Guard against closed socket */
-    if (s->sock_fd < 0)
+    if (s->sock_fd == INVALID_SOCKET)
         return SOCKET_HAS_BEEN_CLOSED;
 
     /* Prefer poll, if available, since you can poll() any fd
@@ -2023,7 +2027,7 @@ _ssl__SSLSocket_shutdown_impl(PySSLSocket *self)
 
     if (sock != NULL) {
         /* Guard against closed socket */
-        if ((((PyObject*)sock) == Py_None) || (sock->sock_fd < 0)) {
+        if ((((PyObject*)sock) == Py_None) || (sock->sock_fd == INVALID_SOCKET)) {
             _setSSLError("Underlying socket connection gone",
                          PY_SSL_ERROR_NO_SOCKET, __FILE__, __LINE__);
             return NULL;

Modules/socketmodule.c

@@ -2568,8 +2568,9 @@ sock_close(PySocketSockObject *s)
      * and http://linux.derkeiler.com/Mailing-Lists/Kernel/2005-09/3000.html
      * for more details.
      */
-    if ((fd = s->sock_fd) != -1) {
-        s->sock_fd = -1;
+    fd = s->sock_fd;
+    if (fd != INVALID_SOCKET) {
+        s->sock_fd = INVALID_SOCKET;
         Py_BEGIN_ALLOW_THREADS
         (void) SOCKETCLOSE(fd);
         Py_END_ALLOW_THREADS
@@ -2587,7 +2588,7 @@ static PyObject *
 sock_detach(PySocketSockObject *s)
 {
     SOCKET_T fd = s->sock_fd;
-    s->sock_fd = -1;
+    s->sock_fd = INVALID_SOCKET;
     return PyLong_FromSocket_t(fd);
 }
 
@@ -4165,7 +4166,7 @@ static PyGetSetDef sock_getsetlist[] = {
 static void
 sock_dealloc(PySocketSockObject *s)
 {
-    if (s->sock_fd != -1) {
+    if (s->sock_fd != INVALID_SOCKET) {
         PyObject *exc, *val, *tb;
         Py_ssize_t old_refcount = Py_REFCNT(s);
         ++Py_REFCNT(s);
@@ -4221,7 +4222,7 @@ sock_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 
     new = type->tp_alloc(type, 0);
     if (new != NULL) {
-        ((PySocketSockObject *)new)->sock_fd = -1;
+        ((PySocketSockObject *)new)->sock_fd = INVALID_SOCKET;
         ((PySocketSockObject *)new)->sock_timeout = _PyTime_FromSeconds(-1);
         ((PySocketSockObject *)new)->errorhandler = &set_error;
     }