krb5_net_read(), krb5_net_write() nad krb5_storage_from_fd() should accept both sockets and fds

When a socket and a file descriptor aren't interchangeable, these
functions should be able to determine whether it has received one or
the other and act accordingly.

This assumes that a fd can be cast into a SOCKET.

lib/krb5/net_read.c

@@ -41,5 +41,19 @@ krb5_net_read (krb5_context context,
 {
     SOCKET fd = *((SOCKET *)p_fd);
 
+#ifdef SOCKET_IS_NOT_AN_FD
+#ifdef _MSC_VER
+    {
+	HANDLE h = _get_osfhandle(fd);
+
+	if (h != INVALID_HANDLE_VALUE) {
+	    return net_read (fd, buf, len);
+	}
+    }
+#else
+#error Don't know how to handle socket that may be an fd
+#endif
+#endif
+
     return net_read_s (fd, buf, len);
 }

lib/krb5/net_write.c

@@ -41,6 +41,20 @@ krb5_net_write (krb5_context context,
 {
     SOCKET fd = *((SOCKET *)p_fd);
 
+#ifdef SOCKET_IS_NOT_AN_FD
+#ifdef _MSC_VER
+    {
+	HANDLE h = _get_osfhandle(fd);
+
+	if (h != INVALID_HANDLE_VALUE) {
+	    return net_write (fd, buf, len);
+	}
+    }
+#else
+#error Don't know how to handle SOCKET that may be an fd
+#endif
+#endif
+
     return net_write_s (fd, buf, len);
 }
 

lib/krb5/store_fd.c

@@ -86,11 +86,25 @@ fd_free(krb5_storage * sp)
  */
 
 KRB5_LIB_FUNCTION krb5_storage * KRB5_LIB_CALL
-krb5_storage_from_fd(int fd)
+krb5_storage_from_fd(SOCKET fd_in)
 {
     krb5_storage *sp;
+    int fd;
+
+#ifdef SOCKET_IS_NOT_AN_FD
+#ifdef _MSC_VER
+    if (_get_osfhandle(fd_in) != -1) {
+	fd = dup(fd_in);
+    } else {
+	fd = _open_osfhandle(fd_in, 0);
+    }
+#else
+#error Don't know how to deal with fd that may or may not be a socket.
+#endif
+#else  /* SOCKET_IS_NOT_AN_FD */
+    fd = dup(fd_in);
+#endif
 
-    fd = dup(fd);
     if (fd < 0)
 	return NULL;