server: Don't block when reading from named pipes in PIPE_NOWAIT mode.

dlls/kernel32/tests/pipe.c

@@ -3910,7 +3910,7 @@ static void test_nowait(void)
     ol.hEvent = CreateEventW(NULL, TRUE, FALSE, NULL);
     SetLastError(0xdeadbeef);
     ok(ReadFile(piperead, readbuf, sizeof(readbuf), &read, &ol) == FALSE, "ReadFile should fail\n");
-    todo_wine ok(GetLastError() == ERROR_NO_DATA, "got %d should be ERROR_NO_DATA\n", GetLastError());
+    ok(GetLastError() == ERROR_NO_DATA, "got %d should be ERROR_NO_DATA\n", GetLastError());
     if (GetLastError() == ERROR_IO_PENDING)
         CancelIo(piperead);
 

server/named_pipe.c

@@ -851,6 +851,11 @@ static int pipe_end_read( struct fd *fd, struct async *async, file_pos_t pos )
     switch (pipe_end->state)
     {
     case FILE_PIPE_CONNECTED_STATE:
+        if ((pipe_end->flags & NAMED_PIPE_NONBLOCKING_MODE) && list_empty( &pipe_end->message_queue ))
+        {
+            set_error( STATUS_PIPE_EMPTY );
+            return 0;
+        }
         break;
     case FILE_PIPE_DISCONNECTED_STATE:
         set_error( STATUS_PIPE_DISCONNECTED );