Check the server for Xrandr support version

src/mss/linux.py

@@ -250,6 +250,7 @@ def _validate(retval: int, func: Any, args: tuple[Any, Any], /) -> tuple[Any, An
     "XGetWindowAttributes": ("xlib", [POINTER(Display), POINTER(XWindowAttributes), POINTER(XWindowAttributes)], c_int),
     "XOpenDisplay": ("xlib", [c_char_p], POINTER(Display)),
     "XQueryExtension": ("xlib", [POINTER(Display), c_char_p, POINTER(c_int), POINTER(c_int), POINTER(c_int)], c_uint),
+    "XRRQueryVersion": ("xrandr", [POINTER(Display), POINTER(c_int), POINTER(c_int)], c_int),
     "XRRFreeCrtcInfo": ("xrandr", [POINTER(XRRCrtcInfo)], c_void_p),
     "XRRFreeScreenResources": ("xrandr", [POINTER(XRRScreenResources)], c_void_p),
     "XRRGetCrtcInfo": ("xrandr", [POINTER(Display), POINTER(XRRScreenResources), c_long], POINTER(XRRCrtcInfo)),
@@ -388,6 +389,10 @@ def _monitors_impl(self) -> None:
         int_ = int
         xrandr = self.xrandr
 
+        xrandr_major = c_int(0)
+        xrandr_minor = c_int(0)
+        xrandr.XRRQueryVersion(display, xrandr_major, xrandr_minor)
+
         # All monitors
         gwa = XWindowAttributes()
         self.xlib.XGetWindowAttributes(display, self._handles.root, byref(gwa))
@@ -400,9 +405,11 @@ def _monitors_impl(self) -> None:
         # XRRGetScreenResources():        0.1755971429956844 s
         # XRRGetScreenResourcesCurrent(): 0.0039125580078689 s
         # The second is faster by a factor of 44! So try to use it first.
-        try:
+        # It doesn't query the monitors for updated information, but it does require the server to support
+        # RANDR 1.3.  We also make sure the client supports 1.3, by checking for the presence of the function.
+        if hasattr(xrandr, "XRRGetScreenResourcesCurrent") and (xrandr_major.value, xrandr_minor.value) >= (1, 3):
             mon = xrandr.XRRGetScreenResourcesCurrent(display, self._handles.drawable).contents
-        except AttributeError:
+        else:
             mon = xrandr.XRRGetScreenResources(display, self._handles.drawable).contents
 
         crtcs = mon.crtcs

src/tests/test_gnu_linux.py

@@ -4,7 +4,9 @@
 
 import platform
 from collections.abc import Generator
-from unittest.mock import Mock, patch
+from ctypes import CFUNCTYPE, POINTER, _Pointer, c_int
+from typing import Any
+from unittest.mock import Mock, NonCallableMock, patch
 
 import pytest
 
@@ -22,6 +24,14 @@
 DEPTH = 24
 
 
+def spy_and_patch(monkeypatch: pytest.MonkeyPatch, obj: Any, name: str) -> Mock:
+    """Replace obj.name with a call-through mock and return the mock."""
+    real = getattr(obj, name)
+    spy = Mock(wraps=real)
+    monkeypatch.setattr(obj, name, spy, raising=False)
+    return spy
+
+
 @pytest.fixture
 def display() -> Generator:
     with pyvirtualdisplay.Display(size=(WIDTH, HEIGHT), color_depth=DEPTH) as vdisplay:
@@ -133,20 +143,70 @@ def test__is_extension_enabled_unknown_name(display: str) -> None:
         assert not sct._is_extension_enabled("NOEXT")
 
 
-def test_missing_fast_function_for_monitor_details_retrieval(display: str) -> None:
+def test_fast_function_for_monitor_details_retrieval(display: str, monkeypatch: pytest.MonkeyPatch) -> None:
     with mss.mss(display=display) as sct:
         assert isinstance(sct, mss.linux.MSS)  # For Mypy
         assert hasattr(sct.xrandr, "XRRGetScreenResourcesCurrent")
+        fast_spy = spy_and_patch(monkeypatch, sct.xrandr, "XRRGetScreenResourcesCurrent")
+        slow_spy = spy_and_patch(monkeypatch, sct.xrandr, "XRRGetScreenResources")
         screenshot_with_fast_fn = sct.grab(sct.monitors[1])
 
+    fast_spy.assert_called()
+    slow_spy.assert_not_called()
+
     assert set(screenshot_with_fast_fn.rgb) == {0}
 
+
+def test_client_missing_fast_function_for_monitor_details_retrieval(
+    display: str, monkeypatch: pytest.MonkeyPatch
+) -> None:
     with mss.mss(display=display) as sct:
         assert isinstance(sct, mss.linux.MSS)  # For Mypy
         assert hasattr(sct.xrandr, "XRRGetScreenResourcesCurrent")
-        del sct.xrandr.XRRGetScreenResourcesCurrent
+        # Even though we're going to delete it, we'll still create a fast spy, to make sure that it isn't somehow
+        # getting accessed through a path we hadn't considered.
+        fast_spy = spy_and_patch(monkeypatch, sct.xrandr, "XRRGetScreenResourcesCurrent")
+        slow_spy = spy_and_patch(monkeypatch, sct.xrandr, "XRRGetScreenResources")
+        # If we just delete sct.xrandr.XRRGetScreenResourcesCurrent, it will get recreated automatically by ctypes
+        # the next time it's accessed.  A Mock will remember that the attribute was explicitly deleted and hide it.
+        mock_xrandr = NonCallableMock(wraps=sct.xrandr)
+        del mock_xrandr.XRRGetScreenResourcesCurrent
+        monkeypatch.setattr(sct, "xrandr", mock_xrandr)
+        assert not hasattr(sct.xrandr, "XRRGetScreenResourcesCurrent")
         screenshot_with_slow_fn = sct.grab(sct.monitors[1])
 
+    fast_spy.assert_not_called()
+    slow_spy.assert_called()
+
+    assert set(screenshot_with_slow_fn.rgb) == {0}
+
+
+def test_server_missing_fast_function_for_monitor_details_retrieval(
+    display: str, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    fake_xrrqueryversion_type = CFUNCTYPE(
+        c_int,  # Status
+        POINTER(mss.linux.Display),  # Display*
+        POINTER(c_int),  # int* major
+        POINTER(c_int),  # int* minor
+    )
+
+    @fake_xrrqueryversion_type
+    def fake_xrrqueryversion(_dpy: _Pointer, major_p: _Pointer, minor_p: _Pointer) -> int:
+        major_p[0] = 1
+        minor_p[0] = 2
+        return 1
+
+    with mss.mss(display=display) as sct:
+        assert isinstance(sct, mss.linux.MSS)  # For Mypy
+        monkeypatch.setattr(sct.xrandr, "XRRQueryVersion", fake_xrrqueryversion)
+        fast_spy = spy_and_patch(monkeypatch, sct.xrandr, "XRRGetScreenResourcesCurrent")
+        slow_spy = spy_and_patch(monkeypatch, sct.xrandr, "XRRGetScreenResources")
+        screenshot_with_slow_fn = sct.grab(sct.monitors[1])
+
+    fast_spy.assert_not_called()
+    slow_spy.assert_called()
+
     assert set(screenshot_with_slow_fn.rgb) == {0}