Add check for correct h2 version range

changelog/3290.feature.rst

@@ -0,0 +1,3 @@
+Added version checking for ``h2`` (https://pypi.org/project/h2/) usage.
+
+Now only accepting supported h2 major version 4.x.x.

src/urllib3/__init__.py

@@ -45,6 +45,21 @@
             "See: https://github.com/urllib3/urllib3/issues/2168"
         )
 
+# Ensure that Python is compiled with h2>=4.0.0 and <5.0.0
+# If the 'h2' module isn't installed at all that's
+# fine, we only care if the module is installed.
+try:
+    import h2  # type: ignore[import-untyped]
+except ImportError:
+    pass
+else:
+    if not (h2.__version__ >= "4.0.0" and h2.__version__ < "5.0.0"):
+        raise ImportError(
+            "urllib3 v2 supports h2 version 4.x.x, currently "
+            f"the 'h2' module is compiled with {h2.__version__!r}. "
+            "See: https://github.com/urllib3/urllib3/issues/3290"
+        )
+
 __author__ = "Andrey Petrov (andrey.petrov@shazow.net)"
 __license__ = "MIT"
 __version__ = __version__

test/test_compatibility.py

@@ -1,7 +1,12 @@
 from __future__ import annotations
 
 import http.cookiejar
+import importlib
+import sys
 import urllib
+from unittest import mock
+
+import pytest
 
 from urllib3.response import HTTPResponse
 
@@ -20,3 +25,27 @@ def test_extract(self) -> None:
             response.headers.add("set-cookie", c)
         cookiejar.extract_cookies(response, request)  # type: ignore[arg-type]
         assert len(cookiejar) == len(cookies)
+
+
+class TestInitialization:
+    def test_h2_version_check(self) -> None:
+        with mock.patch.dict("sys.modules", {}):
+            importlib.reload(sys.modules["urllib3"])
+
+        mock_h2 = mock.Mock()
+
+        mock_h2.__version__ = "4.1.0"
+        with mock.patch.dict("sys.modules", {"h2": mock_h2}):
+            importlib.reload(sys.modules["urllib3"])
+
+        mock_h2.__version__ = "3.9.9"
+        with mock.patch.dict("sys.modules", {"h2": mock_h2}):
+            with pytest.raises(ImportError) as excinfo:
+                importlib.reload(sys.modules["urllib3"])
+            assert "h2 version 4.x.x" in str(excinfo.value)
+
+        mock_h2.__version__ = "5.0.0"
+        with mock.patch.dict("sys.modules", {"h2": mock_h2}):
+            with pytest.raises(ImportError) as excinfo:
+                importlib.reload(sys.modules["urllib3"])
+            assert "h2 version 4.x.x" in str(excinfo.value)