Fix for problem caused by SSL_WANT_READ or SSL_WANT_WRITE errors.

When SSL_WANT_READ or SSL_WANT_WRITE are encountered, it's typical to retry the call but this must be repeated with the exact same arguments. Without this change, openSSL requires that the address of the buffer passed is the same. However, buffers in python can change location in some circumstances which cause the retry to fail.  By add the setting SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER, the requirement for the same buffer address is forgiven and the retry has a better chance of success.  See cherrypy/cheroot#245 for discussion.

CHANGELOG.rst

@@ -4,6 +4,23 @@ Changelog
 Versions are year-based with a strict backward-compatibility policy.
 The third digit is only for regressions.
 
+24.1.0 (UNRELEASED)
+-------------------
+
+Backward-incompatible changes:
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+- ``pyOpenSSL`` now sets ``SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER`` by default, matching CPython's behavior. `#1287 <https://github.com/pyca/pyopenssl/pull/1287>`_.
+- The minimum ``cryptography`` version is now 42.0.0.
+
+Deprecations:
+^^^^^^^^^^^^^
+
+Changes:
+^^^^^^^^
+
+
+
 24.0.0 (2024-01-22)
 -------------------
 

setup.py

@@ -93,7 +93,7 @@ def find_meta(meta):
         packages=find_packages(where="src"),
         package_dir={"": "src"},
         install_requires=[
-            "cryptography>=41.0.5,<43",
+            "cryptography>=42.0.0,<43",
         ],
         extras_require={
             "test": ["flaky", "pretend", "pytest>=3.0.1"],

src/OpenSSL/SSL.py

@@ -855,8 +855,10 @@ def __init__(self, method):
         self._ocsp_data = None
         self._cookie_generate_helper = None
         self._cookie_verify_helper = None
-
-        self.set_mode(_lib.SSL_MODE_ENABLE_PARTIAL_WRITE)
+        self.set_mode(
+            _lib.SSL_MODE_ENABLE_PARTIAL_WRITE
+            | _lib.SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER
+        )
         if version is not None:
             self.set_min_proto_version(version)
             self.set_max_proto_version(version)

tox.ini

@@ -18,7 +18,7 @@ extras =
     test
 deps =
     coverage>=4.2
-    cryptographyMinimum: cryptography==41.0.5
+    cryptographyMinimum: cryptography==42.0.0
     randomorder: pytest-randomly
 setenv =
     # Do not allow the executing environment to pollute the test environment