Windows: use Winsock values for errno socket constants (PROD-1626 part 1)

Lib/test/test_errno.py

@@ -3,6 +3,7 @@
 """
 
 import errno
+import sys
 from test import test_support
 import unittest
 
@@ -31,8 +32,38 @@ def test_attributes_in_errorcode(self):
                               'no %s attr in errno.errorcode' % attribute)
 
 
+@unittest.skipUnless(sys.platform == 'win32', 'Windows specific')
+class WinsockErrnoTests(unittest.TestCase):
+
+    # VS2010+ errno.h defines its own values for these; sockets report the
+    # Winsock ones, so the errno module must use those.
+    names = ['EADDRINUSE', 'EADDRNOTAVAIL', 'EAFNOSUPPORT', 'EALREADY',
+             'ECONNABORTED', 'ECONNREFUSED', 'ECONNRESET', 'EDESTADDRREQ',
+             'EHOSTUNREACH', 'EINPROGRESS', 'EISCONN', 'ELOOP', 'EMSGSIZE',
+             'ENETDOWN', 'ENETRESET', 'ENETUNREACH', 'ENOBUFS', 'ENOPROTOOPT',
+             'ENOTCONN', 'ENOTSOCK', 'EOPNOTSUPP', 'EPROTONOSUPPORT',
+             'EPROTOTYPE', 'ETIMEDOUT', 'EWOULDBLOCK']
+
+    def test_socket_constants_are_winsock_values(self):
+        for name in self.names:
+            self.assertEqual(getattr(errno, name), getattr(errno, 'WSA' + name),
+                             name)
+
+    def test_socket_error_matches_errno(self):
+        import socket
+        s = socket.socket()
+        try:
+            s.setblocking(False)
+            # Connecting to a non-routable address does not complete at once.
+            self.assertEqual(s.connect_ex(('10.255.255.1', 80)),
+                             errno.EWOULDBLOCK)
+        finally:
+            s.close()
+
+
 def test_main():
-    test_support.run_unittest(ErrnoAttributeTests, ErrorcodeTests)
+    test_support.run_unittest(ErrnoAttributeTests, ErrorcodeTests,
+                              WinsockErrnoTests)
 
 
 if __name__ == '__main__':

Misc/NEWS.d/2.7.18.16.rst

@@ -256,3 +256,19 @@ Removed an unused function from ``Modules/socketmodule.c`` that referenced
 a symbol Python 2.7 does not build, so ``-O0`` and ``--with-pydebug`` builds
 produced a ``_socket`` module (and :mod:`ssl`) that failed to import.
 ``test_ssl`` no longer needs the third-party ``mock`` package.
+
+.. bpo: 0
+.. date: 2026-10-28
+.. nonce: as1916
+.. release date: 2026-10-28
+.. original section: Windows
+.. section: Windows
+
+Use the Winsock values for socket errno constants on Windows
+
+Visual Studio 2010 and later define their own ``ECONNRESET``,
+``EWOULDBLOCK``, ``ETIMEDOUT`` and other socket error numbers in
+``errno.h``, but Windows sockets report the Winsock ``WSAE*`` codes, so
+``errno.EWOULDBLOCK`` (140) never matched a socket error (10035). The
+:mod:`errno` module now uses the Winsock values for these 25 constants, as
+Python 3.5 and later do.

Modules/errnomodule.c

@@ -6,6 +6,34 @@
 /* Windows socket errors (WSA*)  */
 #ifdef MS_WINDOWS
 #include <windows.h>
+/* The following constants were added to errno.h in VS2010 but have
+   preferred WSA equivalents: the socket module reports Winsock errors,
+   so errno.ECONNRESET and friends must be the WSAE* values (as in 3.5+). */
+#undef EADDRINUSE
+#undef EADDRNOTAVAIL
+#undef EAFNOSUPPORT
+#undef EALREADY
+#undef ECONNABORTED
+#undef ECONNREFUSED
+#undef ECONNRESET
+#undef EDESTADDRREQ
+#undef EHOSTUNREACH
+#undef EINPROGRESS
+#undef EISCONN
+#undef ELOOP
+#undef EMSGSIZE
+#undef ENETDOWN
+#undef ENETRESET
+#undef ENETUNREACH
+#undef ENOBUFS
+#undef ENOPROTOOPT
+#undef ENOTCONN
+#undef ENOTSOCK
+#undef EOPNOTSUPP
+#undef EPROTONOSUPPORT
+#undef EPROTOTYPE
+#undef ETIMEDOUT
+#undef EWOULDBLOCK
 #endif
 
 /*