Backport of socket.has_dualstack_ipv6() implementation (python 3.8)

Author: giampaolo

pyftpdlib/handlers.py

@@ -15,6 +15,8 @@
 import traceback
 from datetime import datetime
 
+from .utils import has_dualstack_ipv6
+
 try:
     import grp
     import pwd
@@ -336,24 +338,6 @@ def _is_ssl_sock(sock):
     return SSL is not None and isinstance(sock, SSL.Connection)
 
 
-def _support_hybrid_ipv6():
-    """Return True if it is possible to use hybrid IPv6/IPv4 sockets
-    on this platform.
-    """
-    # Note: IPPROTO_IPV6 constant is broken on Windows, see:
-    # https://bugs.python.org/issue6926
-    try:
-        if not socket.has_ipv6:
-            return False
-        with contextlib.closing(socket.socket(socket.AF_INET6)) as sock:
-            return not sock.getsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY)
-    except (OSError, AttributeError):
-        return False
-
-
-SUPPORTS_HYBRID_IPV6 = _support_hybrid_ipv6()
-
-
 class _FileReadWriteError(OSError):
     """Exception raised when reading or writing a file during a transfer."""
 
@@ -2195,7 +2179,7 @@ def ftp_EPRT(self, line):
             # test if AF_INET6 and IPV6_V6ONLY
             if (
                 self.socket.family == socket.AF_INET6
-                and not SUPPORTS_HYBRID_IPV6
+                and not has_dualstack_ipv6()
             ):
                 self.respond("522 Network protocol not supported (use 2).")
             else:

pyftpdlib/utils.py

@@ -2,7 +2,9 @@
 # Use of this source code is governed by MIT license that can be
 # found in the LICENSE file.
 
+import contextlib
 import os
+import socket
 import sys
 
 
@@ -73,3 +75,25 @@ def strerror(err):
     if isinstance(err, OSError):
         return os.strerror(err.errno)
     return str(err)
+
+
+# backport of Python 3.8 socket.has_dualstack_ipv6()
+@memoize
+def has_dualstack_ipv6():
+    """Return True if the platform supports creating a SOCK_STREAM socket
+    which can handle both AF_INET and AF_INET6 (IPv4 / IPv6) connections.
+    """
+    if (
+        not socket.has_ipv6
+        or not hasattr(socket, "IPPROTO_IPV6")
+        or not hasattr(socket, "IPV6_V6ONLY")
+    ):
+        return False
+    try:
+        with contextlib.closing(
+            socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
+        ) as sock:
+            sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
+            return True
+    except OSError:
+        return False

tests/test_functional.py

@@ -21,12 +21,12 @@
 import pytest
 
 from pyftpdlib.filesystems import AbstractedFS
-from pyftpdlib.handlers import SUPPORTS_HYBRID_IPV6
 from pyftpdlib.handlers import DTPHandler
 from pyftpdlib.handlers import FTPHandler
 from pyftpdlib.handlers import ThrottledDTPHandler
 from pyftpdlib.ioloop import IOLoop
 from pyftpdlib.servers import FTPServer
+from pyftpdlib.utils import has_dualstack_ipv6
 
 from . import BUFSIZE
 from . import CI_TESTING
@@ -2130,7 +2130,7 @@ def cmdresp(self, cmd):
 
     @disable_log_warning
     def test_eprt(self):
-        if not SUPPORTS_HYBRID_IPV6:
+        if not has_dualstack_ipv6():
             # test wrong proto
             with pytest.raises(ftplib.error_perm, match="522"):
                 self.client.sendcmd(
@@ -2294,7 +2294,7 @@ def test_eprt_v6(self):
 
 
 @pytest.mark.skipif(
-    not SUPPORTS_HYBRID_IPV6, reason="IPv4/6 dual stack not supported"
+    not has_dualstack_ipv6(), reason="IPv4/6 dual stack not supported"
 )
 class TestIPv6MixedEnvironment(PyftpdlibTestCase):
     """By running the server by specifying "::" as IP address the