From 50231c5752206b5169bc261ba7c563db6231e048 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 14 Nov 2024 21:02:53 +0000
Subject: [PATCH 01/20] GH-126838: `url2pathname()`: handle non-empty authority
 section on POSIX

Adjust `urllib.request.url2pathname()` to parse the URL authority and path
with `urlsplit()` on POSIX. If the authority is empty or resolves to the
current host, it is ignored and the URL path is used as the pathname.
If not, we raise `URLError`.
---
 Lib/test/test_urllib.py                       |  9 ++--
 Lib/urllib/request.py                         | 46 ++++++-------------
 ...-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst |  4 ++
 3 files changed, 25 insertions(+), 34 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst

diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index 2c53ce3f99e675..f41e37f2b490b6 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -13,6 +13,7 @@
 from test.support import socket_helper
 from test.support import warnings_helper
 import os
+import socket
 try:
     import ssl
 except ImportError:
@@ -713,7 +714,7 @@ def constructLocalFileUrl(self, filePath):
             filePath.encode("utf-8")
         except UnicodeEncodeError:
             raise unittest.SkipTest("filePath is not encodable to utf8")
-        return "file://%s" % urllib.request.pathname2url(filePath)
+        return "file:%s" % urllib.request.pathname2url(filePath)
 
     def createNewTempFile(self, data=b""):
         """Creates a new temporary file containing the specified data,
@@ -1607,10 +1608,12 @@ def test_url2pathname_win(self):
     def test_url2pathname_posix(self):
         fn = urllib.request.url2pathname
         self.assertEqual(fn('/foo/bar'), '/foo/bar')
-        self.assertEqual(fn('//foo/bar'), '//foo/bar')
+        self.assertRaises(urllib.error.URLError, fn, '//foo/bar')
         self.assertEqual(fn('///foo/bar'), '/foo/bar')
         self.assertEqual(fn('////foo/bar'), '//foo/bar')
-        self.assertEqual(fn('//localhost/foo/bar'), '//localhost/foo/bar')
+        self.assertEqual(fn('//localhost/foo/bar'), '/foo/bar')
+        self.assertEqual(fn('//127.0.0.1/foo/bar'), '/foo/bar')
+        self.assertEqual(fn(f'//{socket.gethostname()}/foo/bar'), '/foo/bar')
 
 class Utility_Tests(unittest.TestCase):
     """Testcase to test the various utility functions in the urllib."""
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index 18a837dd57ed59..89c06daa7d96c2 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -1448,16 +1448,6 @@ def parse_http_list(s):
     return [part.strip() for part in res]
 
 class FileHandler(BaseHandler):
-    # Use local file or FTP depending on form of URL
-    def file_open(self, req):
-        url = req.selector
-        if url[:2] == '//' and url[2:3] != '/' and (req.host and
-                req.host != 'localhost'):
-            if not req.host in self.get_names():
-                raise URLError("file:// scheme is supported only on localhost")
-        else:
-            return self.open_local_file(req)
-
     # names for the localhost
     names = None
     def get_names(self):
@@ -1474,9 +1464,8 @@ def get_names(self):
     def open_local_file(self, req):
         import email.utils
         import mimetypes
-        host = req.host
-        filename = req.selector
-        localfile = url2pathname(filename)
+        filename = req.full_url
+        localfile = url2pathname(filename.removeprefix('file:'))
         try:
             stats = os.stat(localfile)
             size = stats.st_size
@@ -1485,24 +1474,20 @@ def open_local_file(self, req):
             headers = email.message_from_string(
                 'Content-type: %s\nContent-length: %d\nLast-modified: %s\n' %
                 (mtype or 'text/plain', size, modified))
-            if host:
-                host, port = _splitport(host)
-            if not host or \
-                (not port and _safe_gethostbyname(host) in self.get_names()):
-                if host:
-                    origurl = 'file://' + host + filename
-                else:
-                    origurl = 'file://' + filename
-                return addinfourl(open(localfile, 'rb'), headers, origurl)
+            return addinfourl(open(localfile, 'rb'), headers, filename)
         except OSError as exp:
             raise URLError(exp)
-        raise URLError('file not on local host')
 
-def _safe_gethostbyname(host):
+    file_open = open_local_file
+
+def _is_local_host(host):
+    if not host or host == 'localhost':
+        return True
     try:
-        return socket.gethostbyname(host)
+        name = socket.gethostbyname(host)
     except socket.gaierror:
-        return None
+        return False
+    return name in FileHandler().get_names()
 
 class FTPHandler(BaseHandler):
     def ftp_open(self, req):
@@ -1653,13 +1638,12 @@ def data_open(self, req):
 if os.name == 'nt':
     from nturl2path import url2pathname, pathname2url
 else:
-    def url2pathname(pathname):
+    def url2pathname(url):
         """OS-specific conversion from a relative URL of the 'file' scheme
         to a file system path; not recommended for general use."""
-        if pathname[:3] == '///':
-            # URL has an empty authority section, so the path begins on the
-            # third character.
-            pathname = pathname[2:]
+        authority, pathname = urlsplit(f'file:{url}')[1:3]
+        if not _is_local_host(authority):
+            raise URLError(f'URL {url!r} uses non-local authority {authority!r}')
         return unquote(pathname)
 
     def pathname2url(pathname):
diff --git a/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst b/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst
new file mode 100644
index 00000000000000..976b5a1f3ae9cb
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst
@@ -0,0 +1,4 @@
+Fix issue where :func:`urllib.request.url2pathname` included any URL
+authority in the resulting path, except on Windows. It now discards a local
+authority, and raises :exc:`urllib.error.URLError` for a non-local
+authority.

From 9032105dfa6e1cb7bd64cafb4e01f9d9804149eb Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 14 Nov 2024 21:34:20 +0000
Subject: [PATCH 02/20] Fix test

---
 Lib/test/test_urllib.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index f41e37f2b490b6..e8325827a0060a 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -529,7 +529,7 @@ def test_missing_localfile(self):
 
     def test_file_notexists(self):
         fd, tmp_file = tempfile.mkstemp()
-        tmp_fileurl = 'file://localhost/' + tmp_file.replace(os.path.sep, '/')
+        tmp_fileurl = 'file://localhost' + tmp_file.replace(os.path.sep, '/')
         try:
             self.assertTrue(os.path.exists(tmp_file))
             with urlopen(tmp_fileurl) as fobj:

From b91afca015c41f826078718a51a44aad6451f1ec Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 14 Nov 2024 21:41:03 +0000
Subject: [PATCH 03/20] Undo unnecessary change

---
 Lib/test/test_urllib.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index e8325827a0060a..5fc05ca3139313 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -714,7 +714,7 @@ def constructLocalFileUrl(self, filePath):
             filePath.encode("utf-8")
         except UnicodeEncodeError:
             raise unittest.SkipTest("filePath is not encodable to utf8")
-        return "file:%s" % urllib.request.pathname2url(filePath)
+        return "file://%s" % urllib.request.pathname2url(filePath)
 
     def createNewTempFile(self, data=b""):
         """Creates a new temporary file containing the specified data,

From 4b320b855025757dacd658cf553ce25bf42921ee Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 14 Nov 2024 21:55:49 +0000
Subject: [PATCH 04/20] Fix Windows tests

---
 Lib/test/test_urllib2.py | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py
index b90ccc2f125b93..d88af6ef2de853 100644
--- a/Lib/test/test_urllib2.py
+++ b/Lib/test/test_urllib2.py
@@ -827,14 +827,17 @@ def test_file(self):
         urls = [
             "file://localhost%s" % urlpath,
             "file://%s" % urlpath,
-            "file://%s%s" % (socket.gethostbyname('localhost'), urlpath),
             ]
-        try:
-            localaddr = socket.gethostbyname(socket.gethostname())
-        except socket.gaierror:
-            localaddr = ''
-        if localaddr:
-            urls.append("file://%s%s" % (localaddr, urlpath))
+        if os.name != 'nt':
+            # On POSIX the local hostname may appear in a local file URL.
+            # On Windows this would be decoded as a UNC path.
+            urls.append("file://%s%s" % (socket.gethostbyname('localhost'), urlpath))
+            try:
+                localaddr = socket.gethostbyname(socket.gethostname())
+            except socket.gaierror:
+                localaddr = ''
+            if localaddr:
+                urls.append("file://%s%s" % (localaddr, urlpath))
 
         for url in urls:
             f = open(TESTFN, "wb")

From 0cc3a673fe7776630a8ccd6951a2085dd0f51137 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 14 Nov 2024 22:02:13 +0000
Subject: [PATCH 05/20] More test fixes

---
 Lib/test/test_urllib.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index 5fc05ca3139313..8b660e8f81abc4 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -529,7 +529,7 @@ def test_missing_localfile(self):
 
     def test_file_notexists(self):
         fd, tmp_file = tempfile.mkstemp()
-        tmp_fileurl = 'file://localhost' + tmp_file.replace(os.path.sep, '/')
+        tmp_fileurl = 'file:' + urllib.request.pathname2url(tmp_file)
         try:
             self.assertTrue(os.path.exists(tmp_file))
             with urlopen(tmp_fileurl) as fobj:

From ab800ab256dca8f67485154c0a701542b4c9bd24 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Wed, 19 Mar 2025 19:51:54 +0000
Subject: [PATCH 06/20] Updatez

---
 Doc/library/urllib.request.rst                |  6 +++
 Lib/urllib/request.py                         | 45 +++++++++----------
 ...-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst | 10 +++--
 3 files changed, 34 insertions(+), 27 deletions(-)

diff --git a/Doc/library/urllib.request.rst b/Doc/library/urllib.request.rst
index 14785d21e74a11..06495cb38847b9 100644
--- a/Doc/library/urllib.request.rst
+++ b/Doc/library/urllib.request.rst
@@ -181,6 +181,12 @@ The :mod:`urllib.request` module defines the following functions:
       >>> url2pathname(url.removeprefix('file:'))
       'C:\\Program Files'
 
+   .. versionchanged:: 3.14
+      On non-Windows platforms, if a URL authority (e.g. a hostname) is
+      present, then it is discarded if it resolves to ``localhost``, otherwise
+      :exc:`~urllib.error.URLError` is raised. In previous versions the
+      authority is included in the returned path.
+
    .. versionchanged:: 3.14
       Windows drive letters are no longer converted to uppercase, and ``:``
       characters not following a drive letter no longer cause an
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index de4cf12a2b12e9..52b8dbfd3a7fd9 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -1450,29 +1450,17 @@ def parse_http_list(s):
     return [part.strip() for part in res]
 
 class FileHandler(BaseHandler):
-    # names for the localhost
-    names = None
-    def get_names(self):
-        if FileHandler.names is None:
-            try:
-                FileHandler.names = tuple(
-                    socket.gethostbyname_ex('localhost')[2] +
-                    socket.gethostbyname_ex(socket.gethostname())[2])
-            except socket.gaierror:
-                FileHandler.names = (socket.gethostbyname('localhost'),)
-        return FileHandler.names
-
     # not entirely sure what the rules are here
     def open_local_file(self, req):
         import email.utils
         import mimetypes
-        filename = req.full_url
-        localfile = url2pathname(filename.removeprefix('file:'))
+        filename = _splittype(req.full_url)[1]
+        localfile = url2pathname(filename)
         try:
             stats = os.stat(localfile)
             size = stats.st_size
             modified = email.utils.formatdate(stats.st_mtime, usegmt=True)
-            mtype = mimetypes.guess_type(filename)[0]
+            mtype = mimetypes.guess_file_type(localfile)[0]
             headers = email.message_from_string(
                 'Content-type: %s\nContent-length: %d\nLast-modified: %s\n' %
                 (mtype or 'text/plain', size, modified))
@@ -1483,14 +1471,25 @@ def open_local_file(self, req):
 
     file_open = open_local_file
 
-def _is_local_host(host):
-    if not host or host == 'localhost':
+_local_addresses = None
+
+def _is_local_authority(authority):
+    global _local_addresses
+
+    if not authority or authority == 'localhost':
         return True
     try:
-        name = socket.gethostbyname(host)
+        address = socket.gethostbyname(authority)
     except socket.gaierror:
         return False
-    return name in FileHandler().get_names()
+    if _local_addresses is None:
+        try:
+            _local_addresses = tuple(
+                socket.gethostbyname_ex('localhost')[2] +
+                socket.gethostbyname_ex(socket.gethostname())[2])
+        except socket.gaierror:
+            _local_addresses = (socket.gethostbyname('localhost'),)
+    return address in _local_addresses
 
 class FTPHandler(BaseHandler):
     def ftp_open(self, req):
@@ -1639,12 +1638,12 @@ def url2pathname(url):
     """OS-specific conversion from a relative URL of the 'file' scheme
     to a file system path; not recommended for general use."""
     authority, url = _splithost(url)
-
     if os.name == 'nt':
         if authority and authority != 'localhost':
+            # e.g. file://server/share/file.txt
             url = '//' + authority + url
         elif url[:3] == '///':
-            # Skip past extra slash before UNC drive in URL path.
+            # e.g. file://///server/share/file.txt
             url = url[1:]
         else:
             if url[:1] == '/' and url[2:3] in (':', '|'):
@@ -1654,8 +1653,8 @@ def url2pathname(url):
                 # Older URLs use a pipe after a drive letter
                 url = url[:1] + ':' + url[2:]
         url = url.replace('/', '\\')
-    elif not _is_local_host(authority):
-        raise URLError(f'URL {url!r} uses non-local authority {authority!r}')
+    elif not _is_local_authority(authority):
+        raise URLError("file:// scheme is supported only on localhost")
     encoding = sys.getfilesystemencoding()
     errors = sys.getfilesystemencodeerrors()
     return unquote(url, encoding=encoding, errors=errors)
diff --git a/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst b/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst
index 976b5a1f3ae9cb..b367a7adc257ea 100644
--- a/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst
+++ b/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst
@@ -1,4 +1,6 @@
-Fix issue where :func:`urllib.request.url2pathname` included any URL
-authority in the resulting path, except on Windows. It now discards a local
-authority, and raises :exc:`urllib.error.URLError` for a non-local
-authority.
+Fix issue where :func:`urllib.request.url2pathname` mishandled file URLs with
+non-empty, non-``localhost`` authorities on non-Windows systems. Authorities
+that resolve to ``localhost`` are now discarded; other authorities now cause
+a :exc:`urllib.error.URLError` to be raised. Previously these authorities
+were incorrectly included in the returned path. This change does not affect
+Windows, where UNC paths are returned for non-local URLs.

From 40d346a901952b37b8398931bdf653929de38927 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Wed, 19 Mar 2025 20:40:10 +0000
Subject: [PATCH 07/20] Fix tests #1

---
 Lib/test/test_urllib2.py | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py
index 088ee4c4f90803..d47984fbe7ff32 100644
--- a/Lib/test/test_urllib2.py
+++ b/Lib/test/test_urllib2.py
@@ -816,14 +816,17 @@ def test_file(self):
         urls = [
             canonurl,
             parsed._replace(netloc='localhost').geturl(),
-            parsed._replace(netloc=socket.gethostbyname('localhost')).geturl(),
             ]
-        try:
-            localaddr = socket.gethostbyname(socket.gethostname())
-        except socket.gaierror:
-            localaddr = ''
-        if localaddr:
-            urls.append(parsed._replace(netloc=localaddr).geturl())
+        if os.name != 'nt':
+            # On POSIX the local hostname may appear in a local file URL.
+            # On Windows this would be decoded as a UNC path.
+            urls.append(parsed._replace(netloc=socket.gethostbyname('localhost')).geturl())
+            try:
+                localaddr = socket.gethostbyname(socket.gethostname())
+            except socket.gaierror:
+                localaddr = ''
+            if localaddr:
+                urls.append(parsed._replace(netloc=localaddr).geturl())
 
         for url in urls:
             f = open(TESTFN, "wb")

From 79f5d05db3ca06e65a7e912fe4fadd60b006de22 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Wed, 19 Mar 2025 21:30:06 +0000
Subject: [PATCH 08/20] Restore previous Windows behaviour

---
 Doc/library/pathlib.rst                         |  9 +++++----
 Doc/library/urllib.request.rst                  |  9 +++++----
 Lib/test/test_pathlib/test_pathlib.py           |  4 +++-
 Lib/test/test_urllib2.py                        | 17 +++++++----------
 Lib/urllib/request.py                           |  2 +-
 ...24-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst |  9 ++++-----
 6 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/Doc/library/pathlib.rst b/Doc/library/pathlib.rst
index 7d3d6d1b9aebf4..95d29faa49a771 100644
--- a/Doc/library/pathlib.rst
+++ b/Doc/library/pathlib.rst
@@ -872,10 +872,11 @@ conforming to :rfc:`8089`.
    .. versionadded:: 3.13
 
    .. versionchanged:: 3.14
-      On non-Windows platforms, if a URL authority (e.g. a hostname) is
-      present, then it is discarded if it resolves to ``localhost``, otherwise
-      :exc:`ValueError` is raised. In previous versions the authority is
-      included in the returned path.
+      If a URL authority (e.g. a hostname) is present and resolves to
+      ``localhost``, it is discarded. If an authority is present and
+      *doesn't* resolve to ``localhost``, then on Windows a UNC path is
+      returned (as before), and on other platforms a :exc:`ValueError` is
+      raised.
 
 .. method:: Path.as_uri()
 
diff --git a/Doc/library/urllib.request.rst b/Doc/library/urllib.request.rst
index 06495cb38847b9..3b73d30a6ea6b3 100644
--- a/Doc/library/urllib.request.rst
+++ b/Doc/library/urllib.request.rst
@@ -182,10 +182,11 @@ The :mod:`urllib.request` module defines the following functions:
       'C:\\Program Files'
 
    .. versionchanged:: 3.14
-      On non-Windows platforms, if a URL authority (e.g. a hostname) is
-      present, then it is discarded if it resolves to ``localhost``, otherwise
-      :exc:`~urllib.error.URLError` is raised. In previous versions the
-      authority is included in the returned path.
+      If a URL authority (e.g. a hostname) is present and resolves to
+      ``localhost``, it is discarded. If an authority is present and
+      *doesn't* resolve to ``localhost``, then on Windows a UNC path is
+      returned (as before), and on other platforms a
+      :exc:`~urllib.error.URLError` is raised.
 
    .. versionchanged:: 3.14
       Windows drive letters are no longer converted to uppercase, and ``:``
diff --git a/Lib/test/test_pathlib/test_pathlib.py b/Lib/test/test_pathlib/test_pathlib.py
index b0fd10909bd789..3ad4b19e5d47df 100644
--- a/Lib/test/test_pathlib/test_pathlib.py
+++ b/Lib/test/test_pathlib/test_pathlib.py
@@ -3284,7 +3284,9 @@ def test_from_uri_posix(self):
         self.assertEqual(P.from_uri('file:////foo/bar'), P('//foo/bar'))
         self.assertEqual(P.from_uri('file://localhost/foo/bar'), P('/foo/bar'))
         self.assertEqual(P.from_uri('file://127.0.0.1/foo/bar'), P('/foo/bar'))
-        self.assertEqual(P.from_uri(f'file://{socket.gethostname()}/foo/bar'), P('/foo/bar'))
+        if not is_wasi:
+            self.assertEqual(P.from_uri(f'file://{socket.gethostname()}/foo/bar'),
+                             P('/foo/bar'))
         self.assertRaises(ValueError, P.from_uri, 'foo/bar')
         self.assertRaises(ValueError, P.from_uri, '/foo/bar')
         self.assertRaises(ValueError, P.from_uri, '//foo/bar')
diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py
index d47984fbe7ff32..088ee4c4f90803 100644
--- a/Lib/test/test_urllib2.py
+++ b/Lib/test/test_urllib2.py
@@ -816,17 +816,14 @@ def test_file(self):
         urls = [
             canonurl,
             parsed._replace(netloc='localhost').geturl(),
+            parsed._replace(netloc=socket.gethostbyname('localhost')).geturl(),
             ]
-        if os.name != 'nt':
-            # On POSIX the local hostname may appear in a local file URL.
-            # On Windows this would be decoded as a UNC path.
-            urls.append(parsed._replace(netloc=socket.gethostbyname('localhost')).geturl())
-            try:
-                localaddr = socket.gethostbyname(socket.gethostname())
-            except socket.gaierror:
-                localaddr = ''
-            if localaddr:
-                urls.append(parsed._replace(netloc=localaddr).geturl())
+        try:
+            localaddr = socket.gethostbyname(socket.gethostname())
+        except socket.gaierror:
+            localaddr = ''
+        if localaddr:
+            urls.append(parsed._replace(netloc=localaddr).geturl())
 
         for url in urls:
             f = open(TESTFN, "wb")
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index bef560ec2cee59..fe8aa09ba11597 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -1639,7 +1639,7 @@ def url2pathname(url):
     to a file system path; not recommended for general use."""
     authority, url = _splithost(url)
     if os.name == 'nt':
-        if authority and authority != 'localhost':
+        if not _is_local_authority(authority):
             # e.g. file://server/share/file.txt
             url = '//' + authority + url
         elif url[:3] == '///':
diff --git a/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst b/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst
index b367a7adc257ea..4c3c488d73ce30 100644
--- a/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst
+++ b/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst
@@ -1,6 +1,5 @@
 Fix issue where :func:`urllib.request.url2pathname` mishandled file URLs with
-non-empty, non-``localhost`` authorities on non-Windows systems. Authorities
-that resolve to ``localhost`` are now discarded; other authorities now cause
-a :exc:`urllib.error.URLError` to be raised. Previously these authorities
-were incorrectly included in the returned path. This change does not affect
-Windows, where UNC paths are returned for non-local URLs.
+authorities. If an authority is present and resolves to ``localhost``, it is
+now discarded. If an authority is present but *doesn't* resolve to
+``localhost``, then on Windows a UNC path is returned (as before), and on
+other platforms a :exc:`urllib.errors.URLError` is now raised.

From bb69e493a5e943e97c98e7a590e73ba1ec1a5fa4 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Wed, 19 Mar 2025 22:10:10 +0000
Subject: [PATCH 09/20] Fix WASI, docs

---
 Lib/pathlib/__init__.py                                        | 3 +--
 Lib/urllib/request.py                                          | 3 +--
 .../Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst     | 2 +-
 3 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/Lib/pathlib/__init__.py b/Lib/pathlib/__init__.py
index 420bfa4a075a52..659a8771a2c02a 100644
--- a/Lib/pathlib/__init__.py
+++ b/Lib/pathlib/__init__.py
@@ -1274,10 +1274,9 @@ def from_uri(cls, uri):
         from urllib.error import URLError
         from urllib.request import url2pathname
         try:
-            pathname = url2pathname(uri.removeprefix('file:'))
+            path = cls(url2pathname(uri.removeprefix('file:')))
         except URLError as exc:
             raise ValueError(exc.reason) from None
-        path = cls(pathname)
         if not path.is_absolute():
             raise ValueError(f"URI is not absolute: {uri!r}")
         return path
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index fe8aa09ba11597..d4a1ef2bb042f2 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -1450,7 +1450,6 @@ def parse_http_list(s):
     return [part.strip() for part in res]
 
 class FileHandler(BaseHandler):
-    # not entirely sure what the rules are here
     def open_local_file(self, req):
         import email.utils
         import mimetypes
@@ -1480,7 +1479,7 @@ def _is_local_authority(authority):
         return True
     try:
         address = socket.gethostbyname(authority)
-    except socket.gaierror:
+    except (socket.gaierror, AttributeError):
         return False
     if _local_addresses is None:
         try:
diff --git a/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst b/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst
index 4c3c488d73ce30..857cc359229daa 100644
--- a/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst
+++ b/Misc/NEWS.d/next/Library/2024-11-14-21-17-48.gh-issue-126838.Yr5vKF.rst
@@ -2,4 +2,4 @@ Fix issue where :func:`urllib.request.url2pathname` mishandled file URLs with
 authorities. If an authority is present and resolves to ``localhost``, it is
 now discarded. If an authority is present but *doesn't* resolve to
 ``localhost``, then on Windows a UNC path is returned (as before), and on
-other platforms a :exc:`urllib.errors.URLError` is now raised.
+other platforms a :exc:`urllib.error.URLError` is now raised.

From 7adddbf4f369dade5b99af2c0313a6e2d0319f9f Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Wed, 19 Mar 2025 22:29:08 +0000
Subject: [PATCH 10/20] wasi yousa problem?

---
 Lib/test/test_pathlib/test_pathlib.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_pathlib/test_pathlib.py b/Lib/test/test_pathlib/test_pathlib.py
index 3ad4b19e5d47df..5346fca330e23c 100644
--- a/Lib/test/test_pathlib/test_pathlib.py
+++ b/Lib/test/test_pathlib/test_pathlib.py
@@ -3283,8 +3283,8 @@ def test_from_uri_posix(self):
         self.assertEqual(P.from_uri('file:///foo/bar'), P('/foo/bar'))
         self.assertEqual(P.from_uri('file:////foo/bar'), P('//foo/bar'))
         self.assertEqual(P.from_uri('file://localhost/foo/bar'), P('/foo/bar'))
-        self.assertEqual(P.from_uri('file://127.0.0.1/foo/bar'), P('/foo/bar'))
         if not is_wasi:
+            self.assertEqual(P.from_uri('file://127.0.0.1/foo/bar'), P('/foo/bar'))
             self.assertEqual(P.from_uri(f'file://{socket.gethostname()}/foo/bar'),
                              P('/foo/bar'))
         self.assertRaises(ValueError, P.from_uri, 'foo/bar')

From b5e54604ac1dc44b17f88019ee0611c3da30323a Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 20 Mar 2025 01:58:56 +0000
Subject: [PATCH 11/20] Update whatsnew

---
 Doc/whatsnew/3.14.rst | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/Doc/whatsnew/3.14.rst b/Doc/whatsnew/3.14.rst
index 767cf9a1f08dc2..0901b5dec34f83 100644
--- a/Doc/whatsnew/3.14.rst
+++ b/Doc/whatsnew/3.14.rst
@@ -998,7 +998,24 @@ urllib
 * Upgrade HTTP digest authentication algorithm for :mod:`urllib.request` by
   supporting SHA-256 digest authentication as specified in :rfc:`7616`.
   (Contributed by Calvin Bui in :gh:`128193`.)
+* Improve support for ``file:`` URLs.
 
+  In :func:`urllib.request.url2pathname`:
+
+  - Discard URL authorities that resolve to ``localhost``.
+  - Raise :exc:`~urllib.error.URLError` if a URL authority doesn't resolve
+    to ``localhost``, except on Windows where we return a UNC path.
+
+  In :func:`urllib.request.pathname2url`:
+
+  - Include an empty URL authority when a path begins with a slash. For
+    example, the path ``/etc/hosts`` is converted to the URL ``///etc/hosts``.
+
+  On Windows, drive letters are no longer converted to uppercase, and ``:``
+  characters not following a drive letter no longer cause an :exc:`OSError`
+  exception to be raised.
+
+  (Contributed by Barney Gale in :gh:`125866`.)
 
 uuid
 ----

From 67fccd53f6221bd1f6d0a684ce5732b7b866c640 Mon Sep 17 00:00:00 2001
From: Barney Gale <barney.gale@gmail.com>
Date: Thu, 20 Mar 2025 02:00:17 +0000
Subject: [PATCH 12/20] Apply suggestions from code review

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
---
 Doc/library/pathlib.rst        | 2 +-
 Doc/library/urllib.request.rst | 2 +-
 Lib/urllib/request.py          | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/Doc/library/pathlib.rst b/Doc/library/pathlib.rst
index f86234ce765043..6f04995c222501 100644
--- a/Doc/library/pathlib.rst
+++ b/Doc/library/pathlib.rst
@@ -871,7 +871,7 @@ conforming to :rfc:`8089`.
 
    .. versionadded:: 3.13
 
-   .. versionchanged:: 3.14
+   .. versionchanged:: next
       If a URL authority (e.g. a hostname) is present and resolves to
       ``localhost``, it is discarded. If an authority is present and
       *doesn't* resolve to ``localhost``, then on Windows a UNC path is
diff --git a/Doc/library/urllib.request.rst b/Doc/library/urllib.request.rst
index 3b73d30a6ea6b3..d475c5459316a7 100644
--- a/Doc/library/urllib.request.rst
+++ b/Doc/library/urllib.request.rst
@@ -181,7 +181,7 @@ The :mod:`urllib.request` module defines the following functions:
       >>> url2pathname(url.removeprefix('file:'))
       'C:\\Program Files'
 
-   .. versionchanged:: 3.14
+   .. versionchanged:: next
       If a URL authority (e.g. a hostname) is present and resolves to
       ``localhost``, it is discarded. If an authority is present and
       *doesn't* resolve to ``localhost``, then on Windows a UNC path is
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index d4a1ef2bb042f2..6a3271b6c376b6 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -1463,7 +1463,7 @@ def open_local_file(self, req):
             headers = email.message_from_string(
                 'Content-type: %s\nContent-length: %d\nLast-modified: %s\n' %
                 (mtype or 'text/plain', size, modified))
-            origurl = 'file:' + pathname2url(localfile)
+            origurl = f'file:{pathname2url(localfile)}'
             return addinfourl(open(localfile, 'rb'), headers, origurl)
         except OSError as exp:
             raise URLError(exp, exp.filename)

From 89ddf7f3cf8d20ae21572b8bdcd7006bccdad2d7 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 20 Mar 2025 02:03:53 +0000
Subject: [PATCH 13/20] Address some review feedback

---
 Doc/library/pathlib.rst        | 9 ++++-----
 Doc/library/urllib.request.rst | 9 ++++-----
 Doc/whatsnew/3.14.rst          | 2 +-
 Lib/urllib/request.py          | 4 ++--
 4 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/Doc/library/pathlib.rst b/Doc/library/pathlib.rst
index 6f04995c222501..8bc394c8e22e20 100644
--- a/Doc/library/pathlib.rst
+++ b/Doc/library/pathlib.rst
@@ -872,11 +872,10 @@ conforming to :rfc:`8089`.
    .. versionadded:: 3.13
 
    .. versionchanged:: next
-      If a URL authority (e.g. a hostname) is present and resolves to
-      ``localhost``, it is discarded. If an authority is present and
-      *doesn't* resolve to ``localhost``, then on Windows a UNC path is
-      returned (as before), and on other platforms a :exc:`ValueError` is
-      raised.
+      If a URL authority (e.g. a hostname) is present and resolves to a local
+      address, it is discarded. If an authority is present and *doesn't*
+      resolve to a local address, then on Windows a UNC path is returned (as
+      before), and on other platforms a :exc:`ValueError` is raised.
 
 .. method:: Path.as_uri()
 
diff --git a/Doc/library/urllib.request.rst b/Doc/library/urllib.request.rst
index d475c5459316a7..38b07cab2e073f 100644
--- a/Doc/library/urllib.request.rst
+++ b/Doc/library/urllib.request.rst
@@ -182,11 +182,10 @@ The :mod:`urllib.request` module defines the following functions:
       'C:\\Program Files'
 
    .. versionchanged:: next
-      If a URL authority (e.g. a hostname) is present and resolves to
-      ``localhost``, it is discarded. If an authority is present and
-      *doesn't* resolve to ``localhost``, then on Windows a UNC path is
-      returned (as before), and on other platforms a
-      :exc:`~urllib.error.URLError` is raised.
+      If a URL authority (e.g. a hostname) is present and resolves to a local
+      address, it is discarded. If an authority is present and *doesn't*
+      resolve to a local address, then on Windows a UNC path is returned (as
+      before), and on other platforms :exc:`~urllib.error.URLError` is raised.
 
    .. versionchanged:: 3.14
       Windows drive letters are no longer converted to uppercase, and ``:``
diff --git a/Doc/whatsnew/3.14.rst b/Doc/whatsnew/3.14.rst
index 0901b5dec34f83..b9e040c94911f4 100644
--- a/Doc/whatsnew/3.14.rst
+++ b/Doc/whatsnew/3.14.rst
@@ -1002,7 +1002,7 @@ urllib
 
   In :func:`urllib.request.url2pathname`:
 
-  - Discard URL authorities that resolve to ``localhost``.
+  - Discard URL authorities that resolve to a local address.
   - Raise :exc:`~urllib.error.URLError` if a URL authority doesn't resolve
     to ``localhost``, except on Windows where we return a UNC path.
 
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index 6a3271b6c376b6..d3a300c9769c42 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -1483,11 +1483,11 @@ def _is_local_authority(authority):
         return False
     if _local_addresses is None:
         try:
-            _local_addresses = tuple(
+            _local_addresses = frozenset(
                 socket.gethostbyname_ex('localhost')[2] +
                 socket.gethostbyname_ex(socket.gethostname())[2])
         except socket.gaierror:
-            _local_addresses = (socket.gethostbyname('localhost'),)
+            _local_addresses = frozenset(socket.gethostbyname('localhost'),)
     return address in _local_addresses
 
 class FTPHandler(BaseHandler):

From d327f34f7afc7578c8da912e74373e6541bb1832 Mon Sep 17 00:00:00 2001
From: Barney Gale <barney.gale@gmail.com>
Date: Sat, 29 Mar 2025 19:51:39 +0000
Subject: [PATCH 14/20] Apply suggestions from code review
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 Doc/library/pathlib.rst | 1 +
 Doc/whatsnew/3.14.rst   | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/Doc/library/pathlib.rst b/Doc/library/pathlib.rst
index 8bc394c8e22e20..b82986902861b2 100644
--- a/Doc/library/pathlib.rst
+++ b/Doc/library/pathlib.rst
@@ -877,6 +877,7 @@ conforming to :rfc:`8089`.
       resolve to a local address, then on Windows a UNC path is returned (as
       before), and on other platforms a :exc:`ValueError` is raised.
 
+
 .. method:: Path.as_uri()
 
    Represent the path as a 'file' URI.  :exc:`ValueError` is raised if
diff --git a/Doc/whatsnew/3.14.rst b/Doc/whatsnew/3.14.rst
index b9e040c94911f4..6dd9f94d3f280b 100644
--- a/Doc/whatsnew/3.14.rst
+++ b/Doc/whatsnew/3.14.rst
@@ -998,6 +998,7 @@ urllib
 * Upgrade HTTP digest authentication algorithm for :mod:`urllib.request` by
   supporting SHA-256 digest authentication as specified in :rfc:`7616`.
   (Contributed by Calvin Bui in :gh:`128193`.)
+
 * Improve support for ``file:`` URLs.
 
   In :func:`urllib.request.url2pathname`:
@@ -1017,6 +1018,7 @@ urllib
 
   (Contributed by Barney Gale in :gh:`125866`.)
 
+
 uuid
 ----
 

From 313a68f23109d0b4fa9f3423a916583917f6ab1a Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Sat, 29 Mar 2025 19:52:51 +0000
Subject: [PATCH 15/20] Swap .. versionchanged:: order

---
 Doc/library/urllib.request.rst | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/Doc/library/urllib.request.rst b/Doc/library/urllib.request.rst
index 38b07cab2e073f..dd2b9e11f758fc 100644
--- a/Doc/library/urllib.request.rst
+++ b/Doc/library/urllib.request.rst
@@ -158,16 +158,16 @@ The :mod:`urllib.request` module defines the following functions:
       >>> 'file:' + pathname2url(path)
       'file:///C:/Program%20Files'
 
-   .. versionchanged:: 3.14
-      Paths beginning with a slash are converted to URLs with authority
-      sections. For example, the path ``/etc/hosts`` is converted to
-      the URL ``///etc/hosts``.
-
    .. versionchanged:: 3.14
       Windows drive letters are no longer converted to uppercase, and ``:``
       characters not following a drive letter no longer cause an
       :exc:`OSError` exception to be raised on Windows.
 
+   .. versionchanged:: 3.14
+      Paths beginning with a slash are converted to URLs with authority
+      sections. For example, the path ``/etc/hosts`` is converted to
+      the URL ``///etc/hosts``.
+
 
 .. function:: url2pathname(url)
 
@@ -181,17 +181,17 @@ The :mod:`urllib.request` module defines the following functions:
       >>> url2pathname(url.removeprefix('file:'))
       'C:\\Program Files'
 
+   .. versionchanged:: 3.14
+      Windows drive letters are no longer converted to uppercase, and ``:``
+      characters not following a drive letter no longer cause an
+      :exc:`OSError` exception to be raised on Windows.
+
    .. versionchanged:: next
       If a URL authority (e.g. a hostname) is present and resolves to a local
       address, it is discarded. If an authority is present and *doesn't*
       resolve to a local address, then on Windows a UNC path is returned (as
       before), and on other platforms :exc:`~urllib.error.URLError` is raised.
 
-   .. versionchanged:: 3.14
-      Windows drive letters are no longer converted to uppercase, and ``:``
-      characters not following a drive letter no longer cause an
-      :exc:`OSError` exception to be raised on Windows.
-
 
 .. function:: getproxies()
 

From e1f6d10db818d6fa8c25defc3df5bef78eff986c Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Sat, 29 Mar 2025 19:55:07 +0000
Subject: [PATCH 16/20] Add test cases involving ports

---
 Lib/test/test_urllib.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index c3062f9e86eef7..ab51bc0f723f32 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -1533,6 +1533,10 @@ def test_url2pathname_posix(self):
         fn = urllib.request.url2pathname
         self.assertEqual(fn('/foo/bar'), '/foo/bar')
         self.assertRaises(urllib.error.URLError, fn, '//foo/bar')
+        self.assertRaises(urllib.error.URLError, fn, '//localhost:/foo/bar')
+        self.assertRaises(urllib.error.URLError, fn, '//:80/foo/bar')
+        self.assertRaises(urllib.error.URLError, fn, '//:/foo/bar')
+        self.assertRaises(urllib.error.URLError, fn, '//c:80/foo/bar')
         self.assertEqual(fn('///foo/bar'), '/foo/bar')
         self.assertEqual(fn('////foo/bar'), '//foo/bar')
         self.assertEqual(fn('//localhost/foo/bar'), '/foo/bar')

From c5f5e24715a6eae6cbbc8dec9873e43c45debc37 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Sat, 29 Mar 2025 20:07:58 +0000
Subject: [PATCH 17/20] Add test methods for common posix/windows results

---
 Lib/test/test_urllib.py | 46 +++++++++++++++++++++++++++--------------
 1 file changed, 30 insertions(+), 16 deletions(-)

diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index ab51bc0f723f32..c4e533abaec089 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -1425,6 +1425,21 @@ def test_quoting(self):
                          "url2pathname() failed; %s != %s" %
                          (expect, result))
 
+    def test_pathname2url(self):
+        # Test cases common to Windows and POSIX.
+        fn = urllib.request.pathname2url
+        sep = os.path.sep
+        self.assertEqual(fn(''), '')
+        self.assertEqual(fn(f'{sep}'), '///')
+        self.assertEqual(fn(f'{sep}{sep}'), '////')
+        self.assertEqual(fn('a'), 'a')
+        self.assertEqual(fn(f'a{sep}b.c'), 'a/b.c')
+        self.assertEqual(fn(f'{sep}a{sep}b.c'), '///a/b.c')
+        self.assertEqual(fn(f'{sep}{sep}a{sep}b.c'), '////a/b.c')
+        self.assertEqual(fn(f'{sep}{sep}{sep}a{sep}b.c'), '/////a/b.c')
+        self.assertEqual(fn(f'{sep}{sep}{sep}{sep}a{sep}b.c'), '//////a/b.c')
+        self.assertEqual(fn(f'{sep}a{sep}b%#c'), '///a/b%25%23c')
+
     @unittest.skipUnless(sys.platform == 'win32',
                          'test specific to Windows pathnames.')
     def test_pathname2url_win(self):
@@ -1463,17 +1478,6 @@ def test_pathname2url_win(self):
         for url in urls:
             self.assertEqual(fn(urllib.request.url2pathname(url)), url)
 
-    @unittest.skipIf(sys.platform == 'win32',
-                     'test specific to POSIX pathnames')
-    def test_pathname2url_posix(self):
-        fn = urllib.request.pathname2url
-        self.assertEqual(fn('/'), '///')
-        self.assertEqual(fn('/a/b.c'), '///a/b.c')
-        self.assertEqual(fn('//a/b.c'), '////a/b.c')
-        self.assertEqual(fn('///a/b.c'), '/////a/b.c')
-        self.assertEqual(fn('////a/b.c'), '//////a/b.c')
-        self.assertEqual(fn('/a/b%#c'), '///a/b%25%23c')
-
     @unittest.skipUnless(os_helper.FS_NONASCII, 'need os_helper.FS_NONASCII')
     def test_pathname2url_nonascii(self):
         encoding = sys.getfilesystemencoding()
@@ -1481,11 +1485,25 @@ def test_pathname2url_nonascii(self):
         url = urllib.parse.quote(os_helper.FS_NONASCII, encoding=encoding, errors=errors)
         self.assertEqual(urllib.request.pathname2url(os_helper.FS_NONASCII), url)
 
+    def test_url2pathname(self):
+        # Test cases common to Windows and POSIX.
+        fn = urllib.request.url2pathname
+        sep = os.path.sep
+        self.assertEqual(fn(''), '')
+        self.assertEqual(fn('/'), f'{sep}')
+        self.assertEqual(fn('///'), f'{sep}')
+        self.assertEqual(fn('////'), f'{sep}{sep}')
+        self.assertEqual(fn('foo'), 'foo')
+        self.assertEqual(fn('foo/bar'), f'foo{sep}bar')
+        self.assertEqual(fn('/foo/bar'), f'{sep}foo{sep}bar')
+        self.assertEqual(fn('//localhost/foo/bar'), f'{sep}foo{sep}bar')
+        self.assertEqual(fn('///foo/bar'), f'{sep}foo{sep}bar')
+        self.assertEqual(fn('////foo/bar'), f'{sep}{sep}foo{sep}bar')
+
     @unittest.skipUnless(sys.platform == 'win32',
                          'test specific to Windows pathnames.')
     def test_url2pathname_win(self):
         fn = urllib.request.url2pathname
-        self.assertEqual(fn('/'), '\\')
         self.assertEqual(fn('/C:/'), 'C:\\')
         self.assertEqual(fn("///C|"), 'C:')
         self.assertEqual(fn("///C:"), 'C:')
@@ -1531,15 +1549,11 @@ def test_url2pathname_win(self):
                      'test specific to POSIX pathnames')
     def test_url2pathname_posix(self):
         fn = urllib.request.url2pathname
-        self.assertEqual(fn('/foo/bar'), '/foo/bar')
         self.assertRaises(urllib.error.URLError, fn, '//foo/bar')
         self.assertRaises(urllib.error.URLError, fn, '//localhost:/foo/bar')
         self.assertRaises(urllib.error.URLError, fn, '//:80/foo/bar')
         self.assertRaises(urllib.error.URLError, fn, '//:/foo/bar')
         self.assertRaises(urllib.error.URLError, fn, '//c:80/foo/bar')
-        self.assertEqual(fn('///foo/bar'), '/foo/bar')
-        self.assertEqual(fn('////foo/bar'), '//foo/bar')
-        self.assertEqual(fn('//localhost/foo/bar'), '/foo/bar')
         self.assertEqual(fn('//127.0.0.1/foo/bar'), '/foo/bar')
         self.assertEqual(fn(f'//{socket.gethostname()}/foo/bar'), '/foo/bar')
 

From 25521c1775e9f64d0da2ad21cde73e496903d919 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Sat, 29 Mar 2025 20:19:30 +0000
Subject: [PATCH 18/20] Windows test fixes

---
 Lib/test/test_urllib.py | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index c4e533abaec089..ecf429e17811a4 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -1430,14 +1430,10 @@ def test_pathname2url(self):
         fn = urllib.request.pathname2url
         sep = os.path.sep
         self.assertEqual(fn(''), '')
-        self.assertEqual(fn(f'{sep}'), '///')
-        self.assertEqual(fn(f'{sep}{sep}'), '////')
+        self.assertEqual(fn(sep), '///')
         self.assertEqual(fn('a'), 'a')
         self.assertEqual(fn(f'a{sep}b.c'), 'a/b.c')
         self.assertEqual(fn(f'{sep}a{sep}b.c'), '///a/b.c')
-        self.assertEqual(fn(f'{sep}{sep}a{sep}b.c'), '////a/b.c')
-        self.assertEqual(fn(f'{sep}{sep}{sep}a{sep}b.c'), '/////a/b.c')
-        self.assertEqual(fn(f'{sep}{sep}{sep}{sep}a{sep}b.c'), '//////a/b.c')
         self.assertEqual(fn(f'{sep}a{sep}b%#c'), '///a/b%25%23c')
 
     @unittest.skipUnless(sys.platform == 'win32',
@@ -1478,6 +1474,14 @@ def test_pathname2url_win(self):
         for url in urls:
             self.assertEqual(fn(urllib.request.url2pathname(url)), url)
 
+    @unittest.skipIf(sys.platform == 'win32',
+                     'test specific to POSIX pathnames')
+    def test_pathname2url_posix(self):
+        fn = urllib.request.pathname2url
+        self.assertEqual(fn('//a/b.c'), '////a/b.c')
+        self.assertEqual(fn('///a/b.c'), '/////a/b.c')
+        self.assertEqual(fn('////a/b.c'), '//////a/b.c')
+
     @unittest.skipUnless(os_helper.FS_NONASCII, 'need os_helper.FS_NONASCII')
     def test_pathname2url_nonascii(self):
         encoding = sys.getfilesystemencoding()

From fa7745691ff9f650e7d6ed07588cf85ea38a1570 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Sat, 29 Mar 2025 20:24:14 +0000
Subject: [PATCH 19/20] Restore FileHandler.names and get_names()

---
 Lib/urllib/request.py | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index d3a300c9769c42..84c075ec8b359f 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -1450,6 +1450,19 @@ def parse_http_list(s):
     return [part.strip() for part in res]
 
 class FileHandler(BaseHandler):
+    # names for the localhost
+    names = None
+    def get_names(self):
+        if FileHandler.names is None:
+            try:
+                FileHandler.names = tuple(
+                    socket.gethostbyname_ex('localhost')[2] +
+                    socket.gethostbyname_ex(socket.gethostname())[2])
+            except socket.gaierror:
+                FileHandler.names = (socket.gethostbyname('localhost'),)
+        return FileHandler.names
+
+    # not entirely sure what the rules are here
     def open_local_file(self, req):
         import email.utils
         import mimetypes
@@ -1470,25 +1483,14 @@ def open_local_file(self, req):
 
     file_open = open_local_file
 
-_local_addresses = None
-
 def _is_local_authority(authority):
-    global _local_addresses
-
     if not authority or authority == 'localhost':
         return True
     try:
         address = socket.gethostbyname(authority)
     except (socket.gaierror, AttributeError):
         return False
-    if _local_addresses is None:
-        try:
-            _local_addresses = frozenset(
-                socket.gethostbyname_ex('localhost')[2] +
-                socket.gethostbyname_ex(socket.gethostname())[2])
-        except socket.gaierror:
-            _local_addresses = frozenset(socket.gethostbyname('localhost'),)
-    return address in _local_addresses
+    return address in FileHandler().get_names()
 
 class FTPHandler(BaseHandler):
     def ftp_open(self, req):

From 3a506418f9aa6b3f05e5dafc11325709596d5ecb Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 10 Apr 2025 04:10:23 +0100
Subject: [PATCH 20/20] Docs improvements

---
 Doc/library/urllib.request.rst | 9 +++++----
 Doc/whatsnew/3.14.rst          | 4 ++--
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/Doc/library/urllib.request.rst b/Doc/library/urllib.request.rst
index dd2b9e11f758fc..bc9e90de9e1918 100644
--- a/Doc/library/urllib.request.rst
+++ b/Doc/library/urllib.request.rst
@@ -187,10 +187,11 @@ The :mod:`urllib.request` module defines the following functions:
       :exc:`OSError` exception to be raised on Windows.
 
    .. versionchanged:: next
-      If a URL authority (e.g. a hostname) is present and resolves to a local
-      address, it is discarded. If an authority is present and *doesn't*
-      resolve to a local address, then on Windows a UNC path is returned (as
-      before), and on other platforms :exc:`~urllib.error.URLError` is raised.
+      This function calls :func:`socket.gethostbyname` if the URL authority
+      isn't empty or ``localhost``. If the authority resolves to a local IP
+      address then it is discarded; otherwise, on Windows a UNC path is
+      returned (as before), and on other platforms a
+      :exc:`~urllib.error.URLError` is raised.
 
 
 .. function:: getproxies()
diff --git a/Doc/whatsnew/3.14.rst b/Doc/whatsnew/3.14.rst
index 6dd9f94d3f280b..ab7477ce468686 100644
--- a/Doc/whatsnew/3.14.rst
+++ b/Doc/whatsnew/3.14.rst
@@ -999,11 +999,11 @@ urllib
   supporting SHA-256 digest authentication as specified in :rfc:`7616`.
   (Contributed by Calvin Bui in :gh:`128193`.)
 
-* Improve support for ``file:`` URLs.
+* Improve standards compliance when parsing and emitting ``file:`` URLs.
 
   In :func:`urllib.request.url2pathname`:
 
-  - Discard URL authorities that resolve to a local address.
+  - Discard URL authorities that resolve to a local IP address.
   - Raise :exc:`~urllib.error.URLError` if a URL authority doesn't resolve
     to ``localhost``, except on Windows where we return a UNC path.