[3.11] gh-81403: Fix for CacheFTPHandler in urllib (GH-13951) (#103705)

* gh-81403: Fix for CacheFTPHandler in urllib (GH-13951)

bpo-37222: Fix for CacheFTPHandler in urllib

A call to FTP.ntransfercmd must be followed by FTP.voidresp to clear
the "end transfer" message. Without this, the client and server get
out of sync, which will result in an error if the FTP instance is
reused to open a second URL. This scenario occurs for even the most
basic usage of CacheFTPHandler.

Reverts the patch merged as a resolution to bpo-16270 and adds a test
case for the CacheFTPHandler in test_urllib2net.py.

(cherry picked from commit e38bebb9ee805df6848f42845e71c8da8a821ad3)

Co-authored-by: Dan Hemberger <846186+hemberger@users.noreply.github.com>
Co-authored-by: Senthil Kumaran <senthil@python.org>
* Added NEWS entry.

---------

Co-authored-by: Dan Hemberger <846186+hemberger@users.noreply.github.com>
Co-authored-by: Senthil Kumaran <senthil@python.org>

diff --git a/Lib/test/test_urllib2net.py b/Lib/test/test_urllib2net.py
index 5da41c37bbfb8eec6844d1f937957a915083c81e..d8d882b2d33589b30ee05f81b4f3afd4ced3cfd2 100644 (file)
--- a/Lib/test/test_urllib2net.py
+++ b/Lib/test/test_urllib2net.py
@@ -134,7 +134,9 @@ class OtherNetworkTests(unittest.TestCase):
     # They do sometimes catch some major disasters, though.
 
     def test_ftp(self):
+        # Testing the same URL twice exercises the caching in CacheFTPHandler
         urls = [
+            'ftp://www.pythontest.net/README',
             'ftp://www.pythontest.net/README',
             ('ftp://www.pythontest.net/non-existent-file',
              None, urllib.error.URLError),

diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index 73ad0127ecc969320e25a3d3608955471486f791..24911bb0190b8e99b61f97bfe4423bbdf7a3cfd7 100644 (file)
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -2469,7 +2469,13 @@ class ftpwrapper:
         return (ftpobj, retrlen)
 
     def endtransfer(self):
+        if not self.busy:
+            return
         self.busy = 0
+        try:
+            self.ftp.voidresp()
+        except ftperrors():
+            pass
 
     def close(self):
         self.keepalive = False

diff --git a/Misc/NEWS.d/next/Library/2023-04-22-22-14-09.gh-issue-81403.zVz9Td.rst b/Misc/NEWS.d/next/Library/2023-04-22-22-14-09.gh-issue-81403.zVz9Td.rst
new file mode 100644 (file)
index 0000000..6adb71f
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-04-22-22-14-09.gh-issue-81403.zVz9Td.rst
@@ -0,0 +1,3 @@
+:class:`urllib.request.CacheFTPHandler` no longer raises :class:`URLError`
+if a cached FTP instance is reused. ftplib's endtransfer method calls
+voidresp to drain the connection to handle FTP instance reuse properly.