gh-88574: Skip spurious blank lines between responses in imaplib

serhiy-storchaka · claude · serhiy-storchaka · commit 4b356f6fbb00 · 2026-07-08T13:42:50.000+03:00
Some servers send the spurious blank line even after a literal that ends
a response (such as a mailbox name returned by LIST as a literal).  It
falls between untagged responses and is now skipped, so a LIST or LSUB
reply with a literal name in every response is read correctly.

Co-Authored-By: Claude Opus 4.8 &lt;noreply@anthropic.com&gt;
diff --git a/Lib/imaplib.py b/Lib/imaplib.py
@@ -1351,6 +1351,13 @@ def _get_response(self, start_timeout=False):
         else:
             resp = self._get_line()
 
+        # Skip spurious blank lines between responses.  Some servers send one
+        # after a literal that ends a response (e.g. a mailbox name returned by
+        # LIST as a literal); it arrives here as an empty line before the next
+        # response.
+        while resp == b'':
+            resp = self._get_line()
+
         # Command completion response?
 
         if self._match(self.tagre, resp):
diff --git a/Lib/test/test_imaplib.py b/Lib/test/test_imaplib.py
@@ -1059,6 +1059,30 @@ def cmd_LIST(self, tag, args):
         self.assertEqual(data, [(b'(\\HasNoChildren) "/" {9}', b'My (box)"'),
                                 b''])
 
+    def test_spurious_blank_lines_between_responses(self):
+        # Some servers send a spurious blank line after every literal, including
+        # one that terminates a response.  Such blanks fall between the untagged
+        # responses and must be skipped, even when several arrive in a row (a
+        # LIST reply with a literal mailbox name in each response).
+        names = [b'My (box)"', b'Another', b'Third']
+        class Handler(SimpleIMAPHandler):
+            def cmd_LIST(self, tag, args):
+                for name in names:
+                    self._send(b'* LIST (\\HasNoChildren) "/" {%d}\r\n'
+                               % len(name))
+                    self._send(name)
+                    self._send(b'\r\n\r\n')     # ends the response, then a blank
+                self._send_tagged(tag, 'OK', 'LIST completed')
+        client, _ = self._setup(Handler)
+        client.login('user', 'pass')
+        typ, data = client.list()
+        self.assertEqual(typ, 'OK')
+        self.assertEqual(data, [
+            (b'(\\HasNoChildren) "/" {9}', b'My (box)"'), b'',
+            (b'(\\HasNoChildren) "/" {7}', b'Another'), b'',
+            (b'(\\HasNoChildren) "/" {5}', b'Third'), b'',
+        ])
+
     def test_unselect(self):
         client, server = self._setup(SimpleIMAPHandler)
         client.login('user', 'pass')
diff --git a/Misc/NEWS.d/next/Library/2026-07-01-10-00-00.gh-issue-88574.Kz3wQm.rst b/Misc/NEWS.d/next/Library/2026-07-01-10-00-00.gh-issue-88574.Kz3wQm.rst
@@ -1,5 +1,4 @@
 :mod:`imaplib` no longer fails when a server sends a spurious blank line
-after the counted data of a literal.  Such a blank line is now skipped,
-but only inside an unclosed parenthesis, so that a literal terminating a
-response (such as a mailbox name returned by ``LIST``) is not mistaken
-for it.
+after the counted data of a literal, including after a literal that
+terminates a response (such as a mailbox name returned by ``LIST``).
+Such blank lines are now skipped without swallowing the following line.
