Issue #16133: The asynchat.async_chat.handle_read() method now ignores

BlockingIOError exceptions. Initial patch written by Xavier de Gaye.

Document also in asyncore documentation that recv() may raise BlockingIOError.

Lib/test/test_asynchat.py

@@ -7,10 +7,12 @@ thread = support.import_module('_thread')
 
 import asynchat
 import asyncore
+import errno
 import socket
 import sys
 import time
 import unittest
+import unittest.mock
 try:
     import threading
 except ImportError:
@@ -273,6 +275,21 @@ class TestAsynchat_WithPoll(TestAsynchat):
     usepoll = True
 
 
+class TestAsynchatMocked(unittest.TestCase):
+    def test_blockingioerror(self):
+        # Issue #16133: handle_read() must ignore BlockingIOError
+        sock = unittest.mock.Mock()
+        sock.recv.side_effect = BlockingIOError(errno.EAGAIN)
+
+        dispatcher = asynchat.async_chat()
+        dispatcher.set_socket(sock)
+        self.addCleanup(dispatcher.del_channel)
+
+        with unittest.mock.patch.object(dispatcher, 'handle_error') as error:
+            dispatcher.handle_read()
+        self.assertFalse(error.called)
+
+
 class TestHelperFunctions(unittest.TestCase):
     def test_find_prefix_at_end(self):
         self.assertEqual(asynchat.find_prefix_at_end("qwerty\r", "\r\n"), 1)