Issue #25738: Don’t send message body for 205 Reset Content

Patch by Susumu Koshiba.
diff --git a/Lib/BaseHTTPServer.py b/Lib/BaseHTTPServer.py
index deaf2f9..3df3323 100644
--- a/Lib/BaseHTTPServer.py
+++ b/Lib/BaseHTTPServer.py
@@ -362,14 +362,25 @@
             message = short
         explain = long
         self.log_error("code %d, message %s", code, message)
-        # using _quote_html to prevent Cross Site Scripting attacks (see bug #1100201)
-        content = (self.error_message_format %
-                   {'code': code, 'message': _quote_html(message), 'explain': explain})
         self.send_response(code, message)
-        self.send_header("Content-Type", self.error_content_type)
         self.send_header('Connection', 'close')
+
+        # Message body is omitted for cases described in:
+        #  - RFC7230: 3.3. 1xx, 204(No Content), 304(Not Modified)
+        #  - RFC7231: 6.3.6. 205(Reset Content)
+        content = None
+        if code >= 200 and code not in (204, 205, 304):
+            # HTML encode to prevent Cross Site Scripting attacks
+            # (see bug #1100201)
+            content = (self.error_message_format % {
+                'code': code,
+                'message': _quote_html(message),
+                'explain': explain
+            })
+            self.send_header("Content-Type", self.error_content_type)
         self.end_headers()
-        if self.command != 'HEAD' and code >= 200 and code not in (204, 304):
+
+        if self.command != 'HEAD' and content:
             self.wfile.write(content)
 
     error_message_format = DEFAULT_ERROR_MESSAGE
diff --git a/Lib/test/test_httpservers.py b/Lib/test/test_httpservers.py
index 672c187..1b6339d 100644
--- a/Lib/test/test_httpservers.py
+++ b/Lib/test/test_httpservers.py
@@ -178,6 +178,12 @@
             self.send_header('Connection', 'close')
             self.end_headers()
 
+        def do_SEND_ERROR(self):
+            self.send_error(int(self.path[1:]))
+
+        def do_HEAD(self):
+            self.send_error(int(self.path[1:]))
+
     def setUp(self):
         BaseTestCase.setUp(self)
         self.con = httplib.HTTPConnection('localhost', self.PORT)
@@ -276,6 +282,38 @@
         res = self.con.getresponse()
         self.assertEqual(res.status, 999)
 
+    def test_send_error(self):
+        allow_transfer_encoding_codes = (205, 304)
+        for code in (101, 102, 204, 205, 304):
+            self.con.request('SEND_ERROR', '/{}'.format(code))
+            res = self.con.getresponse()
+            self.assertEqual(code, res.status)
+            self.assertEqual(None, res.getheader('Content-Length'))
+            self.assertEqual(None, res.getheader('Content-Type'))
+            if code not in allow_transfer_encoding_codes:
+                self.assertEqual(None, res.getheader('Transfer-Encoding'))
+
+            data = res.read()
+            self.assertEqual(b'', data)
+
+    def test_head_via_send_error(self):
+        allow_transfer_encoding_codes = (205, 304)
+        for code in (101, 200, 204, 205, 304):
+            self.con.request('HEAD', '/{}'.format(code))
+            res = self.con.getresponse()
+            self.assertEqual(code, res.status)
+            if code == 200:
+                self.assertEqual(None, res.getheader('Content-Length'))
+                self.assertIn('text/html', res.getheader('Content-Type'))
+            else:
+                self.assertEqual(None, res.getheader('Content-Length'))
+                self.assertEqual(None, res.getheader('Content-Type'))
+            if code not in allow_transfer_encoding_codes:
+                self.assertEqual(None, res.getheader('Transfer-Encoding'))
+
+            data = res.read()
+            self.assertEqual(b'', data)
+
 
 class SimpleHTTPServerTestCase(BaseTestCase):
     class request_handler(NoLogRequestHandler, SimpleHTTPRequestHandler):