#1291 http.server's send_error takes an optional explain argument

Doc/library/http.server.rst

@@ -170,15 +170,19 @@ of which this module provides three different variants:
 
       .. versionadded:: 3.2
 
-   .. method:: send_error(code, message=None)
+   .. method:: send_error(code, message=None, explain=None)
 
       Sends and logs a complete error reply to the client. The numeric *code*
-      specifies the HTTP error code, with *message* as optional, more specific text. A
-      complete set of headers is sent, followed by text composed using the
-      :attr:`error_message_format` class variable.
+      specifies the HTTP error code, with *message* as optional, more specific
+      text, usually referring to short message response.  The *explain*
+      argument can be used to send a detailed information about the error in
+      response content body.  A complete set of headers is sent, followed by
+      text composed using the :attr:`error_message_format` class variable.
 
       .. versionchanged:: 3.4
          The error response includes a Content-Length header.
+         explain argument was added.
+
 
    .. method:: send_response(code, message=None)
 

Lib/http/server.py

@@ -401,12 +401,17 @@ class BaseHTTPRequestHandler(socketserver.StreamRequestHandler):
         while not self.close_connection:
             self.handle_one_request()
 
-    def send_error(self, code, message=None):
+    def send_error(self, code, message=None, explain=None):
         """Send and log an error reply.
 
-        Arguments are the error code, and a detailed message.
-        The detailed message defaults to the short entry matching the
-        response code.
+        Arguments are
+        * code:    an HTTP error code
+                   3 digits
+        * message: a simple optional 1 line reason phrase.
+                   *( HTAB / SP / VCHAR / %x80-FF )
+                   defaults to short entry matching the response code
+        * explain: a detailed message defaults to the long entry
+                   matching the response code.
 
         This sends an error response (so it must be called before any
         output has been generated), logs the error, and finally sends
@@ -420,11 +425,12 @@ class BaseHTTPRequestHandler(socketserver.StreamRequestHandler):
             shortmsg, longmsg = '???', '???'
         if message is None:
             message = shortmsg
+        if explain is None:
             explain = longmsg
         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})
+                   {'code': code, 'message': _quote_html(message), 'explain': _quote_html(explain)})
         body = content.encode('UTF-8', 'replace')
         self.send_response(code, message)
         self.send_header("Content-Type", self.error_content_type)

Lib/test/test_httpservers.py

@@ -95,6 +95,10 @@ class BaseHTTPServerTestCase(BaseTestCase):
         def do_NOTFOUND(self):
             self.send_error(404)
 
+        def do_EXPLAINERROR(self):
+            self.send_error(999, "Short Message",
+                            "This is a long \n explaination")
+
         def do_CUSTOM(self):
             self.send_response(999)
             self.send_header('Content-Type', 'text/html')
@@ -206,6 +210,12 @@ class BaseHTTPServerTestCase(BaseTestCase):
         res = self.con.getresponse()
         self.assertEqual(res.status, 999)
 
+    def test_return_explain_error(self):
+        self.con.request('EXPLAINERROR', '/')
+        res = self.con.getresponse()
+        self.assertEqual(res.status, 999)
+        self.assertTrue(int(res.getheader('Content-Length')))
+
     def test_latin1_header(self):
         self.con.request('LATINONEHEADER', '/', headers={
             'X-Special-Incoming':       'Ärger mit Unicode'

Misc/NEWS

@@ -280,6 +280,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #12921: http.server's send_error takes an explain argument to send more
+  information in response. Patch contributed by Karl.
+
 - Issue #17414: Add timeit, repeat, and default_timer to timeit.__all__.
 
 - Issue #1285086: Get rid of the refcounting hack and speed up