work around odd problem (see comment in code)

setup.py

@@ -40,7 +40,7 @@ except:
 
 setuptools.setup(
         name='warcprox',
-        version='2.4b2.dev159',
+        version='2.4b2.dev160',
         description='WARC writing MITM HTTP/S proxy',
         url='https://github.com/internetarchive/warcprox',
         author='Noah Levitt',

warcprox/mitmproxy.py

@@ -390,6 +390,28 @@ class MitmProxyHandler(http_server.BaseHTTPRequestHandler):
             self.send_error(502, str(e))
             return
 
+    def send_error(self, code, message=None, explain=None):
+        # BaseHTTPRequestHandler.send_response_only() in http/server.py
+        # does this:
+        #     if not hasattr(self, '_headers_buffer'):
+        #         self._headers_buffer = []
+        # but we sometimes see self._headers_buffer == None
+        # (This happened before! see commit dc9fdc34125dd2357)
+        # Workaround:
+        if hasattr(self, '_headers_buffer') and not self._headers_buffer:
+            self._headers_buffer = []
+        try:
+            return http_server.BaseHTTPRequestHandler.send_error(
+                    self, code, message, explain)
+        except:
+            self.logger.error(
+                    '''WTF: self=%r hasattr(self,'_headers_buffer')=%r''',
+                    self, hasattr(self,'_headers_buffer'))
+            if hasattr(self,'_headers_buffer'):
+                self.logger.error(
+                        'WTF: self._headers_buffer=%r', self._headers_buffer)
+            return None
+
     def _proxy_request(self, extra_response_headers={}):
         '''
         Sends the request to the remote server, then uses a ProxyingRecorder to