Add separate handling of the /favicon.ico path in the default wsgi implementation (prometheus#631)

ngehrsitz · Norman Gehrsitz · web-flow · commit 5dffc77b9ff1 · 2021-02-25T14:42:12.000-07:00
Signed-off-by: Norman Gehrsitz &lt;gehrsitz.norman@student.dhbw-kahlsruhe.de&gt;

Co-authored-by: Norman Gehrsitz &lt;gehrsitz.norman@student.dhbw-kahlsruhe.de&gt;
diff --git a/prometheus_client/exposition.py b/prometheus_client/exposition.py
@@ -113,8 +113,14 @@ def prometheus_app(environ, start_response):
         # Prepare parameters
         accept_header = environ.get('HTTP_ACCEPT')
         params = parse_qs(environ.get('QUERY_STRING', ''))
-        # Bake output
-        status, header, output = _bake_output(registry, accept_header, params)
+        if environ['PATH_INFO'] == '/favicon.ico':
+            # Serve empty response for browsers
+            status = '200 OK'
+            header = ('', '')
+            output = b''
+        else:
+            # Bake output
+            status, header, output = _bake_output(registry, accept_header, params)
         # Return output
         start_response(status, [header])
         return [output]
diff --git a/tests/test_wsgi.py b/tests/test_wsgi.py
@@ -1,10 +1,12 @@
 from __future__ import absolute_import, unicode_literals
 
+import sys
+import unittest
 from unittest import TestCase
 from wsgiref.util import setup_testing_defaults
 
 from prometheus_client import CollectorRegistry, Counter, make_wsgi_app
-from prometheus_client.exposition import CONTENT_TYPE_LATEST
+from prometheus_client.exposition import _bake_output, CONTENT_TYPE_LATEST
 
 
 class WSGITest(TestCase):
@@ -65,3 +67,22 @@ def test_report_metrics_3(self):
 
     def test_report_metrics_4(self):
         self.validate_metrics("failed_requests", "Number of failed requests", 7)
+
+    @unittest.skipIf(sys.version_info < (3, 3), "Test requires Python 3.3+.")
+    def test_favicon_path(self):
+        from unittest.mock import patch
+
+        # Create mock to enable counting access of _bake_output
+        with patch("prometheus_client.exposition._bake_output", side_effect=_bake_output) as mock:
+            # Create and run WSGI app
+            app = make_wsgi_app(self.registry)
+            # Try accessing the favicon path
+            favicon_environ = dict(self.environ)
+            favicon_environ['PATH_INFO'] = '/favicon.ico'
+            outputs = app(favicon_environ, self.capture)
+            # Test empty response
+            self.assertEqual(outputs, [b''])
+            self.assertEqual(mock.call_count, 0)
+            # Try accessing normal paths
+            app(self.environ, self.capture)
+            self.assertEqual(mock.call_count, 1)
