Fix instance_ip_grouping_key not working on macOS (#687)

* Fix instance_ip_grouping_key not working on macOS

Fixes #629

The solution is adapted from this StackOverflow answer: https://stackoverflow.com/a/28950776

Signed-off-by: Jethro Muller <git@jethromuller.co.za>

* Remove conditional skip for macos

Signed-off-by: Jethro Muller <git@jethromuller.co.za>

* Add platform check with explanatory comment

Signed-off-by: Jethro Muller <git@jethromuller.co.za>

Author: AceFire6

prometheus_client/exposition.py

@@ -481,7 +481,16 @@ def _escape_grouping_key(k, v):
 def instance_ip_grouping_key():
     """Grouping key with instance set to the IP Address of this host."""
     with closing(socket.socket(socket.AF_INET, socket.SOCK_DGRAM)) as s:
-        s.connect(('localhost', 0))
+        if sys.platform == 'darwin':
+            # This check is done this way only on MacOS devices
+            # it is done this way because the localhost method does
+            # not work.
+            # This method was adapted from this StackOverflow answer:
+            # https://stackoverflow.com/a/28950776
+            s.connect(('10.255.255.255', 1))
+        else:
+            s.connect(('localhost', 0))
+
         return {'instance': s.getsockname()[0]}
 
 

tests/test_exposition.py

@@ -376,10 +376,6 @@ def my_redirect_handler(url, method, timeout, headers, data):
         # ensure the redirect took place at the expected redirect location.
         self.assertEqual(self.requests[1][0].path, "/" + self.redirect_flag)
 
-    @unittest.skipIf(
-        sys.platform == "darwin",
-        "instance_ip_grouping_key() does not work on macOS."
-    )
     def test_instance_ip_grouping_key(self):
         self.assertTrue('' != instance_ip_grouping_key()['instance'])