feat(api): add OpenMetrics renderer for metrics

This makes it compatible with Prometheus.

Fixes #9285

docs/api.rst

@@ -2560,6 +2560,10 @@ Metrics
 
     Returns server metrics.
 
+    .. versionchanged:: 5.6.1
+
+       Metrics can now be exposed in OpenMetrics compatible format with ``?format=openmetrics``.
+
     :>json int units: Number of units
     :>json int units_translated: Number of translated units
     :>json int users: Number of users

docs/changes.rst

@@ -8,6 +8,7 @@ Not yet released.
 **Improvements**
 
 * Docker container accepts :envvar:`WEBLATE_REMOVE_ADDONS` and :envvar:`WEBLATE_ADD_MACHINERY` to customize automatic suggestion services.
+* Added OpenMetrics compatibility for :http:get:`/api/metrics/`.
 
 **Bug fixes**
 

weblate/api/renderers.py

@@ -0,0 +1,28 @@
+# Copyright © Michal Čihař <michal@weblate.org>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from rest_framework.renderers import BaseRenderer
+
+
+class OpenMetricsRenderer(BaseRenderer):
+    media_type = "application/openmetrics-text"
+    format = "openmetrics"
+    charset = "utf-8"
+    render_style = "text"
+
+    def render(self, data, accepted_media_type=None, renderer_context=None):
+        result = []
+        for key, value in data.items():
+            if isinstance(value, str):
+                # Strings not supported
+                continue
+            if isinstance(value, int | float):
+                result.append(f"{key} {value}")
+            elif isinstance(value, dict):
+                # Celery queues
+                for queue, stat in value.items():
+                    result.append(f'{key}(queue="{queue}") {stat}')
+
+        result.append("# EOF")
+        return "\n".join(result)

weblate/api/tests.py

@@ -3908,6 +3908,11 @@ def test_metrics(self) -> None:
         response = self.client.get(reverse("api:metrics"))
         self.assertEqual(response.data["projects"], 1)
 
+    def test_metrics_openmetrics(self) -> None:
+        self.authenticate()
+        response = self.client.get(reverse("api:metrics"), {"format": "openmetrics"})
+        self.assertContains(response, "# EOF")
+
     def test_forbidden(self) -> None:
         response = self.client.get(reverse("api:metrics"))
         self.assertEqual(response.data["detail"].code, "not_authenticated")

weblate/api/views.py

@@ -24,6 +24,7 @@
 from rest_framework.exceptions import ValidationError
 from rest_framework.mixins import CreateModelMixin, DestroyModelMixin, UpdateModelMixin
 from rest_framework.permissions import IsAuthenticated
+from rest_framework.renderers import BrowsableAPIRenderer, JSONRenderer
 from rest_framework.response import Response
 from rest_framework.reverse import reverse
 from rest_framework.settings import api_settings
@@ -115,6 +116,8 @@
 from weblate.utils.views import download_translation_file, zip_download
 from weblate.wladmin.models import ConfigurationError
 
+from .renderers import OpenMetricsRenderer
+
 REPO_OPERATIONS = {
     "push": ("vcs.push", "do_push", (), True),
     "pull": ("vcs.update", "do_update", (), True),
@@ -1812,6 +1815,7 @@ class Metrics(APIView):
     """Metrics view for monitoring."""
 
     permission_classes = (IsAuthenticated,)
+    renderer_classes = (JSONRenderer, BrowsableAPIRenderer, OpenMetricsRenderer)
 
     def get(self, request, format=None):  # noqa: A002
         stats = GlobalStats()