web: serve prometheus metricsdevelopment

1 files changed, 23 insertions, 2 deletions

diff --git a/at/web.py b/at/web.py
index e30c13e..34b6337 100644
--- a/at/web.py
+++ b/at/web.py
@@ -5,7 +5,8 @@ from datetime import datetime
 from typing import NamedTuple, Iterable, Iterator, List
 from functools import wraps
 from flask import Flask, render_template, abort, g, \
-    redirect, request, url_for, make_response, send_file
+    redirect, request, url_for, make_response, send_file, \
+    Response
 from base64 import b64decode
 
 
@@ -136,7 +137,27 @@ def app(instance_path, devices_api, config):
     @app.route('/')
     def main_view():
         return render_template('main.html', **now_at())
-    
+
+    @app.route('/metrics')
+    def metrics_view():
+        """Render count of different entities, per kind, in Prometheus format."""
+        now = now_at()
+        lines = [
+            "# HELP entities present at the hackerspace according to checkinator / DHCP",
+            "# TYPE people gauge",
+        ]
+        for kind, devices in now.items():
+            # The kind is being directly text-pasted into the metric below -
+            # let's make sure a new kind with special characters doesn't mess
+            # things up too much.
+            if '"' in kind:
+                continue
+            # Not using formatting, as the Prometheus format contains '{' and
+            # '}' characters which throw off Python's .format().
+            line = 'checkinator_now_present_entities{entity_kind="' + kind + '"} '
+            line += str(len(devices))
+            lines.append(line)
+        return Response('\n'.join(lines), mimetype='text/plain')
     
     @app.route('/api')
     def list_all():