Merge branch 'dirty-metrics' into 'staging'

Quick-and-dirty Prometheus metrics exposing

See merge request s3lph/matemat!71

matemat/webserver/pagelets/__init__.py

@@ -11,6 +11,7 @@ from .touchkey import touchkey_page
 from .buy import buy
 from .deposit import deposit
 from .admin import admin
+from .metrics import metrics
 from .moduser import moduser
 from .modproduct import modproduct
 from .userbootstrap import userbootstrap

matemat/webserver/pagelets/metrics.py

@@ -0,0 +1,23 @@
+from bottle import abort, response, route
+
+from matemat.db import MatematDatabase
+from matemat.webserver.config import get_app_config
+
+
+@route('/metrics')
+def metrics():
+    config = get_app_config()
+    if config.get('MetricsEnabled', '0') != '1':
+        return abort(403,
+                     'Prometheus metrics are disable in configuration. '
+                     'If you believe this is an error, contact your administrator.')
+    with MatematDatabase(config['DatabaseFile']) as db:
+        products = db.list_products()
+    m = '''# TYPE matemat_beverage_supply_count gauge
+# HELP matemat_beverage_supply_count Number of bottles available
+'''
+    for product in products:
+        name = product.name.replace('"', '\\"')
+        m += f'matemat_beverage_supply_count{{product="{name}"}} {product.stock}\n'
+    response.headers['Content-Type'] = 'text/plain'
+    return m