Add basic instrumentation possibilities to pretix (#271)

* add basic instrumentation possibilities to pretix

* make tabs to spaces

* apply flake8

* implement upstreams suggestions, round 1

* adjust naming of redis-connection

* address noredis

* add view for metrics

* implement HTTP basic auth in front of metrics-endpoint

* rename labelset

* make flake8-clean

* implement upstreams suggestions, round 2

* correct minor slipups

* fix missing return

* let isort add an empty line

* implement test for counter

* implement upstream suggestions, round 3

* correct typo

* implement first test for view

* finish view-test

* fix deprecated keyword

* implement upstream-suggestions, round 4

* implement test for gauge

* test exceptions as well

* add db-decorator

src/tests/base/test_metrics.py

@@ -0,0 +1,140 @@
+# pytest
+
+import base64
+
+import pytest
+from django.test import override_settings
+
+from pretix.base import metrics
+from pretix.base.views import metrics as metricsview
+
+
+class FakeRedis(object):
+
+    def __init__(self):
+        self.storage = {}
+
+    def incrbyfloat(self, rkey, amount):
+        if rkey in self.storage:
+            self.storage[rkey] += amount
+        else:
+            self.set(rkey, amount)
+
+    def set(self, rkey, value):
+        self.storage[rkey] = value
+
+    def get(self, rkey):
+        # bytes-conversion here for emulating redis behavior without making incr too hard
+        return bytes(self.storage[rkey], encoding='utf-8')
+
+
+@override_settings(HAS_REDIS=True)
+def test_counter(monkeypatch):
+
+    fake_redis = FakeRedis()
+
+    monkeypatch.setattr(metrics, "redis", fake_redis, raising=False)
+
+    # now test
+    fullname_GET = metrics.http_requests_total._construct_metric_identifier('http_requests_total', {"code": "200", "handler": "/foo", "method": "GET"})
+    fullname_POST = metrics.http_requests_total._construct_metric_identifier('http_requests_total', {"code": "200", "handler": "/foo", "method": "POST"})
+    metrics.http_requests_total.inc(code="200", handler="/foo", method="GET")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_GET] == 1
+    metrics.http_requests_total.inc(code="200", handler="/foo", method="GET")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_GET] == 2
+    metrics.http_requests_total.inc(7, code="200", handler="/foo", method="GET")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_GET] == 9
+    metrics.http_requests_total.inc(7, code="200", handler="/foo", method="POST")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_GET] == 9
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_POST] == 7
+
+    with pytest.raises(ValueError):
+        metrics.http_requests_total.inc(-4, code="200", handler="/foo", method="POST")
+
+    with pytest.raises(ValueError):
+        metrics.http_requests_total.inc(-4, code="200", handler="/foo", method="POST", too="much")
+
+    # test dimensionless counters
+    dimless_counter = metrics.Counter("dimless_counter", "this is a helpstring")
+    fullname_dimless = dimless_counter._construct_metric_identifier('dimless_counter')
+    dimless_counter.inc(20)
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_dimless] == 20
+
+
+@override_settings(HAS_REDIS=True)
+def test_gauge(monkeypatch):
+
+    fake_redis = FakeRedis()
+
+    monkeypatch.setattr(metrics, "redis", fake_redis, raising=False)
+
+    test_gauge = metrics.Gauge("my_gauge", "this is a helpstring", ["dimension"])
+
+    # now test
+    fullname_one = test_gauge._construct_metric_identifier('my_gauge', {"dimension": "one"})
+    fullname_two = test_gauge._construct_metric_identifier('my_gauge', {"dimension": "two"})
+    fullname_three = test_gauge._construct_metric_identifier('my_gauge', {"dimension": "three"})
+
+    test_gauge.inc(dimension="one")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_one] == 1
+    test_gauge.inc(7, dimension="one")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_one] == 8
+    test_gauge.dec(2, dimension="one")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_one] == 6
+    test_gauge.set(3, dimension="two")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_one] == 6
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_two] == 3
+    test_gauge.set(4, dimension="two")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_one] == 6
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_two] == 4
+    test_gauge.dec(7, dimension="three")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_one] == 6
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_two] == 4
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_three] == -7
+    test_gauge.inc(14, dimension="three")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_one] == 6
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_two] == 4
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_three] == 7
+    test_gauge.set(17, dimension="three")
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_one] == 6
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_two] == 4
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_three] == 17
+
+    with pytest.raises(ValueError):
+        test_gauge.inc(-17, dimension="three")
+
+    with pytest.raises(ValueError):
+        test_gauge.dec(-17, dimension="three")
+
+    with pytest.raises(ValueError):
+        test_gauge.set(7, unknown_label="foo")
+
+    with pytest.raises(ValueError):
+        test_gauge.set(7, dimension="one", too="much")
+
+    # test dimensionless gauges
+    dimless_gauge = metrics.Gauge("dimless_gauge", "this is a helpstring")
+    fullname_dimless = dimless_gauge._construct_metric_identifier('dimless_gauge')
+    dimless_gauge.set(20)
+    assert fake_redis.storage[metrics.REDIS_KEY_PREFIX + fullname_dimless] == 20
+
+
+@pytest.mark.django_db
+@override_settings(HAS_REDIS=True, METRICS_USER="foo", METRICS_PASSPHRASE="bar")
+def test_metrics_view(monkeypatch, client):
+
+    fake_redis = FakeRedis()
+    monkeypatch.setattr(metricsview.metrics, "redis", fake_redis, raising=False)
+
+    counter_value = 3
+    fullname = metrics.http_requests_total._construct_metric_identifier('http_requests_total', {"code": "200", "handler": "/foo", "method": "GET"})
+    metricsview.metrics.http_requests_total.inc(counter_value, code="200", handler="/foo", method="GET")
+
+    # test unauthorized-page
+    assert "You are not authorized" in metricsview.serve_metrics(None).content.decode('utf-8')
+    assert "You are not authorized" in client.get('/metrics').content.decode('utf-8')
+    assert "{} {}".format(fullname, counter_value) not in client.get('/metrics')
+
+    # test metrics-view
+    basic_auth = {"HTTP_AUTHORIZATION": base64.b64encode(bytes("foo:bar", "utf-8"))}
+    assert "{} {}".format(fullname, counter_value) not in client.get("/metrics", headers=basic_auth)