Add Request exceptions to default metrics

Counts exceptions arriving at ``teardown_request``.

It currently does not allow tracking further http
codes in range of 405-5xx.

prometheus_flask_exporter/__init__.py

@@ -293,6 +293,7 @@ def export_defaults(self, buckets=None, group_by='path',
         """
         Export the default metrics:
             - HTTP request latencies
+            - HTTP request exceptions
             - Number of HTTP requests
 
         :param buckets: the time buckets for request latencies
@@ -353,18 +354,26 @@ def export_defaults(self, buckets=None, group_by='path',
 
         labels = self._get_combined_labels(None)
 
-        histogram = Histogram(
+        request_duration_metric = Histogram(
             '%shttp_request_duration_seconds' % prefix,
             'Flask HTTP request duration in seconds',
             ('method', duration_group_name, 'status') + labels.keys(),
             registry=self.registry,
             **buckets_as_kwargs
         )
 
-        counter = Counter(
+        counter_labels = ('method', 'status') + labels.keys()
+        request_total_metric = Counter(
             '%shttp_request_total' % prefix,
             'Total number of HTTP requests',
-            ('method', 'status') + labels.keys(),
+            counter_labels,
+            registry=self.registry
+        )
+
+        request_exceptions_metric = Counter(
+            '%shttp_request_exceptions_total' % prefix,
+            'Total number of HTTP requests which resulted in an exception',
+            counter_labels,
             registry=self.registry
         )
 
@@ -387,16 +396,16 @@ def after_request(response):
                 else:
                     group = getattr(request, duration_group)
 
-                histogram_labels = {
+                request_duration_labels = {
                     'method': request.method,
                     'status': _to_status_code(response.status_code),
                     duration_group_name: group
                 }
-                histogram_labels.update(labels.values_for(response))
+                request_duration_labels.update(labels.values_for(response))
 
-                histogram.labels(**histogram_labels).observe(total_time)
+                request_duration_metric.labels(**request_duration_labels).observe(total_time)
 
-            counter.labels(
+            request_total_metric.labels(
                 method=request.method, status=_to_status_code(response.status_code),
                 **labels.values_for(response)
             ).inc()
@@ -411,26 +420,40 @@ def teardown_request(exception=None):
                 if any(pattern.match(request.path) for pattern in self.excluded_paths):
                     return
 
-            response = make_response('Exception: %s' % exception, 500)
+            # Check if the exception was raised using a response object and use
+            # its status_code if present. This will only work for ``werkzeug.exceptions.HTTPException``
+            # and subclasses thereof. Otherwise we assume it's a 500.
+            try:
+                response = exception.get_response()
+                status_code = _to_status_code(response.status_code)
+            except:
+                status_code = 500
+            finally:
+                response = make_response('Exception: %s' % exception, status_code)
+
+            if callable(duration_group):
+                group = duration_group(request)
+            else:
+                group = getattr(request, duration_group)
+
+            request_exceptions_metric.labels(
+                method=request.method, status=status_code,
+                **labels.values_for(response)
+            ).inc()
 
             if hasattr(request, 'prom_start_time'):
                 total_time = max(default_timer() - request.prom_start_time, 0)
 
-                if callable(duration_group):
-                    group = duration_group(request)
-                else:
-                    group = getattr(request, duration_group)
-
-                histogram_labels = {
+                request_duration_labels = {
                     'method': request.method,
-                    'status': 500,
+                    'status': status_code,
                     duration_group_name: group
                 }
-                histogram_labels.update(labels.values_for(response))
+                request_duration_labels.update(labels.values_for(response))
 
-                histogram.labels(**histogram_labels).observe(total_time)
+                request_duration_metric.labels(**request_duration_labels).observe(total_time)
 
-            counter.labels(
+            request_total_metric.labels(
                 method=request.method, status=500,
                 **labels.values_for(response)
             ).inc()

tests/test_defaults.py

@@ -1,7 +1,7 @@
 from unittest_helper import BaseTestCase
 
 from prometheus_flask_exporter import NO_PREFIX
-from flask import request, make_response
+from flask import request, make_response, abort
 
 
 class DefaultsTest(BaseTestCase):
@@ -52,7 +52,10 @@ def test():
             'flask_http_request_duration_seconds_bucket', '2.0',
             ('le', '+Inf'), ('method', 'GET'), ('path', '/test'), ('status', 200)
         )
-
+        self.assertAbsent(
+            'flask_http_request_exceptions_total',
+            ('method', 'GET'), ('path', '/skip/defaults'), ('status', 200)
+        )
         self.client.get('/test')
 
         self.assertMetric(
@@ -109,6 +112,33 @@ def test():
             ('method', 'GET'), ('path', '/skip'), ('status', 200)
         )
 
+    def test_exception_counter_metric(self):
+        metrics = self.metrics()
+
+        @self.app.route('/error')
+        def test():
+            raise AttributeError
+
+        try:
+            self.client.get('/error')
+        except AttributeError:
+            pass
+
+        self.assertMetric(
+            'flask_http_request_exceptions_total', '1.0',
+            ('method', 'GET'), ('path', '/error'), ('status', 500)
+        )
+
+        try:
+            self.client.get('/error')
+        except AttributeError:
+            pass
+
+        self.assertMetric(
+            'flask_http_request_exceptions_total', '2.0',
+            ('method', 'GET'), ('path', '/error'), ('status', 500)
+        )
+
     def test_do_not_track_only_excludes_defaults(self):
         metrics = self.metrics()
 
@@ -130,6 +160,10 @@ def test():
             'flask_http_request_duration_seconds_count',
             ('method', 'GET'), ('path', '/skip/defaults'), ('status', 200)
         )
+        self.assertAbsent(
+            'flask_http_request_exceptions_total',
+            ('method', 'GET'), ('path', '/skip/defaults'),
+        )
 
         self.assertMetric('cnt_before_total', 2.0)
         self.assertMetric('cnt_after_total', 2.0)
@@ -178,6 +212,11 @@ def test():
             ('method', 'GET'), ('path', '/test'), ('status', 200),
             endpoint='/my-metrics'
         )
+        self.assertAbsent(
+            'flask_http_request_exceptions_total',
+            ('method', 'GET'), ('path', '/test'),
+            endpoint='/my-metrics'
+        )
 
     def test_no_default_export(self):
         self.metrics(export_defaults=False)
@@ -198,6 +237,11 @@ def test():
             ('method', 'GET'), ('path', '/test'), ('status', 200),
             endpoint='/metrics'
         )
+        self.assertAbsent(
+            'flask_http_request_exceptions_total',
+            ('method', 'GET'), ('path', '/test'), ('status', 200),
+            endpoint='/metrics'
+        )
 
     def test_custom_defaults_prefix(self):
         metrics = self.metrics(defaults_prefix='www')
@@ -291,7 +335,10 @@ def test():
             'late_http_request_total',
             ('method', 'GET'), ('status', 200)
         )
-
+        self.assertAbsent(
+            'flask_http_request_exceptions_total',
+            ('method', 'GET'), ('path', '/test'),
+        )
         metrics.export_defaults(prefix='late')
 
         self.assertMetric(
@@ -311,6 +358,10 @@ def test():
             'late_http_request_duration_seconds_count', '3.0',
             ('method', 'GET'), ('path', '/test'), ('status', 200)
         )
+        self.assertAbsent(
+            'flask_http_request_exceptions_total',
+            ('method', 'GET'), ('path', '/test'),
+        )
 
     def test_non_automatic_endpoint_registration(self):
         metrics = self.metrics(path=None)