Merge pull request #2599 from bblommers/feature/#2010

CloudWatch - Implement list_metrics pagination

moto/cloudwatch/models.py

@@ -5,6 +5,7 @@ from moto.core.exceptions import RESTError
 import boto.ec2.cloudwatch
 from datetime import datetime, timedelta
 from dateutil.tz import tzutc
+from uuid import uuid4
 from .utils import make_arn_for_dashboard
 
 DEFAULT_ACCOUNT_ID = 123456789012
@@ -193,6 +194,7 @@ class CloudWatchBackend(BaseBackend):
         self.alarms = {}
         self.dashboards = {}
         self.metric_data = []
+        self.paged_metric_data = {}
 
     def put_metric_alarm(
         self,
@@ -377,6 +379,36 @@ class CloudWatchBackend(BaseBackend):
 
         self.alarms[alarm_name].update_state(reason, reason_data, state_value)
 
+    def list_metrics(self, next_token, namespace, metric_name):
+        if next_token:
+            if next_token not in self.paged_metric_data:
+                raise RESTError(
+                    "PaginationException", "Request parameter NextToken is invalid"
+                )
+            else:
+                metrics = self.paged_metric_data[next_token]
+                del self.paged_metric_data[next_token]  # Cant reuse same token twice
+                return self._get_paginated(metrics)
+        else:
+            metrics = self.get_filtered_metrics(metric_name, namespace)
+            return self._get_paginated(metrics)
+
+    def get_filtered_metrics(self, metric_name, namespace):
+        metrics = self.get_all_metrics()
+        if namespace:
+            metrics = [md for md in metrics if md.namespace == namespace]
+        if metric_name:
+            metrics = [md for md in metrics if md.name == metric_name]
+        return metrics
+
+    def _get_paginated(self, metrics):
+        if len(metrics) > 500:
+            next_token = str(uuid4())
+            self.paged_metric_data[next_token] = metrics[500:]
+            return next_token, metrics[0:500]
+        else:
+            return None, metrics
+
 
 class LogGroup(BaseModel):
     def __init__(self, spec):

moto/cloudwatch/responses.py

@@ -120,9 +120,14 @@ class CloudWatchResponse(BaseResponse):
 
     @amzn_request_id
     def list_metrics(self):
-        metrics = self.cloudwatch_backend.get_all_metrics()
+        namespace = self._get_param("Namespace")
+        metric_name = self._get_param("MetricName")
+        next_token = self._get_param("NextToken")
+        next_token, metrics = self.cloudwatch_backend.list_metrics(
+            next_token, namespace, metric_name
+        )
         template = self.response_template(LIST_METRICS_TEMPLATE)
-        return template.render(metrics=metrics)
+        return template.render(metrics=metrics, next_token=next_token)
 
     @amzn_request_id
     def delete_dashboards(self):
@@ -340,9 +345,11 @@ LIST_METRICS_TEMPLATE = """<ListMetricsResponse xmlns="http://monitoring.amazona
             </member>
             {% endfor %}
         </Metrics>
+        {% if next_token is not none %}
         <NextToken>
-            96e88479-4662-450b-8a13-239ded6ce9fe
+            {{ next_token }}
         </NextToken>
+        {% endif %}
     </ListMetricsResult>
 </ListMetricsResponse>"""