Allow static scrape targets without a port set (#332)

This commit ensures that Metrics Endpoint Consumer accepts
static scrape targets that do not have a port set.

closes #327

lib/charms/prometheus_k8s/v0/prometheus_scrape.py

@@ -1128,7 +1128,7 @@ def _labeled_static_job_config(self, job, job_name_prefix, hosts, scrape_metadat
             ports = []
             unitless_targets = []
             for target in all_targets:
-                host, port = target.split(":")
+                host, port = self._target_parts(target)
                 if host.strip() == "*":
                     ports.append(port.strip())
                 else:
@@ -1157,6 +1157,26 @@ def _labeled_static_job_config(self, job, job_name_prefix, hosts, scrape_metadat
 
         return labeled_job
 
+    def _target_parts(self, target) -> list:
+        """Extract host and port from a wildcard target.
+
+        Args:
+            target: a string specifying a scrape target. A
+              scrape target is expected to have the format
+              "host:port". The host part may be a wildcard
+              "*" and the port part can be missing (along
+              with ":") in which case port is set to 80.
+
+        Returns:
+            a list with target host and port as in [host, port]
+        """
+        if ":" in target:
+            parts = target.split(":")
+        else:
+            parts = [target, "80"]
+
+        return parts
+
     def _set_juju_labels(self, labels, scrape_metadata) -> dict:
         """Create a copy of metric labels with Juju topology information.
 

tests/unit/test_endpoint_consumer.py

@@ -392,6 +392,39 @@ def test_consumer_overwrites_juju_topology_labels(self):
         for label_name, label_value in labels.items():
             self.assertNotEqual(label_value, bad_labels[label_name])
 
+    def test_consumer_accepts_targets_without_a_port_set(self):
+        self.assertEqual(self.harness.charm._stored.num_events, 0)
+
+        rel_id = self.harness.add_relation(RELATION_NAME, "consumer")
+        jobs = DEFAULT_JOBS.copy()
+        jobs[0]["static_configs"] = [
+            {
+                "targets": ["*"],
+            }
+        ]
+        self.harness.update_relation_data(
+            rel_id,
+            "consumer",
+            {
+                "scrape_metadata": json.dumps(SCRAPE_METADATA),
+                "scrape_jobs": json.dumps(jobs),
+            },
+        )
+        self.assertEqual(self.harness.charm._stored.num_events, 1)
+        self.harness.add_relation_unit(rel_id, "consumer/0")
+        self.harness.update_relation_data(
+            rel_id,
+            "consumer/0",
+            {
+                "prometheus_scrape_unit_address": "1.1.1.1",
+                "prometheus_scrape_unit_name": "provider/0",
+            },
+        )
+        self.assertEqual(self.harness.charm._stored.num_events, 2)
+
+        jobs = self.harness.charm.prometheus_consumer.jobs()
+        self.validate_jobs(jobs)
+
     def test_consumer_returns_alerts_rules_file(self):
         self.assertEqual(self.harness.charm._stored.num_events, 0)