feat(metrics): add basic metrics type support (#789)

Co-authored-by: Michi Hoffmann <cleptric@users.noreply.github.com>

interfaces.go

@@ -25,6 +25,9 @@ const profileType = "profile"
 // checkInType is the type of a check in event.
 const checkInType = "check_in"
 
+// metricType is the type of a metric event.
+const metricType = "statsd"
+
 // Level marks the severity of the event.
 type Level string
 
@@ -320,6 +323,7 @@ type Event struct {
 	Exception   []Exception            `json:"exception,omitempty"`
 	DebugMeta   *DebugMeta             `json:"debug_meta,omitempty"`
 	Attachments []*Attachment          `json:"-"`
+	Metrics     []Metric               `json:"-"`
 
 	// The fields below are only relevant for transactions.
 

interfaces_test.go

@@ -513,3 +513,39 @@ func TestStructSnapshots(t *testing.T) {
 		})
 	}
 }
+
+func TestMarshalMetrics(t *testing.T) {
+	tests := []struct {
+		name    string
+		metrics []Metric
+		want    string
+	}{
+		{
+			name: "allowed characters",
+			metrics: []Metric{
+				NewCounterMetric("counter", Second(), map[string]string{"foo": "bar", "route": "GET /foo"}, 1597790835, 1.0),
+				NewDistributionMetric("distribution", Second(), map[string]string{"$foo$": "%bar%"}, 1597790835, 1.0),
+				NewGaugeMetric("gauge", Second(), map[string]string{"föö": "bär"}, 1597790835, 1.0),
+				NewSetMetric[int]("set", Second(), map[string]string{"%{key}": "$value$"}, 1597790835, 1),
+				NewCounterMetric("no_tags", Second(), nil, 1597790835, 1.0),
+			},
+
+			want: strings.Join([]string{
+				"counter@second:1|c|#foo:bar,route:GET /foo|T1597790835",
+				"distribution@second:1|d|#_foo_:bar|T1597790835",
+				"gauge@second:1:1:1:1:1|g|#f_:br|T1597790835",
+				"set@second:1|s|#_key_:$value$|T1597790835",
+				"no_tags@second:1|c|T1597790835",
+			}, "\n"),
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			serializedMetric := marshalMetrics(test.metrics)
+			if diff := cmp.Diff(string(serializedMetric), test.want); diff != "" {
+				t.Errorf("Context mismatch (-want +got):\n%s", diff)
+			}
+		})
+	}
+}