Add openmetrics format parser

expfmt/decode.go

@@ -76,6 +76,8 @@ func NewDecoder(r io.Reader, format Format) Decoder {
 	switch format.FormatType() {
 	case TypeProtoDelim:
 		return &protoDecoder{r: bufio.NewReader(r)}
+	case TypeOpenMetrics:
+		return &openMetricsDecoder{}
 	}
 	return &textDecoder{r: r}
 }
@@ -115,6 +117,36 @@ func (d *protoDecoder) Decode(v *dto.MetricFamily) error {
 	return nil
 }
 
+type openMetricsDecoder struct {
+	r    io.Reader
+	fams map[string]*dto.MetricFamily
+	err  error
+}
+
+// Decode implements Decoder.
+func (d *openMetricsDecoder) Decode(v *dto.MetricFamily) error {
+	if d.err == nil {
+		// Read all metrics in one shot.
+		var p OpenMetricsParser
+		d.fams, d.err = p.OpenMetricsToMetricFamilies(d.r)
+		// If we don't get an error, store io.EOF for the end.
+		if d.err == nil {
+			d.err = io.EOF
+		}
+	}
+	// Pick off one MetricFamily per Decode until there's nothing left.
+	for key, fam := range d.fams {
+		v.Name = fam.Name
+		v.Help = fam.Help
+		v.Type = fam.Type
+		v.Unit = fam.Unit
+		v.Metric = fam.Metric
+		delete(d.fams, key)
+		return nil
+	}
+	return d.err
+}
+
 // textDecoder implements the Decoder interface for the text protocol.
 type textDecoder struct {
 	r    io.Reader

expfmt/decode_test.go

@@ -103,6 +103,78 @@ mf2 4
 	}
 }
 
+func TestOpenMetricsDecoder(t *testing.T) {
+	var (
+		ts = model.Now()
+		in = `
+# Only a quite simple scenario with two metric families.
+# More complicated tests of the parser itself can be found in the openmetrics package.
+# TYPE metric1 counter
+metric1_total 3
+mf1{label="value1"} -3.14 123456
+mf1{label="value2"} 42
+metric1_total 4
+# EOF
+`
+		out = model.Vector{
+			&model.Sample{
+				Metric: model.Metric{
+					model.MetricNameLabel: "mf1",
+					"label":               "value1",
+				},
+				Value:     -3.14,
+				Timestamp: 123456,
+			},
+			&model.Sample{
+				Metric: model.Metric{
+					model.MetricNameLabel: "mf1",
+					"label":               "value2",
+				},
+				Value:     42,
+				Timestamp: ts,
+			},
+			&model.Sample{
+				Metric: model.Metric{
+					model.MetricNameLabel: "metric1",
+				},
+				Value:     3,
+				Timestamp: ts,
+			},
+			&model.Sample{
+				Metric: model.Metric{
+					model.MetricNameLabel: "metric1",
+				},
+				Value:     4,
+				Timestamp: ts,
+			},
+		}
+	)
+
+	dec := &SampleDecoder{
+		Dec: &openMetricsDecoder{r: strings.NewReader(in)},
+		Opts: &DecodeOptions{
+			Timestamp: ts,
+		},
+	}
+	var all model.Vector
+	for {
+		var smpls model.Vector
+		err := dec.Decode(&smpls)
+		if err != nil && errors.Is(err, io.EOF) {
+			break
+		}
+		if err != nil {
+			t.Fatal(err)
+		}
+		all = append(all, smpls...)
+	}
+	sort.Sort(all)
+	sort.Sort(out)
+	if !reflect.DeepEqual(all, out) {
+		t.Fatalf("output does not match")
+	}
+}
+
 func TestProtoDecoder(t *testing.T) {
 	testTime := model.Now()