API Client: Support new metadata endpoint in v1

Introduces support for the new metadata endpoint from Prometheus. The new endpoint provides information independent of targets and collapses the unique combinations of HELP, TYPE and UNIT.

Fixes #705

Signed-off-by: gotjosh <josue@grafana.com>

api/prometheus/v1/api.go

@@ -130,6 +130,7 @@ const (
 	epSeries          = apiPrefix + "/series"
 	epTargets         = apiPrefix + "/targets"
 	epTargetsMetadata = apiPrefix + "/targets/metadata"
+	epMetricsMetadata = apiPrefix + "/metadata"
 	epRules           = apiPrefix + "/rules"
 	epSnapshot        = apiPrefix + "/admin/tsdb/snapshot"
 	epDeleteSeries    = apiPrefix + "/admin/tsdb/delete_series"
@@ -248,6 +249,8 @@ type API interface {
 	Targets(ctx context.Context) (TargetsResult, error)
 	// TargetsMetadata returns metadata about metrics currently scraped by the target.
 	TargetsMetadata(ctx context.Context, matchTarget string, metric string, limit string) ([]MetricMetadata, error)
+	// MetricMetadata returns metadata about metrics currently scraped by the metric name.
+	MetricsMetadata(ctx context.Context, metric string, limit string) (map[string][]Metadata, error)
 }
 
 // AlertsResult contains the result from querying the alerts endpoint.
@@ -357,7 +360,7 @@ type DroppedTarget struct {
 	DiscoveredLabels map[string]string `json:"discoveredLabels"`
 }
 
-// MetricMetadata models the metadata of a metric.
+// MetricMetadata models the metadata of a metric with its scrape target and name.
 type MetricMetadata struct {
 	Target map[string]string `json:"target"`
 	Metric string            `json:"metric,omitempty"`
@@ -366,6 +369,13 @@ type MetricMetadata struct {
 	Unit   string            `json:"unit"`
 }
 
+// Metadata models the metadata of a metric.
+type Metadata struct {
+	Type MetricType `json:"type"`
+	Help string     `json:"help"`
+	Unit string     `json:"unit"`
+}
+
 // queryResult contains result data for a query.
 type queryResult struct {
 	Type   model.ValueType `json:"resultType"`
@@ -802,6 +812,29 @@ func (h *httpAPI) TargetsMetadata(ctx context.Context, matchTarget string, metri
 	return res, json.Unmarshal(body, &res)
 }
 
+func (h *httpAPI) MetricsMetadata(ctx context.Context, metric string, limit string) (map[string][]Metadata, error) {
+	u := h.client.URL(epMetricsMetadata, nil)
+	q := u.Query()
+
+	q.Set("metric", metric)
+	q.Set("limit", limit)
+
+	u.RawQuery = q.Encode()
+
+	req, err := http.NewRequest(http.MethodGet, u.String(), nil)
+	if err != nil {
+		return nil, err
+	}
+
+	_, body, _, err := h.client.Do(ctx, req)
+	if err != nil {
+		return nil, err
+	}
+
+	var res map[string][]Metadata
+	return res, json.Unmarshal(body, &res)
+}
+
 // Warnings is an array of non critical errors
 type Warnings []string
 

api/prometheus/v1/api_test.go

@@ -202,6 +202,13 @@ func TestAPIs(t *testing.T) {
 		}
 	}
 
+	doMetricsMetadata := func(metring string, limit string) func() (interface{}, Warnings, error) {
+		return func() (interface{}, Warnings, error) {
+			v, err := promAPI.MetricsMetadata(context.Background(), metring, limit)
+			return v, nil, err
+		}
+	}
+
 	queryTests := []apiTest{
 		{
 			do: doQuery("2", testTime),
@@ -857,6 +864,46 @@ func TestAPIs(t *testing.T) {
 			},
 			err: fmt.Errorf("some error"),
 		},
+
+		{
+			do: doMetricsMetadata("go_goroutines", "1"),
+			inRes: map[string]interface{}{
+				"go_goroutines": []map[string]interface{}{
+					{
+						"type": "gauge",
+						"help": "Number of goroutines that currently exist.",
+						"unit": "",
+					},
+				},
+			},
+			reqMethod: "GET",
+			reqPath:   "/api/v1/metadata",
+			reqParam: url.Values{
+				"metric": []string{"go_goroutines"},
+				"limit":  []string{"1"},
+			},
+			res: map[string][]Metadata{
+				"go_goroutines": []Metadata{
+					{
+						Type: "gauge",
+						Help: "Number of goroutines that currently exist.",
+						Unit: "",
+					},
+				},
+			},
+		},
+
+		{
+			do:        doMetricsMetadata("", "1"),
+			inErr:     fmt.Errorf("some error"),
+			reqMethod: "GET",
+			reqPath:   "/api/v1/metadata",
+			reqParam: url.Values{
+				"metric": []string{""},
+				"limit":  []string{"1"},
+			},
+			err: fmt.Errorf("some error"),
+		},
 	}
 
 	var tests []apiTest