Fix ExternalLabels() for Prometheus v3.0

Prometheus v3.0.0-rc.0 introduces a new scrape protocol
(`PrometheusText1.0.0`) which is present by default in the global
configuration. It breaks the Thanos sidecar when it wants to retrieve
the external labels.

This change replaces the use of the Prometheus `GlobalConfig` struct by
a minimal struct which unmarshals only the `external_labels` key.

Signed-off-by: Simon Pasquier <[email protected]>

pkg/promclient/promclient.go

@@ -27,7 +27,6 @@ import (
 	"github.com/pkg/errors"
 	"github.com/prometheus/common/expfmt"
 	"github.com/prometheus/common/model"
-	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/model/timestamp"
 	"github.com/prometheus/prometheus/promql"
@@ -201,13 +200,15 @@ func (c *Client) ExternalLabels(ctx context.Context, base *url.URL) (labels.Labe
 		return labels.EmptyLabels(), errors.Wrapf(err, "unmarshal response: %v", string(body))
 	}
 	var cfg struct {
-		GlobalConfig config.GlobalConfig `yaml:"global"`
+		GlobalConfig struct {
+			ExternalLabels map[string]string `yaml:"external_labels"`
+		} `yaml:"global"`
 	}
 	if err := yaml.Unmarshal([]byte(d.Data.YAML), &cfg); err != nil {
 		return labels.EmptyLabels(), errors.Wrapf(err, "parse Prometheus config: %v", d.Data.YAML)
 	}
 
-	return cfg.GlobalConfig.ExternalLabels, nil
+	return labels.FromMap(cfg.GlobalConfig.ExternalLabels), nil
 }
 
 type Flags struct {

pkg/promclient/promclient_test.go

@@ -0,0 +1,67 @@
+// Copyright (c) The Thanos Authors.
+// Licensed under the Apache License 2.0.
+
+// Package promclient offers helper client function for various API endpoints.
+
+package promclient
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+
+	"github.com/efficientgo/core/testutil"
+)
+
+func TestExternalLabels(t *testing.T) {
+	for _, tc := range []struct {
+		name     string
+		response string
+		err      bool
+		labels   map[string]string
+	}{
+		{
+			name:     "invalid payload",
+			response: `{`,
+			err:      true,
+		},
+		{
+			name:     "unknown scrape protocol",
+			response: `{"status":"success","data":{"yaml":"global:\n  scrape_interval: 1m\n  scrape_timeout: 10s\n  scrape_protocols:\n  - OpenMetricsText1.0.0\n  - OpenMetricsText0.0.1\n  - PrometheusText1.0.0\n  - PrometheusText0.0.4\n  - UnknownScrapeProto\n  evaluation_interval: 1m\n  external_labels:\n    az: \"1\"\n    region: eu-west\nruntime:\n  gogc: 75\n"}}`,
+			labels: map[string]string{
+				"region": "eu-west",
+				"az":     "1",
+			},
+		},
+		{
+			name:     "no external labels",
+			response: `{"status":"success","data":{"yaml":"global:\n  scrape_interval: 1m\n  scrape_timeout: 10s\n  scrape_protocols:\n  - OpenMetricsText1.0.0\n  - OpenMetricsText0.0.1\n  - PrometheusText1.0.0\n  - PrometheusText0.0.4\n  - UnknownScrapeProto\n  evaluation_interval: 1m\nruntime:\n  gogc: 75\n"}}`,
+			labels:   map[string]string{},
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				fmt.Fprintln(w, tc.response)
+			}))
+			defer ts.Close()
+
+			u, err := url.Parse(ts.URL)
+			testutil.Ok(t, err)
+
+			ext, err := NewDefaultClient().ExternalLabels(context.Background(), u)
+			if tc.err {
+				testutil.NotOk(t, err)
+				return
+			}
+
+			testutil.Ok(t, err)
+			testutil.Equals(t, len(tc.labels), ext.Len())
+			for k, v := range tc.labels {
+				testutil.Equals(t, v, ext.Get(k))
+			}
+		})
+	}
+}