Switch prometheus/client_golang to a fork with support for /metrics endpoint filtering by name[] (#13746)

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#### What this PR does

Switches to a fork of `client_golang` that contains the PR
prometheus/client_golang#1925 which supports
`/metrics` endpoint handler filtering through the use of `name[]` query
param. I added a test to make sure this functionality doesn't disappear
in a possible future removal of this replace directive.

Also updates the costattribution package as this version now has changes
introduced by @duricanikolic in
prometheus/client_golang#1902

#### Which issue(s) this PR fixes or relates to

Fixes an internal issue

#### Checklist

- [x] Tests updated.
- [ ] Documentation added.
- [x] `CHANGELOG.md` updated - the order of entries should be
`[CHANGE]`, `[FEATURE]`, `[ENHANCEMENT]`, `[BUGFIX]`. If changelog entry
is not needed, please add the `changelog-not-needed` label to the PR.
- [ ]
[`about-versioning.md`](https://github.com/grafana/mimir/blob/main/docs/sources/mimir/configure/about-versioning.md)
updated with experimental features.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Switch to a forked `client_golang` to add `/metrics` filtering via
`name[]`, update cost-attribution validation and tests, adapt API usage,
and bump `compress`.
> 
> - **Server/HTTP metrics**:
> - Enable metric filtering on `/metrics` via `name[]` query param
(promhttp handler change). Added test
`TestMetricsEndpointSupportsMetricFiltering`.
> - **Dependencies**:
> - Replace `github.com/prometheus/client_golang` with fork
`github.com/colega/prometheus-client_golang` (pulls in filtering
support) and vendor updates.
> - Bump `github.com/klauspost/compress` to `v1.18.2` and vendor
changes.
> - **Cost attribution**:
> - Simplify metric descriptor validation using `prometheus.Desc.Err()`;
adjust error expectations in tests.
> - **Integration tests client**:
> - Adapt `LabelNames` to new `model.LabelNames` return type and convert
to `[]string`.
> - **Changelog**:
>   - Document `/metrics` filtering enhancement.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
94aa553. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Signed-off-by: Oleg Zaytsev <[email protected]>

Author: colega

CHANGELOG.md

@@ -73,6 +73,7 @@
 * [ENHANCEMENT] OTLP: Add metric `cortex_distributor_otlp_requests_by_content_type_total` to track content type (json or proto) of OTLP packets. #13525
 * [ENHANCEMENT] OTLP: Add experimental metric `cortex_distributor_otlp_array_lengths` to better understand the layout of OTLP packets in practice. #13525
 * [ENHANCEMENT] Ruler: gRPC errors without details are classified as `operator` errors, and rule evaluation failures (such as duplicate labelsets) are classified as `user` errors. #13586
+* [ENHANCEMENT] Server: The `/metrics` endpoint now supports metrics filtering by providing one or more `name[]` query parameters. #13746
 * [BUGFIX] Compactor: Fix potential concurrent map writes. #13053
 * [BUGFIX] Query-frontend: Fix issue where queries sometimes fail with `failed to receive query result stream message: rpc error: code = Canceled desc = context canceled` if remote execution is enabled. #13084
 * [BUGFIX] Query-frontend: Fix issue where query stats, such as series read, did not include the parameters to the `histogram_quantile` and `histogram_fraction` functions if remote execution was enabled. #13084

go.mod

@@ -382,3 +382,7 @@ replace github.com/prometheus/alertmanager => github.com/grafana/prometheus-aler
 // Use Mimir fork of prometheus/otlptranslator to allow for higher velocity of upstream development,
 // while allowing Mimir to move at a more conservative pace.
 replace github.com/prometheus/otlptranslator => github.com/grafana/mimir-otlptranslator v0.0.0-20251017074411-ea1e8f863e1d
+
+// Use a fork of client_golang with changes from:
+// - https://github.com/prometheus/client_golang/pull/1925
+replace github.com/prometheus/client_golang => github.com/colega/prometheus-client_golang v1.19.1-0.20251204143415-11cda2079634

go.sum

@@ -522,7 +522,16 @@ func (c *Client) LabelNames(start, end time.Time, matches []string, opts ...prom
 	defer cancel()
 
 	result, _, err := c.querierClient.LabelNames(ctx, matches, start, end, opts...)
-	return result, err
+	if err != nil {
+		return nil, err
+	}
+
+	// Convert model.LabelNames to []string
+	names := make([]string, len(result))
+	for i, name := range result {
+		names[i] = string(name)
+	}
+	return names, nil
 }
 
 // LabelNamesAndValues returns distinct label values per label name.

integration/e2emimir/client.go

@@ -36,14 +36,14 @@ func TestNewActiveTracker(t *testing.T) {
 		},
 		"incorrect label name causes an error single label": {
 			costAttributionLabels: costattributionmodel.Labels{{Input: "__bad_label__", Output: "__bad_label__"}},
-			expectedErr:           fmt.Errorf(`failed to create an active series tracker for tenant tenant-1: descriptor Desc{fqName: "cortex_ingester_attributed_active_series", help: "The total number of active series per user and attribution.", constLabels: {}, variableLabels: {__bad_label__,tenant}} is invalid: "__bad_label__" is not a valid label name for metric "cortex_ingester_attributed_active_series"`),
+			expectedErr:           fmt.Errorf(`failed to create an active series tracker for tenant tenant-1: "__bad_label__" is not a valid label name for metric "cortex_ingester_attributed_active_series"`),
 		},
 		"incorrect label name causes an error multiple labels": {
 			costAttributionLabels: costattributionmodel.Labels{
 				{Input: "good_label", Output: "good_label"},
 				{Input: "__bad_label__", Output: "__bad_label__"},
 			},
-			expectedErr: fmt.Errorf(`failed to create an active series tracker for tenant tenant-1: descriptor Desc{fqName: "cortex_ingester_attributed_active_series", help: "The total number of active series per user and attribution.", constLabels: {}, variableLabels: {good_label,__bad_label__,tenant}} is invalid: "__bad_label__" is not a valid label name for metric "cortex_ingester_attributed_active_series"`),
+			expectedErr: fmt.Errorf(`failed to create an active series tracker for tenant tenant-1: "__bad_label__" is not a valid label name for metric "cortex_ingester_attributed_active_series"`),
 		},
 	}
 

pkg/costattribution/active_tracker_test.go

@@ -11,8 +11,7 @@ import (
 // descriptor wraps a prometheus.Desc with additional metadata for metric validation and creation.
 // This wrapper is needed because prometheus.Desc doesn't expose important information about the
 // descriptor itself, such as metric name, label names, and a possible error obtained during the
-// descriptor construction. The first two are accessible via the name and labels fields, while
-// construction error can be obtained by calling validate().
+// descriptor construction. The first two are accessible via the name and labels fields.
 type descriptor struct {
 	desc   *prometheus.Desc
 	name   string
@@ -23,30 +22,15 @@ type descriptor struct {
 // It returns an error if a creation of the underlying prometheus.Desc is not successful, for example when the metric name
 // or any of the label names don't conform to Prometheus naming conventions.
 func newDescriptor(name string, help string, labels []string, constLabels prometheus.Labels) (*descriptor, error) {
-	desc := &descriptor{
-		desc:   prometheus.NewDesc(name, help, labels, constLabels),
+	desc := prometheus.NewDesc(name, help, labels, constLabels)
+	if desc.Err() != nil {
+		return nil, desc.Err()
+	}
+	return &descriptor{
+		desc:   desc,
 		name:   name,
 		labels: labels,
-	}
-	if err := desc.validate(); err != nil {
-		return nil, err
-	}
-	return desc, nil
-}
-
-// validate checks whether the underlying prometheus.Desc is valid.
-//
-// A prometheus.Desc may contain an internal error if created with invalid
-// metric or label names. Since this error is unexported, validate detects
-// such cases and returns the underlying error if present. Otherwise, it
-// returns nil.
-func (d *descriptor) validate() error {
-	reg := prometheus.NewRegistry()
-	if err := reg.Register(d); err != nil {
-		return err
-	}
-
-	return nil
+	}, nil
 }
 
 // Describe implements the prometheus.Collector interface by sending this descriptor to the provided channel.

pkg/costattribution/metrics.go

@@ -38,7 +38,7 @@ func TestNewDescriptor(t *testing.T) {
 			help:        "Metric with invalid label",
 			labels:      []string{"__bad_label__"},
 			constLabels: nil,
-			expectedErr: fmt.Errorf(`descriptor Desc{fqName: "test_metric", help: "Metric with invalid label", constLabels: {}, variableLabels: {__bad_label__}} is invalid: "__bad_label__" is not a valid label name for metric "test_metric"`),
+			expectedErr: fmt.Errorf(`"__bad_label__" is not a valid label name for metric "test_metric"`),
 		},
 	}
 

pkg/costattribution/metrics_test.go

@@ -37,14 +37,14 @@ func TestNewSampleTracker(t *testing.T) {
 		},
 		"incorrect label name causes an error single label": {
 			costAttributionLabels: costattributionmodel.Labels{{Input: "__bad_label__", Output: "__bad_label__"}},
-			expectedErr:           fmt.Errorf(`failed to create a sample tracker for tenant tenant-1: descriptor Desc{fqName: "cortex_distributor_received_attributed_samples_total", help: "The total number of samples that were received per attribution.", constLabels: {}, variableLabels: {__bad_label__,tenant}} is invalid: "__bad_label__" is not a valid label name for metric "cortex_distributor_received_attributed_samples_total"`),
+			expectedErr:           fmt.Errorf(`failed to create a sample tracker for tenant tenant-1: "__bad_label__" is not a valid label name for metric "cortex_distributor_received_attributed_samples_total"`),
 		},
 		"incorrect label name causes an error multiple labels": {
 			costAttributionLabels: costattributionmodel.Labels{
 				{Input: "good_label", Output: "good_label"},
 				{Input: "__bad_label__", Output: "__bad_label__"},
 			},
-			expectedErr: fmt.Errorf(`failed to create a sample tracker for tenant tenant-1: descriptor Desc{fqName: "cortex_distributor_received_attributed_samples_total", help: "The total number of samples that were received per attribution.", constLabels: {}, variableLabels: {good_label,__bad_label__,tenant}} is invalid: "__bad_label__" is not a valid label name for metric "cortex_distributor_received_attributed_samples_total"`),
+			expectedErr: fmt.Errorf(`failed to create a sample tracker for tenant tenant-1: "__bad_label__" is not a valid label name for metric "cortex_distributor_received_attributed_samples_total"`),
 		},
 	}
 

pkg/costattribution/sample_tracker_test.go

@@ -12,10 +12,12 @@ import (
 	"flag"
 	"fmt"
 	"io"
+	"maps"
 	"net"
 	"net/http"
 	"os"
 	"path/filepath"
+	"slices"
 	"strconv"
 	"strings"
 	"syscall"
@@ -283,6 +285,66 @@ func TestMimirServerShutdownWithActivityTrackerEnabled(t *testing.T) {
 	}
 }
 
+func TestMetricsEndpointSupportsMetricFiltering(t *testing.T) {
+	// This test checks that our /metrics endpoint handler supports metric filtering through the usage of name[] query param.
+	// This is added to prometheus/client_golang in https://github.com/prometheus/client_golang/pull/1925,
+	// but not merged yet so we use a replace directive on the module to bring this functionality.
+	// This test check that we haven't lost that replace directive (and functionality).
+	//
+	// We target OverridesExporter because it's the target with least dependencies and easier to set up.
+	args := []string{
+		"-target=" + OverridesExporter,
+		"-server.http-listen-port=0",
+		"-server.grpc-listen-port=0",
+	}
+	var cfg Config
+	fs := flag.NewFlagSet("test", flag.PanicOnError)
+	cfg.RegisterFlags(fs, log.NewNopLogger())
+	require.NoError(t, fs.Parse(args))
+	require.NoError(t, cfg.Validate(log.NewNopLogger()))
+
+	c, err := New(cfg, prometheus.NewPedanticRegistry())
+	require.NoError(t, err)
+
+	serviceMap, err := c.ModuleManager.InitModuleServices(cfg.Target...)
+	require.NoError(t, err)
+	require.NotNil(t, serviceMap)
+
+	servs := slices.Collect(maps.Values(serviceMap))
+	sm, err := services.NewManager(servs...)
+	require.NoError(t, err)
+
+	assert.NoError(t, sm.StartAsync(t.Context()))
+	t.Cleanup(sm.StopAsync)
+
+	{
+		// One metric
+		res, err := http.Get(fmt.Sprintf("http://%s/metrics?name[]=go_info", c.Server.HTTPListenAddr()))
+		require.NoError(t, err)
+		defer res.Body.Close()
+		assert.Equal(t, http.StatusOK, res.StatusCode)
+		body, err := io.ReadAll(res.Body)
+		require.NoError(t, err)
+		assert.Contains(t, string(body), "go_info")
+		assert.NotContains(t, string(body), "deprecated_flags_inuse_total")
+		require.Equal(t, 1, strings.Count(string(body), "HELP"))
+	}
+
+	{
+		// Two metrics
+		res, err := http.Get(fmt.Sprintf("http://%s/metrics?name[]=go_info&name[]=deprecated_flags_inuse_total", c.Server.HTTPListenAddr()))
+		require.NoError(t, err)
+		defer res.Body.Close()
+		assert.Equal(t, http.StatusOK, res.StatusCode)
+		body, err := io.ReadAll(res.Body)
+		require.NoError(t, err)
+		assert.Contains(t, string(body), "go_info")
+		assert.Contains(t, string(body), "deprecated_flags_inuse_total")
+		assert.NotContains(t, string(body), "go_gc_duration_seconds")
+		require.Equal(t, 2, strings.Count(string(body), "HELP"))
+	}
+}
+
 func TestConfigValidation(t *testing.T) {
 	for _, tc := range []struct {
 		name           string