fix: support UTF-8 label names for label values API (#8499)

Related to #6931

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

Author: simonpasquier

CHANGELOG.md

@@ -14,6 +14,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 
 - [#8334](https://github.com/thanos-io/thanos/pull/8334) Query: wait for initial endpoint discovery before becoming ready
 - [#8486](https://github.com/thanos-io/thanos/pull/8486) Receive: fix exemplar label corruption from Cap'n Proto memory references
+- [#8499](https://github.com/thanos-io/thanos/pull/8499) Query: support UTF-8 label names for the `/api/v1/label/:name/values` API.
 
 ### Added
 

pkg/api/query/v1.go

@@ -1025,7 +1025,8 @@ func (qapi *QueryAPI) labelValues(r *http.Request) (any, []error, *api.ApiError,
 	ctx := r.Context()
 	name := route.Param(ctx, "name")
 
-	if !model.LabelNameRE.MatchString(name) {
+	label := model.LabelName(name)
+	if !label.IsValid() {
 		return nil, nil, &api.ApiError{Typ: api.ErrorBadData, Err: errors.Errorf("invalid label name: %q", name)}, func() {}
 	}
 

pkg/api/query/v1_test.go

@@ -955,13 +955,13 @@ func TestMetadataEndpoints(t *testing.T) {
 			},
 			response: []string{"a"},
 		},
-		// Bad name parameter.
+		// UTF-8 label name.
 		{
 			endpoint: api.labelValues,
 			params: map[string]string{
-				"name": "not!!!allowed",
+				"name": "http.request.method",
 			},
-			errType: baseAPI.ErrorBadData,
+			response: []string{},
 		},
 		{
 			endpoint: api.series,