app/vmselect/graphite: add /tags handler from Graphite Tags API

See https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags

README.md

@@ -548,6 +548,7 @@ VictoriaMetrics supports the following handlers from [Graphite Tags API](https:/
 
 * [/tags/tagSeries](https://graphite.readthedocs.io/en/stable/tags.html#adding-series-to-the-tagdb)
 * [/tags/tagMultiSeries](https://graphite.readthedocs.io/en/stable/tags.html#adding-series-to-the-tagdb)
+* [/tags](https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags)
 
 
 ### How to build from sources

app/vmselect/graphite/tags_api.go

@@ -0,0 +1,65 @@
+package graphite
+
+import (
+	"fmt"
+	"net/http"
+	"regexp"
+	"strconv"
+	"time"
+
+	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/bufferedwriter"
+	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/netstorage"
+	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/searchutils"
+	"github.com/VictoriaMetrics/metrics"
+)
+
+// TagsHandler implements handler for /tags endpoint.
+//
+// See https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags
+func TagsHandler(startTime time.Time, w http.ResponseWriter, r *http.Request) error {
+	deadline := searchutils.GetDeadlineForQuery(r, startTime)
+	if err := r.ParseForm(); err != nil {
+		return fmt.Errorf("cannot parse form values: %w", err)
+	}
+	limit := 0
+	if limitStr := r.FormValue("limit"); len(limitStr) > 0 {
+		var err error
+		limit, err = strconv.Atoi(limitStr)
+		if err != nil {
+			return fmt.Errorf("cannot parse limit=%q: %w", limit, err)
+		}
+	}
+	labels, err := netstorage.GetGraphiteTags(limit, deadline)
+	if err != nil {
+		return err
+	}
+	filter := r.FormValue("filter")
+	if len(filter) > 0 {
+		// Anchor filter regexp to the beginning of the string as Graphite does.
+		// See https://github.com/graphite-project/graphite-web/blob/3ad279df5cb90b211953e39161df416e54a84948/webapp/graphite/tags/localdatabase.py#L157
+		filter = "^(?:" + filter + ")"
+		re, err := regexp.Compile(filter)
+		if err != nil {
+			return fmt.Errorf("cannot parse regexp filter=%q: %w", filter, err)
+		}
+		dst := labels[:0]
+		for _, label := range labels {
+			if re.MatchString(label) {
+				dst = append(dst, label)
+			}
+		}
+		labels = dst
+	}
+
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	bw := bufferedwriter.Get(w)
+	defer bufferedwriter.Put(bw)
+	WriteTagsResponse(bw, labels)
+	if err := bw.Flush(); err != nil {
+		return err
+	}
+	tagsDuration.UpdateDuration(startTime)
+	return nil
+}
+
+var tagsDuration = metrics.NewSummary(`vm_request_duration_seconds{path="/tags"}`)

app/vmselect/graphite/tags_response.qtpl

@@ -0,0 +1,16 @@
+{% stripspace %}
+
+Tags generates response for /tags handler
+See https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags
+{% func TagsResponse(tags []string) %}
+[
+	{% for i, tag := range tags %}
+		{
+			"tag":{%q= tag %}
+		}
+		{% if i+1 < len(tags) %},{% endif %}
+	{% endfor %}
+]
+{% endfunc %}
+
+{% endstripspace %}

app/vmselect/graphite/tags_response.qtpl.go

@@ -0,0 +1,71 @@
+// Code generated by qtc from "tags_response.qtpl". DO NOT EDIT.
+// See https://github.com/valyala/quicktemplate for details.
+
+// Tags generates response for /tags handlerSee https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags
+
+//line app/vmselect/graphite/tags_response.qtpl:5
+package graphite
+
+//line app/vmselect/graphite/tags_response.qtpl:5
+import (
+	qtio422016 "io"
+
+	qt422016 "github.com/valyala/quicktemplate"
+)
+
+//line app/vmselect/graphite/tags_response.qtpl:5
+var (
+	_ = qtio422016.Copy
+	_ = qt422016.AcquireByteBuffer
+)
+
+//line app/vmselect/graphite/tags_response.qtpl:5
+func StreamTagsResponse(qw422016 *qt422016.Writer, tags []string) {
+//line app/vmselect/graphite/tags_response.qtpl:5
+	qw422016.N().S(`[`)
+//line app/vmselect/graphite/tags_response.qtpl:7
+	for i, tag := range tags {
+//line app/vmselect/graphite/tags_response.qtpl:7
+		qw422016.N().S(`{"tag":`)
+//line app/vmselect/graphite/tags_response.qtpl:9
+		qw422016.N().Q(tag)
+//line app/vmselect/graphite/tags_response.qtpl:9
+		qw422016.N().S(`}`)
+//line app/vmselect/graphite/tags_response.qtpl:11
+		if i+1 < len(tags) {
+//line app/vmselect/graphite/tags_response.qtpl:11
+			qw422016.N().S(`,`)
+//line app/vmselect/graphite/tags_response.qtpl:11
+		}
+//line app/vmselect/graphite/tags_response.qtpl:12
+	}
+//line app/vmselect/graphite/tags_response.qtpl:12
+	qw422016.N().S(`]`)
+//line app/vmselect/graphite/tags_response.qtpl:14
+}
+
+//line app/vmselect/graphite/tags_response.qtpl:14
+func WriteTagsResponse(qq422016 qtio422016.Writer, tags []string) {
+//line app/vmselect/graphite/tags_response.qtpl:14
+	qw422016 := qt422016.AcquireWriter(qq422016)
+//line app/vmselect/graphite/tags_response.qtpl:14
+	StreamTagsResponse(qw422016, tags)
+//line app/vmselect/graphite/tags_response.qtpl:14
+	qt422016.ReleaseWriter(qw422016)
+//line app/vmselect/graphite/tags_response.qtpl:14
+}
+
+//line app/vmselect/graphite/tags_response.qtpl:14
+func TagsResponse(tags []string) string {
+//line app/vmselect/graphite/tags_response.qtpl:14
+	qb422016 := qt422016.AcquireByteBuffer()
+//line app/vmselect/graphite/tags_response.qtpl:14
+	WriteTagsResponse(qb422016, tags)
+//line app/vmselect/graphite/tags_response.qtpl:14
+	qs422016 := string(qb422016.B)
+//line app/vmselect/graphite/tags_response.qtpl:14
+	qt422016.ReleaseByteBuffer(qb422016)
+//line app/vmselect/graphite/tags_response.qtpl:14
+	return qs422016
+//line app/vmselect/graphite/tags_response.qtpl:14
+}

app/vmselect/main.go

@@ -259,6 +259,14 @@ func RequestHandler(w http.ResponseWriter, r *http.Request) bool {
 			return true
 		}
 		return true
+	case "/tags":
+		graphiteTagsRequests.Inc()
+		if err := graphite.TagsHandler(startTime, w, r); err != nil {
+			graphiteTagsErrors.Inc()
+			httpserver.Errorf(w, r, "error in %q: %s", r.URL.Path, err)
+			return true
+		}
+		return true
 	case "/api/v1/rules":
 		// Return dumb placeholder
 		rulesRequests.Inc()
@@ -360,6 +368,9 @@ var (
 	graphiteMetricsIndexRequests = metrics.NewCounter(`vm_http_requests_total{path="/metrics/index.json"}`)
 	graphiteMetricsIndexErrors   = metrics.NewCounter(`vm_http_request_errors_total{path="/metrics/index.json"}`)
 
+	graphiteTagsRequests = metrics.NewCounter(`vm_http_requests_total{path="/tags"}`)
+	graphiteTagsErrors   = metrics.NewCounter(`vm_http_request_errors_total{path="/tags"}`)
+
 	rulesRequests    = metrics.NewCounter(`vm_http_requests_total{path="/api/v1/rules"}`)
 	alertsRequests   = metrics.NewCounter(`vm_http_requests_total{path="/api/v1/alerts"}`)
 	metadataRequests = metrics.NewCounter(`vm_http_requests_total{path="/api/v1/metadata"}`)

app/vmselect/netstorage/netstorage.go

@@ -473,6 +473,33 @@ func GetLabelsOnTimeRange(tr storage.TimeRange, deadline searchutils.Deadline) (
 	return labels, nil
 }
 
+// GetGraphiteTags returns Graphite tags until the given deadline.
+func GetGraphiteTags(limit int, deadline searchutils.Deadline) ([]string, error) {
+	if deadline.Exceeded() {
+		return nil, fmt.Errorf("timeout exceeded before starting the query processing: %s", deadline.String())
+	}
+	if limit <= 0 {
+		limit = *maxTagKeysPerSearch
+	}
+	if limit > *maxTagKeysPerSearch {
+		return nil, fmt.Errorf("limit=%d exceeds -search.maxTagKeys=%d; either decrease limit or increase -search.maxTagKeys command-line flag value",
+			limit, *maxTagKeysPerSearch)
+	}
+	labels, err := vmstorage.SearchTagKeys(limit, deadline.Deadline())
+	if err != nil {
+		return nil, fmt.Errorf("error during tags search: %w", err)
+	}
+	// Substitute "" with "name" for Graphite compatibility
+	for i := range labels {
+		if labels[i] == "" {
+			labels[i] = "name"
+		}
+	}
+	// Sort labels like Graphite does
+	sort.Strings(labels)
+	return labels, nil
+}
+
 // GetLabels returns labels until the given deadline.
 func GetLabels(deadline searchutils.Deadline) ([]string, error) {
 	if deadline.Exceeded() {

docs/Single-server-VictoriaMetrics.md

@@ -548,6 +548,7 @@ VictoriaMetrics supports the following handlers from [Graphite Tags API](https:/
 
 * [/tags/tagSeries](https://graphite.readthedocs.io/en/stable/tags.html#adding-series-to-the-tagdb)
 * [/tags/tagMultiSeries](https://graphite.readthedocs.io/en/stable/tags.html#adding-series-to-the-tagdb)
+* [/tags](https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags)
 
 
 ### How to build from sources