[extension/zpages] Add feature gate summary page (#4834)

* [extension/zpages] Add feature gate summary page

Signed-off-by: Anthony J Mirabella <a9@aneurysm9.com>

* Add link to featurez on servicez, add featurez to README

Signed-off-by: Anthony J Mirabella <a9@aneurysm9.com>

CHANGELOG.md

@@ -11,6 +11,7 @@
 
 - Reject invalid queue size exporterhelper (#4799)
 - Transform configmapprovider.Retrieved interface to a struct (#4789)
+- Added feature gate summary to zpages extension (#4834)
 
 ## 🚩 Deprecations 🚩
 

extension/zpagesextension/README.md

@@ -28,9 +28,9 @@ The collector exposes the following zPage routes:
 
 ### ServiceZ
 
-ServiceZ gives an overview of the collector services by gives quick access to the
-`pipelinez` and `extensionz` zPages.  The page also provides build and runtime 
-information.
+ServiceZ gives an overview of the collector services and quick access to the
+`pipelinez`, `extensionz`, and `featurez` zPages.  The page also provides build 
+and runtime information.
 
 Example URL: http://localhost:55679/debug/servicez
 
@@ -48,6 +48,13 @@ ExtensionZ shows the extensions that are active in the collector.
 
 Example URL: http://localhost:55679/debug/extensionz
 
+### FeatureZ
+
+FeatureZ lists the feature gates available along with their current status 
+and description.
+
+Example URL: http://localhost:55679/debug/featurez
+
 ### TraceZ
 The TraceZ route is available to examine and bucketize spans by latency buckets for 
 example

service/internal/zpages/templates.go

@@ -51,6 +51,10 @@ var (
 	//go:embed templates/properties_table.html
 	propertiesTableBytes    []byte
 	propertiesTableTemplate = parseTemplate("properties_table", propertiesTableBytes)
+
+	//go:embed templates/features_table.html
+	featuresTableBytes    []byte
+	featuresTableTemplate = parseTemplate("features_table", featuresTableBytes)
 )
 
 func parseTemplate(name string, bytes []byte) *template.Template {
@@ -156,3 +160,22 @@ func getKey(row [2]string) string {
 func getValue(row [2]string) string {
 	return row[1]
 }
+
+// FeatureGateTableData contains data for feature gate table template.
+type FeatureGateTableData struct {
+	Rows []FeatureGateTableRowData
+}
+
+// FeatureGateTableRowData contains data for one row in feature gate table template.
+type FeatureGateTableRowData struct {
+	ID          string
+	Enabled     bool
+	Description string
+}
+
+// WriteHTMLFeaturesTable writes a table summarizing registered feature gates.
+func WriteHTMLFeaturesTable(w io.Writer, ftd FeatureGateTableData) {
+	if err := featuresTableTemplate.Execute(w, ftd); err != nil {
+		log.Printf("zpages: executing template: %v", err)
+	}
+}

service/internal/zpages/templates/features_table.html

@@ -0,0 +1,19 @@
+<table style="border-spacing: 0">
+    <tr>
+        <td colspan=1 style="text-align: left"><b>ID</b></td>
+        <td>&nbsp;&nbsp;|&nbsp;&nbsp;</td>
+        <td colspan=1 style="text-align: center"><b>Enabled</b></td>
+        <td>&nbsp;&nbsp;|&nbsp;&nbsp;</td>
+        <td colspan=1 style="text-align: center"><b>Description</b></td>
+    </tr>
+    {{range $rowindex, $row := .Rows}}
+        {{- if even $rowindex}}
+            <tr style="background: #eee">
+        {{else}}
+            <tr>{{end -}}
+        <td>{{$row.ID}}</td><td>&nbsp;&nbsp;|&nbsp;&nbsp;</td>
+        <td>{{$row.Enabled}}</td><td>&nbsp;&nbsp;|&nbsp;&nbsp;</td>
+        <td>{{$row.Description}}</td><td>&nbsp;&nbsp;|&nbsp;&nbsp;</td>
+        </tr>
+    {{end}}
+</table>

service/internal/zpages/templates_test.go

@@ -80,6 +80,15 @@ func TestNoCrash(t *testing.T) {
 	assert.NotPanics(t, func() {
 		WriteHTMLPropertiesTable(buf, PropertiesTableData{Name: "Bar", Properties: [][2]string{{"key", "value"}}})
 	})
+	assert.NotPanics(t, func() {
+		WriteHTMLFeaturesTable(buf, FeatureGateTableData{Rows: []FeatureGateTableRowData{
+			{
+				ID:          "test",
+				Enabled:     false,
+				Description: "test gate",
+			},
+		}})
+	})
 	assert.NotPanics(t, func() { WriteHTMLPageFooter(buf) })
 	assert.NotPanics(t, func() { WriteHTMLPageFooter(buf) })
 }

service/zpages.go

@@ -23,6 +23,7 @@ import (
 
 	"go.opentelemetry.io/collector/component"
 	"go.opentelemetry.io/collector/internal/version"
+	"go.opentelemetry.io/collector/service/featuregate"
 	"go.opentelemetry.io/collector/service/internal/zpages"
 )
 
@@ -31,6 +32,7 @@ const (
 	servicezPath   = "servicez"
 	pipelinezPath  = "pipelinez"
 	extensionzPath = "extensionz"
+	featurezPath   = "featurez"
 
 	zPipelineName  = "zpipelinename"
 	zComponentName = "zcomponentname"
@@ -42,6 +44,7 @@ func (srv *service) RegisterZPages(mux *http.ServeMux, pathPrefix string) {
 	mux.Handle(path.Join(pathPrefix, tracezPath), otelzpages.NewTracezHandler(srv.zPagesSpanProcessor))
 	mux.HandleFunc(path.Join(pathPrefix, servicezPath), srv.handleServicezRequest)
 	mux.HandleFunc(path.Join(pathPrefix, pipelinezPath), srv.handlePipelinezRequest)
+	mux.HandleFunc(path.Join(pathPrefix, featurezPath), handleFeaturezRequest)
 	mux.HandleFunc(path.Join(pathPrefix, extensionzPath), func(w http.ResponseWriter, r *http.Request) {
 		handleExtensionzRequest(srv, w, r)
 	})
@@ -60,6 +63,11 @@ func (srv *service) handleServicezRequest(w http.ResponseWriter, r *http.Request
 		ComponentEndpoint: extensionzPath,
 		Link:              true,
 	})
+	zpages.WriteHTMLComponentHeader(w, zpages.ComponentHeaderData{
+		Name:              "Features",
+		ComponentEndpoint: featurezPath,
+		Link:              true,
+	})
 	zpages.WriteHTMLPropertiesTable(w, zpages.PropertiesTableData{Name: "Build And Runtime", Properties: version.RuntimeVar()})
 	zpages.WriteHTMLPageFooter(w)
 }
@@ -151,3 +159,23 @@ func getExtensionsSummaryTableData(host component.Host) zpages.SummaryExtensions
 	})
 	return data
 }
+
+func handleFeaturezRequest(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	zpages.WriteHTMLPageHeader(w, zpages.HeaderData{Title: "Feature Gates"})
+	zpages.WriteHTMLFeaturesTable(w, getFeaturesTableData())
+	zpages.WriteHTMLPageFooter(w)
+}
+
+func getFeaturesTableData() zpages.FeatureGateTableData {
+	data := zpages.FeatureGateTableData{}
+	for _, g := range featuregate.List() {
+		data.Rows = append(data.Rows, zpages.FeatureGateTableRowData{
+			ID:          g.ID,
+			Enabled:     g.Enabled,
+			Description: g.Description,
+		})
+	}
+
+	return data
+}