trace: export /debug/requests and /debug/events handlers

Fixes #20478.

Change-Id: I739b6f1368889b735944d74be2d16b7e09eb11a2
Reviewed-on: https://go-review.googlesource.com/45998Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

trace/events.go

@@ -39,9 +39,9 @@ var buckets = []bucket{
 }
 
 // RenderEvents renders the HTML page typically served at /debug/events.
-// It does not do any auth checking; see AuthRequest for the default auth check
-// used by the handler registered on http.DefaultServeMux.
-// req may be nil.
+// It does not do any auth checking. The request may be nil.
+//
+// Most users will use the Events handler.
 func RenderEvents(w http.ResponseWriter, req *http.Request, sensitive bool) {
 	now := time.Now()
 	data := &struct {

trace/trace.go

@@ -110,30 +110,46 @@ var AuthRequest = func(req *http.Request) (any, sensitive bool) {
 }
 
 func init() {
-	http.HandleFunc("/debug/requests", func(w http.ResponseWriter, req *http.Request) {
-		any, sensitive := AuthRequest(req)
-		if !any {
-			http.Error(w, "not allowed", http.StatusUnauthorized)
-			return
-		}
-		w.Header().Set("Content-Type", "text/html; charset=utf-8")
-		Render(w, req, sensitive)
-	})
-	http.HandleFunc("/debug/events", func(w http.ResponseWriter, req *http.Request) {
-		any, sensitive := AuthRequest(req)
-		if !any {
-			http.Error(w, "not allowed", http.StatusUnauthorized)
-			return
-		}
-		w.Header().Set("Content-Type", "text/html; charset=utf-8")
-		RenderEvents(w, req, sensitive)
-	})
+	// TODO(jbd): Serve Traces from /debug/traces in the future?
+	// There is no requirement for a request to be present to have traces.
+	http.HandleFunc("/debug/requests", Traces)
+	http.HandleFunc("/debug/events", Events)
+}
+
+// Traces responds with traces from the program.
+// The package initialization registers it in http.DefaultServeMux
+// at /debug/requests.
+//
+// It performs authorization by running AuthRequest.
+func Traces(w http.ResponseWriter, req *http.Request) {
+	any, sensitive := AuthRequest(req)
+	if !any {
+		http.Error(w, "not allowed", http.StatusUnauthorized)
+		return
+	}
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	Render(w, req, sensitive)
+}
+
+// Events responds with a page of events collected by EventLogs.
+// The package initialization registers it in http.DefaultServeMux
+// at /debug/events.
+//
+// It performs authorization by running AuthRequest.
+func Events(w http.ResponseWriter, req *http.Request) {
+	any, sensitive := AuthRequest(req)
+	if !any {
+		http.Error(w, "not allowed", http.StatusUnauthorized)
+		return
+	}
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	RenderEvents(w, req, sensitive)
 }
 
 // Render renders the HTML page typically served at /debug/requests.
-// It does not do any auth checking; see AuthRequest for the default auth check
-// used by the handler registered on http.DefaultServeMux.
-// req may be nil.
+// It does not do any auth checking. The request may be nil.
+//
+// Most users will use the Traces handler.
 func Render(w io.Writer, req *http.Request, sensitive bool) {
 	data := &struct {
 		Families         []string