http/pprof: cpu profiling support

R=r
CC=golang-dev
https://golang.org/cl/4280060

src/pkg/http/pprof/pprof.go

@@ -18,6 +18,10 @@
 //
 //	pprof http://localhost:6060/debug/pprof/heap
 //
+// Or to look at a 30-second CPU profile:
+//
+//	pprof http://localhost:6060/debug/pprof/profile
+//
 package pprof
 
 import (
@@ -29,10 +33,12 @@ import (
 	"runtime/pprof"
 	"strconv"
 	"strings"
+	"time"
 )
 
 func init() {
 	http.Handle("/debug/pprof/cmdline", http.HandlerFunc(Cmdline))
+	http.Handle("/debug/pprof/profile", http.HandlerFunc(Profile))
 	http.Handle("/debug/pprof/heap", http.HandlerFunc(Heap))
 	http.Handle("/debug/pprof/symbol", http.HandlerFunc(Symbol))
 }
@@ -41,22 +47,46 @@ func init() {
 // command line, with arguments separated by NUL bytes.
 // The package initialization registers it as /debug/pprof/cmdline.
 func Cmdline(w http.ResponseWriter, r *http.Request) {
-	w.Header().Set("content-type", "text/plain; charset=utf-8")
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
 	fmt.Fprintf(w, strings.Join(os.Args, "\x00"))
 }
 
 // Heap responds with the pprof-formatted heap profile.
 // The package initialization registers it as /debug/pprof/heap.
 func Heap(w http.ResponseWriter, r *http.Request) {
-	w.Header().Set("content-type", "text/plain; charset=utf-8")
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
 	pprof.WriteHeapProfile(w)
 }
 
+// Profile responds with the pprof-formatted cpu profile.
+// The package initialization registers it as /debug/pprof/profile.
+func Profile(w http.ResponseWriter, r *http.Request) {
+	sec, _ := strconv.Atoi64(r.FormValue("seconds"))
+	if sec == 0 {
+		sec = 30
+	}
+
+	// Set Content Type assuming StartCPUProfile will work,
+	// because if it does it starts writing.
+	w.Header().Set("Content-Type", "application/octet-stream")
+	if err := pprof.StartCPUProfile(w); err != nil {
+		// StartCPUProfile failed, so no writes yet.
+		// Can change header back to text content
+		// and send error code.
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+		w.WriteHeader(http.StatusInternalServerError)
+		fmt.Fprintf(w, "Could not enable CPU profiling: %s\n", err)
+		return
+	}
+	time.Sleep(sec * 1e9)
+	pprof.StopCPUProfile()
+}
+
 // Symbol looks up the program counters listed in the request,
 // responding with a table mapping program counters to function names.
 // The package initialization registers it as /debug/pprof/symbol.
 func Symbol(w http.ResponseWriter, r *http.Request) {
-	w.Header().Set("content-type", "text/plain; charset=utf-8")
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
 
 	// We don't know how many symbols we have, but we
 	// do have symbol information.  Pprof only cares whether