http profiling: fix mount of default http mux as a subroute (#359)

This adds a new config option --httpprofprefix to specify the URL path prefix for the HTTP profiler. For example, given -p --httpprofprefix "/pp", the http hander will be available at:

/pp/debug/pprof/
Note that the "/debug/pprof/ part is not changeable, and the trailing slash is required. But this path may be hidden via the prefix.

config.go

@@ -39,6 +39,7 @@ var (
 	defaultConfigFile        = filepath.Join(curDir, defaultConfigFilename)
 	defaultLogDir            = filepath.Join(curDir, defaultLogDirname)
 	defaultHost              = "localhost"
+	defaultHTTPProfPath      = "/p"
 
 	defaultAPIProto           = "http"
 	defaultAPIListen          = "127.0.0.1:7777"
@@ -60,15 +61,16 @@ var (
 
 type config struct {
 	// General application behavior
-	ConfigFile  string `short:"C" long:"configfile" description:"Path to configuration file"`
-	ShowVersion bool   `short:"V" long:"version" description:"Display version information and exit"`
-	TestNet     bool   `long:"testnet" description:"Use the test network (default mainnet)"`
-	SimNet      bool   `long:"simnet" description:"Use the simulation test network (default mainnet)"`
-	DebugLevel  string `short:"d" long:"debuglevel" description:"Logging level {trace, debug, info, warn, error, critical}"`
-	Quiet       bool   `short:"q" long:"quiet" description:"Easy way to set debuglevel to error"`
-	LogDir      string `long:"logdir" description:"Directory to log output"`
-	HTTPProfile bool   `long:"httpprof" short:"p" description:"Start HTTP profiler."`
-	CPUProfile  string `long:"cpuprofile" description:"File for CPU profiling."`
+	ConfigFile   string `short:"C" long:"configfile" description:"Path to configuration file"`
+	ShowVersion  bool   `short:"V" long:"version" description:"Display version information and exit"`
+	TestNet      bool   `long:"testnet" description:"Use the test network (default mainnet)"`
+	SimNet       bool   `long:"simnet" description:"Use the simulation test network (default mainnet)"`
+	DebugLevel   string `short:"d" long:"debuglevel" description:"Logging level {trace, debug, info, warn, error, critical}"`
+	Quiet        bool   `short:"q" long:"quiet" description:"Easy way to set debuglevel to error"`
+	LogDir       string `long:"logdir" description:"Directory to log output"`
+	HTTPProfile  bool   `long:"httpprof" short:"p" description:"Start HTTP profiler."`
+	HTTPProfPath string `long:"httpprofprefix" description:"URL path prefix for the HTTP profiler."`
+	CPUProfile   string `long:"cpuprofile" description:"File for CPU profiling."`
 
 	// API
 	APIProto           string `long:"apiproto" description:"Protocol for API (http or https)"`
@@ -119,6 +121,7 @@ var (
 		DebugLevel:         defaultLogLevel,
 		ConfigFile:         defaultConfigFile,
 		LogDir:             defaultLogDir,
+		HTTPProfPath:       defaultHTTPProfPath,
 		APIProto:           defaultAPIProto,
 		APIListen:          defaultAPIListen,
 		IndentJSON:         defaultIndentJSON,
@@ -352,6 +355,11 @@ func loadConfig() (*config, error) {
 		os.Exit(0)
 	}
 
+	// Ensure HTTP profiler is mounted with a valid path prefix
+	if cfg.HTTPProfile && (cfg.HTTPProfPath == "/" || len(defaultHTTPProfPath) == 0) {
+		return loadConfigError(fmt.Errorf("httpprofprefix must not be \"\" or \"/\""))
+	}
+
 	// Initialize log rotation.  After log rotation has been initialized, the
 	// logger variables may be used.
 	initLogRotator(filepath.Join(cfg.LogDir, defaultLogFilename))

main.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"net"
 	"net/http"
+	_ "net/http/pprof"
 	"os"
 	"os/signal"
 	"runtime/pprof"
@@ -426,8 +427,11 @@ func mainCore() error {
 
 	// HTTP profiler
 	if cfg.HTTPProfile {
-		http.Handle("/", http.RedirectHandler("/debug/pprof", http.StatusSeeOther))
-		webMux.Mount("/p", http.DefaultServeMux)
+		profPath := cfg.HTTPProfPath
+		log.Warnf("Starting the HTTP profiler on path %s.", profPath)
+		// http pprof uses http.DefaultServeMux
+		http.Handle("/", http.RedirectHandler(profPath+"/debug/pprof/", http.StatusSeeOther))
+		webMux.Mount(profPath, http.StripPrefix(profPath, http.DefaultServeMux))
 	}
 
 	if err = listenAndServeProto(cfg.APIListen, cfg.APIProto, webMux); err != nil {
@@ -475,8 +479,8 @@ func listenAndServeProto(listen, proto string, mux http.Handler) error {
 	case err := <-errChan:
 		return fmt.Errorf("Failed to bind web server: %v", err)
 	case <-t.C:
-		expLog.Infof("Now serving on %s://%v/", proto, listen)
-		apiLog.Infof("Now serving on %s://%v/", proto, listen)
+		expLog.Infof("Now serving explorer on %s://%v/", proto, listen)
+		apiLog.Infof("Now serving API on %s://%v/", proto, listen)
 		return nil
 	}
 }