pprof.go

Documentation: net/http/pprof

  // Copyright 2010 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // Package pprof serves via its HTTP server runtime profiling data
  // in the format expected by the pprof visualization tool.
  //
  // The package is typically only imported for the side effect of
  // registering its HTTP handlers.
  // The handled paths all begin with /debug/pprof/.
  //
  // To use pprof, link this package into your program:
  //	import _ "net/http/pprof"
  //
  // If your application is not already running an http server, you
  // need to start one. Add "net/http" and "log" to your imports and
  // the following code to your main function:
  //
  // 	go func() {
  // 		log.Println(http.ListenAndServe("localhost:6060", nil))
  // 	}()
  //
  // Then use the pprof tool to look at the heap profile:
  //
  //	go tool pprof http://localhost:6060/debug/pprof/heap
  //
  // Or to look at a 30-second CPU profile:
  //
  //	go tool pprof http://localhost:6060/debug/pprof/profile
  //
  // Or to look at the goroutine blocking profile, after calling
  // runtime.SetBlockProfileRate in your program:
  //
  //	go tool pprof http://localhost:6060/debug/pprof/block
  //
  // Or to collect a 5-second execution trace:
  //
  //	wget http://localhost:6060/debug/pprof/trace?seconds=5
  //
  // Or to look at the holders of contended mutexes, after calling
  // runtime.SetMutexProfileFraction in your program:
  //
  //	go tool pprof http://localhost:6060/debug/pprof/mutex
  //
  // To view all available profiles, open http://localhost:6060/debug/pprof/
  // in your browser.
  //
  // For a study of the facility in action, visit
  //
  //	https://blog.golang.org/2011/06/profiling-go-programs.html
  //
  package pprof
  
  import (
  	"bufio"
  	"bytes"
  	"fmt"
  	"html/template"
  	"io"
  	"log"
  	"net/http"
  	"os"
  	"runtime"
  	"runtime/pprof"
  	"runtime/trace"
  	"strconv"
  	"strings"
  	"time"
  )
  
  func init() {
  	http.Handle("/debug/pprof/", http.HandlerFunc(Index))
  	http.Handle("/debug/pprof/cmdline", http.HandlerFunc(Cmdline))
  	http.Handle("/debug/pprof/profile", http.HandlerFunc(Profile))
  	http.Handle("/debug/pprof/symbol", http.HandlerFunc(Symbol))
  	http.Handle("/debug/pprof/trace", http.HandlerFunc(Trace))
  }
  
  // Cmdline responds with the running program's
  // 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")
  	fmt.Fprintf(w, strings.Join(os.Args, "\x00"))
  }
  
  func sleep(w http.ResponseWriter, d time.Duration) {
  	var clientGone <-chan bool
  	if cn, ok := w.(http.CloseNotifier); ok {
  		clientGone = cn.CloseNotify()
  	}
  	select {
  	case <-time.After(d):
  	case <-clientGone:
  	}
  }
  
  func durationExceedsWriteTimeout(r *http.Request, seconds float64) bool {
  	srv, ok := r.Context().Value(http.ServerContextKey).(*http.Server)
  	return ok && srv.WriteTimeout != 0 && seconds >= srv.WriteTimeout.Seconds()
  }
  
  // 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.ParseInt(r.FormValue("seconds"), 10, 64)
  	if sec == 0 {
  		sec = 30
  	}
  
  	if durationExceedsWriteTimeout(r, float64(sec)) {
  		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
  		w.Header().Set("X-Go-Pprof", "1")
  		w.WriteHeader(http.StatusBadRequest)
  		fmt.Fprintln(w, "profile duration exceeds server's WriteTimeout")
  		return
  	}
  
  	// 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.Header().Set("X-Go-Pprof", "1")
  		w.WriteHeader(http.StatusInternalServerError)
  		fmt.Fprintf(w, "Could not enable CPU profiling: %s\n", err)
  		return
  	}
  	sleep(w, time.Duration(sec)*time.Second)
  	pprof.StopCPUProfile()
  }
  
  // Trace responds with the execution trace in binary form.
  // Tracing lasts for duration specified in seconds GET parameter, or for 1 second if not specified.
  // The package initialization registers it as /debug/pprof/trace.
  func Trace(w http.ResponseWriter, r *http.Request) {
  	sec, err := strconv.ParseFloat(r.FormValue("seconds"), 64)
  	if sec <= 0 || err != nil {
  		sec = 1
  	}
  
  	if durationExceedsWriteTimeout(r, sec) {
  		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
  		w.Header().Set("X-Go-Pprof", "1")
  		w.WriteHeader(http.StatusBadRequest)
  		fmt.Fprintln(w, "profile duration exceeds server's WriteTimeout")
  		return
  	}
  
  	// Set Content Type assuming trace.Start will work,
  	// because if it does it starts writing.
  	w.Header().Set("Content-Type", "application/octet-stream")
  	if err := trace.Start(w); err != nil {
  		// trace.Start 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.Header().Set("X-Go-Pprof", "1")
  		w.WriteHeader(http.StatusInternalServerError)
  		fmt.Fprintf(w, "Could not enable tracing: %s\n", err)
  		return
  	}
  	sleep(w, time.Duration(sec*float64(time.Second)))
  	trace.Stop()
  }
  
  // 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")
  
  	// We have to read the whole POST body before
  	// writing any output. Buffer the output here.
  	var buf bytes.Buffer
  
  	// We don't know how many symbols we have, but we
  	// do have symbol information. Pprof only cares whether
  	// this number is 0 (no symbols available) or > 0.
  	fmt.Fprintf(&buf, "num_symbols: 1\n")
  
  	var b *bufio.Reader
  	if r.Method == "POST" {
  		b = bufio.NewReader(r.Body)
  	} else {
  		b = bufio.NewReader(strings.NewReader(r.URL.RawQuery))
  	}
  
  	for {
  		word, err := b.ReadSlice('+')
  		if err == nil {
  			word = word[0 : len(word)-1] // trim +
  		}
  		pc, _ := strconv.ParseUint(string(word), 0, 64)
  		if pc != 0 {
  			f := runtime.FuncForPC(uintptr(pc))
  			if f != nil {
  				fmt.Fprintf(&buf, "%#x %s\n", pc, f.Name())
  			}
  		}
  
  		// Wait until here to check for err; the last
  		// symbol will have an err because it doesn't end in +.
  		if err != nil {
  			if err != io.EOF {
  				fmt.Fprintf(&buf, "reading request: %v\n", err)
  			}
  			break
  		}
  	}
  
  	w.Write(buf.Bytes())
  }
  
  // Handler returns an HTTP handler that serves the named profile.
  func Handler(name string) http.Handler {
  	return handler(name)
  }
  
  type handler string
  
  func (name handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
  	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
  	debug, _ := strconv.Atoi(r.FormValue("debug"))
  	p := pprof.Lookup(string(name))
  	if p == nil {
  		w.WriteHeader(404)
  		fmt.Fprintf(w, "Unknown profile: %s\n", name)
  		return
  	}
  	gc, _ := strconv.Atoi(r.FormValue("gc"))
  	if name == "heap" && gc > 0 {
  		runtime.GC()
  	}
  	p.WriteTo(w, debug)
  }
  
  // Index responds with the pprof-formatted profile named by the request.
  // For example, "/debug/pprof/heap" serves the "heap" profile.
  // Index responds to a request for "/debug/pprof/" with an HTML page
  // listing the available profiles.
  func Index(w http.ResponseWriter, r *http.Request) {
  	if strings.HasPrefix(r.URL.Path, "/debug/pprof/") {
  		name := strings.TrimPrefix(r.URL.Path, "/debug/pprof/")
  		if name != "" {
  			handler(name).ServeHTTP(w, r)
  			return
  		}
  	}
  
  	profiles := pprof.Profiles()
  	if err := indexTmpl.Execute(w, profiles); err != nil {
  		log.Print(err)
  	}
  }
  
  var indexTmpl = template.Must(template.New("index").Parse(`<html>
  <head>
  <title>/debug/pprof/</title>
  </head>
  <body>
  /debug/pprof/<br>
  <br>
  profiles:<br>
  <table>
  {{range .}}
  <tr><td align=right>{{.Count}}<td><a href="{{.Name}}?debug=1">{{.Name}}</a>
  {{end}}
  </table>
  <br>
  <a href="goroutine?debug=2">full goroutine stack dump</a><br>
  </body>
  </html>
  `))
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