+ config: add "debug_pprof" setting

Squashed commit of the following:

commit 96d185cf4acc55b21a00d10072e0a641ef7655b8
Merge: 3b75a8cb 9b7c1181
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Wed Apr 22 15:57:50 2020 +0300

    Merge remote-tracking branch 'origin/master' into add-pprof

commit 3b75a8cbec5d72be8865a56bfd7ebb8b0673c3bc
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Wed Apr 22 13:52:36 2020 +0300

    * use localhost:6060 for pprof

commit f66f2fbd7409b98cd9f7d297c268fca998f85e3b
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Wed Apr 22 12:46:25 2020 +0300

    minor

commit 6e38712fb5542f612675858eb957efdefc38f9b0
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Wed Apr 22 11:59:39 2020 +0300

    use separate HTTP server for pprof

commit 988d95b5fad22f536bf9204b6b96f3697cf9a589
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Apr 21 17:04:04 2020 +0300

    minor

commit 90ee6e9753be2af49467687cdf71c35b3943b78b
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Apr 21 16:57:38 2020 +0300

    * use modified version of pprof

commit 413002220fe0717950539a8b7e6b0f31cef31bb8
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Mon Apr 20 16:35:21 2020 +0300

    minor

commit d4655d3849de1d9fe97efdb7f18fc21d5ac19eda
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Mon Apr 20 15:57:57 2020 +0300

    + config: add "enable_pprof" setting

.golangci.yml

@@ -13,6 +13,7 @@ run:
   skip-files:
     - ".*generated.*"
     - dnsfilter/rule_to_regexp.go
+    - util/pprof.go
     - ".*_test.go"
 
 
@@ -65,5 +66,7 @@ issues:
     - Error return value of ..*.Shutdown.
     # goconst
     - string .forcesafesearch.google.com. has 3 occurrences
+    # gosec: Profiling endpoint is automatically exposed on /debug/pprof
+    - G108
     # gosec: Subprocess launched with function call as argument or cmd arguments
     - G204

home/config.go

@@ -45,6 +45,7 @@ type configuration struct {
 	ProxyURL     string `yaml:"http_proxy"`    // Proxy address for our HTTP client
 	Language     string `yaml:"language"`      // two-letter ISO 639-1 language code
 	RlimitNoFile uint   `yaml:"rlimit_nofile"` // Maximum number of opened fd's per process (0: default)
+	DebugPProf   bool   `yaml:"debug_pprof"`   // Enable pprof HTTP server on port 6060
 
 	// TTL for a web session (in hours)
 	// An active session is automatically refreshed once a day.

home/home.go

@@ -242,6 +242,16 @@ func run(args options) {
 		if err != nil {
 			log.Fatal(err)
 		}
+
+		if config.DebugPProf {
+			mux := http.NewServeMux()
+			util.PProfRegisterWebHandlers(mux)
+			go func() {
+				log.Info("pprof: listening on localhost:6060")
+				err := http.ListenAndServe("localhost:6060", mux)
+				log.Error("Error while running the pprof server: %s", err)
+			}()
+		}
 	}
 
 	err := os.MkdirAll(Context.getDataDir(), 0755)

util/pprof.go

@@ -0,0 +1,352 @@
+// Modified pprof package
+// The problem with the mainstream package is that it registers HTTP handlers
+//  inside init() function.
+// This behaviour makes it impossible to enable pprof on demand in runtime.
+// But this package has a separate function for this -
+//  PProfRegisterWebHandlers().
+
+// 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))
+// 	}()
+//
+// If you are not using DefaultServeMux, you will have to register handlers
+// with the mux you are using.
+//
+// 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?seconds=30
+//
+// 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 util
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"html/template"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"runtime"
+	"runtime/pprof"
+	"runtime/trace"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// PProfRegisterWebHandlers - register HTTP handlers for pprof
+func PProfRegisterWebHandlers(mux *http.ServeMux) {
+	mux.HandleFunc("/debug/pprof/", Index)
+	mux.HandleFunc("/debug/pprof/cmdline", Cmdline)
+	mux.HandleFunc("/debug/pprof/profile", Profile)
+	mux.HandleFunc("/debug/pprof/symbol", Symbol)
+	mux.HandleFunc("/debug/pprof/trace", 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("X-Content-Type-Options", "nosniff")
+	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()
+}
+
+func serveError(w http.ResponseWriter, status int, txt string) {
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+	w.Header().Set("X-Go-Pprof", "1")
+	w.Header().Del("Content-Disposition")
+	w.WriteHeader(status)
+	fmt.Fprintln(w, txt)
+}
+
+// Profile responds with the pprof-formatted cpu profile.
+// Profiling lasts for duration specified in seconds GET parameter, or for 30 seconds if not specified.
+// The package initialization registers it as /debug/pprof/profile.
+func Profile(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+	sec, err := strconv.ParseInt(r.FormValue("seconds"), 10, 64)
+	if sec <= 0 || err != nil {
+		sec = 30
+	}
+
+	if durationExceedsWriteTimeout(r, float64(sec)) {
+		serveError(w, http.StatusBadRequest, "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")
+	w.Header().Set("Content-Disposition", `attachment; filename="profile"`)
+	if err := pprof.StartCPUProfile(w); err != nil {
+		// StartCPUProfile failed, so no writes yet.
+		serveError(w, http.StatusInternalServerError,
+			fmt.Sprintf("Could not enable CPU profiling: %s", 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) {
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+	sec, err := strconv.ParseFloat(r.FormValue("seconds"), 64)
+	if sec <= 0 || err != nil {
+		sec = 1
+	}
+
+	if durationExceedsWriteTimeout(r, sec) {
+		serveError(w, http.StatusBadRequest, "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")
+	w.Header().Set("Content-Disposition", `attachment; filename="trace"`)
+	if err := trace.Start(w); err != nil {
+		// trace.Start failed, so no writes yet.
+		serveError(w, http.StatusInternalServerError,
+			fmt.Sprintf("Could not enable tracing: %s", 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("X-Content-Type-Options", "nosniff")
+	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("X-Content-Type-Options", "nosniff")
+	p := pprof.Lookup(string(name))
+	if p == nil {
+		serveError(w, http.StatusNotFound, "Unknown profile")
+		return
+	}
+	gc, _ := strconv.Atoi(r.FormValue("gc"))
+	if name == "heap" && gc > 0 {
+		runtime.GC()
+	}
+	debug, _ := strconv.Atoi(r.FormValue("debug"))
+	if debug != 0 {
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+	} else {
+		w.Header().Set("Content-Type", "application/octet-stream")
+		w.Header().Set("Content-Disposition", fmt.Sprintf(`attachment; filename="%s"`, name))
+	}
+	p.WriteTo(w, debug)
+}
+
+var profileDescriptions = map[string]string{
+	"allocs":       "A sampling of all past memory allocations",
+	"block":        "Stack traces that led to blocking on synchronization primitives",
+	"cmdline":      "The command line invocation of the current program",
+	"goroutine":    "Stack traces of all current goroutines",
+	"heap":         "A sampling of memory allocations of live objects. You can specify the gc GET parameter to run GC before taking the heap sample.",
+	"mutex":        "Stack traces of holders of contended mutexes",
+	"profile":      "CPU profile. You can specify the duration in the seconds GET parameter. After you get the profile file, use the go tool pprof command to investigate the profile.",
+	"threadcreate": "Stack traces that led to the creation of new OS threads",
+	"trace":        "A trace of execution of the current program. You can specify the duration in the seconds GET parameter. After you get the trace file, use the go tool trace command to investigate the trace.",
+}
+
+// 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
+		}
+	}
+
+	type profile struct {
+		Name  string
+		Href  string
+		Desc  string
+		Count int
+	}
+	var profiles []profile
+	for _, p := range pprof.Profiles() {
+		profiles = append(profiles, profile{
+			Name:  p.Name(),
+			Href:  p.Name() + "?debug=1",
+			Desc:  profileDescriptions[p.Name()],
+			Count: p.Count(),
+		})
+	}
+
+	// Adding other profiles exposed from within this package
+	for _, p := range []string{"cmdline", "profile", "trace"} {
+		profiles = append(profiles, profile{
+			Name: p,
+			Href: p,
+			Desc: profileDescriptions[p],
+		})
+	}
+
+	sort.Slice(profiles, func(i, j int) bool {
+		return profiles[i].Name < profiles[j].Name
+	})
+
+	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>
+<style>
+.profile-name{
+	display:inline-block;
+	width:6rem;
+}
+</style>
+</head>
+<body>
+/debug/pprof/<br>
+<br>
+Types of profiles available:
+<table>
+<thead><td>Count</td><td>Profile</td></thead>
+{{range .}}
+	<tr>
+	<td>{{.Count}}</td><td><a href={{.Href}}>{{.Name}}</a></td>
+	</tr>
+{{end}}
+</table>
+<a href="goroutine?debug=2">full goroutine stack dump</a>
+<br/>
+<p>
+Profile Descriptions:
+<ul>
+{{range .}}
+<li><div class=profile-name>{{.Name}}:</div> {{.Desc}}</li>
+{{end}}
+</ul>
+</p>
+</body>
+</html>
+`))