src

start.go (12009B)

---

 // Copyright 2024 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 telemetry
 
 import (
 	"fmt"
 	"log"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"sync"
 	"time"
 
 	"golang.org/x/sync/errgroup"
 	"golang.org/x/telemetry/counter"
 	"golang.org/x/telemetry/internal/crashmonitor"
 	"golang.org/x/telemetry/internal/telemetry"
 	"golang.org/x/telemetry/internal/upload"
 )
 
 // Config controls the behavior of [Start].
 type Config struct {
 	// ReportCrashes, if set, will enable crash reporting.
 	// ReportCrashes uses the [debug.SetCrashOutput] mechanism, which is a
 	// process-wide resource.
 	// Do not make other calls to that function within your application.
 	// ReportCrashes is a non-functional unless the program is built with go1.23+.
 	ReportCrashes bool
 
 	// Upload causes this program to periodically upload approved counters
 	// from the local telemetry database to telemetry.go.dev.
 	//
 	// This option has no effect unless the user has given consent
 	// to enable data collection, for example by running
 	// cmd/gotelemetry or affirming the gopls dialog.
 	//
 	// (This feature is expected to be used only by gopls.
 	// Longer term, the go command may become the sole program
 	// responsible for uploading.)
 	Upload bool
 
 	// TelemetryDir, if set, will specify an alternate telemetry
 	// directory to write data to. If not set, it uses the default
 	// directory.
 	// This field is intended to be used for isolating testing environments.
 	TelemetryDir string
 
 	// UploadStartTime, if set, overrides the time used as the upload start time,
 	// which is the time used by the upload logic to determine whether counter
 	// file data should be uploaded. Only counter files that have expired before
 	// the start time are considered for upload.
 	//
 	// This field can be used to simulate a future upload that collects recently
 	// modified counters.
 	UploadStartTime time.Time
 
 	// UploadURL, if set, overrides the URL used to receive uploaded reports. If
 	// unset, this URL defaults to https://telemetry.go.dev/upload.
 	UploadURL string
 }
 
 // Start initializes telemetry using the specified configuration.
 //
 // Start opens the local telemetry database so that counter increment
 // operations are durably recorded in the local file system.
 //
 // If [Config.Upload] is set, and the user has opted in to telemetry
 // uploading, this process may attempt to upload approved counters
 // to telemetry.go.dev.
 //
 // If [Config.ReportCrashes] is set, any fatal crash will be
 // recorded by incrementing a counter named for the stack of the
 // first running goroutine in the traceback.
 //
 // If either of these flags is set, Start re-executes the current
 // executable as a child process, in a special mode in which it
 // acts as a telemetry sidecar for the parent process (the application).
 // In that mode, the call to Start will never return, so Start must
 // be called immediately within main, even before such things as
 // inspecting the command line. The application should avoid expensive
 // steps or external side effects in init functions, as they will
 // be executed twice (parent and child).
 //
 // Start returns a StartResult, which may be awaited via [StartResult.Wait] to
 // wait for all work done by Start to complete.
 func Start(config Config) *StartResult {
 	switch v := os.Getenv(telemetryChildVar); v {
 	case "":
 		// The subprocess started by parent has GO_TELEMETRY_CHILD=1.
 		return parent(config)
 	case "1":
 		child(config) // child will exit the process when it's done.
 	case "2":
 		// Do nothing: this was executed directly or indirectly by a child.
 	default:
 		log.Fatalf("unexpected value for %q: %q", telemetryChildVar, v)
 	}
 
 	return &StartResult{}
 }
 
 // MaybeChild executes the telemetry child logic if the calling program is
 // the telemetry child process, and does nothing otherwise. It is meant to be
 // called as the first thing in a program that uses telemetry.Start but cannot
 // call telemetry.Start immediately when it starts.
 func MaybeChild(config Config) {
 	if v := os.Getenv(telemetryChildVar); v == "1" {
 		child(config) // child will exit the process when it's done.
 	}
 	// other values of the telemetryChildVar environment variable
 	// will be handled by telemetry.Start.
 }
 
 // A StartResult is a handle to the result of a call to [Start]. Call
 // [StartResult.Wait] to wait for the completion of all work done on behalf of
 // Start.
 type StartResult struct {
 	wg sync.WaitGroup
 }
 
 // Wait waits for the completion of all work initiated by [Start].
 func (res *StartResult) Wait() {
 	if res == nil {
 		return
 	}
 	res.wg.Wait()
 }
 
 var daemonize = func(cmd *exec.Cmd) {}
 
 // If telemetryChildVar is set to "1" in the environment, this is the telemetry
 // child.
 //
 // If telemetryChildVar is set to "2", this is a child of the child, and no
 // further forking should occur.
 const telemetryChildVar = "GO_TELEMETRY_CHILD"
 
 // If telemetryUploadVar is set to "1" in the environment, the upload token has been
 // acquired by the parent, and the child should attempt an upload.
 const telemetryUploadVar = "GO_TELEMETRY_CHILD_UPLOAD"
 
 func parent(config Config) *StartResult {
 	if config.TelemetryDir != "" {
 		telemetry.Default = telemetry.NewDir(config.TelemetryDir)
 	}
 	result := new(StartResult)
 
 	mode, _ := telemetry.Default.Mode()
 	if mode == "off" {
 		// Telemetry is turned off. Crash reporting doesn't work without telemetry
 		// at least set to "local". The upload process runs in both "on" and "local" modes.
 		// In local mode the upload process builds local reports but does not do the upload.
 		return result
 	}
 
 	counter.Open()
 
 	if _, err := os.Stat(telemetry.Default.LocalDir()); err != nil {
 		// There was a problem statting LocalDir, which is needed for both
 		// crash monitoring and counter uploading. Most likely, there was an
 		// error creating telemetry.LocalDir in the counter.Open call above.
 		// Don't start the child.
 		return result
 	}
 
 	childShouldUpload := config.Upload && acquireUploadToken()
 	reportCrashes := config.ReportCrashes
 
 	if reportCrashes || childShouldUpload {
 		startChild(reportCrashes, childShouldUpload, result)
 	}
 
 	return result
 }
 
 func startChild(reportCrashes, upload bool, result *StartResult) {
 	// This process is the application (parent).
 	// Fork+exec the telemetry child.
 	exe, err := os.Executable()
 	if err != nil {
 		// There was an error getting os.Executable. It's possible
 		// for this to happen on AIX if os.Args[0] is not an absolute
 		// path and we can't find os.Args[0] in PATH.
 		log.Printf("failed to start telemetry sidecar: os.Executable: %v", err)
 		return
 	}
 	cmd := exec.Command(exe, "** telemetry **") // this unused arg is just for ps(1)
 	daemonize(cmd)
 	cmd.Env = append(os.Environ(), telemetryChildVar+"=1")
 	if upload {
 		cmd.Env = append(cmd.Env, telemetryUploadVar+"=1")
 	}
 	cmd.Dir = telemetry.Default.LocalDir()
 
 	// The child process must write to a log file, not
 	// the stderr file it inherited from the parent, as
 	// the child may outlive the parent but should not prolong
 	// the life of any pipes created (by the grandparent)
 	// to gather the output of the parent.
 	//
 	// By default, we discard the child process's stderr,
 	// but in line with the uploader, log to a file in debug
 	// only if that directory was created by the user.
 	fd, err := os.Stat(telemetry.Default.DebugDir())
 	if err != nil {
 		if !os.IsNotExist(err) {
 			log.Printf("failed to stat debug directory: %v", err)
 			return
 		}
 	} else if fd.IsDir() {
 		// local/debug exists and is a directory. Set stderr to a log file path
 		// in local/debug.
 		childLogPath := filepath.Join(telemetry.Default.DebugDir(), "sidecar.log")
 		childLog, err := os.OpenFile(childLogPath, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0600)
 		if err != nil {
 			log.Printf("opening sidecar log file for child: %v", err)
 			return
 		}
 		defer childLog.Close()
 		cmd.Stderr = childLog
 	}
 
 	var crashOutputFile *os.File
 	if reportCrashes {
 		pipe, err := cmd.StdinPipe()
 		if err != nil {
 			log.Printf("StdinPipe: %v", err)
 			return
 		}
 
 		crashOutputFile = pipe.(*os.File) // (this conversion is safe)
 	}
 
 	if err := cmd.Start(); err != nil {
 		// The child couldn't be started. Log the failure.
 		log.Printf("can't start telemetry child process: %v", err)
 		return
 	}
 	if reportCrashes {
 		crashmonitor.Parent(crashOutputFile)
 	}
 	result.wg.Add(1)
 	go func() {
 		cmd.Wait() // Release resources if cmd happens not to outlive this process.
 		result.wg.Done()
 	}()
 }
 
 func child(config Config) {
 	log.SetPrefix(fmt.Sprintf("telemetry-sidecar (pid %v): ", os.Getpid()))
 
 	if config.TelemetryDir != "" {
 		telemetry.Default = telemetry.NewDir(config.TelemetryDir)
 	}
 
 	// golang/go#67211: be sure to set telemetryChildVar before running the
 	// child, because the child itself invokes the go command to download the
 	// upload config. If the telemetryChildVar variable is still set to "1",
 	// that delegated go command may think that it is itself a telemetry
 	// child.
 	//
 	// On the other hand, if telemetryChildVar were simply unset, then the
 	// delegated go commands would fork themselves recursively. Short-circuit
 	// this recursion.
 	os.Setenv(telemetryChildVar, "2")
 	upload := os.Getenv(telemetryUploadVar) == "1"
 
 	// The crashmonitor and/or upload process may themselves record counters.
 	counter.Open()
 
 	// Start crashmonitoring and uploading depending on what's requested
 	// and wait for the longer running child to complete before exiting:
 	// if we collected a crash before the upload finished, wait for the
 	// upload to finish before exiting
 	var g errgroup.Group
 
 	if config.ReportCrashes {
 		g.Go(func() error {
 			crashmonitor.Child()
 			return nil
 		})
 	}
 	if upload {
 		g.Go(func() error {
 			uploaderChild(config.UploadStartTime, config.UploadURL)
 			return nil
 		})
 	}
 	g.Wait()
 
 	os.Exit(0)
 }
 
 func uploaderChild(asof time.Time, uploadURL string) {
 	if err := upload.Run(upload.RunConfig{
 		UploadURL: uploadURL,
 		LogWriter: os.Stderr,
 		StartTime: asof,
 	}); err != nil {
 		log.Printf("upload failed: %v", err)
 	}
 }
 
 // acquireUploadToken acquires a token permitting the caller to upload.
 // To limit the frequency of uploads, only one token is issue per
 // machine per time period.
 // The boolean indicates whether the token was acquired.
 func acquireUploadToken() bool {
 	if telemetry.Default.LocalDir() == "" {
 		// The telemetry dir wasn't initialized properly, probably because
 		// os.UserConfigDir did not complete successfully. In that case
 		// there are no counters to upload, so we should just do nothing.
 		return false
 	}
 	tokenfile := filepath.Join(telemetry.Default.LocalDir(), "upload.token")
 	const period = 24 * time.Hour
 
 	// A process acquires a token by successfully creating a
 	// well-known file. If the file already exists and has an
 	// mtime age less then than the period, the process does
 	// not acquire the token. If the file is older than the
 	// period, the process is allowed to remove the file and
 	// try to re-create it.
 	fi, err := os.Stat(tokenfile)
 	if err == nil {
 		if time.Since(fi.ModTime()) < period {
 			return false
 		}
 		// There's a possible race here where two processes check the
 		// token file and see that it's older than the period, then the
 		// first one removes it and creates another, and then a second one
 		// removes the newly created file and creates yet another
 		// file. Then both processes would act as though they had the token.
 		// This is very rare, but it's also okay because we're only grabbing
 		// the token to do rate limiting, not for correctness.
 		_ = os.Remove(tokenfile)
 	} else if !os.IsNotExist(err) {
 		log.Printf("error acquiring upload taken: statting token file: %v", err)
 		return false
 	}
 
 	f, err := os.OpenFile(tokenfile, os.O_CREATE|os.O_EXCL, 0666)
 	if err != nil {
 		if os.IsExist(err) {
 			return false
 		}
 		log.Printf("error acquiring upload token: creating token file: %v", err)
 		return false
 	}
 	_ = f.Close()
 	return true
 }