signals.go

/*
Copyright 2017 Gravitational, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package service

import (
	"context"
	"encoding/json"
	"net"
	"os"
	"os/exec"
	"os/signal"
	"strings"
	"syscall"
	"time"

	"github.com/gravitational/teleport/lib/utils"
	"github.com/gravitational/trace"
	"github.com/sirupsen/logrus"
)

// printShutdownStatus prints running services until shut down
func (process *TeleportProcess) printShutdownStatus(ctx context.Context) {
	t := time.NewTicker(5 * time.Second)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-t.C:
			log.Infof("Waiting for services: %v to finish.", process.Supervisor.Services())
		}
	}
}

// WaitForSignals waits for system signals and processes them.
// Should not be called twice by the process.
func (process *TeleportProcess) WaitForSignals(ctx context.Context) error {

	sigC := make(chan os.Signal, 1024)
	signal.Notify(sigC,
		syscall.SIGQUIT, // graceful shutdown
		syscall.SIGTERM, // fast shutdown
		syscall.SIGINT,  // fast shutdown
		syscall.SIGKILL, // fast shutdown
		syscall.SIGUSR1, // log process diagnostic info
		syscall.SIGUSR2, // initiate process restart procedure
		syscall.SIGHUP,  // graceful restart procedure
		syscall.SIGCHLD, // collect child status
	)

	doneContext, cancel := context.WithCancel(ctx)
	defer cancel()

	// Block until a signal is received or handler got an error.
	// Notice how this handler is serialized - it will only receive
	// signals in sequence and will not run in parallel.
	for {
		select {
		case signal := <-sigC:
			switch signal {
			case syscall.SIGQUIT:
				go process.printShutdownStatus(doneContext)
				process.Shutdown(ctx)
				log.Infof("All services stopped, exiting.")
				return nil
			case syscall.SIGTERM, syscall.SIGKILL, syscall.SIGINT:
				log.Infof("Got signal %q, exiting immediately.", signal)
				process.Close()
				return nil
			case syscall.SIGUSR1:
				// All programs placed diagnostics on the standard output.
				// This had always caused trouble when the output was redirected into a file, but became intolerable
				// when the output was sent to an unsuspecting process.
				// Nevertheless, unwilling to violate the simplicity of the standard-input-standard-output model,
				// people tolerated this state of affairs through v6. Shortly thereafter Dennis Ritchie cut the Gordian
				// knot by introducing the standard error file.
				// That was not quite enough. With pipelines diagnostics could come from any of several programs running simultaneously.
				// Diagnostics needed to identify themselves.
				// - Doug McIllroy, "A Research UNIX Reader: Annotated Excerpts from the Programmer’s Manual, 1971-1986"
				log.Infof("Got signal %q, logging diagostic info to stderr.", signal)
				writeDebugInfo(os.Stderr)
			case syscall.SIGUSR2:
				if !process.backendSupportsForks() {
					log.Warningf("Process is using backend that does not support multiple processes, switch to another backend to use USR2.")
					continue
				}
				log.Infof("Got signal %q, forking a new process.", signal)
				if err := process.forkChild(); err != nil {
					log.Infof("Failed to fork: %s", trace.DebugReport(err))
				} else {
					log.Infof("Successfully started new process.")
				}
			case syscall.SIGHUP:
				if !process.backendSupportsForks() {
					log.Warningf("Process is using backend that does not support multiple processes, switch to another backend to use HUP.")
					continue
				}
				log.Infof("Got signal %q, performing graceful restart.", signal)
				if err := process.forkChild(); err != nil {
					log.Infof("Failed to fork: %s", trace.DebugReport(err))
				} else {
					log.Infof("Successfully started new process.")
				}
				log.Infof("Shutting down gracefully.")
				go process.printShutdownStatus(doneContext)
				process.Shutdown(ctx)
				log.Infof("All services stopped, exiting.")
				return nil
			case syscall.SIGCHLD:
				process.collectStatuses()
			default:
				log.Infof("Ignoring %q.", signal)
			}
		case <-ctx.Done():
			process.Close()
			process.Wait()
			log.Info("Got request to shutdown, context is closing")
			return nil
		}
	}
}

// closeImportedDescriptors closes imported but unused file descriptors,
// what could happen if service has updated configuration
func (process *TeleportProcess) closeImportedDescriptors(prefix string) error {
	process.Lock()
	defer process.Unlock()

	var errors []error
	for i := range process.importedDescriptors {
		d := process.importedDescriptors[i]
		if strings.HasPrefix(d.Type, prefix) {
			log.Infof("Closing imported but unused descriptor %v %v.", d.Type, d.Address)
			errors = append(errors, d.File.Close())
		}
	}
	return trace.NewAggregate(errors...)
}

// importOrCreateListener imports listener passed by the parent process (happens during live reload)
// or creates a new listener if there was no listener registered
func (process *TeleportProcess) importOrCreateListener(listenerType, address string) (net.Listener, error) {
	l, err := process.importListener(listenerType, address)
	if err == nil {
		log.Infof("Using file descriptor %v %v passed by the parent process.", listenerType, address)
		return l, nil
	}
	if !trace.IsNotFound(err) {
		return nil, trace.Wrap(err)
	}
	log.Infof("Service %v is creating new listener on %v.", listenerType, address)
	return process.createListener(listenerType, address)
}

// importListener imports listener passed by the parent process, if no listener is found
// returns NotFound, otherwise removes the file from the list
func (process *TeleportProcess) importListener(listenerType, address string) (net.Listener, error) {
	process.Lock()
	defer process.Unlock()

	for i := range process.importedDescriptors {
		d := process.importedDescriptors[i]
		if d.Type == listenerType && d.Address == address {
			l, err := d.ToListener()
			if err != nil {
				return nil, trace.Wrap(err)
			}
			process.importedDescriptors = append(process.importedDescriptors[:i], process.importedDescriptors[i+1:]...)
			process.registeredListeners = append(process.registeredListeners, RegisteredListener{Type: listenerType, Address: address, Listener: l})
			return l, nil
		}
	}

	return nil, trace.NotFound("no file descriptor for type %v and address %v has been imported", listenerType, address)
}

// createListener creates listener and adds to a list of tracked listeners
func (process *TeleportProcess) createListener(listenerType, address string) (net.Listener, error) {
	listener, err := net.Listen("tcp", address)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	process.Lock()
	defer process.Unlock()
	r := RegisteredListener{Type: listenerType, Address: address, Listener: listener}
	process.registeredListeners = append(process.registeredListeners, r)
	return listener, nil
}

// exportFileDescriptors exports file descriptors to be passed to child process
func (process *TeleportProcess) exportFileDescriptors() ([]FileDescriptor, error) {
	var out []FileDescriptor
	process.Lock()
	defer process.Unlock()
	for _, r := range process.registeredListeners {
		file, err := utils.GetListenerFile(r.Listener)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		out = append(out, FileDescriptor{File: file, Type: r.Type, Address: r.Address})
	}
	return out, nil
}

// importFileDescriptors imports file descriptors from environment if there are any
func importFileDescriptors() ([]FileDescriptor, error) {
	// These files may be passed in by the parent process
	filesString := os.Getenv(teleportFilesEnvVar)
	if filesString == "" {
		return nil, nil
	}

	files, err := filesFromString(filesString)
	if err != nil {
		return nil, trace.BadParameter("child process has failed to read files, error %q", err)
	}

	if len(files) != 0 {
		log.Infof("Child has been passed files: %v", files)
	}

	return files, nil
}

// RegisteredListener is a listener registered
// within teleport process, can be passed to child process
type RegisteredListener struct {
	// Type is a listener type, e.g. auth:ssh
	Type string
	// Address is an address listener is serving on, e.g. 127.0.0.1:3025
	Address string
	// Listener is a file listener object
	Listener net.Listener
}

// FileDescriptor is a file descriptor associated
// with a listener
type FileDescriptor struct {
	// Type is a listener type, e.g. auth:ssh
	Type string
	// Address is an addresss of the listener, e.g. 127.0.0.1:3025
	Address string
	// File is a file descriptor associated with the listener
	File *os.File
}

func (fd *FileDescriptor) ToListener() (net.Listener, error) {
	listener, err := net.FileListener(fd.File)
	if err != nil {
		return nil, err
	}
	fd.File.Close()
	return listener, nil
}

type fileDescriptor struct {
	Address  string `json:"addr"`
	Type     string `json:"type"`
	FileFD   int    `json:"fd"`
	FileName string `json:"fileName"`
}

// filesToString serializes file descriptors as well as accompanying information (like socket host and port)
func filesToString(files []FileDescriptor) (string, error) {
	out := make([]fileDescriptor, len(files))
	for i, f := range files {
		out[i] = fileDescriptor{
			// Once files will be passed to the child process and their FDs will change.
			// The first three passed files are stdin, stdout and stderr, every next file will have the index + 3
			// That's why we rearrange the FDs for child processes to get the correct file descriptors.
			FileFD:   i + 3,
			FileName: f.File.Name(),
			Address:  f.Address,
			Type:     f.Type,
		}
	}
	bytes, err := json.Marshal(out)
	if err != nil {
		return "", err
	}
	return string(bytes), nil
}

const teleportFilesEnvVar = "TELEPORT_OS_FILES"

func execPath() (string, error) {
	name, err := exec.LookPath(os.Args[0])
	if err != nil {
		return "", err
	}
	if _, err = os.Stat(name); nil != err {
		return "", err
	}
	return name, err
}

// filesFromString de-serializes the file descriptors and turns them in the os.Files
func filesFromString(in string) ([]FileDescriptor, error) {
	var out []fileDescriptor
	if err := json.Unmarshal([]byte(in), &out); err != nil {
		return nil, err
	}
	files := make([]FileDescriptor, len(out))
	for i, o := range out {
		files[i] = FileDescriptor{
			File:    os.NewFile(uintptr(o.FileFD), o.FileName),
			Address: o.Address,
			Type:    o.Type,
		}
	}
	return files, nil
}

func (process *TeleportProcess) forkChild() error {
	path, err := execPath()
	if err != nil {
		return trace.Wrap(err)
	}

	workingDir, err := os.Getwd()
	if nil != err {
		return err
	}

	log := log.WithFields(logrus.Fields{"path": path, "workingDir": workingDir})

	log.Info("Forking child.")

	listenerFiles, err := process.exportFileDescriptors()
	if err != nil {
		return trace.Wrap(err)
	}

	// These files will be passed to the child process
	files := []*os.File{os.Stdin, os.Stdout, os.Stderr}
	for _, f := range listenerFiles {
		files = append(files, f.File)
	}

	// Serialize files to JSON string representation
	vals, err := filesToString(listenerFiles)
	if err != nil {
		return err
	}

	log.Infof("Passing %s to child", vals)
	os.Setenv(teleportFilesEnvVar, vals)

	p, err := os.StartProcess(path, os.Args, &os.ProcAttr{
		Dir:   workingDir,
		Env:   os.Environ(),
		Files: files,
		Sys:   &syscall.SysProcAttr{},
	})
	if err != nil {
		return trace.ConvertSystemError(err)
	}
	process.pushForkedPID(p.Pid)

	log.WithFields(logrus.Fields{"pid": p.Pid}).Infof("Started new child process.")
	return nil
}

// collectStatuses attempts to collect exit statuses from
// forked teleport child processes.
// If forked teleport process exited with an error during graceful
// restart, parent process has to collect the child process status
// otherwise the child process will become a zombie process.
// Call Wait4(-1) is trying to collect status of any child
// leads to warnings in logs, because other parts of the program could
// have tried to collect the status of this process.
// Instead this logic tries to collect statuses of the processes
// forked during restart procedure.
func (process *TeleportProcess) collectStatuses() {
	pids := process.getForkedPIDs()
	if len(pids) == 0 {
		return
	}
	for _, pid := range pids {
		var wait syscall.WaitStatus
		rpid, err := syscall.Wait4(pid, &wait, syscall.WNOHANG, nil)
		if err != nil {
			log.Errorf("Wait call failed: %v.", err)
			continue
		}
		if rpid == pid {
			process.popForkedPID(pid)
			log.Warningf("Forked teleport process %v has exited with status: %v.", pid, wait.ExitStatus())
		}
	}
}

func (process *TeleportProcess) pushForkedPID(pid int) {
	process.Lock()
	defer process.Unlock()
	process.forkedPIDs = append(process.forkedPIDs, pid)
}

func (process *TeleportProcess) popForkedPID(pid int) {
	process.Lock()
	defer process.Unlock()
	for i, p := range process.forkedPIDs {
		if p == pid {
			process.forkedPIDs = append(process.forkedPIDs[:i], process.forkedPIDs[i+1:]...)
			return
		}
	}
}

func (process *TeleportProcess) getForkedPIDs() []int {
	process.Lock()
	defer process.Unlock()
	if len(process.forkedPIDs) == 0 {
		return nil
	}
	out := make([]int, len(process.forkedPIDs))
	copy(out, process.forkedPIDs)
	return out
}