// Copyright 2018 The containerd Authors.
// Copyright 2019 The gVisor Authors.
//
// 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
//
//     https://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 main

import (
	"bytes"
	"context"
	"flag"
	"fmt"
	"net"
	"os"
	"os/exec"
	"os/signal"
	"path/filepath"
	"runtime"
	"runtime/debug"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/containerd/containerd/events"
	"github.com/containerd/containerd/namespaces"
	"github.com/containerd/containerd/runtime/v1/linux/proc"
	containerdshim "github.com/containerd/containerd/runtime/v1/shim"
	shimapi "github.com/containerd/containerd/runtime/v1/shim/v1"
	"github.com/containerd/ttrpc"
	"github.com/containerd/typeurl"
	ptypes "github.com/gogo/protobuf/types"
	"github.com/opencontainers/runc/libcontainer/system"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
	"golang.org/x/sys/unix"

	"gvisor.dev/gvisor/pkg/shim/runsc"
	"gvisor.dev/gvisor/pkg/shim/v1/shim"
)

var (
	debugFlag            bool
	namespaceFlag        string
	socketFlag           string
	addressFlag          string
	workdirFlag          string
	runtimeRootFlag      string
	containerdBinaryFlag string
	shimConfigFlag       string
)

// ShimConfigPath is the default shim config file path.
const ShimConfigPath = "/etc/containerd/gvisor-containerd-shim.toml"

func init() {
	flag.BoolVar(&debugFlag, "debug", false, "enable debug output in logs")
	flag.StringVar(&namespaceFlag, "namespace", "", "namespace that owns the shim")
	flag.StringVar(&socketFlag, "socket", "", "abstract socket path to serve")
	flag.StringVar(&addressFlag, "address", "", "grpc address back to main containerd")
	flag.StringVar(&workdirFlag, "workdir", "", "path used to storge large temporary data")
	// Containerd default to runc, unless another runtime is explicitly specified.
	// We keep the same default to make the default behavior consistent.
	flag.StringVar(&runtimeRootFlag, "runtime-root", proc.RuncRoot, "root directory for the runtime")
	// currently, the `containerd publish` utility is embedded in the daemon binary.
	// The daemon invokes `containerd-shim -containerd-binary ...` with its own os.Executable() path.
	flag.StringVar(&containerdBinaryFlag, "containerd-binary", "containerd", "path to containerd binary (used for `containerd publish`)")
	flag.StringVar(&shimConfigFlag, "config", ShimConfigPath, "path to the shim configuration file")
	flag.Parse()
}

func main() {
	// This is a hack. Exec current process to run standard containerd-shim
	// if runtime root is not `runsc`. We don't need this for shim v2 api.
	if filepath.Base(runtimeRootFlag) != "runsc" {
		if err := executeRuncShim(); err != nil {
			fmt.Fprintf(os.Stderr, "gvisor-containerd-shim: %s\n", err)
			os.Exit(1)
		}
	}

	debug.SetGCPercent(40)
	go func() {
		for range time.Tick(30 * time.Second) {
			debug.FreeOSMemory()
		}
	}()

	if debugFlag {
		logrus.SetLevel(logrus.DebugLevel)
	}

	if os.Getenv("GOMAXPROCS") == "" {
		// If GOMAXPROCS hasn't been set, we default to a value of 2 to reduce
		// the number of Go stacks present in the shim.
		runtime.GOMAXPROCS(2)
	}

	// Run regular shim if needed.
	if err := executeShim(); err != nil {
		fmt.Fprintf(os.Stderr, "gvisor-containerd-shim: %s\n", err)
		os.Exit(1)
	}
}

// executeRuncShim execs current process to a containerd-shim process and
// retains all flags and envs.
func executeRuncShim() error {
	c, err := loadConfig(shimConfigFlag)
	if err != nil && !os.IsNotExist(err) {
		return errors.Wrap(err, "failed to load shim config")
	}
	shimPath := c.RuncShim
	if shimPath == "" {
		shimPath, err = exec.LookPath("containerd-shim")
		if err != nil {
			return errors.Wrapf(err, "lookup containerd-shim")
		}
	}

	args := append([]string{shimPath}, os.Args[1:]...)
	if err := syscall.Exec(shimPath, args, os.Environ()); err != nil {
		return errors.Wrapf(err, "exec containerd-shim %q", shimPath)
	}
	return nil
}

func executeShim() error {
	// start handling signals as soon as possible so that things are properly reaped
	// or if runtime exits before we hit the handler
	signals, err := setupSignals()
	if err != nil {
		return err
	}
	dump := make(chan os.Signal, 32)
	signal.Notify(dump, syscall.SIGUSR1)

	path, err := os.Getwd()
	if err != nil {
		return err
	}
	server, err := ttrpc.NewServer(ttrpc.WithServerHandshaker(ttrpc.UnixSocketRequireSameUser()))
	if err != nil {
		return errors.Wrap(err, "failed creating server")
	}
	c, err := loadConfig(shimConfigFlag)
	if err != nil && !os.IsNotExist(err) {
		return errors.Wrap(err, "failed to load shim config")
	}
	sv, err := shim.NewService(
		shim.Config{
			Path:        path,
			Namespace:   namespaceFlag,
			WorkDir:     workdirFlag,
			RuntimeRoot: runtimeRootFlag,
			RunscConfig: c.RunscConfig,
		},
		&remoteEventsPublisher{address: addressFlag},
	)
	if err != nil {
		return err
	}
	logrus.Debug("registering ttrpc server")
	shimapi.RegisterShimService(server, sv)

	socket := socketFlag
	if err := serve(server, socket); err != nil {
		return err
	}
	logger := logrus.WithFields(logrus.Fields{
		"pid":       os.Getpid(),
		"path":      path,
		"namespace": namespaceFlag,
	})
	go func() {
		for range dump {
			dumpStacks(logger)
		}
	}()
	return handleSignals(logger, signals, server, sv)
}

// serve serves the ttrpc API over a unix socket at the provided path
// this function does not block
func serve(server *ttrpc.Server, path string) error {
	var (
		l   net.Listener
		err error
	)
	if path == "" {
		l, err = net.FileListener(os.NewFile(3, "socket"))
		path = "[inherited from parent]"
	} else {
		if len(path) > 106 {
			return errors.Errorf("%q: unix socket path too long (> 106)", path)
		}
		l, err = net.Listen("unix", "\x00"+path)
	}
	if err != nil {
		return err
	}
	logrus.WithField("socket", path).Debug("serving api on unix socket")
	go func() {
		defer l.Close()
		if err := server.Serve(context.Background(), l); err != nil &&
			!strings.Contains(err.Error(), "use of closed network connection") {
			logrus.WithError(err).Fatal("gvisor-containerd-shim: ttrpc server failure")
		}
	}()
	return nil
}

// setupSignals creates a new signal handler for all signals and sets the shim as a
// sub-reaper so that the container processes are reparented
func setupSignals() (chan os.Signal, error) {
	signals := make(chan os.Signal, 32)
	signal.Notify(signals, unix.SIGTERM, unix.SIGINT, unix.SIGCHLD, unix.SIGPIPE)
	// make sure runc is setup to use the monitor
	// for waiting on processes
	// TODO(random-liu): Move shim/reaper.go to a separate package.
	runsc.Monitor = containerdshim.Default
	// set the shim as the subreaper for all orphaned processes created by the container
	if err := system.SetSubreaper(1); err != nil {
		return nil, err
	}
	return signals, nil
}

func handleSignals(logger *logrus.Entry, signals chan os.Signal, server *ttrpc.Server, sv *shim.Service) error {
	var (
		termOnce sync.Once
		done     = make(chan struct{})
	)

	for {
		select {
		case <-done:
			return nil
		case s := <-signals:
			switch s {
			case unix.SIGCHLD:
				if err := containerdshim.Reap(); err != nil {
					logger.WithError(err).Error("reap exit status")
				}
			case unix.SIGTERM, unix.SIGINT:
				go termOnce.Do(func() {
					ctx := context.TODO()
					if err := server.Shutdown(ctx); err != nil {
						logger.WithError(err).Error("failed to shutdown server")
					}
					// Ensure our child is dead if any
					sv.Kill(ctx, &shimapi.KillRequest{
						Signal: uint32(syscall.SIGKILL),
						All:    true,
					})
					sv.Delete(context.Background(), &ptypes.Empty{})
					close(done)
				})
			case unix.SIGPIPE:
			}
		}
	}
}

func dumpStacks(logger *logrus.Entry) {
	var (
		buf       []byte
		stackSize int
	)
	bufferLen := 16384
	for stackSize == len(buf) {
		buf = make([]byte, bufferLen)
		stackSize = runtime.Stack(buf, true)
		bufferLen *= 2
	}
	buf = buf[:stackSize]
	logger.Infof("=== BEGIN goroutine stack dump ===\n%s\n=== END goroutine stack dump ===", buf)
}

type remoteEventsPublisher struct {
	address string
}

func (l *remoteEventsPublisher) Publish(ctx context.Context, topic string, event events.Event) error {
	ns, _ := namespaces.Namespace(ctx)
	encoded, err := typeurl.MarshalAny(event)
	if err != nil {
		return err
	}
	data, err := encoded.Marshal()
	if err != nil {
		return err
	}
	cmd := exec.CommandContext(ctx, containerdBinaryFlag, "--address", l.address, "publish", "--topic", topic, "--namespace", ns)
	cmd.Stdin = bytes.NewReader(data)
	c, err := containerdshim.Default.Start(cmd)
	if err != nil {
		return err
	}
	status, err := containerdshim.Default.Wait(cmd, c)
	if err != nil {
		return err
	}
	if status != 0 {
		return errors.New("failed to publish event")
	}
	return nil
}