pid1_launcher.go

package main

import (
	"os"
	"os/signal"
	"syscall"

	cmd "github.com/buildpacks/lifecycle/cmd"
	launcher "github.com/buildpacks/lifecycle/cmd/launcher/cli"
	reaper "github.com/ramr/go-reaper"
)

func main() {
	if os.Getpid() == 1 {
		//  Start background reaping of orphaned child processes.
		go reaper.Reap()

		signalsBuffer := make(chan os.Signal, 3)
		signal.Notify(signalsBuffer)

		go func() {
			for {
				signalReceived := <-signalsBuffer
				if signalReceived == syscall.SIGCHLD {
					// Ignore SIGCHLD and let go-reaper handle them as per.
					continue
				}

				signalId := signalReceived.(syscall.Signal)

				// `man 2 kill`
				// If pid equals -1, then sig is sent to every process for which the calling
				// process has permission to send signals, except for process 1 (init)
				_ = syscall.Kill(-1, signalId)
			}
		}()

		pwd, err := os.Getwd()
		if err != nil {
			panic(err)
		}

		var wstatus syscall.WaitStatus
		pattrs := &syscall.ProcAttr{
			Dir: pwd,
			Env: os.Environ(),
			Sys: &syscall.SysProcAttr{Setsid: true},
			Files: []uintptr{
				uintptr(syscall.Stdin),
				uintptr(syscall.Stdout),
				uintptr(syscall.Stderr),
			},
		}

		args := os.Args
		pid, _ := syscall.ForkExec(args[0], args, pattrs)

		_, err = syscall.Wait4(pid, &wstatus, 0, nil)
		for syscall.EINTR == err {
			_, err = syscall.Wait4(pid, &wstatus, 0, nil)
		}

		os.Exit(0)
		return
	}

	cmd.Exit(launcher.RunLaunch())
}