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package main
import (
"errors"
"fmt"
"os"
"os/exec"
"os/signal"
"path/filepath"
"strconv"
"syscall"
"time"
"github.com/sirupsen/logrus"
"gitlab.com/gitlab-org/gitaly/v16/internal/bootstrap"
"gitlab.com/gitlab-org/gitaly/v16/internal/helper/env"
"gitlab.com/gitlab-org/gitaly/v16/internal/log"
"gitlab.com/gitlab-org/gitaly/v16/internal/ps"
"golang.org/x/sys/unix"
)
const (
envJSONLogging = "WRAPPER_JSON_LOGGING"
)
func main() {
var logFormat string
if jsonLogging() {
logFormat = "json"
}
log.Configure(log.Loggers, logFormat, "")
if len(os.Args) < 2 {
logrus.Fatalf("usage: %s forking_binary [args]", os.Args[0])
}
binary, arguments := os.Args[1], os.Args[2:]
logger := log.Default().WithField("wrapper", os.Getpid())
logger.Info("Wrapper started")
pidFilePath := os.Getenv(bootstrap.EnvPidFile)
if pidFilePath == "" {
logger.Fatalf("missing pid file ENV variable %q", bootstrap.EnvPidFile)
}
logger.WithField("pid_file", pidFilePath).Info("finding process")
process, err := findProcess(pidFilePath)
if err != nil && !isRecoverable(err) {
logger.WithError(err).Fatal("find process")
} else if err != nil {
logger.WithError(err).Error("find process")
}
if process != nil && isExpectedProcess(process, binary) {
logger.Info("adopting a process")
} else {
logger.Info("spawning a process")
proc, err := spawnProcess(logger, binary, arguments)
if err != nil {
logger.WithError(err).Fatal("spawn gitaly")
}
process = proc
}
logger = logger.WithField("process", process.Pid)
logger.Info("monitoring process")
forwardSignals(process, logger)
// wait
for isProcessAlive(process) {
time.Sleep(1 * time.Second)
}
logger.Error("wrapper for process shutting down")
}
func isRecoverable(err error) bool {
var numError *strconv.NumError
return os.IsNotExist(err) || errors.As(err, &numError)
}
func findProcess(pidFilePath string) (*os.Process, error) {
pid, err := readPIDFile(pidFilePath)
if err != nil {
return nil, err
}
// os.FindProcess on unix do not return an error if the process does not exist
process, err := os.FindProcess(pid)
if err != nil {
return nil, err
}
if isProcessAlive(process) {
return process, nil
}
return nil, nil
}
func spawnProcess(logger *logrus.Entry, bin string, args []string) (*os.Process, error) {
cmd := exec.Command(bin, args...)
cmd.Env = append(os.Environ(), fmt.Sprintf("%s=true", bootstrap.EnvUpgradesEnabled))
cmd.Stdin = os.Stdin
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
if err := cmd.Start(); err != nil {
return nil, err
}
// This cmd.Wait() is crucial. Without it we cannot detect if the command we just spawned has crashed.
go func() {
if err := cmd.Wait(); err != nil {
logger.WithError(err).Error("waiting for supervised command")
}
}()
return cmd.Process, nil
}
func isRuntimeSig(s os.Signal) bool {
return s == unix.SIGURG
}
func forwardSignals(gitaly *os.Process, log *logrus.Entry) {
sigs := make(chan os.Signal, 1)
go func() {
for sig := range sigs {
// In go1.14+, the go runtime issues SIGURG as an interrupt
// to support pre-emptible system calls on Linux. We ignore
// this signal since it's not relevant to the Gitaly process.
if isRuntimeSig(sig) {
continue
}
log.WithField("signal", sig).Warning("forwarding signal")
if err := gitaly.Signal(sig); err != nil {
log.WithField("signal", sig).WithError(err).Error("can't forward the signal")
}
}
}()
signal.Notify(sigs)
}
func readPIDFile(pidFilePath string) (int, error) {
data, err := os.ReadFile(pidFilePath)
if err != nil {
return 0, err
}
return strconv.Atoi(string(data))
}
func isProcessAlive(p *os.Process) bool {
// After p exits, and after it gets reaped, this p.Signal will fail. It is crucial that p gets reaped.
// If p was spawned by the current process, it will get reaped from a goroutine that does cmd.Wait().
// If p was spawned by someone else we rely on them to reap it, or on p to become an orphan.
// In the orphan case p should get reaped by the OS (PID 1).
return p.Signal(syscall.Signal(0)) == nil
}
func isExpectedProcess(p *os.Process, binary string) bool {
command, err := ps.Comm(p.Pid)
if err != nil {
return false
}
if filepath.Base(command) == filepath.Base(binary) {
return true
}
return false
}
func jsonLogging() bool {
enabled, _ := env.GetBool(envJSONLogging, false)
return enabled
}
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