Add handling for outdated PID files (#43)

* Add handling for outdated PID files

* goimports

* Fix goreleaser config

* Bump Goreleaser & Goreleaser workflow

.github/workflows/build.yaml

@@ -18,7 +18,7 @@ jobs:
           go-version: 1.16
 
       - name: Run GoReleaser
-        uses: goreleaser/goreleaser-action@v2
+        uses: goreleaser/goreleaser-action@v3
         with:
-          version: latest
+          version: v1.13.0
           args: release --rm-dist --snapshot --skip-publish

.github/workflows/release.yaml

@@ -20,9 +20,9 @@ jobs:
           go-version: 1.16
 
       - name: Run GoReleaser
-        uses: goreleaser/goreleaser-action@v2
+        uses: goreleaser/goreleaser-action@v3
         with:
-          version: latest
+          version: v1.13.0
           args: release --rm-dist
         env:
           GITHUB_TOKEN: ${{ secrets.RELEASE_USER_TOKEN }}

.goreleaser.yml

@@ -31,8 +31,9 @@ nfpms:
       - deb
       - rpm
     bindir: /usr/bin
-    empty_folders:
-      - /etc/mittnite.d
+    contents:
+      - dst: /etc/mittnite.d
+        type: dir
 checksum:
   name_template: 'checksums.txt'
 snapshot:

cmd/up.go

@@ -1,16 +1,15 @@
 package cmd
 
 import (
-	"bytes"
 	"context"
 	"fmt"
 	"os"
 	"os/signal"
-	"path/filepath"
 	"syscall"
 
 	"github.com/mittwald/mittnite/internal/config"
 	"github.com/mittwald/mittnite/pkg/files"
+	"github.com/mittwald/mittnite/pkg/pidfile"
 	"github.com/mittwald/mittnite/pkg/probe"
 	"github.com/mittwald/mittnite/pkg/proc"
 	log "github.com/sirupsen/logrus"
@@ -45,11 +44,14 @@ var up = &cobra.Command{
 			Jobs:   nil,
 		}
 
-		if err := writePidFile(); err != nil {
+		pidFileHandle := pidfile.New(pidFile)
+
+		if err := pidFileHandle.Acquire(); err != nil {
 			log.Fatalf("failed to write pid file to %q: %s", pidFile, err)
 		}
+
 		defer func() {
-			if err := deletePidFile(); err != nil {
+			if err := pidFileHandle.Release(); err != nil {
 				log.Errorf("error while cleaning up the pid file: %s", err)
 			}
 		}()
@@ -121,43 +123,3 @@ var up = &cobra.Command{
 		}
 	},
 }
-
-func writePidFile() error {
-	if pidFile == "" {
-		return nil
-	}
-
-	if err := os.MkdirAll(filepath.Dir(pidFile), 0o755); err != nil {
-		return err
-	}
-	if stats, err := os.Stat(pidFile); err == nil {
-		if stats.Size() > 0 {
-			return fmt.Errorf("pidFile %q already exists", pidFile)
-		}
-	}
-
-	return os.WriteFile(pidFile, pidToByteString(), 0644)
-
-}
-
-func deletePidFile() error {
-	if pidFile == "" {
-		return nil
-	}
-
-	pid := pidToByteString()
-	content, err := os.ReadFile(pidFile)
-	if err != nil {
-		return err
-	}
-
-	if bytes.Compare(pid, content) != 0 {
-		return fmt.Errorf("won't delete pid file %q because it does not contain the expected content", pidFile)
-	}
-
-	return os.Remove(pidFile)
-}
-
-func pidToByteString() []byte {
-	return []byte(fmt.Sprintf("%d", os.Getpid()))
-}

pkg/pidfile/pidfile.go

@@ -0,0 +1,104 @@
+package pidfile
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"syscall"
+
+	"github.com/pkg/errors"
+	log "github.com/sirupsen/logrus"
+)
+
+type PIDFile struct {
+	path string
+	fd   int
+}
+
+func New(path string) PIDFile {
+	return PIDFile{
+		path: path,
+	}
+}
+
+func (f PIDFile) Acquire() error {
+	if f.path == "" {
+		return nil
+	}
+
+	if err := os.MkdirAll(filepath.Dir(f.path), 0o755); err != nil {
+		return errors.Wrapf(err, "failed to create pid file directory %q", filepath.Dir(f.path))
+	}
+
+	fd, err := syscall.Open(f.path, syscall.O_CREAT|syscall.O_EXCL|syscall.O_WRONLY, 0o644)
+	switch err {
+	case syscall.EEXIST:
+		if err := f.removePIDFileIfOutdated(); err != nil {
+			return err
+		}
+
+		return f.Acquire()
+	case nil:
+		if _, err := syscall.Write(fd, pidToByteString()); err != nil {
+			return errors.Wrapf(err, "failed to write pid to pid file %q", f.path)
+		}
+
+		log.Info("acquired pid file ", f.path)
+	default:
+		return errors.Wrapf(err, "failed to open pid file %q", f.path)
+	}
+
+	f.fd = fd
+	return nil
+}
+
+func (f PIDFile) removePIDFileIfOutdated() error {
+	pidStr, err := os.ReadFile(f.path)
+	if err != nil {
+		return errors.Wrapf(err, "failed to read pid file '%s'", f.path)
+	}
+
+	pid, err := strconv.Atoi(string(pidStr))
+	if err != nil {
+		return errors.Wrapf(err, "failed to parse pid file '%s'", f.path)
+	}
+
+	process, err := os.FindProcess(pid)
+	if err != nil {
+		return errors.Wrapf(err, "failed to find process with pid %d", pid)
+	}
+
+	if err := process.Signal(syscall.Signal(0)); err == nil {
+		return fmt.Errorf("pid file %q already exists and contains the PID of a running process", f.path)
+	}
+
+	log.Info("existing pid file contains the PID of a non-running process; removing it")
+
+	if err := os.Remove(f.path); err != nil {
+		return errors.Wrapf(err, "failed to remove pid file %q", f.path)
+	}
+
+	return nil
+}
+
+func (f PIDFile) Release() error {
+	if f.path == "" {
+		return nil
+	}
+
+	if err := syscall.Close(f.fd); err != nil {
+		return errors.Wrapf(err, "failed to close pid file %q", f.path)
+	}
+
+	if err := os.Remove(f.path); err != nil {
+		return errors.Wrapf(err, "failed to remove pid file %q", f.path)
+	}
+
+	log.Info("released pid file ", f.path)
+	return nil
+}
+
+func pidToByteString() []byte {
+	return []byte(fmt.Sprintf("%d", os.Getpid()))
+}

pkg/pidfile/pidfile_test.go

@@ -0,0 +1,53 @@
+package pidfile_test
+
+import (
+	"os"
+	"testing"
+
+	"github.com/mittwald/mittnite/pkg/pidfile"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPidFileCanBeAcquiredAndReleased(t *testing.T) {
+	f := pidfile.New("./test1.pid")
+
+	require.NoError(t, f.Acquire())
+	require.NoError(t, f.Release())
+
+	_, err := os.Stat("./test1.pid")
+	require.True(t, os.IsNotExist(err))
+}
+
+func TestPidFileCanBeAcquiredWhenOutdatedFileExists(t *testing.T) {
+	f := pidfile.New("./test3.pid")
+
+	require.NoError(t, os.WriteFile("./test3.pid", []byte("12345"), 0o644))
+	require.NoError(t, f.Acquire())
+	require.NoError(t, f.Release())
+
+	_, err := os.Stat("./test3.pid")
+	require.True(t, os.IsNotExist(err))
+}
+
+func TestPidFileCannotBeAcquiredWhileAlreadyHeld(t *testing.T) {
+	f1 := pidfile.New("./test2.pid")
+	f2 := pidfile.New("./test2.pid")
+
+	closeF1 := make(chan struct{})
+	f1Acquired := make(chan struct{})
+	f1Closed := make(chan struct{})
+
+	go func() {
+		require.NoError(t, f1.Acquire())
+		close(f1Acquired)
+		<-closeF1
+		require.NoError(t, f1.Release())
+		close(f1Closed)
+	}()
+
+	<-f1Acquired
+
+	require.Error(t, f2.Acquire())
+	close(closeF1)
+	<-f1Closed
+}

pkg/proc/job_common.go

@@ -4,13 +4,13 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"github.com/mittwald/mittnite/internal/config"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"syscall"
 	"time"
 
+	"github.com/mittwald/mittnite/internal/config"
 	log "github.com/sirupsen/logrus"
 )