fix lockfile mechanism

cmd/backup/main.go

@@ -18,6 +18,7 @@ import (
 	"github.com/docker/docker/api/types/filters"
 	"github.com/docker/docker/api/types/swarm"
 	"github.com/docker/docker/client"
+	"github.com/gofrs/flock"
 	"github.com/joho/godotenv"
 	"github.com/leekchan/timeutil"
 	minio "github.com/minio/minio-go/v7"
@@ -228,7 +229,10 @@ func (s *script) stopContainersAndRun(thunk func() error) error {
 				err,
 			)
 		}
-		s.logger.Infof("Restarted %d container(s) and the matching service(s).", len(stoppedContainers))
+		s.logger.Infof(
+			"Restarted %d container(s) and the matching service(s).",
+			len(stoppedContainers),
+		)
 		return nil
 	}()
 
@@ -356,7 +360,10 @@ func (s *script) pruneOldBackups() error {
 		for candidate := range candidates {
 			lenCandidates++
 			if candidate.Err != nil {
-				return fmt.Errorf("pruneOldBackups: error looking up candidates from remote storage: %w", candidate.Err)
+				return fmt.Errorf(
+					"pruneOldBackups: error looking up candidates from remote storage: %w",
+					candidate.Err,
+				)
 			}
 			if candidate.LastModified.Before(deadline) {
 				matches = append(matches, candidate)
@@ -393,9 +400,10 @@ func (s *script) pruneOldBackups() error {
 			)
 		} else if len(matches) != 0 && len(matches) == lenCandidates {
 			s.logger.Warnf(
-				"The current configuration would delete all %d remote backup copies. Refusing to do so, please check your configuration.",
+				"The current configuration would delete all %d remote backup copies.",
 				len(matches),
 			)
+			s.logger.Warn("Refusing to do so, please check your configuration.")
 		} else {
 			s.logger.Infof("None of %d remote backup(s) were pruned.", lenCandidates)
 		}
@@ -448,9 +456,10 @@ func (s *script) pruneOldBackups() error {
 			)
 		} else if len(matches) != 0 && len(matches) == len(candidates) {
 			s.logger.Warnf(
-				"The current configuration would delete all %d local backup copies. Refusing to do so, please check your configuration.",
+				"The current configuration would delete all %d local backup copies.",
 				len(matches),
 			)
+			s.logger.Warn("Refusing to do so, please check your configuration.")
 		} else {
 			s.logger.Infof("None of %d local backup(s) were pruned.", len(candidates))
 		}
@@ -472,19 +481,15 @@ func (s *script) must(err error) {
 // caller invokes the returned release func. When invoked while the file is
 // still locked the function panics.
 func lock(lockfile string) func() error {
-	lf, err := os.OpenFile(lockfile, os.O_CREATE|os.O_RDWR, os.ModeAppend)
+	fileLock := flock.New(lockfile)
+	acquired, err := fileLock.TryLock()
 	if err != nil {
 		panic(err)
 	}
-	return func() error {
+	if !acquired {
-		if err := lf.Close(); err != nil {
+		panic("unable to acquire file lock")
-			return fmt.Errorf("lock: error releasing file lock: %w", err)
-		}
-		if err := os.Remove(lockfile); err != nil {
-			return fmt.Errorf("lock: error removing lock file: %w", err)
-		}
-		return nil
 	}
+	return fileLock.Unlock
 }
 
 // copy creates a copy of the file located at `dst` at `src`.

go.mod

@@ -4,6 +4,7 @@ go 1.17
 
 require (
 	github.com/docker/docker v20.10.8+incompatible
+	github.com/gofrs/flock v0.8.1
 	github.com/joho/godotenv v1.3.0
 	github.com/leekchan/timeutil v0.0.0-20150802142658-28917288c48d
 	github.com/minio/minio-go/v7 v7.0.12

go.sum

@@ -274,6 +274,8 @@ github.com/godbus/dbus v0.0.0-20180201030542-885f9cc04c9c/go.mod h1:/YcGZj5zSblf
 github.com/godbus/dbus v0.0.0-20190422162347-ade71ed3457e/go.mod h1:bBOAhwG1umN6/6ZUMtDFBMQR8jRg9O75tm9K00oMsK4=
 github.com/godbus/dbus/v5 v5.0.3/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
 github.com/godbus/dbus/v5 v5.0.4/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
+github.com/gofrs/flock v0.8.1 h1:+gYjHKf32LDeiEEFhQaotPbLuUXjY5ZqxKgXy7n59aw=
+github.com/gofrs/flock v0.8.1/go.mod h1:F1TvTiK9OcQqauNUHlbJvyl9Qa1QvF/gOUDKA14jxHU=
 github.com/gogo/googleapis v1.2.0/go.mod h1:Njal3psf3qN6dwBtQfUmBZh2ybovJ0tlu3o/AC7HYjU=
 github.com/gogo/googleapis v1.4.0/go.mod h1:5YRNX2z1oM5gXdAkurHa942MDgEJyk02w4OecKY87+c=
 github.com/gogo/protobuf v1.1.1/go.mod h1:r8qH/GZQm5c6nD/R0oafs1akxWv10x8SbQlK7atdtwQ=
@@ -397,9 +399,11 @@ github.com/konsorten/go-windows-terminal-sequences v1.0.3/go.mod h1:T0+1ngSBFLxv
 github.com/kr/logfmt v0.0.0-20140226030751-b84e30acd515/go.mod h1:+0opPa2QZZtGFBFZlji/RkVcI2GknAs/DXo4wKdlNEc=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pretty v0.2.0/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
+github.com/kr/pretty v0.2.1 h1:Fmg33tUaq4/8ym9TJN1x7sLJnHVwhP33CNkpYV/7rwI=
 github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/pty v1.1.5/go.mod h1:9r2w37qlBe7rQ6e1fg1S/9xpWHSnaqNdHD3WcMdbPDA=
+github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/leekchan/timeutil v0.0.0-20150802142658-28917288c48d h1:2puqoOQwi3Ai1oznMOsFIbifm6kIfJaLLyYzWD4IzTs=
 github.com/leekchan/timeutil v0.0.0-20150802142658-28917288c48d/go.mod h1:hO90vCP2x3exaSH58BIAowSKvV+0OsY21TtzuFGHON4=
@@ -907,6 +911,7 @@ gopkg.in/alecthomas/kingpin.v2 v2.2.6/go.mod h1:FMv+mEhP44yOT+4EoQTLFTRgOQ1FBLks
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20141024133853-64131543e789/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 h1:YR8cESwS4TdDjEe65xsg0ogRM/Nc3DYOhEAlW+xobZo=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/cheggaaa/pb.v1 v1.0.25/go.mod h1:V/YB90LKu/1FcN3WVnfiiE5oMCibMjukxqG/qStrOgw=
 gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=