From c59b40f2df37c7470674df584f929e50e472732b Mon Sep 17 00:00:00 2001
From: Frederik Ring <frederik.ring@gmail.com>
Date: Fri, 1 Oct 2021 10:07:46 +0200
Subject: [PATCH] automatically create symlink to latest local backup if
 configured

---
 README.md                       |  8 ++++++++
 cmd/backup/main.go              | 13 ++++++++++++-
 test/compose/docker-compose.yml |  1 +
 test/compose/run.sh             |  1 +
 4 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 4083a06..22caf78 100644
--- a/README.md
+++ b/README.md
@@ -120,6 +120,11 @@ You can populate below template according to your requirements and use it as you
 
 # BACKUP_FILENAME="backup-%Y-%m-%dT%H-%M-%S.tar.gz"
 
+# When storing local backups, a symlink to the latest backup can be created
+# in case a value is given for this key. This has no effect on remote backups.
+
+# BACKUP_LATEST_SYMLINK="backup.latest.tar.gz"
+
 ########### BACKUP STORAGE
 
 # The name of the remote bucket that should be used for storing backups. If
@@ -437,6 +442,9 @@ services:
   # ... define other services using the `data` volume here
   backup:
     image: offen/docker-volume-backup:latest
+    environment:
+      BACKUP_FILENAME: backup-%Y-%m-%dT%H-%M-%S.tar.gz
+      BACKUP_LATEST_SYMLINK: backup-latest.tar.gz
     volumes:
       - data:/backup/my-app-backup:ro
       - /var/run/docker.sock:/var/run/docker.sock:ro
diff --git a/cmd/backup/main.go b/cmd/backup/main.go
index 3309a72..f294094 100644
--- a/cmd/backup/main.go
+++ b/cmd/backup/main.go
@@ -89,6 +89,7 @@ type script struct {
 type config struct {
 	BackupSources              string        `split_words:"true" default:"/backup"`
 	BackupFilename             string        `split_words:"true" default:"backup-%Y-%m-%dT%H-%M-%S.tar.gz"`
+	BackupLatestSymlink        string        `split_words:"true"`
 	BackupArchive              string        `split_words:"true" default:"/archive"`
 	BackupRetentionDays        int32         `split_words:"true" default:"-1"`
 	BackupPruningLeeway        time.Duration `split_words:"true" default:"1m"`
@@ -380,6 +381,16 @@ func (s *script) copyBackup() error {
 			return fmt.Errorf("copyBackup: error copying file to local archive: %w", err)
 		}
 		s.logger.Infof("Stored copy of backup `%s` in local archive `%s`.", s.file, s.c.BackupArchive)
+		if s.c.BackupLatestSymlink != "" {
+			symlink := path.Join(s.c.BackupArchive, s.c.BackupLatestSymlink)
+			if _, err := os.Lstat(symlink); err == nil {
+				os.Remove(symlink)
+			}
+			if err := os.Symlink(name, symlink); err != nil {
+				return fmt.Errorf("copyBackup: error creating latest symlink: %w", err)
+			}
+			s.logger.Infof("Created/Updated symlink `%s` for latest backup.", s.c.BackupLatestSymlink)
+		}
 	}
 	return nil
 }
@@ -497,7 +508,7 @@ func (s *script) pruneOldBackups() error {
 				)
 			}
 
-			if fi.ModTime().Before(deadline) {
+			if fi.Mode() != os.ModeSymlink && fi.ModTime().Before(deadline) {
 				matches = append(matches, candidate)
 			}
 		}
diff --git a/test/compose/docker-compose.yml b/test/compose/docker-compose.yml
index a61d106..b9ade86 100644
--- a/test/compose/docker-compose.yml
+++ b/test/compose/docker-compose.yml
@@ -24,6 +24,7 @@ services:
       AWS_ENDPOINT_PROTO: http
       AWS_S3_BUCKET_NAME: backup
       BACKUP_FILENAME: test.tar.gz
+      BACKUP_LATEST_SYMLINK: test.latest.tar.gz.gpg
       BACKUP_CRON_EXPRESSION: 0 0 5 31 2 ?
       BACKUP_RETENTION_DAYS: ${BACKUP_RETENTION_DAYS:-7}
       BACKUP_PRUNING_LEEWAY: 5s
diff --git a/test/compose/run.sh b/test/compose/run.sh
index a00142f..22fe8c7 100755
--- a/test/compose/run.sh
+++ b/test/compose/run.sh
@@ -18,6 +18,7 @@ docker run --rm -it \
 
 echo "[TEST:PASS] Found relevant files in untared remote backup."
 
+test -L ./local/test.latest.tar.gz.gpg
 echo 1234secret | gpg -d --yes --passphrase-fd 0 ./local/test.tar.gz.gpg > ./local/decrypted.tar.gz
 tar -xf ./local/decrypted.tar.gz -C /tmp && test -f /tmp/backup/app_data/offen.db
 rm ./local/decrypted.tar.gz