Allow to optionally set cache dirs for restic

Cache directories are sharded by source name, enabling re-use.

repository_restic.go

@@ -26,6 +26,7 @@ type resticRepository struct {
 	excludes     []string
 	excludeFiles []string
 	autoPrune    bool
+	cacheDirPath string
 
 	initialized sync.Once
 }
@@ -96,6 +97,11 @@ func newResticRepository(params map[string]interface{}) (Repository, error) {
 		autoPrune = b
 	}
 
+	var cacheDir string
+	if s, ok := params["cache_dir"].(string); ok {
+		cacheDir = s
+	}
+
 	tmpf, err := ioutil.TempFile("", "restic-pw-")
 	if err != nil {
 		return nil, err
@@ -116,6 +122,7 @@ func newResticRepository(params map[string]interface{}) (Repository, error) {
 		excludes:     ex,
 		excludeFiles: exf,
 		autoPrune:    autoPrune,
+		cacheDirPath: cacheDir,
 	}, nil
 }
 
@@ -152,10 +159,22 @@ func resticBackupTags(backup *Backup, ds *Dataset) string {
 	return fmt.Sprintf("--tag dataset_id=%s --tag backup_id=%s", ds.ID, backup.ID)
 }
 
+func (r *resticRepository) cacheArgs(ds *Dataset) string {
+	if r.cacheDirPath == "" {
+		return "--no-cache"
+	}
+	dir := filepath.Join(r.cacheDirPath, strings.Replace(ds.Source, "/", "_", -1))
+	if _, err := os.Stat(dir); os.IsNotExist(err) {
+		os.MkdirAll(dir, 0700)
+	}
+	return fmt.Sprintf("--cache-dir %s", dir)
+}
+
 func (r *resticRepository) BackupCmd(backup *Backup, ds *Dataset, inputFile string) string {
 	return fmt.Sprintf(
-		"%s backup --no-cache --exclude-caches --one-file-system %s --files-from %s",
+		"%s backup %s --exclude-caches --one-file-system %s --files-from %s",
 		r.resticCmd(),
+		r.cacheArgs(ds),
 		resticBackupTags(backup, ds),
 		inputFile,
 	)
@@ -210,8 +229,9 @@ func (r *resticRepository) BackupStreamCmd(backup *Backup, ds *Dataset) string {
 	fakePath := datasetStdinPath(ds)
 	return fmt.Sprintf(
 		// The --force prevents restic from trying to find a previous snapshot.
-		"%s backup --no-cache %s --force --stdin --stdin-filename %s",
+		"%s backup %s %s --force --stdin --stdin-filename %s",
 		r.resticCmd(),
+		r.cacheArgs(ds),
 		resticBackupTags(backup, ds),
 		fakePath,
 	)

types.go

@@ -42,7 +42,7 @@ func (p Params) GetBool(key string) (bool, bool) {
 // operation. Backups are initiated autonomously by individual hosts,
 // so each Backup belongs to a single Host.
 type Backup struct {
-	// Backup ID (globally unique identifier).
+	// Unique identifier.
 	ID string `json:"id"`
 
 	// Timestamp (backup start).
@@ -75,9 +75,7 @@ type Atom struct {
 // databases (the atom we're interested in), which we might want to
 // restore independently.
 type Dataset struct {
-	// Name of the dataset (path-like). Will be prepended to atom
-	// paths.
-	//Name string `json:"name"`
+	// Unique identifier.
 	ID string `json:"id"`
 
 	// Source is the name of the source that created this Dataset,