Add 'autoprune' config parameter for restic backend

If disabled, we won't run "restic prune" on the remote
repository. Allows support of append-only repositories.

repository_restic.go

@@ -24,6 +24,7 @@ type resticRepository struct {
 	shell        *Shell
 	excludes     []string
 	excludeFiles []string
+	autoPrune    bool
 }
 
 func (r *resticRepository) resticCmd() string {
@@ -80,13 +81,17 @@ func newResticRepository(params map[string]interface{}, shell *Shell) (Repositor
 
 	ex, _ := params["exclude"].([]string)
 	exf, _ := params["exclude_files"].([]string)
-	bin, _ := params["restic_binary"].(string)
-	if bin == "" {
-		bin = "restic"
+	bin := "restic"
+	if s, ok := params["restic_binary"].(string); ok {
+		bin = s
 	}
 	if err := checkResticVersion(bin); err != nil {
 		return nil, err
 	}
+	autoPrune := true
+	if b, ok := params["autoprune"].(bool); ok {
+		autoPrune = b
+	}
 
 	tmpf, err := ioutil.TempFile("", "restic-pw-")
 	if err != nil {
@@ -108,6 +113,7 @@ func newResticRepository(params map[string]interface{}, shell *Shell) (Repositor
 		excludes:     ex,
 		excludeFiles: exf,
 		shell:        shell,
+		autoPrune:    autoPrune,
 	}, nil
 }
 
@@ -125,6 +131,9 @@ func (r *resticRepository) Init(ctx context.Context) error {
 }
 
 func (r *resticRepository) Prepare(ctx context.Context, backup Backup) error {
+	if !r.autoPrune {
+		return nil
+	}
 	return r.shell.Run(ctx, fmt.Sprintf(
 		"%s forget --host %s --keep-last 10 --prune",
 		r.resticCmd(),
@@ -221,6 +230,9 @@ type resticSnapshot struct {
 }
 
 func parseResticSnapshots(output []byte) (snapshots []resticSnapshot, err error) {
-	err = json.Unmarshal(output, &snapshots)
+	// An empty input is not necessarily an error.
+	if len(output) > 0 {
+		err = json.Unmarshal(output, &snapshots)
+	}
 	return
 }

repository_restic_test.go

@@ -15,6 +15,8 @@ import (
 // Create a temporary directory with two subdirs: 'data', for
 // the test backup data, and 'repo' to store the (remote)
 // repository. Populate 'data' with two tiny files.
+//
+// nolint
 func createTempDirWithData(t *testing.T) string {
 	tmpdir, err := ioutil.TempDir("", "")
 	if err != nil {
@@ -112,10 +114,13 @@ func TestRestic(t *testing.T) {
 	}
 
 	// Check the 'restic snapshots' output.
-	output, _ := exec.Command("env", "RESTIC_PASSWORD=testpass", "restic", "-r", tmpdir+"/repo", "snapshots", "--json").Output()
+	output, err := exec.Command("env", "RESTIC_PASSWORD=testpass", "restic", "-r", tmpdir+"/repo", "snapshots", "--json").Output()
+	if err != nil {
+		t.Fatalf("'restic snapshots' failed: %v", err)
+	}
 	snaps, err := parseResticSnapshots(output)
 	if err != nil {
-		t.Fatalf("parsing restic snaphots output: %v", err)
+		t.Fatalf("parsing restic snaphots output: %v, output:\n%s", err, string(output))
 	}
 	if len(snaps) != 1 {
 		t.Fatalf("wrong number of snapshots: %+v", snaps)