Use array instead of hash for backend.ID

Since backend.ID is always a slice of constant length, use an array
instead of a slice. Mostly, arrays behave as slices, except that an
array cannot be nil, so use `*backend.ID` insteaf of `backend.ID` in
places where the absence of an ID is possible (e.g. for the Subtree of a
Node, which may not present when the node is a file node).

This change allows to directly use backend.ID as the the key for a map,
so that arbitrary data structures (e.g. a Set implemented as a
map[backend.ID]struct{}) can easily be formed.

cmd/restic/cmd_backup.go

@@ -185,23 +185,31 @@ func samePaths(expected, actual []string) bool {
 	return true
 }
 
+var errNoSnapshotFound = errors.New("no snapshot found")
+
 func findLatestSnapshot(repo *repository.Repository, targets []string) (backend.ID, error) {
 	var (
 		latest   time.Time
 		latestID backend.ID
+		found    bool
 	)
 
 	for snapshotID := range repo.List(backend.Snapshot, make(chan struct{})) {
 		snapshot, err := restic.LoadSnapshot(repo, snapshotID)
 		if err != nil {
-			return nil, fmt.Errorf("Error listing snapshot: %v", err)
+			return backend.ID{}, fmt.Errorf("Error listing snapshot: %v", err)
 		}
 		if snapshot.Time.After(latest) && samePaths(snapshot.Paths, targets) {
 			latest = snapshot.Time
 			latestID = snapshotID
+			found = true
 		}
 	}
 
+	if !found {
+		return backend.ID{}, errNoSnapshotFound
+	}
+
 	return latestID, nil
 }
 
@@ -258,27 +266,27 @@ func (cmd CmdBackup) Execute(args []string) error {
 		return err
 	}
 
-	var parentSnapshotID backend.ID
+	var parentSnapshotID *backend.ID
 
 	// Force using a parent
 	if !cmd.Force && cmd.Parent != "" {
-		parentSnapshotID, err = restic.FindSnapshot(repo, cmd.Parent)
+		id, err := restic.FindSnapshot(repo, cmd.Parent)
 		if err != nil {
 			return fmt.Errorf("invalid id %q: %v", cmd.Parent, err)
 		}
 
+		parentSnapshotID = &id
 		cmd.global.Verbosef("found parent snapshot %v\n", parentSnapshotID.Str())
 	}
 
 	// Find last snapshot to set it as parent, if not already set
 	if !cmd.Force && parentSnapshotID == nil {
-		parentSnapshotID, err = findLatestSnapshot(repo, target)
-		if err != nil {
-			return err
-		}
-
-		if parentSnapshotID != nil {
+		id, err := findLatestSnapshot(repo, target)
+		if err == nil {
 			cmd.global.Verbosef("using parent snapshot %v\n", parentSnapshotID)
+			parentSnapshotID = &id
+		} else if err != errNoSnapshotFound {
+			return err
 		}
 	}
 

cmd/restic/cmd_cat.go

@@ -54,8 +54,6 @@ func (cmd CmdCat) Execute(args []string) error {
 	if tpe != "masterkey" && tpe != "config" {
 		id, err = backend.ParseID(args[1])
 		if err != nil {
-			id = nil
-
 			if tpe != "snapshot" {
 				return err
 			}

cmd/restic/cmd_find.go

@@ -114,7 +114,7 @@ func (c CmdFind) findInSnapshot(repo *repository.Repository, id backend.ID) erro
 		return err
 	}
 
-	results, err := c.findInTree(repo, sn.Tree, "")
+	results, err := c.findInTree(repo, *sn.Tree, "")
 	if err != nil {
 		return err
 	}

cmd/restic/cmd_ls.go

@@ -56,7 +56,7 @@ func (cmd CmdLs) printTree(prefix string, repo *repository.Repository, id backen
 		cmd.global.Printf(cmd.printNode(prefix, entry) + "\n")
 
 		if entry.Type == "dir" && entry.Subtree != nil {
-			err = cmd.printTree(filepath.Join(prefix, entry.Name), repo, entry.Subtree)
+			err = cmd.printTree(filepath.Join(prefix, entry.Name), repo, *entry.Subtree)
 			if err != nil {
 				return err
 			}
@@ -97,5 +97,5 @@ func (cmd CmdLs) Execute(args []string) error {
 
 	cmd.global.Verbosef("snapshot of %v at %s:\n", sn.Paths, sn.Time)
 
-	return cmd.printTree("", repo, sn.Tree)
+	return cmd.printTree("", repo, *sn.Tree)
 }

cmd/restic/cmd_snapshots.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"encoding/hex"
 	"fmt"
 	"io"
 	"os"
@@ -142,7 +143,8 @@ func (cmd CmdSnapshots) Execute(args []string) error {
 		if len(sn.Paths) == 0 {
 			continue
 		}
-		tab.Rows = append(tab.Rows, []interface{}{sn.ID()[:plen/2], sn.Time.Format(TimeFormat), sn.Hostname, sn.Paths[0]})
+		id := sn.ID()
+		tab.Rows = append(tab.Rows, []interface{}{hex.EncodeToString(id[:plen/2]), sn.Time.Format(TimeFormat), sn.Hostname, sn.Paths[0]})
 
 		if len(sn.Paths) > 1 {
 			for _, path := range sn.Paths[1:] {

cmd/restic/fuse/dir.go

@@ -22,7 +22,7 @@ type dir struct {
 }
 
 func newDir(repo *repository.Repository, node *restic.Node) (*dir, error) {
-	tree, err := restic.LoadTree(repo, node.Subtree)
+	tree, err := restic.LoadTree(repo, *node.Subtree)
 	if err != nil {
 		return nil, err
 	}
@@ -39,7 +39,7 @@ func newDir(repo *repository.Repository, node *restic.Node) (*dir, error) {
 }
 
 func newDirFromSnapshot(repo *repository.Repository, snapshot SnapshotWithId) (*dir, error) {
-	tree, err := restic.LoadTree(repo, snapshot.Tree)
+	tree, err := restic.LoadTree(repo, *snapshot.Tree)
 	if err != nil {
 		return nil, err
 	}

cmd/restic/integration_fuse_test.go

@@ -147,7 +147,7 @@ func TestMount(t *testing.T) {
 		checkSnapshots(repo, mountpoint, snapshotIDs)
 
 		// third backup, explicit incremental
-		cmdBackup(t, global, []string{env.testdata}, snapshotIDs[0])
+		cmdBackup(t, global, []string{env.testdata}, &snapshotIDs[0])
 		snapshotIDs = cmdList(t, global, "snapshots")
 		Assert(t, len(snapshotIDs) == 3,
 			"expected three snapshots, got %v", snapshotIDs)

cmd/restic/integration_test.go

@@ -45,13 +45,15 @@ func cmdInit(t testing.TB, global GlobalOptions) {
 	t.Logf("repository initialized at %v", global.Repo)
 }
 
-func cmdBackup(t testing.TB, global GlobalOptions, target []string, parentID backend.ID) {
+func cmdBackup(t testing.TB, global GlobalOptions, target []string, parentID *backend.ID) {
 	cmdBackupExcludes(t, global, target, parentID, nil)
 }
 
-func cmdBackupExcludes(t testing.TB, global GlobalOptions, target []string, parentID backend.ID, excludes []string) {
+func cmdBackupExcludes(t testing.TB, global GlobalOptions, target []string, parentID *backend.ID, excludes []string) {
 	cmd := &CmdBackup{global: &global, Excludes: excludes}
-	cmd.Parent = parentID.String()
+	if parentID != nil {
+		cmd.Parent = parentID.String()
+	}
 
 	t.Logf("backing up %v", target)
 
@@ -136,7 +138,7 @@ func TestBackup(t *testing.T) {
 
 		cmdCheck(t, global)
 		// third backup, explicit incremental
-		cmdBackup(t, global, []string{env.testdata}, snapshotIDs[0])
+		cmdBackup(t, global, []string{env.testdata}, &snapshotIDs[0])
 		snapshotIDs = cmdList(t, global, "snapshots")
 		Assert(t, len(snapshotIDs) == 3,
 			"expected three snapshots, got %v", snapshotIDs)