Add support for snapshot:subpath syntax

This snapshot specification syntax is supported by the cat, diff, dump,
ls and restore command.

internal/restic/snapshot_find.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"path/filepath"
+	"strings"
 	"time"
 
 	"github.com/restic/restic/internal/errors"
@@ -82,31 +83,40 @@ func (f *SnapshotFilter) findLatest(ctx context.Context, be Lister, loader Loade
 	return latest, nil
 }
 
+func splitSnapshotID(s string) (id, subpath string) {
+	id, subpath, _ = strings.Cut(s, ":")
+	return
+}
+
 // FindSnapshot takes a string and tries to find a snapshot whose ID matches
 // the string as closely as possible.
-func FindSnapshot(ctx context.Context, be Lister, loader LoaderUnpacked, s string) (*Snapshot, error) {
+func FindSnapshot(ctx context.Context, be Lister, loader LoaderUnpacked, s string) (*Snapshot, string, error) {
+	s, subpath := splitSnapshotID(s)
+
 	// no need to list snapshots if `s` is already a full id
 	id, err := ParseID(s)
 	if err != nil {
 		// find snapshot id with prefix
 		id, err = Find(ctx, be, SnapshotFile, s)
 		if err != nil {
-			return nil, err
+			return nil, "", err
 		}
 	}
-	return LoadSnapshot(ctx, loader, id)
+	sn, err := LoadSnapshot(ctx, loader, id)
+	return sn, subpath, err
 }
 
 // FindLatest returns either the latest of a filtered list of all snapshots
 // or a snapshot specified by `snapshotID`.
-func (f *SnapshotFilter) FindLatest(ctx context.Context, be Lister, loader LoaderUnpacked, snapshotID string) (*Snapshot, error) {
-	if snapshotID == "latest" {
+func (f *SnapshotFilter) FindLatest(ctx context.Context, be Lister, loader LoaderUnpacked, snapshotID string) (*Snapshot, string, error) {
+	id, subpath := splitSnapshotID(snapshotID)
+	if id == "latest" {
 		sn, err := f.findLatest(ctx, be, loader)
 		if err == ErrNoSnapshotFound {
 			err = fmt.Errorf("snapshot filter (Paths:%v Tags:%v Hosts:%v): %w",
 				f.Paths, f.Tags, f.Hosts, err)
 		}
-		return sn, err
+		return sn, subpath, err
 	}
 	return FindSnapshot(ctx, be, loader, snapshotID)
 }
@@ -139,8 +149,11 @@ func (f *SnapshotFilter) FindAll(ctx context.Context, be Lister, loader LoaderUn
 					ids.Insert(*sn.ID())
 				}
 			} else {
-				sn, err = FindSnapshot(ctx, be, loader, s)
-				if err == nil {
+				var subpath string
+				sn, subpath, err = FindSnapshot(ctx, be, loader, s)
+				if err == nil && subpath != "" {
+					err = errors.New("snapshot:path syntax not allowed")
+				} else if err == nil {
 					if ids.Has(*sn.ID()) {
 						continue
 					}

internal/restic/snapshot_find_test.go

@@ -15,7 +15,7 @@ func TestFindLatestSnapshot(t *testing.T) {
 	latestSnapshot := restic.TestCreateSnapshot(t, repo, parseTimeUTC("2019-09-09 09:09:09"), 1, 0)
 
 	f := restic.SnapshotFilter{Hosts: []string{"foo"}}
-	sn, err := f.FindLatest(context.TODO(), repo.Backend(), repo, "latest")
+	sn, _, err := f.FindLatest(context.TODO(), repo.Backend(), repo, "latest")
 	if err != nil {
 		t.Fatalf("FindLatest returned error: %v", err)
 	}
@@ -31,7 +31,7 @@ func TestFindLatestSnapshotWithMaxTimestamp(t *testing.T) {
 	desiredSnapshot := restic.TestCreateSnapshot(t, repo, parseTimeUTC("2017-07-07 07:07:07"), 1, 0)
 	restic.TestCreateSnapshot(t, repo, parseTimeUTC("2019-09-09 09:09:09"), 1, 0)
 
-	sn, err := (&restic.SnapshotFilter{
+	sn, _, err := (&restic.SnapshotFilter{
 		Hosts:          []string{"foo"},
 		TimestampLimit: parseTimeUTC("2018-08-08 08:08:08"),
 	}).FindLatest(context.TODO(), repo.Backend(), repo, "latest")

internal/restic/tree.go

@@ -5,7 +5,9 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"path"
 	"sort"
+	"strings"
 
 	"github.com/restic/restic/internal/errors"
 
@@ -184,3 +186,32 @@ func (builder *TreeJSONBuilder) Finalize() ([]byte, error) {
 	builder.buf = bytes.Buffer{}
 	return buf, nil
 }
+
+func FindTreeDirectory(ctx context.Context, repo BlobLoader, id *ID, dir string) (*ID, error) {
+	if id == nil {
+		return nil, errors.New("tree id is null")
+	}
+
+	dirs := strings.Split(path.Clean(dir), "/")
+	subpath := ""
+
+	for _, name := range dirs {
+		if name == "" || name == "." {
+			continue
+		}
+		subpath = path.Join(subpath, name)
+		tree, err := LoadTree(ctx, repo, *id)
+		if err != nil {
+			return nil, fmt.Errorf("path %s: %w", subpath, err)
+		}
+		node := tree.Find(name)
+		if node == nil {
+			return nil, fmt.Errorf("path %s: not found", subpath)
+		}
+		if node.Type != "dir" || node.Subtree == nil {
+			return nil, fmt.Errorf("path %s: not a directory", subpath)
+		}
+		id = node.Subtree
+	}
+	return id, nil
+}