Fix combined partial and incremental updates.

It seems that I forgot to implement incremental update support for
partial updates entirely.

src/extract.go

@@ -15,7 +15,6 @@ import (
 	"strings"
 
 	"github.com/c2h5oh/datasize"
-	"github.com/go-git/go-git/v6/plumbing"
 	"github.com/klauspost/compress/zstd"
 )
 
@@ -52,16 +51,6 @@ func ExtractZstd(
 	return next(ctx, boundArchiveStream(stream))
 }
 
-const BlobReferencePrefix = "/git/blobs/"
-
-type UnresolvedRefError struct {
-	missing []string
-}
-
-func (err UnresolvedRefError) Error() string {
-	return fmt.Sprintf("%d unresolved blob references", len(err.missing))
-}
-
 func normalizeArchiveMemberName(fileName string) string {
 	// Strip the leading slash and any extraneous path segments.
 	fileName = path.Clean(fileName)
@@ -72,21 +61,6 @@ func normalizeArchiveMemberName(fileName string) string {
 	return fileName
 }
 
-// Returns a map of git hash to entry. If `manifest` is nil, returns an empty map.
-func indexManifestByGitHash(manifest *Manifest) map[string]*Entry {
-	index := map[string]*Entry{}
-	for _, entry := range manifest.GetContents() {
-		if hash := entry.GetGitHash(); hash != "" {
-			if _, ok := plumbing.FromHex(hash); ok {
-				index[hash] = entry
-			} else {
-				panic(fmt.Errorf("index: malformed hash: %s", hash))
-			}
-		}
-	}
-	return index
-}
-
 func addSymlinkOrBlobReference(
 	manifest *Manifest, fileName string, target string,
 	index map[string]*Entry, missing *[]string,
@@ -110,7 +84,7 @@ func ExtractTar(ctx context.Context, reader io.Reader, oldManifest *Manifest) (*
 	var dataBytesRecycled int64
 	var dataBytesTransferred int64
 
-	index := indexManifestByGitHash(oldManifest)
+	index := IndexManifestByGitHash(oldManifest)
 	missing := []string{}
 	manifest := NewManifest()
 	for {
@@ -202,7 +176,7 @@ func ExtractZip(ctx context.Context, reader io.Reader, oldManifest *Manifest) (*
 	var dataBytesRecycled int64
 	var dataBytesTransferred int64
 
-	index := indexManifestByGitHash(oldManifest)
+	index := IndexManifestByGitHash(oldManifest)
 	missing := []string{}
 	manifest := NewManifest()
 	for _, file := range archive.File {

src/manifest.go

@@ -145,6 +145,21 @@ func AddProblem(manifest *Manifest, pathName, format string, args ...any) error
 	return fmt.Errorf("%s: %s", pathName, cause)
 }
 
+// Returns a map of git hash to entry. If `manifest` is nil, returns an empty map.
+func IndexManifestByGitHash(manifest *Manifest) map[string]*Entry {
+	index := map[string]*Entry{}
+	for _, entry := range manifest.GetContents() {
+		if hash := entry.GetGitHash(); hash != "" {
+			if _, ok := plumbing.FromHex(hash); ok {
+				index[hash] = entry
+			} else {
+				panic(fmt.Errorf("index: malformed hash: %s", hash))
+			}
+		}
+	}
+	return index
+}
+
 func IsEntryRegularFile(entry *Entry) bool {
 	return entry.GetType() == Type_InlineFile ||
 		entry.GetType() == Type_ExternalFile

src/patch.go

@@ -30,8 +30,12 @@ func ApplyTarPatch(manifest *Manifest, reader io.Reader, parents CreateParentsMo
 		children map[string]*Node
 	}
 
+	// Index the manifest for incremental update operations.
+	index := IndexManifestByGitHash(manifest)
+	missing := []string{}
+
 	// Extract the manifest contents (which is using a flat hash map) into a directory tree
-	// so that recursive delete operations have O(1) complexity. s
+	// so that recursive delete operations have O(1) complexity.
 	var root *Node
 	sortedNames := slices.Sorted(maps.Keys(manifest.GetContents()))
 	for _, name := range sortedNames {
@@ -107,8 +111,16 @@ func ApplyTarPatch(manifest *Manifest, reader io.Reader, parents CreateParentsMo
 				entry: NewManifestEntry(Type_InlineFile, fileData),
 			}
 		case tar.TypeSymlink:
-			node.children[fileName] = &Node{
-				entry: NewManifestEntry(Type_Symlink, []byte(header.Linkname)),
+			if hash, found := strings.CutPrefix(header.Linkname, BlobReferencePrefix); found {
+				if entry, found := index[hash]; found {
+					node.children[fileName] = &Node{entry: entry}
+				} else {
+					missing = append(missing, hash)
+				}
+			} else {
+				node.children[fileName] = &Node{
+					entry: NewManifestEntry(Type_Symlink, []byte(header.Linkname)),
+				}
 			}
 		case tar.TypeDir:
 			node.children[fileName] = &Node{
@@ -129,6 +141,10 @@ func ApplyTarPatch(manifest *Manifest, reader io.Reader, parents CreateParentsMo
 		}
 	}
 
+	if len(missing) > 0 {
+		return UnresolvedRefError{missing}
+	}
+
 	// Repopulate manifest contents with the updated directory tree.
 	var traverse func([]string, *Node)
 	traverse = func(segments []string, node *Node) {

src/update.go

@@ -10,6 +10,16 @@ import (
 	"google.golang.org/protobuf/proto"
 )
 
+const BlobReferencePrefix = "/git/blobs/"
+
+type UnresolvedRefError struct {
+	missing []string
+}
+
+func (err UnresolvedRefError) Error() string {
+	return fmt.Sprintf("%d unresolved blob references", len(err.missing))
+}
+
 type UpdateOutcome int
 
 const (