1 files changed, 46 insertions, 0 deletions
diff --git a/object/storer/packed/read_size.go b/object/storer/packed/read_size.go
new file mode 100644
index 00000000..9d6c8e7d
--- /dev/null
+++ b/object/storer/packed/read_size.go
@@ -0,0 +1,46 @@
+package packed
+
+import (
+	"fmt"
+
+	objectid "codeberg.org/lindenii/furgit/object/id"
+	objecttype "codeberg.org/lindenii/furgit/object/type"
+	packfmt "codeberg.org/lindenii/furgit/packfile"
+)
+
+// ReadSize reads an object's declared content size.
+//
+// Like ReadHeader, it resolves header metadata only. It does not verify that
+// the full pack entry payload is readable and does not verify any zlib
+// Adler-32 trailer for compressed entry data.
+func (store *Store) ReadSize(id objectid.ObjectID) (int64, error) {
+	loc, err := store.lookup(id)
+	if err != nil {
+		return 0, err
+	}
+
+	return store.resolveSizeAt(loc)
+}
+
+// resolveSizeAt resolves one object's declared content size from location.
+func (store *Store) resolveSizeAt(start location) (int64, error) {
+	pack, meta, err := store.entryMetaAt(start)
+	if err != nil {
+		return 0, err
+	}
+
+	if packfmt.IsBaseObjectType(meta.ty) {
+		return meta.size, nil
+	}
+
+	switch meta.ty {
+	case objecttype.TypeRefDelta, objecttype.TypeOfsDelta:
+		return deltaDeclaredSizeAt(pack, meta.dataOffset)
+	case objecttype.TypeInvalid, objecttype.TypeFuture:
+		return 0, fmt.Errorf("objectstorer/packed: unsupported pack type %d", meta.ty)
+	case objecttype.TypeCommit, objecttype.TypeTree, objecttype.TypeBlob, objecttype.TypeTag:
+		return 0, fmt.Errorf("objectstorer/packed: internal invariant violation for base type %d", meta.ty)
+	default:
+		return 0, fmt.Errorf("objectstorer/packed: unsupported pack type %d", meta.ty)
+	}
+}