objectstore/*, repository: Add ReadSize v0.1.28

For cases where knowing the type is unnecessary and incurs extra
overhead.

1 files changed, 39 insertions, 0 deletions

diff --git a/objectstore/packed/read_size.go b/objectstore/packed/read_size.go
new file mode 100644
index 00000000..e162586a
--- /dev/null
+++ b/objectstore/packed/read_size.go
@@ -0,0 +1,39 @@
+package packed
+
+import (
+	"fmt"
+
+	packfmt "codeberg.org/lindenii/furgit/format/pack"
+	"codeberg.org/lindenii/furgit/objectid"
+	"codeberg.org/lindenii/furgit/objecttype"
+)
+
+// ReadSize reads an object's declared content size.
+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("objectstore/packed: unsupported pack type %d", meta.ty)
+	case objecttype.TypeCommit, objecttype.TypeTree, objecttype.TypeBlob, objecttype.TypeTag:
+		return 0, fmt.Errorf("objectstore/packed: internal invariant violation for base type %d", meta.ty)
+	default:
+		return 0, fmt.Errorf("objectstore/packed: unsupported pack type %d", meta.ty)
+	}
+}