object/store/packed: Start the internal/reading split

1 files changed, 65 insertions, 0 deletions

diff --git a/object/store/packed/internal/reading/read_header_resolve.go b/object/store/packed/internal/reading/read_header_resolve.go
new file mode 100644
index 00000000..a2916b73
--- /dev/null
+++ b/object/store/packed/internal/reading/read_header_resolve.go
@@ -0,0 +1,65 @@
+package reading
+
+import (
+	"fmt"
+
+	objecttype "codeberg.org/lindenii/furgit/object/type"
+)
+
+// resolveHeaderAt resolves one object's canonical type and declared content size.
+func (store *Store) resolveHeaderAt(start location) (objecttype.Type, int64, error) {
+	visited := make(map[location]struct{})
+	current := start
+	declaredSize := int64(-1)
+
+	for {
+		if _, ok := visited[current]; ok {
+			return objecttype.TypeInvalid, 0, fmt.Errorf("objectstore/packed: delta cycle while resolving object header")
+		}
+
+		visited[current] = struct{}{}
+
+		pack, meta, err := store.entryMetaAt(current)
+		if err != nil {
+			return objecttype.TypeInvalid, 0, err
+		}
+
+		if declaredSize < 0 {
+			if meta.ty.IsBaseObject() {
+				declaredSize = meta.size
+			} else {
+				size, err := deltaDeclaredSizeAt(pack, meta.dataOffset)
+				if err != nil {
+					return objecttype.TypeInvalid, 0, err
+				}
+
+				declaredSize = size
+			}
+		}
+
+		if meta.ty.IsBaseObject() {
+			return meta.ty, declaredSize, nil
+		}
+
+		switch meta.ty {
+		case objecttype.TypeRefDelta:
+			next, err := store.lookup(meta.baseRefID)
+			if err != nil {
+				return objecttype.TypeInvalid, 0, err
+			}
+
+			current = next
+		case objecttype.TypeOfsDelta:
+			current = location{
+				packName: current.packName,
+				offset:   meta.baseOfs,
+			}
+		case objecttype.TypeCommit, objecttype.TypeTree, objecttype.TypeBlob, objecttype.TypeTag:
+			return objecttype.TypeInvalid, 0, fmt.Errorf("objectstore/packed: internal invariant violation for base type %d", meta.ty)
+		case objecttype.TypeInvalid, objecttype.TypeFuture:
+			return objecttype.TypeInvalid, 0, fmt.Errorf("objectstore/packed: unsupported pack type %d", meta.ty)
+		default:
+			return objecttype.TypeInvalid, 0, fmt.Errorf("objectstore/packed: unsupported pack type %d", meta.ty)
+		}
+	}
+}