1 files changed, 27 insertions, 0 deletions
diff --git a/object/store/packed/delta_size.go b/object/store/packed/delta_size.go
new file mode 100644
index 00000000..4c89733c
--- /dev/null
+++ b/object/store/packed/delta_size.go
@@ -0,0 +1,27 @@
+package packed
+
+import (
+	"bufio"
+
+	deltaapply "codeberg.org/lindenii/furgit/delta/apply"
+)
+
+// deltaDeclaredSizeAt returns the resolved object size declared by one delta
+// stream header at dataOffset.
+func deltaDeclaredSizeAt(pack *packFile, dataOffset int) (int64, error) {
+	reader, err := zlibReaderAt(pack, dataOffset)
+	if err != nil {
+		return 0, err
+	}
+
+	defer func() { _ = reader.Close() }()
+
+	br := bufio.NewReaderSize(reader, 32)
+
+	_, size, err := deltaapply.ReadHeaderSizes(br)
+	if err != nil {
+		return 0, err
+	}
+
+	return int64(size), nil
+}