lib: eagerly unmarshal items

1 files changed, 21 insertions, 0 deletions

diff --git a/pkg/btrfs/btrfsitem/items.go b/pkg/btrfs/btrfsitem/items.go
index 51e6344..91b7029 100644
--- a/pkg/btrfs/btrfsitem/items.go
+++ b/pkg/btrfs/btrfsitem/items.go
@@ -1,6 +1,10 @@
 package btrfsitem
 
 import (
+	"fmt"
+	"reflect"
+
+	"lukeshu.com/btrfs-tools/pkg/binstruct"
 	"lukeshu.com/btrfs-tools/pkg/btrfs/internal"
 )
 
@@ -9,3 +13,20 @@ type Type = internal.ItemType
 type Item interface {
 	isItem()
 }
+
+func UnmarshalItem(keytyp Type, dat []byte) (Item, error) {
+	gotyp, ok := keytype2gotype[keytyp]
+	if !ok {
+		return nil, fmt.Errorf("btrfsitem.UnmarshalItem: unknown item type: %v", keytyp)
+	}
+	retPtr := reflect.New(gotyp)
+	n, err := binstruct.Unmarshal(dat, retPtr.Interface())
+	if err != nil {
+		return nil, fmt.Errorf("btrfsitem.UnmarshalItem: %w", err)
+	}
+	if n < len(dat) {
+		return nil, fmt.Errorf("btrfsitem.UnmarshalItem: left over data: got %d bytes but only consumed %d",
+			len(dat), n)
+	}
+	return retPtr.Elem().Interface().(Item), nil
+}