lib: eagerly unmarshal items

2 files changed, 41 insertions, 1 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
+}
diff --git a/pkg/btrfs/btrfsitem/items_gen.go b/pkg/btrfs/btrfsitem/items_gen.go
index 5234c96..40a0b53 100644
--- a/pkg/btrfs/btrfsitem/items_gen.go
+++ b/pkg/btrfs/btrfsitem/items_gen.go
@@ -1,6 +1,10 @@
 package btrfsitem
 
-import "lukeshu.com/btrfs-tools/pkg/btrfs/internal"
+import (
+	"reflect"
+
+	"lukeshu.com/btrfs-tools/pkg/btrfs/internal"
+)
 
 const (
 	CHUNK_ITEM_KEY           = internal.CHUNK_ITEM_KEY
@@ -17,6 +21,21 @@ const (
 	UUID_RECEIVED_SUBVOL_KEY = internal.UUID_RECEIVED_SUBVOL_KEY
 )
 
+var keytype2gotype = map[Type]reflect.Type{
+	CHUNK_ITEM_KEY:           reflect.TypeOf(Chunk{}),
+	DEV_ITEM_KEY:             reflect.TypeOf(Dev{}),
+	DEV_EXTENT_KEY:           reflect.TypeOf(DevExtent{}),
+	UNTYPED_KEY:              reflect.TypeOf(Empty{}),
+	QGROUP_RELATION_KEY:      reflect.TypeOf(Empty{}),
+	INODE_ITEM_KEY:           reflect.TypeOf(Inode{}),
+	INODE_REF_KEY:            reflect.TypeOf(InodeRef{}),
+	ORPHAN_ITEM_KEY:          reflect.TypeOf(Orphan{}),
+	PERSISTENT_ITEM_KEY:      reflect.TypeOf(DevStats{}),
+	ROOT_ITEM_KEY:            reflect.TypeOf(Root{}),
+	UUID_SUBVOL_KEY:          reflect.TypeOf(UUIDMap{}),
+	UUID_RECEIVED_SUBVOL_KEY: reflect.TypeOf(UUIDMap{}),
+}
+
 func (Chunk) isItem()     {}
 func (Dev) isItem()       {}
 func (DevExtent) isItem() {}