better error tolerance

4 files changed, 82 insertions, 30 deletions

diff --git a/pkg/btrfs/btrfsitem/item_empty.go b/pkg/btrfs/btrfsitem/item_empty.go
index ed0f66f..fe7ae90 100644
--- a/pkg/btrfs/btrfsitem/item_empty.go
+++ b/pkg/btrfs/btrfsitem/item_empty.go
@@ -5,5 +5,5 @@ import (
 )
 
 type Empty struct { // UNTYPED=0, QGROUP_RELATION=246
-	binstruct.End `bin:"off=48"`
+	binstruct.End `bin:"off=0"`
 }
diff --git a/pkg/btrfs/btrfsitem/items.go b/pkg/btrfs/btrfsitem/items.go
index 91b7029..3c4392e 100644
--- a/pkg/btrfs/btrfsitem/items.go
+++ b/pkg/btrfs/btrfsitem/items.go
@@ -14,19 +14,46 @@ type Item interface {
 	isItem()
 }
 
-func UnmarshalItem(keytyp Type, dat []byte) (Item, error) {
+type Error struct {
+	Dat []byte
+	Err error
+}
+
+func (Error) isItem() {}
+
+func (o Error) MarshalBinary() ([]byte, error) {
+	return o.Dat, nil
+}
+
+func (o *Error) UnmarshalBinary(dat []byte) (int, error) {
+	o.Dat = dat
+	return len(dat), nil
+}
+
+// Rather than returning a separate error  value, return an Error item.
+func UnmarshalItem(keytyp Type, dat []byte) Item {
 	gotyp, ok := keytype2gotype[keytyp]
 	if !ok {
-		return nil, fmt.Errorf("btrfsitem.UnmarshalItem: unknown item type: %v", keytyp)
+		return Error{
+			Dat: dat,
+			Err: fmt.Errorf("btrfsitem.UnmarshalItem(typ=%v, dat): unknown item type", keytyp),
+		}
 	}
 	retPtr := reflect.New(gotyp)
 	n, err := binstruct.Unmarshal(dat, retPtr.Interface())
 	if err != nil {
-		return nil, fmt.Errorf("btrfsitem.UnmarshalItem: %w", err)
+		return Error{
+			Dat: dat,
+			Err: fmt.Errorf("btrfsitem.UnmarshalItem(typ=%v, dat): %w", keytyp, 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 Error{
+			Dat: dat,
+			Err: fmt.Errorf("btrfsitem.UnmarshalItem(typ=%v, dat): left over data: got %d bytes but only consumed %d",
+				keytyp, len(dat), n),
+		}
 	}
-	return retPtr.Elem().Interface().(Item), nil
+	return retPtr.Elem().Interface().(Item)
 }
diff --git a/pkg/btrfs/io2_fs.go b/pkg/btrfs/io2_fs.go
index b7752c7..f8ebe93 100644
--- a/pkg/btrfs/io2_fs.go
+++ b/pkg/btrfs/io2_fs.go
@@ -122,15 +122,17 @@ func (fs *FS) Init() error {
 		for _, chunk := range syschunks {
 			fs.chunks = append(fs.chunks, chunk)
 		}
-		if err := fs.WalkTree(sb.Data.ChunkTree, func(key Key, body btrfsitem.Item) error {
-			if key.ItemType != btrfsitem.CHUNK_ITEM_KEY {
+		if err := fs.WalkTree(sb.Data.ChunkTree, WalkTreeHandler{
+			Item: func(key Key, body btrfsitem.Item) error {
+				if key.ItemType != btrfsitem.CHUNK_ITEM_KEY {
+					return nil
+				}
+				fs.chunks = append(fs.chunks, SysChunk{
+					Key:   key,
+					Chunk: body.(btrfsitem.Chunk),
+				})
 				return nil
-			}
-			fs.chunks = append(fs.chunks, SysChunk{
-				Key:   key,
-				Chunk: body.(btrfsitem.Chunk),
-			})
-			return nil
+			},
 		}); err != nil {
 			fs.initErr = err
 			return fs.initErr
diff --git a/pkg/btrfs/types_btree.go b/pkg/btrfs/types_btree.go
index cac5f9a..88b9eb2 100644
--- a/pkg/btrfs/types_btree.go
+++ b/pkg/btrfs/types_btree.go
@@ -138,10 +138,7 @@ func (node *Node) UnmarshalBinary(nodeBuf []byte) (int, error) {
 			}
 			dataBuf := nodeBuf[dataOff : dataOff+dataSize]
 			lastRead = max(lastRead, dataOff+dataSize)
-			item.Body, err = btrfsitem.UnmarshalItem(item.Head.Key.ItemType, dataBuf)
-			if err != nil {
-				return max(n, lastRead), fmt.Errorf("(leaf): item %d: %w", i, err)
-			}
+			item.Body = btrfsitem.UnmarshalItem(item.Head.Key.ItemType, dataBuf)
 
 			node.BodyLeaf = append(node.BodyLeaf, item)
 		}
@@ -171,7 +168,7 @@ func (fs *FS) ReadNode(addr LogicalAddr) (util.Ref[LogicalAddr, Node], error) {
 
 	sb, err := fs.Superblock()
 	if err != nil {
-		return ret, err
+		return ret, fmt.Errorf("btrfs.FS.ReadNode: %w", err)
 	}
 
 	// read
@@ -185,24 +182,24 @@ func (fs *FS) ReadNode(addr LogicalAddr) (util.Ref[LogicalAddr, Node], error) {
 	node.Size = sb.Data.NodeSize
 
 	if _, err := node.UnmarshalBinary(nodeBuf); err != nil {
-		return ret, fmt.Errorf("node@%d: %w", addr, err)
+		return ret, fmt.Errorf("btrfs.FS.ReadNode: node@%d: %w", addr, err)
 	}
 
 	// sanity checking
 
 	if !node.Head.MetadataUUID.Equal(sb.Data.EffectiveMetadataUUID()) {
-		return ret, fmt.Errorf("node@%d: does not look like a node", addr)
+		return ret, fmt.Errorf("btrfs.FS.ReadNode: node@%d: does not look like a node", addr)
 	}
 
 	if node.Head.Addr != addr {
-		return ret, fmt.Errorf("node@%d: read from laddr=%d but claims to be at laddr=%d",
+		return ret, fmt.Errorf("btrfs.FS.ReadNode: node@%d: read from laddr=%d but claims to be at laddr=%d",
 			addr, addr, node.Head.Addr)
 	}
 
 	stored := node.Head.Checksum
 	calced := CRC32c(nodeBuf[binstruct.StaticSize(CSum{}):])
 	if !calced.Equal(stored) {
-		return ret, fmt.Errorf("node@%d: checksum mismatch: stored=%s calculated=%s",
+		return ret, fmt.Errorf("btrfs.FS.ReadNode: node@%d: checksum mismatch: stored=%s calculated=%s",
 			addr, stored, calced)
 	}
 
@@ -215,23 +212,49 @@ func (fs *FS) ReadNode(addr LogicalAddr) (util.Ref[LogicalAddr, Node], error) {
 	}, nil
 }
 
-func (fs *FS) WalkTree(nodeAddr LogicalAddr, fn func(Key, btrfsitem.Item) error) error {
+type WalkTreeHandler struct {
+	// Callbacks for items on internal nodes
+	PreKeyPointer  func(KeyPointer) error
+	PostKeyPointer func(KeyPointer) error
+	// Callbacks for items on leaf nodes
+	Item func(Key, btrfsitem.Item) error
+	// Error handler
+	NodeError func(error) error
+}
+
+func (fs *FS) WalkTree(nodeAddr LogicalAddr, cbs WalkTreeHandler) error {
 	if nodeAddr == 0 {
 		return nil
 	}
 	node, err := fs.ReadNode(nodeAddr)
 	if err != nil {
-		return err
+		if cbs.NodeError != nil {
+			err = cbs.NodeError(err)
+		}
+		if err != nil {
+			return fmt.Errorf("btrfs.FS.WalkTree: %w", err)
+		}
 	}
 	for _, item := range node.Data.BodyInternal {
-		// fn(item.Data.Key, TODO)
-		if err := fs.WalkTree(item.BlockPtr, fn); err != nil {
+		if cbs.PreKeyPointer != nil {
+			if err := cbs.PreKeyPointer(item); err != nil {
+				return err
+			}
+		}
+		if err := fs.WalkTree(item.BlockPtr, cbs); err != nil {
 			return err
 		}
+		if cbs.PostKeyPointer != nil {
+			if err := cbs.PostKeyPointer(item); err != nil {
+				return err
+			}
+		}
 	}
 	for _, item := range node.Data.BodyLeaf {
-		if err := fn(item.Head.Key, item.Body); err != nil {
-			return err
+		if cbs.Item != nil {
+			if err := cbs.Item(item.Head.Key, item.Body); err != nil {
+				return fmt.Errorf("btrfs.FS.WalkTree: callback: %w", err)
+			}
 		}
 	}
 	return nil