Add sanity check to currentNodeData.Seek

io/dagreader.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"errors"
+	"fmt"
 	"io"
 
 	ipld "github.com/ipfs/go-ipld-format"
@@ -426,10 +427,14 @@ func (dr *dagReader) Seek(offset int64, whence int) (int64, error) {
 					return err
 				}
 
-				_, err = dr.currentNodeData.Seek(left, io.SeekStart)
+				n, err := dr.currentNodeData.Seek(left, io.SeekStart)
 				if err != nil {
 					return err
 				}
+
+				if n != left {
+					return fmt.Errorf("nodeData seeked to wrong position %d, ekpected %d", n, left)
+				}
 				// The corner case of a DAG consisting only of a single (leaf)
 				// node should make no difference here. In that case, where the
 				// node doesn't have a parent UnixFS node with size hints, this