From 96b8be306b5f295c2d3949ae95a597564c2ba6dc Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Wed, 20 Mar 2024 14:03:22 +1100
Subject: [PATCH] Verify piece layers while adding

---
 client.go  |  2 +-
 torrent.go | 26 +++++++++++++++++++-------
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/client.go b/client.go
index c70e4133..23decf6e 100644
--- a/client.go
+++ b/client.go
@@ -1507,7 +1507,7 @@ func (t *Torrent) MergeSpec(spec *TorrentSpec) error {
 	t.maybeNewConns()
 	t.dataDownloadDisallowed.SetBool(spec.DisallowDataDownload)
 	t.dataUploadDisallowed = spec.DisallowDataUpload
-	return t.AddPieceLayers(spec.PieceLayers)
+	return errors.Join(t.AddPieceLayers(spec.PieceLayers)...)
 }
 
 func (cl *Client) dropTorrent(t *Torrent, wg *sync.WaitGroup) (err error) {
diff --git a/torrent.go b/torrent.go
index b952e3ce..fe1a1972 100644
--- a/torrent.go
+++ b/torrent.go
@@ -425,22 +425,26 @@ func (t *Torrent) makePieces() {
 	}
 }
 
-func (t *Torrent) AddPieceLayers(layers map[string]string) (err error) {
+func (t *Torrent) AddPieceLayers(layers map[string]string) (errs []error) {
 	if layers == nil {
 		return
 	}
+files:
 	for _, f := range *t.files {
 		if !f.piecesRoot.Ok {
-			err = fmt.Errorf("no piece root set for file %v", f)
-			return
+			err := fmt.Errorf("no piece root set for file %v", f)
+			errs = append(errs, err)
+			continue files
 		}
 		compactLayer, ok := layers[string(f.piecesRoot.Value[:])]
 		var hashes [][32]byte
 		if ok {
+			var err error
 			hashes, err = merkle.CompactLayerToSliceHashes(compactLayer)
 			if err != nil {
 				err = fmt.Errorf("bad piece layers for file %q: %w", f, err)
-				return
+				errs = append(errs, err)
+				continue files
 			}
 		} else if f.length > t.info.PieceLength {
 			// BEP 52 is pretty strongly worded about this, even though we should be able to
@@ -452,8 +456,16 @@ func (t *Torrent) AddPieceLayers(layers map[string]string) (err error) {
 			hashes = [][32]byte{f.piecesRoot.Value}
 		}
 		if len(hashes) != f.numPieces() {
-			err = fmt.Errorf("file %q: got %v hashes expected %v", f, len(hashes), f.numPieces())
-			return
+			errs = append(
+				errs,
+				fmt.Errorf("file %q: got %v hashes expected %v", f, len(hashes), f.numPieces()),
+			)
+			continue files
+		}
+		root := merkle.RootWithPadHash(hashes, metainfo.HashForPiecePad(t.info.PieceLength))
+		if root != f.piecesRoot.Value {
+			errs = append(errs, fmt.Errorf("%v: expected hash %x got %x", f, f.piecesRoot.Value, root))
+			continue files
 		}
 		for i := range f.numPieces() {
 			pi := f.BeginPieceIndex() + i
@@ -461,7 +473,7 @@ func (t *Torrent) AddPieceLayers(layers map[string]string) (err error) {
 			p.setV2Hash(hashes[i])
 		}
 	}
-	return nil
+	return
 }
 
 // Returns the index of the first file containing the piece. files must be
-- 
2.48.1