From: Matt Joiner <anacrolix@gmail.com>
Date: Tue, 11 Jun 2024 06:21:04 +0000 (+1000)
Subject: Correctly hash hybrid torrents with trailing v1 padding file
X-Git-Tag: v1.56.1
X-Git-Url: http://www.git.stargrave.org/?a=commitdiff_plain;h=3bbe1c34f0dcd92fb5ba8fa673fd85ffa942952b;p=btrtrc.git

Correctly hash hybrid torrents with trailing v1 padding file

Fixes #949.
---

diff --git a/issue-949_test.go b/issue-949_test.go
new file mode 100644
index 00000000..f04bd557
--- /dev/null
+++ b/issue-949_test.go
@@ -0,0 +1,27 @@
+package torrent
+
+import (
+	"github.com/anacrolix/torrent/metainfo"
+	qt "github.com/frankban/quicktest"
+	"testing"
+)
+
+func TestIssue949LastPieceZeroPadding(t *testing.T) {
+	// This torrent has a padding file after the last file listed in the v2 info file tree.
+	mi, err := metainfo.LoadFromFile("testdata/issue-949.torrent")
+	if err != nil {
+		panic(err)
+	}
+	info, err := mi.UnmarshalInfo()
+	if err != nil {
+		panic(err)
+	}
+	lastPiece := info.Piece(info.NumPieces() - 1)
+	c := qt.New(t)
+	c.Assert(info.FilesArePieceAligned(), qt.IsTrue)
+	// Check the v1 piece length includes the trailing padding file.
+	c.Check(lastPiece.V1Length(), qt.Equals, info.PieceLength)
+	// The v2 piece should only include the file data, which fits inside the piece length for this
+	// file.
+	c.Check(lastPiece.Length(), qt.Equals, int64(3677645))
+}
diff --git a/metainfo/info.go b/metainfo/info.go
index 3f14b08b..5252e209 100644
--- a/metainfo/info.go
+++ b/metainfo/info.go
@@ -150,9 +150,8 @@ func (info *Info) IsDir() bool {
 	return len(info.Files) != 0
 }
 
-// The files field, converted up from the old single-file in the parent info
-// dict if necessary. This is a helper to avoid having to conditionally handle
-// single and multi-file torrent infos.
+// The files field, converted up from the old single-file in the parent info dict if necessary. This
+// is a helper to avoid having to conditionally handle single and multi-file torrent infos.
 func (info *Info) UpvertedFiles() (files []FileInfo) {
 	if info.HasV2() {
 		info.FileTree.upvertedFiles(info.PieceLength, func(fi FileInfo) {
@@ -160,6 +159,12 @@ func (info *Info) UpvertedFiles() (files []FileInfo) {
 		})
 		return
 	}
+	return info.UpvertedV1Files()
+}
+
+// UpvertedFiles but specific to the files listed in the v1 info fields. This will include padding
+// files for example that wouldn't appear in v2 file trees.
+func (info *Info) UpvertedV1Files() (files []FileInfo) {
 	if len(info.Files) == 0 {
 		return []FileInfo{{
 			Length: info.Length,
diff --git a/metainfo/piece.go b/metainfo/piece.go
index c4101a6d..946e874b 100644
--- a/metainfo/piece.go
+++ b/metainfo/piece.go
@@ -45,7 +45,7 @@ func (p Piece) V1Length() int64 {
 	case 0 <= i && i < lastPiece:
 		return p.Info.PieceLength
 	case lastPiece >= 0 && i == lastPiece:
-		files := p.Info.UpvertedFiles()
+		files := p.Info.UpvertedV1Files()
 		lastFile := files[len(files)-1]
 		length := lastFile.TorrentOffset + lastFile.Length - int64(i)*p.Info.PieceLength
 		if length <= 0 || length > p.Info.PieceLength {
diff --git a/testdata/issue-949.torrent b/testdata/issue-949.torrent
new file mode 100644
index 00000000..7ebf67d6
Binary files /dev/null and b/testdata/issue-949.torrent differ
diff --git a/torrent.go b/torrent.go
index 3a5d358c..26c1714d 100644
--- a/torrent.go
+++ b/torrent.go
@@ -1157,8 +1157,8 @@ func (t *Torrent) hashPiece(piece pieceIndex) (
 		}
 		h := pieceHash.New()
 		differingPeers, err = t.hashPieceWithSpecificHash(piece, h)
-		// For a hybrid torrent, we work with the v2 files, but if we use a v1 hash, we can assume that
-		// the pieces are padded with zeroes.
+		// For a hybrid torrent, we work with the v2 files, but if we use a v1 hash, we can assume
+		// that the pieces are padded with zeroes.
 		if t.info.FilesArePieceAligned() {
 			paddingLen := p.Info().V1Length() - p.Info().Length()
 			written, err := io.CopyN(h, zeroReader, paddingLen)