From: Matt Joiner <anacrolix@gmail.com>
Date: Thu, 25 Jan 2018 06:01:29 +0000 (+1100)
Subject: Fix file piece index offset calculations
X-Git-Tag: v1.0.0~268
X-Git-Url: http://www.git.stargrave.org/?a=commitdiff_plain;h=21108bf6ec0547a9640f19f4ce5b64a3c391a361;p=btrtrc.git

Fix file piece index offset calculations
---

diff --git a/file.go b/file.go
index 7cc0ad64..5983b855 100644
--- a/file.go
+++ b/file.go
@@ -121,7 +121,7 @@ func (f *File) SetPriority(prio piecePriority) {
 		return
 	}
 	f.prio = prio
-	f.t.updatePiecePriorities(f.firstPieceIndex().Int(), f.lastPieceIndex().Int()+1)
+	f.t.updatePiecePriorities(f.firstPieceIndex().Int(), f.endPieceIndex().Int())
 }
 
 // Returns the priority per File.SetPriority.
@@ -132,9 +132,15 @@ func (f *File) Priority() piecePriority {
 }
 
 func (f *File) firstPieceIndex() pwp.Integer {
+	if f.t.usualPieceSize() == 0 {
+		return 0
+	}
 	return pwp.Integer(f.offset / int64(f.t.usualPieceSize()))
 }
 
-func (f *File) lastPieceIndex() pwp.Integer {
-	return pwp.Integer((f.offset + f.length) / int64(f.t.usualPieceSize()))
+func (f *File) endPieceIndex() pwp.Integer {
+	if f.t.usualPieceSize() == 0 {
+		return 0
+	}
+	return pwp.Integer((f.offset+f.length-1)/int64(f.t.usualPieceSize())) + 1
 }
diff --git a/torrent.go b/torrent.go
index 981f5b85..6440a3f8 100644
--- a/torrent.go
+++ b/torrent.go
@@ -305,26 +305,33 @@ func (t *Torrent) makePieces() {
 		piece.index = i
 		piece.noPendingWrites.L = &piece.pendingWritesMutex
 		missinggo.CopyExact(piece.hash[:], hash)
-		piece.files = (*t.files)[pieceFirstFileIndex(piece.torrentBeginOffset(), *t.files):pieceLastFileIndex(piece.torrentEndOffset(), *t.files)]
+		files := *t.files
+		beginFile := pieceFirstFileIndex(piece.torrentBeginOffset(), files)
+		endFile := pieceEndFileIndex(piece.torrentEndOffset(), files)
+		piece.files = files[beginFile:endFile]
 	}
 }
 
+// Returns the index of the first file containing the piece. files must be
+// ordered by offset.
 func pieceFirstFileIndex(pieceOffset int64, files []*File) int {
 	for i, f := range files {
 		if f.offset+f.length > pieceOffset {
 			return i
 		}
 	}
-	return -1
+	return 0
 }
 
-func pieceLastFileIndex(pieceEndOffset int64, files []*File) int {
+// Returns the index after the last file containing the piece. files must be
+// ordered by offset.
+func pieceEndFileIndex(pieceEndOffset int64, files []*File) int {
 	for i, f := range files {
 		if f.offset+f.length >= pieceEndOffset {
-			return i
+			return i + 1
 		}
 	}
-	return -1
+	return 0
 }
 
 func (t *Torrent) cacheLength(info *metainfo.Info) {