From 73b5efbb23110cb31991789c8f4de2cfab057a1d Mon Sep 17 00:00:00 2001
From: Chocobo1 <Chocobo1@users.noreply.github.com>
Date: Sun, 29 Jul 2018 16:14:17 +0800
Subject: [PATCH] Avoid potentially setting the wrong piece priorities

Updating file priorities is an async operation in libtorrent, when we
just updated it and immediately query it, we might get the
old/wrong values, so we rely on `updatedFilePrio` in this case.
---
 src/base/bittorrent/torrenthandle.cpp | 14 +++++++++++---
 src/base/bittorrent/torrenthandle.h   |  1 +
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/base/bittorrent/torrenthandle.cpp b/src/base/bittorrent/torrenthandle.cpp
index 962f5c6e0..7fa4015e9 100644
--- a/src/base/bittorrent/torrenthandle.cpp
+++ b/src/base/bittorrent/torrenthandle.cpp
@@ -1300,13 +1300,21 @@ void TorrentHandle::toggleSequentialDownload()
 
 void TorrentHandle::setFirstLastPiecePriority(const bool enabled)
 {
+    setFirstLastPiecePriorityImpl(enabled);
+}
+
+void TorrentHandle::setFirstLastPiecePriorityImpl(const bool enabled, const QVector<int> &updatedFilePrio)
+{
+    // Download first and last pieces first for every file in the torrent
+
     if (!hasMetadata()) {
         m_needsToSetFirstLastPiecePriority = enabled;
         return;
     }
 
-    // Download first and last pieces first for every file in the torrent
-    const std::vector<int> filePriorities = nativeHandle().file_priorities();
+    // Updating file priorities is an async operation in libtorrent, when we just updated it and immediately query it
+    // we might get the old/wrong values, so we rely on `updatedFilePrio` in this case.
+    const std::vector<int> filePriorities = !updatedFilePrio.isEmpty() ? updatedFilePrio.toStdVector() : nativeHandle().file_priorities();
     std::vector<int> piecePriorities = nativeHandle().piece_priorities();
     for (int index = 0; index < static_cast<int>(filePriorities.size()); ++index) {
         const int filePrio = filePriorities[index];
@@ -2064,7 +2072,7 @@ void TorrentHandle::prioritizeFiles(const QVector<int> &priorities)
 
     // Restore first/last piece first option if necessary
     if (firstLastPieceFirst)
-        setFirstLastPiecePriority(true);
+        setFirstLastPiecePriorityImpl(true, priorities);
 
     updateStatus();
 }
diff --git a/src/base/bittorrent/torrenthandle.h b/src/base/bittorrent/torrenthandle.h
index d5ad32bf7..88fe62946 100644
--- a/src/base/bittorrent/torrenthandle.h
+++ b/src/base/bittorrent/torrenthandle.h
@@ -420,6 +420,7 @@ namespace BitTorrent
         bool addTracker(const TrackerEntry &tracker);
         bool addUrlSeed(const QUrl &urlSeed);
         bool removeUrlSeed(const QUrl &urlSeed);
+        void setFirstLastPiecePriorityImpl(bool enabled, const QVector<int> &updatedFilePrio = {});
 
         Session *const m_session;
         libtorrent::torrent_handle m_nativeHandle;