add download sequentially

src/download/chunk_selector.cc

@@ -80,8 +80,13 @@ ChunkSelector::update_priorities() {
 
   m_sharedQueue.clear();
 
-  if (m_position == invalid_chunk)
-    m_position = random() % size();
+  if (m_position == invalid_chunk) {
+    if (m_sequential) {
+      m_position = 0;
+    } else {
+      m_position = random() % size();
+    }
+  }
 
   advance_position();
 }
@@ -99,12 +104,14 @@ ChunkSelector::find(PeerChunks* pc, [[maybe_unused]] bool highPriority) {
   // set.
   rak::partial_queue* queue = pc->is_seeder() ? &m_sharedQueue : pc->download_cache();
 
-  // Randomize position on average every 16 chunks to prevent
-  // inefficient distribution with a slow seed and fast peers
-  // all arriving at the same position.
-  if ((random() & 63) == 0) {
-    m_position = random() % size();
-    queue->clear();
+  if (!m_sequential) {
+    // Randomize position on average every 16 chunks to prevent
+    // inefficient distribution with a slow seed and fast peers
+    // all arriving at the same position.
+    if ((random() & 63) == 0) {
+      m_position = random() % size();
+      queue->clear();
+    }
   }
 
   if (queue->is_enabled()) {

src/download/chunk_selector.h

@@ -76,6 +76,15 @@ class ChunkSelector {
   void                initialize(ChunkStatistics* cs);
   void                cleanup();
 
+    // Sequential chunk selection
+  bool is_sequential_enabled() {
+    return m_sequential;
+  };
+  void set_sequential_enabled(bool enabled) {
+    m_sequential = enabled;
+  };
+
+
   // Call this once you've modified the bitfield or priorities to
   // update cached information. This must be called once before using
   // find.
@@ -118,6 +127,8 @@ class ChunkSelector {
   rak::partial_queue  m_sharedQueue;
 
   uint32_t            m_position;
+
+  bool                m_sequential = false;
 };
 
 }

src/torrent/download.cc

@@ -247,6 +247,17 @@ Download::set_pex_enabled(bool enabled) {
     m_ptr->info()->unset_flags(DownloadInfo::flag_pex_enabled);
 }
 
+bool
+Download::is_sequential_enabled() {
+  return m_ptr->main()->chunk_selector()->is_sequential_enabled();
+}
+
+void
+Download::set_sequential_enabled(bool enabled) {
+  m_ptr->main()->chunk_selector()->set_sequential_enabled(enabled);
+}
+
+
 Object*
 Download::bencode() {
   return m_ptr->bencode();

src/torrent/download.h

@@ -99,6 +99,10 @@ class LIBTORRENT_EXPORT Download {
 
   void                set_pex_enabled(bool enabled);
 
+  // Sequential download
+  bool                is_sequential_enabled();
+  void                set_sequential_enabled(bool enabled);
+
   Object*             bencode();
   const Object*       bencode() const;