fixed bug in add_piece() that would trigger asserts

ChangeLog

@@ -28,6 +28,7 @@
 	  incoming connection
 	* added more detailed instrumentation of the disk I/O thread
 
+	* fixed bug in add_piece() that would trigger asserts
 	* fixed vs 2010 build
 	* recognizes more clients in identify_client()
 	* fixed bug where trackers wouldn't be retried if they failed

include/libtorrent/piece_picker.hpp

@@ -276,7 +276,10 @@ namespace libtorrent
 		// marks this piece-block as queued for downloading
 		bool mark_as_downloading(piece_block block, void* peer
 			, piece_state_t s);
-		void mark_as_writing(piece_block block, void* peer);
+		// returns true if the block was marked as writing,
+		// and false if the block is already finished or writing
+		bool mark_as_writing(piece_block block, void* peer);
+
 		void mark_as_finished(piece_block block, void* peer);
 		void write_failed(piece_block block);
 		int num_peers(piece_block block) const;

src/piece_picker.cpp

@@ -2089,7 +2089,7 @@ namespace libtorrent
 			*j = i->peer_count + m_seeds;
 	}
 
-	void piece_picker::mark_as_writing(piece_block block, void* peer)
+	bool piece_picker::mark_as_writing(piece_block block, void* peer)
 	{
 #ifdef TORRENT_EXPENSIVE_INVARIANT_CHECKS
 		TORRENT_PIECE_PICKER_INVARIANT_CHECK;
@@ -2133,7 +2133,10 @@ namespace libtorrent
 			info.peer = peer;
 			if (info.state == block_info::state_requested) --i->requested;
 			TORRENT_ASSERT(i->requested >= 0);
-			TORRENT_ASSERT(info.state != block_info::state_writing);
+			if (info.state == block_info::state_writing
+				|| info.state == block_info::state_finished)
+				return false;
+
 			++i->writing;
 			info.state = block_info::state_writing;
 
@@ -2149,6 +2152,7 @@ namespace libtorrent
 			}
 			sort_piece(i);
 		}
+		return true;
 	}
 
 	void piece_picker::write_failed(piece_block block)

src/torrent.cpp

@@ -676,7 +676,9 @@ namespace libtorrent
 		// avoid crash trying to access the picker when there is nont
 		if (is_seed()) return;
 
-		if (picker().have_piece(piece)) return;
+		if (picker().have_piece(piece)
+			&& (flags & torrent::overwrite_existing) == 0)
+			return;
 
 		peer_request p;
 		p.piece = piece;