factor out a helper for payload_blocks_in_piece()

Author: arvidn

include/libtorrent/aux_/piece_picker.hpp

@@ -408,6 +408,10 @@ namespace libtorrent::aux {
 		// returns the number of blocks there is in the given piece
 		int blocks_in_piece(piece_index_t) const;
 
+		// number of blocks in the given piece that carry real payload,
+		// i.e. excluding any trailing pad blocks
+		int payload_blocks_in_piece(piece_index_t) const;
+
 		// return the peer pointers to all peers that participated in
 		// this piece
 		std::vector<aux::torrent_peer*> get_downloaders(piece_index_t) const;

src/piece_picker.cpp

@@ -266,7 +266,7 @@ namespace libtorrent::aux {
 		// the number of non-pad blocks in this piece. Any blocks past this will
 		// be assumed we have already
 
-		int const payload_blocks = blocks_per_piece() - pad_bytes_in_piece(piece) / block_size();
+		int const payload_blocks = payload_blocks_in_piece(piece);
 
 		int block_idx = 0;
 		for (auto& info : mutable_blocks_for_piece(ret))
@@ -2531,6 +2531,11 @@ namespace {
 			return blocks_per_piece();
 	}
 
+	int piece_picker::payload_blocks_in_piece(piece_index_t const index) const
+	{
+		return blocks_in_piece(index) - pad_bytes_in_piece(index) / block_size();
+	}
+
 	bool piece_picker::is_piece_free(piece_index_t const piece
 		, typed_bitfield<piece_index_t> const& bitmask) const
 	{
@@ -2653,7 +2658,7 @@ namespace {
 		}
 
 		// pick a new piece
-		int payload_blocks = blocks_in_piece(piece) - pad_bytes_in_piece(piece) / block_size();
+		int payload_blocks = payload_blocks_in_piece(piece);
 
 		if (prefer_contiguous_blocks == 0)
 		{
@@ -2683,7 +2688,7 @@ namespace {
 				ignore.push_back(k);
 
 				TORRENT_ASSERT(m_piece_map[k].priority(this) > 0);
-				payload_blocks = blocks_in_piece(k) - pad_bytes_in_piece(k) / block_size();
+				payload_blocks = payload_blocks_in_piece(k);
 				TORRENT_ASSERT(is_piece_free(k, pieces));
 				for (int j = 0; j < payload_blocks; ++j)
 				{

test/test_piece_picker.cpp

@@ -2324,6 +2324,33 @@ TORRENT_TEST(set_pad_bytes)
 	TEST_EQUAL(blocks[3].state, piece_picker::block_info::state_finished);
 }
 
+TORRENT_TEST(set_pad_bytes_short_last_piece)
+{
+	// the last piece is shorter than a full piece (2 blocks instead of 4)
+	// and its last block is a pad block. add_download_piece() must use the
+	// actual number of blocks in this short piece, not the nominal
+	// per-piece block count, to tell payload blocks from pad blocks.
+	auto p = std::make_shared<piece_picker>(
+		std::int64_t(default_piece_size) + 2 * default_block_size, default_piece_size);
+	p->set_pad_bytes(1_piece, default_block_size);
+
+	bool const ret = p->mark_as_downloading({1_piece, 0}, tmp_peer);
+	TEST_EQUAL(ret, true);
+
+	auto const dl = p->get_download_queue();
+
+	TEST_EQUAL(dl.size(), 1);
+	TEST_EQUAL(dl[0].finished, 1);
+	TEST_EQUAL(dl[0].writing, 0);
+	TEST_EQUAL(dl[0].requested, 1);
+	TEST_EQUAL(dl[0].index, 1_piece);
+
+	auto const blocks = p->blocks_for_piece(dl[0]);
+	TEST_EQUAL(blocks.size(), 2);
+	TEST_EQUAL(blocks[0].state, piece_picker::block_info::state_requested);
+	TEST_EQUAL(blocks[1].state, piece_picker::block_info::state_finished);
+}
+
 TORRENT_TEST(set_pad_bytes_overflow)
 {
 	int const ps = file_storage::max_piece_size;