improve support for merkle tree torrent creation

ChangeLog

@@ -87,6 +87,7 @@
 	  incoming connection
 	* added more detailed instrumentation of the disk I/O thread
 
+	* improve support for merkle tree torrent creation
 	* exposed comparison operators on torrent_handle to python
 	* exposed alert error_codes to python
 	* fixed bug in announce_entry::next_announce_in and min_announce_in

docs/make_torrent.rst

@@ -341,6 +341,9 @@ merkle
 	The benefit is that the resulting torrent file will be much smaller and
 	not grow with more pieces. When this option is specified, it is
 	recommended to have a fairly small piece size, say 64 kiB.
+	When creating merkle torrents, the full hash tree is also generated
+	and should be saved off separately. It is accessed through  the 
+	``merkle_tree()`` function.
 
 modification_time
 	This will include the file modification time as part of the torrent.
@@ -488,3 +491,19 @@ set_priv() priv()
 
 Sets and queries the private flag of the torrent.
 
+merkle_tree()
+-------------
+
+	::
+
+		std::vector<sha1_hash> const& merkle_tree() const;
+
+This function returns the merkle hash tree, if the torrent was created as a merkle
+torrent. The tree is created by ``generate()`` and won't be valid until that function
+has been called. When creating a merkle tree torrent, the actual tree itself has to
+be saved off separately and fed into libtorrent the first time you start seeding it,
+through the ``torrent_info::set_merkle_tree()`` function. From that point onwards, the
+tree will be saved in the resume data.
+
+
+

docs/manual.rst

@@ -1666,6 +1666,9 @@ The ``torrent_info`` has the following synopsis::
 		sha1_hash const& hash_for_piece(unsigned int index) const;
 		char const* hash_for_piece_ptr(unsigned int index) const;
 
+		std::vector<sha1_hash> const& merkle_tree() const;
+		void set_merkle_tree(std::vector<sha1_hash>& h);
+
 		boost::shared_array<char> metadata() const;
 		int metadata_size() const;
 	};
@@ -2079,6 +2082,23 @@ torrent file. For more information on the ``sha1_hash``, see the big_number_ cla
 ``hash_for_piece_ptr()`` returns a pointer to the 20 byte sha1 digest for the piece. 
 Note that the string is not null-terminated.
 
+merkle_tree() set_merkle_tree()
+-------------------------------
+
+	::
+
+		std::vector<sha1_hash> const& merkle_tree() const;
+		void set_merkle_tree(std::vector<sha1_hash>& h);
+
+``merkle_tree()`` returns a reference to the merkle tree for this torrent, if any.
+
+``set_merkle_tree()`` moves the passed in merkle tree into the torrent_info object.
+i.e. ``h`` will not be identical after the call. You need to set the merkle tree for
+a torrent that you've just created (as a merkle torrent). The merkle tree is retrieved
+from the ``create_torrent::merkle_tree()`` function, and need to be saved separately
+from the torrent file itself. Once it's added to libtorrent, the merkle tree will be
+persisted in the resume data.
+
 
 name() comment() creation_date() creator()
 ------------------------------------------

examples/make_torrent.cpp

@@ -64,8 +64,10 @@ void print_usage()
 		"Generates a torrent file from the specified file\n"
 		"or directory and writes it to standard out\n\n"
 		"OPTIONS:\n"
-		"-m          generate a merkle hash tree torrent.\n"
+		"-m file     generate a merkle hash tree torrent.\n"
 		"            merkle torrents require client support\n"
+		"            the resulting full merkle tree is written to\n"
+		"            the specified file\n"
 		"-f          include sha-1 file hashes in the torrent\n"
 		"            this helps supporting mixing sources from\n"
 		"            other networks\n"
@@ -109,6 +111,7 @@ int main(int argc, char* argv[])
 		int flags = 0;
 
 		std::string outfile;
+		std::string merklefile;
 #ifdef TORRENT_WINDOWS
 		// don't ever write binary data to the console on windows
 		// it will just be interpreted as text and corrupted
@@ -143,6 +146,8 @@ int main(int argc, char* argv[])
 					piece_size = atoi(argv[i]);
 					break;
 				case 'm':
+					++i;
+					merklefile = argv[i];
 					flags |= create_torrent::merkle;
 					break;
 				case 'o':
@@ -204,6 +209,18 @@ int main(int argc, char* argv[])
 		if (output != stdout)
 			fclose(output);
 
+		if (!merklefile.empty())
+		{
+			output = fopen(merklefile.c_str(), "wb+");
+			int ret = fwrite(&t.merkle_tree()[0], 1, t.merkle_tree().size(), output);
+			if (ret != t.merkle_tree().size())
+			{
+				fprintf(stderr, "failed to write %s: (%d) %s\n"
+					, merklefile.c_str(), errno, strerror(errno));
+			}
+			fclose(output);
+		}
+
 #ifndef BOOST_NO_EXCEPTIONS
 	}
 	catch (std::exception& e)

include/libtorrent/create_torrent.hpp

@@ -97,6 +97,7 @@ namespace libtorrent
 		bool priv() const { return m_private; }
 
 		bool should_add_file_hashes() const { return m_calculate_file_hashes; }
+		std::vector<sha1_hash> const& merkle_tree() const { return m_merkle_tree; }
 
 	private:
 
@@ -117,6 +118,11 @@ namespace libtorrent
 
 		std::vector<sha1_hash> m_filehashes;
 
+		// if we're generating a merkle torrent, this is the
+		// merkle tree we got. This should be saved in fast-resume
+		// in order to start seeding the torrent
+		mutable std::vector<sha1_hash> m_merkle_tree;
+
 		// dht nodes to add to the routing table/bootstrap from
 		typedef std::vector<std::pair<std::string, int> > nodes_t;
 		nodes_t m_nodes;

src/create_torrent.cpp

@@ -387,18 +387,16 @@ namespace libtorrent
 		info["piece length"] = m_files.piece_length();
 		if (m_merkle_torrent)
 		{
-			std::vector<sha1_hash> merkle_tree;
-			
 			int num_leafs = merkle_num_leafs(m_files.num_pieces());
 			int num_nodes = merkle_num_nodes(num_leafs);
 			int first_leaf = num_nodes - num_leafs;
-			merkle_tree.resize(num_nodes);
+			m_merkle_tree.resize(num_nodes);
 			int num_pieces = m_piece_hash.size();
 			for (int i = 0; i < num_pieces; ++i)
-				merkle_tree[first_leaf + i] = m_piece_hash[i];
+				m_merkle_tree[first_leaf + i] = m_piece_hash[i];
 			sha1_hash filler(0);
 			for (int i = num_pieces; i < num_leafs; ++i)
-				merkle_tree[first_leaf + i] = filler;
+				m_merkle_tree[first_leaf + i] = filler;
 
 			// now that we have initialized all leaves, build
 			// each level bottom-up
@@ -410,16 +408,16 @@ namespace libtorrent
 				for (int i = level_start; i < level_start + level_size; i += 2, ++parent)
 				{
 					hasher h;
-					h.update((char const*)&merkle_tree[i][0], 20);
-					h.update((char const*)&merkle_tree[i+1][0], 20);
-					merkle_tree[parent] = h.final();
+					h.update((char const*)&m_merkle_tree[i][0], 20);
+					h.update((char const*)&m_merkle_tree[i+1][0], 20);
+					m_merkle_tree[parent] = h.final();
 				}
 				level_start = merkle_get_parent(level_start);
 				level_size /= 2;
 			}
 			TORRENT_ASSERT(level_size == 1);
 			std::string& p = info["root hash"].string();
-			p.assign((char const*)&merkle_tree[0][0], 20);
+			p.assign((char const*)&m_merkle_tree[0][0], 20);
 		}
 		else
 		{