improve support for loading torrents out of resume files

docs/manual.rst

@@ -6330,8 +6330,8 @@ The specific alerts are:
 torrent_added_alert
 -------------------
 
-The ``torrent_added_alert`` is posted once every time a torrent is added.
-It doesn't contain any members of its own, but inherits the torrent handle
+The ``torrent_added_alert`` is posted once every time a torrent is successfully
+added. It doesn't contain any members of its own, but inherits the torrent handle
 from its base class.
 It's posted when the ``status_notification`` bit is set in the alert mask.
 
@@ -6346,9 +6346,10 @@ It's posted when the ``status_notification`` bit is set in the alert mask.
 add_torrent_alert
 -----------------
 
-This alert is always posted when a torrent was added via ``async_add_torrent()``
+This alert is always posted when a torrent was attempted to be added
 and contains the return status of the add operation. The torrent handle of the new
-torrent can be found in the base class' ``handle`` member.
+torrent can be found in the base class' ``handle`` member. If adding
+the torrent failed, ``error`` contains the error code.
 
 ::
 
@@ -6362,7 +6363,7 @@ torrent can be found in the base class' ``handle`` member.
 ``params`` is a copy of the parameters used when adding the torrent, it can be used
 to identify which invocation to ``async_add_torrent()`` caused this alert.
 
-``error`` is set to the error, if any, adding the torrent.
+``error`` is set to the error, if one occurred while adding the torrent.
 
 
 torrent_removed_alert
@@ -6373,6 +6374,14 @@ the torrent handle in its baseclass will always be invalid (since the torrent
 is already removed) it has the info hash as a member, to identify it.
 It's posted when the ``status_notification`` bit is set in the alert mask.
 
+Even though the ``handle`` member doesn't point to an existing torrent anymore,
+it is still useful for comparing to other handles, which may also no
+longer point to existing torrents, but to the same non-existing torrents.
+
+The ``torrent_handle`` acts as a ``weak_ptr``, even though its object no
+longer exists, it can still compare equal to another weak pointer which
+points to the same non-existent object.
+
 ::
 
 	struct torrent_removed_alert: torrent_alert

include/libtorrent/aux_/session_impl.hpp

@@ -348,6 +348,7 @@ namespace libtorrent
 			bool is_listening() const;
 
 			torrent_handle add_torrent(add_torrent_params const&, error_code& ec);
+			torrent_handle add_torrent_impl(add_torrent_params const&, error_code& ec);
 			void async_add_torrent(add_torrent_params* params);
 
 			void remove_torrent(torrent_handle const& h, int options);

src/alert.cpp

@@ -624,7 +624,12 @@ namespace libtorrent {
 		}
 		else
 		{
-			snprintf(msg, sizeof(msg), "added torrent: %s", !params.url.empty() ? params.url.c_str() : params.ti->name().c_str());
+			snprintf(msg, sizeof(msg), "added torrent: %s"
+				, !params.url.empty() ? params.url.c_str()
+				: params.ti ? params.ti->name().c_str()
+				: !params.name.empty() ? params.name.c_str()
+				: !params.uuid.empty() ? params.uuid.c_str()
+				: "");
 		}
 		return msg;
 	}

src/session_impl.cpp

@@ -4916,13 +4916,20 @@ retry:
 	{
 		error_code ec;
 		torrent_handle handle = add_torrent(*params, ec);
-		m_alerts.post_alert(add_torrent_alert(handle, *params, ec));
 		delete params->resume_data;
 		delete params;
 	}
 
 	torrent_handle session_impl::add_torrent(add_torrent_params const& p
 		, error_code& ec)
+	{
+		torrent_handle h = add_torrent_impl(p, ec);
+		m_alerts.post_alert(add_torrent_alert(h, p, ec));
+		return h;
+	}
+
+	torrent_handle session_impl::add_torrent_impl(add_torrent_params const& p
+		, error_code& ec)
 	{
 		TORRENT_ASSERT(!p.save_path.empty());
 
@@ -4978,6 +4985,76 @@ retry:
 		}
 		else ih = &params.info_hash;
 
+		// we don't have a torrent file. If the user provided
+		// resume data, there may be some metadata in there
+		if ((!params.ti || !params.ti->is_valid())
+			&& params.resume_data)
+		{
+			int pos;
+			error_code ec;
+			lazy_entry tmp;
+			lazy_entry const* info = 0;
+#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
+			debug_log("adding magnet link with resume data");
+#endif
+			if (lazy_bdecode(&(*params.resume_data)[0], &(*params.resume_data)[0]
+					+ params.resume_data->size(), tmp, ec, &pos) == 0
+				&& tmp.type() == lazy_entry::dict_t
+				&& (info = tmp.dict_find_dict("info")))
+			{
+#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
+				debug_log("found metadata in resume data");
+#endif
+				// verify the info-hash of the metadata stored in the resume file matches
+				// the torrent we're loading
+
+				std::pair<char const*, int> buf = info->data_section();
+				sha1_hash resume_ih = hasher(buf.first, buf.second).final();
+
+				// if url is set, the info_hash is not actually the info-hash of the
+				// torrent, but the hash of the URL, until we have the full torrent
+				// only require the info-hash to match if we actually passed in one
+				if (resume_ih == params.info_hash
+					|| !params.url.empty()
+					|| params.info_hash.is_all_zeros())
+				{
+#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
+					debug_log("info-hash matched");
+#endif
+					params.ti = new torrent_info(resume_ih);
+
+					if (params.ti->parse_info_section(*info, ec, 0))
+					{
+#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
+						debug_log("successfully loaded metadata from resume file");
+#endif
+						// make the info-hash be the one in the resume file
+						params.info_hash = resume_ih;
+						ih = &params.info_hash;
+					}
+					else
+					{
+#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
+						debug_log("failed to load metadata from resume file: %s"
+								, ec.message().c_str());
+#endif
+					}
+				}
+#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
+				else
+				{
+					debug_log("metadata info-hash failed");
+				}
+#endif
+			}
+#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
+			else
+			{
+				debug_log("no metadata found");
+			}
+#endif
+		}
+
 		// is the torrent already active?
 		boost::shared_ptr<torrent> torrent_ptr = find_torrent(*ih).lock();
 		if (!torrent_ptr && !params.uuid.empty()) torrent_ptr = find_torrent(params.uuid).lock();

src/torrent.cpp

@@ -446,69 +446,6 @@ namespace libtorrent
 			// extension. Make sure that when we save resume data for this
 			// torrent, we also save the metadata
 			m_magnet_link = true;
-	
-			// did the user provide resume data?
-			// maybe the metadata is in there
-			if (p.resume_data)
-			{
-				int pos;
-				error_code ec;
-				lazy_entry tmp;
-				lazy_entry const* info = 0;
-#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
-				debug_log("adding magnet link with resume data");
-#endif
-				if (lazy_bdecode(&(*p.resume_data)[0], &(*p.resume_data)[0]
-					+ p.resume_data->size(), tmp, ec, &pos) == 0
-					&& tmp.type() == lazy_entry::dict_t
-					&& (info = tmp.dict_find_dict("info")))
-				{
-#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
-					debug_log("found metadata in resume data");
-#endif
-					// verify the info-hash of the metadata stored in the resume file matches
-					// the torrent we're loading
-
-					std::pair<char const*, int> buf = info->data_section();
-					sha1_hash resume_ih = hasher(buf.first, buf.second).final();
-
-					// if url is set, the info_hash is not actually the info-hash of the
-					// torrent, but the hash of the URL, until we have the full torrent
-					if (resume_ih == info_hash || !p.url.empty())
-					{
-#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
-						debug_log("info-hash matched");
-#endif
-						m_torrent_file = (p.ti ? p.ti : new torrent_info(resume_ih));
-
-						if (!m_torrent_file->parse_info_section(*info, ec, 0))
-						{
-#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
-							debug_log("failed to load metadata from resume file: %s"
-								, ec.message().c_str());
-#endif
-						}
-#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
-						else
-						{
-							debug_log("successfully loaded metadata from resume file");
-						}
-#endif
-					}
-#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
-					else
-					{
-						debug_log("metadata info-hash failed");
-					}
-#endif
-				}
-#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
-				else
-				{
-					debug_log("no metadata found");
-				}
-#endif
-			}
 		}
 
 		if (!m_torrent_file)