introduced a new alert torrent_update_alert, for when a torrent_handle changes info-hash

bindings/python/src/alert.cpp

@@ -521,4 +521,10 @@ void bind_alert()
        .def_readonly("error", &add_torrent_alert::error)
        .add_property("params", &get_params)
        ;
+
+    class_<torrent_update_alert, bases<torrent_alert>, noncopyable>(
+       "torrent_update_alert", no_init)
+        .def_readonly("old_ih", &torrent_update_alert::old_ih)
+        .def_readonly("new_ih", &torrent_update_alert::new_ih)
+        ;
 }

docs/manual.rst

@@ -463,6 +463,12 @@ the torrent will be stopped and the torrent error state (``torrent_status::error
 will indicate what went wrong. The ``url`` may refer to a magnet link or a regular
 http URL.
 
+If it refers to an HTTP URL, the info-hash for the added torrent will not be the
+true info-hash of the .torrent. Instead a placeholder, unique, info-hash is used
+which is later updated once the .torrent file has been downloaded.
+
+Once the info-hash change happens, a torrent_update_alert_ is posted.
+
 ``dht_nodes`` is a list of hostname and port pairs, representing DHT nodes to be
 added to the session (if DHT is enabled). The hostname may be an IP address.
 
@@ -7702,6 +7708,26 @@ this message was posted. Note that you can map a torrent status to a specific to
 via its ``handle`` member. The receiving end is suggested to have all torrents sorted
 by the ``torrent_handle`` or hashed by it, for efficient updates.
 
+torrent_update_alert
+--------------------
+
+When a torrent changes its info-hash, this alert is posted. This only happens in very
+specific cases. For instance, when a torrent is downloaded from a URL, the true info
+hash is not known immediately. First the .torrent file must be downloaded and parsed.
+
+Once this download completes, the ``torrent_update_alert`` is posted to notify the client
+of the info-hash changing.
+
+::
+
+	struct torrent_update_alert: torrent_alert
+	{
+		// ...
+		sha1_hash old_ih;
+		sha1_hash new_ih;
+	};
+
+``old_ih`` and ``new_ih`` are the previous and new info-hash for the torrent, respectively.
 
 alert dispatcher
 ================

include/libtorrent/alert_types.hpp

@@ -1343,6 +1343,25 @@ namespace libtorrent
 		std::vector<torrent_status> status;
 	};
 
+	struct TORRENT_EXPORT torrent_update_alert : torrent_alert
+	{
+		torrent_update_alert(torrent_handle h, sha1_hash const& old_hash, sha1_hash const& new_hash)
+			: torrent_alert(h)
+			, old_ih(old_hash)
+			, new_ih(new_hash)
+		{}
+
+		TORRENT_DEFINE_ALERT(torrent_update_alert);
+
+		const static int static_category = alert::status_notification;
+		virtual std::string message() const;
+		virtual bool discardable() const { return false; }
+
+		sha1_hash old_ih;
+		sha1_hash new_ih;
+	};
+
+
 #undef TORRENT_DEFINE_ALERT
 
 }

src/alert.cpp

@@ -479,5 +479,14 @@ namespace libtorrent {
 		return msg;
 	}
 
+	std::string torrent_update_alert::message() const
+	{
+		char msg[200];
+		snprintf(msg, sizeof(msg), " torrent changed info-hash from: %s to %s"
+			, to_hex(old_ih.to_string()).c_str()
+			, to_hex(new_ih.to_string()).c_str());
+		return torrent_alert::message() + msg;
+	}
+
 } // namespace libtorrent
 

src/torrent.cpp

@@ -725,6 +725,9 @@ namespace libtorrent
 
 		m_ses.remove_torrent_impl(me, 0);
 
+		if (alerts().should_post<torrent_update_alert>())
+			alerts().post_alert(torrent_update_alert(get_handle(), info_hash(), tf->info_hash()));
+
 		m_torrent_file = tf;
 
 		// now, we might already have this torrent in the session.