fix race condition when resolving the hostname of a web seed and removing it

include/libtorrent/torrent.hpp

@@ -366,7 +366,7 @@ namespace libtorrent
 			std::list<web_seed_entry>::iterator i = std::find_if(m_web_seeds.begin(), m_web_seeds.end()
 				, (boost::bind(&web_seed_entry::url, _1)
 					== url && boost::bind(&web_seed_entry::type, _1) == type));
-			if (i != m_web_seeds.end()) m_web_seeds.erase(i);
+			if (i != m_web_seeds.end()) remove_web_seed(i);
 		}
 
 		void disconnect_web_seed(peer_connection* p)
@@ -630,6 +630,10 @@ namespace libtorrent
 		void on_proxy_name_lookup(error_code const& e, tcp::resolver::iterator i
 			, std::list<web_seed_entry>::iterator url);
 
+		// remove a web seed, or schedule it for removal in case there
+		// are outstanding operations on it
+		void remove_web_seed(std::list<web_seed_entry>::iterator web);
+
 		// this is called when the torrent has finished. i.e.
 		// all the pieces we have not filtered have been downloaded.
 		// If no pieces are filtered, this is called first and then

include/libtorrent/torrent_info.hpp

@@ -186,7 +186,8 @@ namespace libtorrent
 			, headers_t const& extra_headers_ = headers_t())
 			: url(url_), type(type_)
 			, auth(auth_), extra_headers(extra_headers_)
-			, retry(time_now()), resolving(false), connection(0)
+			, retry(time_now()), resolving(false), removed(false)
+			, connection(0)
 		{}
 
 		bool operator==(web_seed_entry const& e) const
@@ -211,6 +212,12 @@ namespace libtorrent
 		// hostname of this URL
 		bool resolving;
 
+		// if the user wanted to remove this while
+		// we were resolving it. In this case, we set
+		// the removed flag to true, to make the resolver
+		// callback remove it
+		bool removed;
+
 		tcp::endpoint endpoint;
 
 		peer_connection* connection;

src/torrent.cpp

@@ -3843,6 +3843,16 @@ namespace libtorrent
 		m_connections.erase(i);
 	}
 
+	void torrent::remove_web_seed(std::list<web_seed_entry>::iterator web)
+	{
+		if (web->resolving)
+		{
+			web->removed = true;
+			return;
+		}
+		m_web_seeds.erase(web);
+	}
+
 	void torrent::connect_to_url_seed(std::list<web_seed_entry>::iterator web)
 	{
 		TORRENT_ASSERT(m_ses.is_network_thread());
@@ -3875,7 +3885,7 @@ namespace libtorrent
 					url_seed_alert(get_handle(), web->url, ec));
 			}
 			// never try it again
-			m_web_seeds.erase(web);
+			remove_web_seed(web);
 			return;
 		}
 		
@@ -3891,7 +3901,7 @@ namespace libtorrent
 					url_seed_alert(get_handle(), web->url, errors::unsupported_url_protocol));
 			}
 			// never try it again
-			m_web_seeds.erase(web);
+			remove_web_seed(web);
 			return;
 		}
 
@@ -3903,7 +3913,7 @@ namespace libtorrent
 					url_seed_alert(get_handle(), web->url, errors::invalid_hostname));
 			}
 			// never try it again
-			m_web_seeds.erase(web);
+			remove_web_seed(web);
 			return;
 		}
 
@@ -3915,7 +3925,7 @@ namespace libtorrent
 					url_seed_alert(get_handle(), web->url, errors::invalid_port));
 			}
 			// never try it again
-			m_web_seeds.erase(web);
+			remove_web_seed(web);
 			return;
 		}
 
@@ -3927,7 +3937,7 @@ namespace libtorrent
 				url_seed_alert(get_handle(), web->url, errors::port_blocked));
 			}
 			// never try it again
-			m_web_seeds.erase(web);
+			remove_web_seed(web);
 			return;
 		}
 
@@ -3987,7 +3997,7 @@ namespace libtorrent
 
 			// the name lookup failed for the http host. Don't try
 			// this host again
-			m_web_seeds.erase(web);
+			remove_web_seed(web);
 			return;
 		}
 
@@ -4009,7 +4019,7 @@ namespace libtorrent
 				m_ses.m_alerts.post_alert(
 					url_seed_alert(get_handle(), web->url, ec));
 			}
-			m_web_seeds.erase(web);
+			remove_web_seed(web);
 			return;
 		}
 
@@ -4039,6 +4049,14 @@ namespace libtorrent
 		(*m_ses.m_logger) << time_now_string() << " completed resolve: " << web->url << "\n";
 #endif
 		web->resolving = false;
+		if (web->removed)
+		{
+#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
+			(*m_ses.m_logger) << time_now_string() << " removed web seed\n";
+#endif
+			remove_web_seed(web);
+			return;
+		}
 
 		if (m_abort) return;