add proper error handling to peer connections and session (#1149)

add proper error handling to peer connections and session. i.e. catch exceptions in asio handlers and catch by const reference

configure.ac

@@ -99,7 +99,7 @@ AX_PTHREAD()
 LIBS="$PTHREAD_LIBS $LIBS"
 CFLAGS="$PTHREAD_CFLAGS $CFLAGS"
 CC="$PTHREAD_CC"
-CXXFLAGS="$CXXFLAGS -ftemplate-depth=128"
+CXXFLAGS="$CXXFLAGS -ftemplate-depth=128 -Wno-format-zero-length"
 
 AS_ECHO "Checking for visibility support:"
 AC_CACHE_CHECK([for __attribute__((visibility("hidden")))],
@@ -166,9 +166,9 @@ AC_ARG_ENABLE(
   [logging],
   [AS_HELP_STRING(
     [--enable-logging],
-    [enable logging to disk (use value "verbose" to enable verbose peer wire logging or "errors" limit logging to errors ) [default=no]])],
+    [enable logging support, enabled by alert mask [default=yes]])],
   [[ARG_ENABLE_LOGGING=$enableval]],
-  [[ARG_ENABLE_LOGGING=no]]
+  [[ARG_ENABLE_LOGGING=yes]]
 )
 
 AC_ARG_ENABLE(
@@ -190,7 +190,7 @@ AC_ARG_ENABLE(
   [dht],
   [AS_HELP_STRING(
     [--enable-dht],
-    [enable dht support (use value "logging" to add extra logging) [default=yes]])],
+    [enable dht support [default=yes]])],
   [[ARG_ENABLE_DHT=$enableval]],
   [[ARG_ENABLE_DHT=yes]]
 )

docs/features.rst

@@ -305,7 +305,7 @@ code to implement a simple bittorrent client::
 		std::cin >> a;
 		return 0;
 	}
-	catch (std::exception& e)
+	catch (std::exception const& e)
 	{
 		std::cerr << ec.what() << std::endl;
 		return 1;

examples/client_test.cpp

@@ -1802,7 +1802,7 @@ int main(int argc, char* argv[])
 		for (std::vector<alert*>::iterator i = alerts.begin()
 			, end(alerts.end()); i != end; ++i)
 		{
-			TORRENT_TRY
+			try
 			{
 				if (!::handle_alert(ses, *i, files, non_files))
 				{
@@ -1812,7 +1812,7 @@ int main(int argc, char* argv[])
 					events.push_back(event_string);
 					if (events.size() >= 20) events.pop_front();
 				}
-			} TORRENT_CATCH(std::exception& ) {}
+			} catch (std::exception const&) {}
 		}
 		alerts.clear();
 

examples/make_torrent.cpp

@@ -377,7 +377,7 @@ int main(int argc, char* argv[])
 
 #ifndef BOOST_NO_EXCEPTIONS
 	}
-	catch (std::exception& e)
+	catch (std::exception const& e)
 	{
 		std::fprintf(stderr, "%s\n", e.what());
 	}

include/libtorrent/aux_/allocating_handler.hpp

@@ -61,6 +61,12 @@ namespace libtorrent { namespace aux
 		handler_storage(handler_storage const&);
 	};
 
+	struct error_handler_interface
+	{
+		virtual void on_exception(std::exception const&) = 0;
+		virtual void on_error(error_code const&) = 0;
+	};
+
 	// this class is a wrapper for an asio handler object. Its main purpose
 	// is to pass along additional parameters to the asio handler allocator
 	// function, as well as providing a distinct type for the handler
@@ -69,15 +75,38 @@ namespace libtorrent { namespace aux
 	struct allocating_handler
 	{
 		allocating_handler(
-			Handler h, handler_storage<Size>& s)
+			Handler h, handler_storage<Size>& s, error_handler_interface& eh)
 			: handler(std::move(h))
 			, storage(s)
+			, error_handler(eh)
 		{}
 
 		template <class... A>
 		void operator()(A&&... a) const
 		{
+#ifdef BOOST_NO_EXCEPTIONS
 			handler(std::forward<A>(a)...);
+#else
+			try
+			{
+				handler(std::forward<A>(a)...);
+			}
+			catch (system_error const& e)
+			{
+				error_handler.on_error(e.code());
+			}
+			catch (std::exception const& e)
+			{
+				error_handler.on_exception(e);
+			}
+			catch (...)
+			{
+				// this is pretty bad
+				TORRENT_ASSERT(false);
+				std::runtime_error e("unknown exception");
+				error_handler.on_exception(e);
+			}
+#endif
 		}
 
 		friend void* asio_handler_allocate(
@@ -108,6 +137,7 @@ namespace libtorrent { namespace aux
 
 		Handler handler;
 		handler_storage<Size>& storage;
+		error_handler_interface& error_handler;
 	};
 
 }

include/libtorrent/aux_/session_impl.hpp

@@ -194,6 +194,7 @@ namespace libtorrent
 			, boost::noncopyable
 			, uncork_interface
 			, single_threaded
+			, aux::error_handler_interface
 		{
 			// the size of each allocation that is chained in the send buffer
 			enum { send_buffer_size_impl = 128 };
@@ -249,6 +250,9 @@ namespace libtorrent
 			bool m_posting_torrent_updates = false;
 #endif
 
+			void on_exception(std::exception const& e) override;
+			void on_error(error_code const& ec) override;
+
 			void reopen_listen_sockets();
 
 			torrent_peer_allocator_interface* get_peer_allocator() override
@@ -1099,7 +1103,7 @@ namespace libtorrent
 			make_tick_handler(Handler const& handler)
 			{
 				return aux::allocating_handler<Handler, TORRENT_READ_HANDLER_MAX_SIZE>(
-					handler, m_tick_handler_storage);
+					handler, m_tick_handler_storage, *this);
 			}
 
 			// torrents are announced on the local network in a

include/libtorrent/operations.hpp

@@ -96,7 +96,10 @@ namespace libtorrent
 		op_ssl_handshake,
 
 		// a connection failed to satisfy the bind interface setting
-		op_get_interface
+		op_get_interface,
+
+		// the error was unexpected and it is unknown which operation caused it
+		op_unknown,
 	};
 
 }

include/libtorrent/peer_connection.hpp

@@ -259,11 +259,15 @@ namespace libtorrent
 		, public disk_observer
 		, public peer_connection_interface
 		, public std::enable_shared_from_this<peer_connection>
+		, public aux::error_handler_interface
 	{
 	friend class invariant_access;
 	friend class torrent;
 	public:
 
+		void on_exception(std::exception const& e) override;
+		void on_error(error_code const& ec) override;
+
 		virtual connection_type type() const = 0;
 
 		enum channels
@@ -283,14 +287,14 @@ namespace libtorrent
 
 		virtual ~peer_connection();
 
-		void set_peer_info(torrent_peer* pi)
+		void set_peer_info(torrent_peer* pi) override
 		{
 			TORRENT_ASSERT(m_peer_info == 0 || pi == 0 );
 			TORRENT_ASSERT(pi != nullptr || m_disconnect_started);
 			m_peer_info = pi;
 		}
 
-		torrent_peer* peer_info_struct() const
+		torrent_peer* peer_info_struct() const override
 		{ return m_peer_info; }
 
 		// this is called when the peer object is created, in case
@@ -358,7 +362,7 @@ namespace libtorrent
 		std::uint32_t peer_rank() const;
 
 		void fast_reconnect(bool r);
-		bool fast_reconnect() const { return m_fast_reconnect; }
+		bool fast_reconnect() const override { return m_fast_reconnect; }
 
 		// this is called when we receive a new piece
 		// (and it has passed the hash check)
@@ -391,12 +395,12 @@ namespace libtorrent
 		void set_upload_only(bool u);
 		bool upload_only() const { return m_upload_only; }
 
-		void set_holepunch_mode();
+		void set_holepunch_mode() override;
 
 		// will send a keep-alive message to the peer
 		void keep_alive();
 
-		peer_id const& pid() const { return m_peer_id; }
+		peer_id const& pid() const override { return m_peer_id; }
 		void set_pid(peer_id const& peer_id) { m_peer_id = peer_id; }
 		bool has_piece(int i) const;
 
@@ -413,7 +417,7 @@ namespace libtorrent
 		time_duration download_queue_time(int extra_bytes = 0) const;
 
 		bool is_interesting() const { return m_interesting; }
-		bool is_choked() const { return m_choked; }
+		bool is_choked() const override { return m_choked; }
 
 		bool is_peer_interested() const { return m_peer_interested; }
 		bool has_peer_choked() const { return m_peer_choked; }
@@ -423,7 +427,7 @@ namespace libtorrent
 
 		void update_interest();
 
-		virtual void get_peer_info(peer_info& p) const;
+		void get_peer_info(peer_info& p) const override;
 
 		// returns the torrent this connection is a part of
 		// may be zero if the connection is an incoming connection
@@ -432,8 +436,8 @@ namespace libtorrent
 		std::weak_ptr<torrent> associated_torrent() const
 		{ return m_torrent; }
 
-		stat const& statistics() const { return m_statistics; }
-		void add_stat(std::int64_t downloaded, std::int64_t uploaded);
+		stat const& statistics() const override { return m_statistics; }
+		void add_stat(std::int64_t downloaded, std::int64_t uploaded) override;
 		void sent_bytes(int bytes_payload, int bytes_protocol);
 		void received_bytes(int bytes_payload, int bytes_protocol);
 		void trancieve_ip_packet(int bytes, bool ipv6);
@@ -446,8 +450,8 @@ namespace libtorrent
 		void timeout_requests();
 
 		std::shared_ptr<socket_type> get_socket() const { return m_socket; }
-		tcp::endpoint const& remote() const { return m_remote; }
-		tcp::endpoint local_endpoint() const { return m_local; }
+		tcp::endpoint const& remote() const override { return m_remote; }
+		tcp::endpoint local_endpoint() const override { return m_local; }
 
 		bitfield const& get_bitfield() const;
 		std::vector<int> const& allowed_fast();
@@ -457,13 +461,13 @@ namespace libtorrent
 		time_point last_received() const { return m_last_receive; }
 
 		// this will cause this peer_connection to be disconnected.
-		virtual void disconnect(error_code const& ec
-			, operation_t op, int error = 0);
+		void disconnect(error_code const& ec
+			, operation_t op, int error = 0) override;
 
 		// called when a connect attempt fails (not when an
 		// established connection fails)
 		void connect_failed(error_code const& e);
-		bool is_disconnecting() const { return m_disconnecting; }
+		bool is_disconnecting() const override { return m_disconnecting; }
 
 		// this is called when the connection attempt has succeeded
 		// and the peer_connection is supposed to set m_connecting
@@ -487,7 +491,7 @@ namespace libtorrent
 
 		// a connection is local if it was initiated by us.
 		// if it was an incoming connection, it is remote
-		bool is_outgoing() const { return m_outgoing; }
+		bool is_outgoing() const override { return m_outgoing; }
 
 		bool received_listen_port() const { return m_received_listen_port; }
 		void received_listen_port()
@@ -496,7 +500,7 @@ namespace libtorrent
 		bool on_local_network() const;
 		bool ignore_unchoke_slots() const;
 
-		bool failed() const { return m_failed; }
+		bool failed() const override { return m_failed; }
 
 		int desired_queue_size() const
 		{
@@ -525,9 +529,9 @@ namespace libtorrent
 		int est_reciprocation_rate() const { return m_est_reciprocation_rate; }
 
 #ifndef TORRENT_DISABLE_LOGGING
-		bool should_log(peer_log_alert::direction_t direction) const;
+		bool should_log(peer_log_alert::direction_t direction) const override;
 		void peer_log(peer_log_alert::direction_t direction
-			, char const* event, char const* fmt, ...) const TORRENT_FORMAT(4,5);
+			, char const* event, char const* fmt, ...) const override TORRENT_FORMAT(4,5);
 		void peer_log(peer_log_alert::direction_t direction
 			, char const* event) const;
 
@@ -608,7 +612,7 @@ namespace libtorrent
 		void cancel_request(piece_block const& b, bool force = false);
 		void send_block_requests();
 
-		void assign_bandwidth(int channel, int amount);
+		void assign_bandwidth(int channel, int amount) override;
 
 #if TORRENT_USE_INVARIANT_CHECKS
 		void check_invariant() const;
@@ -677,7 +681,7 @@ namespace libtorrent
 
 		// called when the disk write buffer is drained again, and we can
 		// start downloading payload again
-		void on_disk();
+		void on_disk() override;
 
 		int num_reading_bytes() const { return m_reading_bytes; }
 
@@ -1181,7 +1185,7 @@ namespace libtorrent
 			make_read_handler(Handler const& handler)
 		{
 			return aux::allocating_handler<Handler, TORRENT_READ_HANDLER_MAX_SIZE>(
-				handler, m_read_handler_storage
+				handler, m_read_handler_storage, *this
 			);
 		}
 
@@ -1190,7 +1194,7 @@ namespace libtorrent
 			make_write_handler(Handler const& handler)
 		{
 			return aux::allocating_handler<Handler, TORRENT_WRITE_HANDLER_MAX_SIZE>(
-				handler, m_write_handler_storage
+				handler, m_write_handler_storage, *this
 			);
 		}
 

src/alert.cpp

@@ -1455,6 +1455,7 @@ namespace libtorrent {
 			"connect",
 			"ssl_handshake",
 			"get_interface",
+			"unknown",
 		};
 
 		if (op < 0 || op >= int(sizeof(names)/sizeof(names[0])))

src/broadcast_socket.cpp

@@ -81,7 +81,7 @@ namespace libtorrent
 				|| (ip & 0xffff0000) == 0xc0a80000 // 192.168.x.x
 				|| (ip & 0xffff0000) == 0xa9fe0000 // 169.254.x.x
 				|| (ip & 0xff000000) == 0x7f000000); // 127.x.x.x
-		} TORRENT_CATCH(std::exception&) { return false; }
+		} TORRENT_CATCH(std::exception const&) { return false; }
 	}
 
 	bool is_loopback(address const& addr)
@@ -92,7 +92,7 @@ namespace libtorrent
 				return addr.to_v4() == address_v4::loopback();
 			else
 				return addr.to_v6() == address_v6::loopback();
-		} TORRENT_CATCH(std::exception&) { return false; }
+		} TORRENT_CATCH(std::exception const&) { return false; }
 #else
 		return addr.to_v4() == address_v4::loopback();
 #endif
@@ -111,7 +111,7 @@ namespace libtorrent
 #else
 		return addr.to_v4() == address_v4::any();
 #endif
-		} TORRENT_CATCH(std::exception&) { return false; }
+		} TORRENT_CATCH(std::exception const&) { return false; }
 	}
 
 	bool is_teredo(address const& addr)
@@ -122,7 +122,7 @@ namespace libtorrent
 			std::uint8_t teredo_prefix[] = {0x20, 0x01, 0, 0};
 			address_v6::bytes_type b = addr.to_v6().to_bytes();
 			return memcmp(&b[0], teredo_prefix, 4) == 0;
-		} TORRENT_CATCH(std::exception&) { return false; }
+		} TORRENT_CATCH(std::exception const&) { return false; }
 #else
 		TORRENT_UNUSED(addr);
 		return false;
@@ -140,7 +140,7 @@ namespace libtorrent
 			error_code ec;
 			address::from_string("::1", ec);
 			return !ec;
-		} TORRENT_CATCH(std::exception&) { return false; }
+		} TORRENT_CATCH(std::exception const&) { return false; }
 #else
 		io_service ios;
 		tcp::socket test(ios);

src/gzip.cpp

@@ -221,7 +221,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				buffer.resize(destlen);
-			} TORRENT_CATCH(std::exception&) {
+			} TORRENT_CATCH (std::exception const&) {
 				ec = errors::no_memory;
 				return;
 			}

src/lsd.cpp

@@ -281,7 +281,7 @@ void lsd::on_announce(udp::endpoint const& from, char const* buf
 			// we got an announce, pass it on through the callback
 			TORRENT_TRY {
 				m_callback.on_lsd_peer(tcp::endpoint(from.address(), port), ih);
-			} TORRENT_CATCH(std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 	}
 }

src/peer_connection.cpp

@@ -196,6 +196,21 @@ namespace libtorrent
 		return ret;
 	}
 
+	void peer_connection::on_exception(std::exception const& e)
+	{
+		TORRENT_UNUSED(e);
+#ifndef TORRENT_DISABLE_LOGGING
+		peer_log(peer_log_alert::info, "PEER_ERROR" ,"error: %s"
+			, e.what());
+#endif
+		disconnect(error_code(), op_unknown, 2);
+	}
+
+	void peer_connection::on_error(error_code const& ec)
+	{
+		disconnect(ec, op_unknown, 2);
+	}
+
 	void peer_connection::increase_est_reciprocation_rate()
 	{
 		TORRENT_ASSERT(is_single_thread());
@@ -1076,7 +1091,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				e->on_piece_pass(index);
-			} TORRENT_CATCH(std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #else
 		TORRENT_UNUSED(index);
@@ -1096,7 +1111,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				e->on_piece_failed(index);
-			} TORRENT_CATCH(std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #else
 		TORRENT_UNUSED(index);

src/session_impl.cpp

@@ -642,7 +642,7 @@ namespace aux {
 		{
 			TORRENT_TRY {
 				ext->save_state(*eptr);
-			} TORRENT_CATCH(std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #endif
 	}
@@ -752,7 +752,7 @@ namespace aux {
 		{
 			TORRENT_TRY {
 				ext->load_state(*e);
-			} TORRENT_CATCH(std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #endif
 	}
@@ -1795,6 +1795,25 @@ namespace aux {
 		return ret;
 	}
 
+	void session_impl::on_exception(std::exception const& e)
+	{
+		TORRENT_UNUSED(e);
+#ifndef TORRENT_DISABLE_LOGGING
+		session_log("FATAL SESSION ERROR [%s]", e.what());
+#endif
+		this->abort();
+	}
+
+	void session_impl::on_error(error_code const& ec)
+	{
+		TORRENT_UNUSED(ec);
+#ifndef TORRENT_DISABLE_LOGGING
+		session_log("FATAL SESSION ERROR (%s : %d) [%s]"
+			, ec.category().name(), ec.value(), ec.message().c_str());
+#endif
+		this->abort();
+	}
+
 	void session_impl::reopen_listen_sockets()
 	{
 #ifndef TORRENT_DISABLE_LOGGING
@@ -3167,7 +3186,7 @@ namespace aux {
 		{
 			TORRENT_TRY {
 				ext->on_tick();
-			} TORRENT_CATCH(std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #endif
 

src/torrent.cpp

@@ -2059,7 +2059,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				e->on_load();
-			} TORRENT_CATCH (std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #endif
 
@@ -2090,7 +2090,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				e->on_unload();
-			} TORRENT_CATCH (std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 
 		// also remove extensions and re-instantiate them when the torrent is loaded again
@@ -4081,7 +4081,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				ext->on_piece_pass(index);
-			} TORRENT_CATCH (std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #endif
 
@@ -4286,7 +4286,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				ext->on_piece_failed(index);
-			} TORRENT_CATCH (std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #endif
 
@@ -6297,7 +6297,7 @@ namespace libtorrent
 				, num_peers());
 #endif
 		}
-		TORRENT_CATCH (std::exception& e)
+		TORRENT_CATCH (std::exception const& e)
 		{
 			TORRENT_DECLARE_DUMMY(std::exception, e);
 			(void)e;
@@ -6949,7 +6949,7 @@ namespace libtorrent
 					std::shared_ptr<peer_plugin> pp(ext->new_connection(
 						peer_connection_handle(c->self())));
 					if (pp) c->add_extension(pp);
-				} TORRENT_CATCH (std::exception&) {}
+				} TORRENT_CATCH (std::exception const&) {}
 			}
 #endif
 
@@ -6969,7 +6969,7 @@ namespace libtorrent
 
 			if (c->is_disconnecting()) return false;
 		}
-		TORRENT_CATCH (std::exception&)
+		TORRENT_CATCH (std::exception const&)
 		{
 			peer_iterator i = sorted_find(m_connections, c.get());
 			if (i != m_connections.end())
@@ -7262,7 +7262,7 @@ namespace libtorrent
 			peers_erased(st.erased);
 			update_want_peers();
 		}
-		TORRENT_CATCH (std::exception& e)
+		TORRENT_CATCH (std::exception const& e)
 		{
 			TORRENT_DECLARE_DUMMY(std::exception, e);
 			(void)e;
@@ -7892,7 +7892,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				ext->on_files_checked();
-			} TORRENT_CATCH (std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #endif
 
@@ -8874,7 +8874,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				if (ext->on_pause()) return;
-			} TORRENT_CATCH (std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #endif
 
@@ -9112,7 +9112,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				if (ext->on_resume()) return;
-			} TORRENT_CATCH (std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #endif
 
@@ -9349,7 +9349,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				ext->tick();
-			} TORRENT_CATCH (std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 
 		if (m_abort) return;
@@ -9465,7 +9465,7 @@ namespace libtorrent
 			TORRENT_TRY {
 				p->second_tick(tick_interval_ms);
 			}
-			TORRENT_CATCH (std::exception& e)
+			TORRENT_CATCH (std::exception const& e)
 			{
 				TORRENT_DECLARE_DUMMY(std::exception, e);
 				(void)e;
@@ -10919,7 +10919,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				ext->on_state(m_state);
-			} TORRENT_CATCH (std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 #endif
 	}
@@ -10932,7 +10932,7 @@ namespace libtorrent
 		{
 			TORRENT_TRY {
 				ext->on_add_peer(ip, src, flags);
-			} TORRENT_CATCH (std::exception&) {}
+			} TORRENT_CATCH (std::exception const&) {}
 		}
 	}
 #endif

src/upnp.cpp

@@ -323,7 +323,7 @@ void upnp::resend_request(error_code const& ec)
 				, std::ref(d), _5)));
 			d.upnp_connection->get(d.url, seconds(30), 1);
 		}
-		TORRENT_CATCH (std::exception& exc)
+		TORRENT_CATCH (std::exception const& exc)
 		{
 			TORRENT_DECLARE_DUMMY(std::exception, exc);
 			TORRENT_UNUSED(exc);
@@ -671,7 +671,7 @@ void upnp::try_map_upnp(bool timer)
 					, std::ref(d), _5)));
 				d.upnp_connection->get(d.url, seconds(30), 1);
 			}
-			TORRENT_CATCH (std::exception& exc)
+			TORRENT_CATCH (std::exception const& exc)
 			{
 				TORRENT_DECLARE_DUMMY(std::exception, exc);
 				TORRENT_UNUSED(exc);

test/dht_server.cpp

@@ -149,7 +149,7 @@ struct dht_server
 #endif
 				++m_dht_requests;
 			}
-			catch (std::exception& e)
+			catch (std::exception const& e)
 			{
 				std::fprintf(stderr, "failed to decode DHT message: %s\n", e.what());
 			}

test/test.hpp

@@ -130,7 +130,7 @@ extern int EXPORT _g_test_failures;
 		if (!(x)) \
 			TEST_REPORT_AUX("TEST_ERROR: check failed: \"" #x "\"", __FILE__, __LINE__); \
 	} \
-	catch (std::exception& e) \
+	catch (std::exception const& e) \
 	{ \
 		TEST_ERROR("TEST_ERROR: Exception thrown: " #x " :" + std::string(e.what())); \
 	} \
@@ -147,7 +147,7 @@ extern int EXPORT _g_test_failures;
 			TEST_REPORT_AUX(s__.str().c_str(), __FILE__, __LINE__); \
 		} \
 	} \
-	catch (std::exception& e) \
+	catch (std::exception const& e) \
 	{ \
 		TEST_ERROR("TEST_ERROR: Exception thrown: " #x " :" + std::string(e.what())); \
 	} \
@@ -163,7 +163,7 @@ extern int EXPORT _g_test_failures;
 			TEST_REPORT_AUX(s__.str().c_str(), __FILE__, __LINE__); \
 		} \
 	} \
-	catch (std::exception& e) \
+	catch (std::exception const& e) \
 	{ \
 		TEST_ERROR("TEST_ERROR: Exception thrown: " #x " :" + std::string(e.what())); \
 	} \

test/test_torrent_info.cpp

@@ -866,7 +866,7 @@ TORRENT_TEST(empty_file2)
 		auto ti = std::make_shared<torrent_info>("", 0);
 		TEST_ERROR("expected exception thrown");
 	}
-	catch (system_error& e)
+	catch (system_error const& e)
 	{
 		std::printf("Expected error: %s\n", e.code().message().c_str());
 	}