Remove Xml_node::attribute accessors

This patch removes the two 'Xml_node::attribute' accessors along with
the 'Nonexistent_attribute' exception.

Issue #5245
Fixes #5246

repos/base-nova/src/test/nova/main.cc

@@ -649,14 +649,15 @@ Main::Main(Env &env) : env(env)
 {
 	log("testing base-nova platform");
 
-	try {
+	{
 		Attached_rom_dataspace config(env, "config");
-		config.xml().attribute("check_pat").value(check_pat);
+		if (!config.xml().has_attribute("check_pat")) {
-	} catch (...) {
 			Genode::error("no check_pat attribute found");
 			env.parent().exit(-__LINE__);
 			return;
 		}
+		check_pat = config.xml().attribute_value("check_pat", check_pat);
+	}
 
 	Thread * myself = Thread::myself();
 	if (!myself) {

repos/base/include/util/xml_node.h

@@ -93,7 +93,7 @@ class Genode::Xml_attribute
 		explicit Xml_attribute(Token t) : _tokens(t)
 		{
 			if (_tokens.name.type() != Token::IDENT)
-				throw Nonexistent_attribute();
+				throw Invalid_syntax();
 
 			if (!_tokens.valid())
 				throw Invalid_syntax();
@@ -111,7 +111,6 @@ class Genode::Xml_attribute
 		 *********************/
 
 		class Invalid_syntax : public Exception { };
-		class Nonexistent_attribute : public Exception { };
 
 
 		typedef String<64> Name;
@@ -121,7 +120,7 @@ class Genode::Xml_attribute
 		/**
 		 * Return true if attribute has specified type
 		 */
-		bool has_type(char const *type) {
+		bool has_type(char const *type) const {
 			return strlen(type) == _tokens.name.len() &&
 			       strcmp(type, _tokens.name.start(), _tokens.name.len()) == 0; }
 
@@ -221,8 +220,6 @@ class Genode::Xml_node
 		 ** Exception types **
 		 *********************/
 
-		typedef Genode::Exception                    Exception;
-		typedef Xml_attribute::Nonexistent_attribute Nonexistent_attribute;
 		typedef Xml_attribute::Invalid_syntax Invalid_syntax;
 
 		class Nonexistent_sub_node  : public Exception { };
@@ -885,41 +882,6 @@ class Genode::Xml_node
 			for_each_sub_node(nullptr, fn);
 		}
 
-		/**
-		 * Return Nth attribute of XML node
-		 *
-		 * \param idx                    attribute index,
-		 *                               first attribute has index 0
-		 * \throw Nonexistent_attribute  no such attribute exists
-		 * \return                       XML attribute
-		 */
-		Xml_attribute attribute(unsigned idx) const
-		{
-			Xml_attribute attr = _tags.start.attribute();
-			for (unsigned i = 0; i < idx; i++)
-				attr = Xml_attribute(attr._next_token());
-
-			return attr;
-		}
-
-		/**
-		 * Return attribute of specified type
-		 *
-		 * \param type                   name of attribute type
-		 * \throw Nonexistent_attribute  no such attribute exists
-		 * \return                       XML attribute
-		 */
-		Xml_attribute attribute(char const *type) const
-		{
-			for (Xml_attribute attr = _tags.start.attribute(); ;) {
-				if (attr.has_type(type))
-					return attr;
-
-				attr = Xml_attribute(attr._next_token());
-			}
-			throw Nonexistent_attribute();
-		}
-
 		/**
 		 * Read attribute value from XML node
 		 *

repos/base/src/test/xml_node/test.cc

@@ -243,11 +243,8 @@ struct Formatted_xml_attribute
  */
 static void print_xml_attr_info(Output &output, Xml_node node, int indent = 0)
 {
-	try {
+	node.for_each_attribute([&] (Xml_attribute const &a) {
-		for (Xml_node::Attribute a = node.attribute(0U); ; a = a.next())
+		print(output, Formatted_xml_attribute(a, indent), "\n"); });
-			print(output, Formatted_xml_attribute(a, indent), "\n");
-
-	} catch (Xml_node::Nonexistent_attribute) { }
 }
 
 

repos/dde_linux/src/driver/usb_net/main.cc

@@ -90,15 +90,12 @@ struct Main
 		usb_config = config_rom.xml().attribute_value("configuration", 0ul);
 
 		/* retrieve possible MAC */
-		try {
+		use_mac_address = config_rom.xml().has_attribute("mac");
-			Nic::Mac_address mac;
+		if (use_mac_address) {
-			Xml_node::Attribute mac_node = config_rom.xml().attribute("mac");
+			auto const mac = config_rom.xml().attribute_value("mac", Nic::Mac_address{});
-			mac_node.value(mac);
 			mac.copy(mac_address);
 			use_mac_address = true;
 			log("Trying to use configured mac: ", mac);
-		} catch (...) {
-			use_mac_address = false;
 		}
 	}
 };

repos/dde_linux/src/lib/vfs/lxip/vfs.cc

@@ -1619,8 +1619,6 @@ class Vfs::Lxip_file_system : public Vfs::File_system,
 				return;
 			}
 
-			try {
-
 			Addr ip_addr    = config.attribute_value("ip_addr", Addr());
 			Addr netmask    = config.attribute_value("netmask", Addr());
 			Addr gateway    = config.attribute_value("gateway", Addr());
@@ -1628,10 +1626,10 @@ class Vfs::Lxip_file_system : public Vfs::File_system,
 
 			if (ip_addr == "") {
 				warning("Missing \"ip_addr\" attribute. Ignoring network interface config.");
-					throw Genode::Xml_node::Nonexistent_attribute();
+				return;
 			} else if (netmask == "") {
 				warning("Missing \"netmask\" attribute. Ignoring network interface config.");
-					throw Genode::Xml_node::Nonexistent_attribute();
+				return;
 			}
 
 			log("static network interface: ip_addr=",ip_addr," netmask=",netmask);
@@ -1645,7 +1643,6 @@ class Vfs::Lxip_file_system : public Vfs::File_system,
 			};
 
 			genode_socket_config_address(&address_config);
-			} catch (...) { }
 		}
 
 

repos/gems/include/gems/xml_anchor.h

@@ -54,10 +54,10 @@ class Anchor
 			if (!node.has_attribute(attr))
 				return;
 
-			Xml_node::Attribute const anchor = node.attribute(attr);
+			auto const v = node.attribute_value(attr, Genode::String<16>());
 
 			for (Value const *value = _values; value->value; value++) {
-				if (anchor.has_value(value->value)) {
+				if (v == value->value) {
 					horizontal = value->horizontal;
 					vertical   = value->vertical;
 					return;

repos/gems/src/app/backdrop/main.cc

@@ -169,6 +169,8 @@ static Surface_base::Area calc_scaled_size(Xml_node operation,
 	if (!operation.has_attribute(attr))
 		return image_size;
 
+	auto const value = operation.attribute_value("scale", String<16>());
+
 	/* prevent division by zero, below */
 	if (image_size.count() == 0)
 		return image_size;
@@ -176,14 +178,13 @@ static Surface_base::Area calc_scaled_size(Xml_node operation,
 	/*
 	 * Determine scale ratio (in 16.16 fixpoint format)
 	 */
-	unsigned const ratio =
+	unsigned const ratio = (value == "fit")
-		operation.attribute(attr).has_value("fit") ?
+	                     ? min((mode_size.w << 16) / image_size.w,
-			min((mode_size.w << 16) / image_size.w,
+	                           (mode_size.h << 16) / image_size.h)
-			    (mode_size.h << 16) / image_size.h) :
+	                     : (value == "zoom")
-		operation.attribute(attr).has_value("zoom") ?
+	                     ? max((mode_size.w << 16) / image_size.w,
-			max((mode_size.w << 16) / image_size.w,
+	                           (mode_size.h << 16) / image_size.h)
-			    (mode_size.h << 16) / image_size.h) :
+	                     : 1 << 16;
-		1 << 16;
 
 	/*
 	 * We add 0.5 (1 << 15) to round instead of truncating the fractional

repos/gems/src/app/decorator/config.h

@@ -219,11 +219,9 @@ class Decorator::Config
 				if (node.has_type("maximizer")) type = Window_control::TYPE_MAXIMIZER;
 				if (node.has_type("minimizer")) type = Window_control::TYPE_MINIMIZER;
 
-				if (node.has_attribute("align")) {
+				auto const align_attr = node.attribute_value("align", Genode::String<16>());
-					Genode::Xml_attribute attr = node.attribute("align");
+				if (align_attr == "left")  align = Window_control::ALIGN_LEFT;
-					if (attr.has_value("left"))  align = Window_control::ALIGN_LEFT;
+				if (align_attr == "right") align = Window_control::ALIGN_RIGHT;
-					if (attr.has_value("right")) align = Window_control::ALIGN_RIGHT;
-				}
 
 				_window_controls[_num_window_controls++] =
 					new (_alloc) Window_control(type, align);

repos/gems/src/app/depot_autopilot/child.cc

@@ -1121,19 +1121,15 @@ Log_event::~Log_event()
 
 Log_prefix Log_event::_init_log_prefix(Xml_node const &xml)
 {
-	if (!xml.has_attribute("log_prefix"))
+	auto const log_prefix = xml.attribute_value("log_prefix", Log_prefix { });
+	if (log_prefix.length() <= 1)
 		return Log_prefix { };
 
-	char buf[Log_prefix::size()];
+	char buf[Log_prefix::size()] { }; /* mutable buffer for filter operation */
-	size_t buf_str_size { 0 };
+	memcpy(buf, log_prefix.string(), log_prefix.length());
-	xml.attribute("log_prefix").with_raw_value([&] (char const *src_ptr, size_t src_size) {
+	size_t const filtered_len = pattern_filters.apply_to(buf, log_prefix.length());
 
-		size_t const cpy_size = min(src_size, sizeof(buf) - 1);
+	return Log_prefix { Cstring { buf, filtered_len } };
-		memcpy(buf, src_ptr, cpy_size);
-		buf[cpy_size] = 0;
-		buf_str_size = pattern_filters.apply_to(buf, cpy_size + 1);
-	});
-	return Cstring { buf, buf_str_size };
 }
 
 

repos/gems/src/app/mixer_gui_qt/main_window.cpp

@@ -442,18 +442,16 @@ Main_window::Main_window(Genode::Env &env)
 
 	using namespace Genode;
 
-	Attached_rom_dataspace config(env, "config");
+	Attached_rom_dataspace const config(env, "config");
-	try {
+	_verbose = config.xml().attribute_value("verbose", false);
-		Xml_node config_node = config.xml();
+	config.xml().with_sub_node("default",
-		_verbose = config_node.attribute("verbose").has_value("yes");
+		[&] (Xml_node const &node) {
-	} catch (...) { _verbose = false; }
+			_default_out_volume = node.attribute_value("out_volume", 0L);
-
+			_default_volume     = node.attribute_value("volume", 0L);
-	try {
+			_default_muted      = node.attribute_value("muted", 1L);
-		Xml_node node = config.xml().sub_node("default");
+		},
-		_default_out_volume = node.attribute_value<long>("out_volume", 0);
+		[&] { warning("no <default> node found, fallback is 'muted=1'"); }
-		_default_volume     = node.attribute_value<long>("volume", 0);
+	);
-		_default_muted      = node.attribute_value<long>("muted", 1);
-	} catch (...) { Genode::warning("no <default> node found, fallback is 'muted=1'"); }
 }
 
 

repos/gems/src/app/nano3d/main.cc

@@ -86,17 +86,15 @@ class Scene : public Nano3d::Scene<PT>
 		{
 			_config.update();
 
-			try {
+			using Value = Genode::String<32>;
-				_shape = SHAPE_DODECAHEDRON;
+
-				if (_config.xml().attribute("shape").has_value("cube"))
+			_shape = SHAPE_DODECAHEDRON;
-					_shape = SHAPE_CUBE;
+			if (_config.xml().attribute_value("shape", Value()) == "cube")
-			} catch (...) { }
+				_shape = SHAPE_CUBE;
 
-			try {
 			_painter = PAINTER_TEXTURED;
-				if (_config.xml().attribute("painter").has_value("shaded"))
+			if (_config.xml().attribute_value("painter", Value()) == "shaded")
 				_painter = PAINTER_SHADED;
-			} catch (...) { }
 		}
 
 		Genode::Signal_handler<Scene> _config_handler;

repos/gems/src/app/sculpt_manager/model/wifi_connection.h

@@ -33,30 +33,32 @@ struct Sculpt::Wifi_connection
 	/**
 	 * Create 'Wifi_connection' object from 'state' report
 	 */
-	static Wifi_connection from_xml(Xml_node node)
+	static Wifi_connection from_xml(Xml_node const &node)
 	{
-		bool const connected =
+		Wifi_connection result { };
-			node.has_sub_node("accesspoint") &&
+
-			node.sub_node("accesspoint").attribute("state").has_value("connected");
+		bool connected   = false;
-		bool const connecting =
+		bool connecting  = false;
-			node.has_sub_node("accesspoint") &&
+		bool auth_failed = false;
-			node.sub_node("accesspoint").attribute("state").has_value("connecting");
+
-		bool const auth_failed =
+		node.with_optional_sub_node("accesspoint", [&] (Xml_node const &ap) {
-			node.has_sub_node("accesspoint") &&
+			connected   = (ap.attribute_value("state", String<32>()) == "connected");
-			node.sub_node("accesspoint").attribute_value("auth_failure", false);
+			connecting  = (ap.attribute_value("state", String<32>()) == "connecting");
+			auth_failed =  ap.attribute_value("auth_failed", false);
 
 			if (!connected && !connecting)
-			return { .state = DISCONNECTED,
+				result = { .state = DISCONNECTED,
 				           .auth_failed = auth_failed,
 				           .bssid = Access_point::Bssid{},
 				           .ssid  = Access_point::Bssid{} };
 
-		Xml_node const ap = node.sub_node("accesspoint");
+			else
-
+				result = { .state = connected ? CONNECTED : CONNECTING,
-		return { .state = connected ? CONNECTED : CONNECTING,
 				           .auth_failed = false,
 				           .bssid = ap.attribute_value("bssid", Access_point::Bssid()),
 				           .ssid  = ap.attribute_value("ssid",  Access_point::Ssid()) };
+		});
+		return result;
 	}
 
 	static Wifi_connection disconnected_wifi_connection()

repos/gems/src/app/tresor_tester/main.cc

@@ -216,15 +216,16 @@ struct Tresor_tester::Request_node : Noncopyable
 	Operation read_op_attr(Xml_node const &node)
 	{
 		ASSERT(node.has_attribute("op"));
-		if (node.attribute("op").has_value("read")) return Operation::READ;
+		auto const value = node.attribute_value("op", String<32>());
-		if (node.attribute("op").has_value("write")) return Operation::WRITE;
+		if (value == "read")             return Operation::READ;
-		if (node.attribute("op").has_value("sync")) return Operation::SYNC;
+		if (value == "write")            return Operation::WRITE;
-		if (node.attribute("op").has_value("create_snapshot")) return Operation::CREATE_SNAPSHOT;
+		if (value == "sync")             return Operation::SYNC;
-		if (node.attribute("op").has_value("discard_snapshot")) return Operation::DISCARD_SNAPSHOT;
+		if (value == "create_snapshot")  return Operation::CREATE_SNAPSHOT;
-		if (node.attribute("op").has_value("extend_ft")) return Operation::EXTEND_FREE_TREE;
+		if (value == "discard_snapshot") return Operation::DISCARD_SNAPSHOT;
-		if (node.attribute("op").has_value("extend_vbd")) return Operation::EXTEND_VBD;
+		if (value == "extend_ft")        return Operation::EXTEND_FREE_TREE;
-		if (node.attribute("op").has_value("rekey")) return Operation::REKEY;
+		if (value == "extend_vbd")       return Operation::EXTEND_VBD;
-		if (node.attribute("op").has_value("deinitialize")) return Operation::DEINITIALIZE;
+		if (value == "rekey")            return Operation::REKEY;
+		if (value == "deinitialize")     return Operation::DEINITIALIZE;
 		ASSERT_NEVER_REACHED;
 	}
 

repos/gems/src/server/gui_fader/main.cc

@@ -500,11 +500,9 @@ void Gui_fader::Main::handle_config_update()
 {
 	config.update();
 
-	Genode::Xml_node config_xml = config.xml();
+	Genode::Xml_node const config_xml = config.xml();
 
-	unsigned new_alpha = alpha;
+	unsigned const new_alpha = config_xml.attribute_value("alpha", 255u);
-	if (config_xml.has_attribute("alpha"))
-		config_xml.attribute("alpha").value(new_alpha);
 
 	fade_in_steps         = config_xml.attribute_value("fade_in_steps",  20U);
 	fade_out_steps        = config_xml.attribute_value("fade_out_steps", 50U);

repos/gems/src/server/wm/gui.h

@@ -1191,18 +1191,11 @@ class Wm::Gui::Root : public Genode::Rpc_object<Genode::Typed_root<Gui::Session>
 				Genode::Xml_node policy =
 					Genode::Session_policy(session_label, _config.xml());
 
-				char const *role_attr = "role";
+				auto const value = policy.attribute_value("role", String<16>());
-				if (policy.has_attribute(role_attr)) {
 
-					if (policy.attribute(role_attr).has_value("layouter"))
+				if (value == "layouter")  role = ROLE_LAYOUTER;
-						role = ROLE_LAYOUTER;
+				if (value == "decorator") role = ROLE_DECORATOR;
-
+				if (value == "direct")    role = ROLE_DIRECT;
-					if (policy.attribute(role_attr).has_value("decorator"))
-						role = ROLE_DECORATOR;
-
-					if (policy.attribute(role_attr).has_value("direct"))
-						role = ROLE_DIRECT;
-				}
 			}
 			catch (...) { }
 

repos/gems/src/server/wm/main.cc

@@ -68,25 +68,22 @@ struct Wm::Main : Pointer::Tracker
 
 	void handle_focus_update()
 	{
-		try {
 		focus_rom.update();
-			if (!focus_rom.valid())
-				return;
 
-			unsigned win_id = 0;
+		focus_rom.xml().with_optional_sub_node("window", [&] (Xml_node const &window) {
 
-			Xml_node(focus_rom.local_addr<char>()).sub_node("window")
+			unsigned const win_id = window.attribute_value("id", 0u);
-				.attribute("id").value(win_id);
 
 			if (win_id) {
+				try {
 					Gui::Session_capability session_cap =
 						gui_root.lookup_gui_session(win_id);
 
 					focus_gui_session.focus(session_cap);
-			}
-
 				} catch (...) { }
 			}
+		});
+	}
 
 	Genode::Signal_handler<Main> focus_handler = {
 		env.ep(), *this, &Main::handle_focus_update };

repos/libports/include/libc/args.h

@@ -26,6 +26,13 @@ static void populate_args_and_env(Libc::Env &env, int &argc, char **&argv, char
 	using Genode::Xml_node;
 	using Genode::Xml_attribute;
 
+	auto with_raw_attr = [] (Xml_node const &node, auto const attr_name, auto const &fn)
+	{
+		node.for_each_attribute([&] (Xml_attribute const &attr) {
+			if (attr.has_type(attr_name))
+				attr.with_raw_value(fn); });
+	};
+
 	env.config([&] (Xml_node const &node) {
 
 		int envc = 0;
@@ -62,9 +69,7 @@ static void populate_args_and_env(Libc::Env &env, int &argc, char **&argv, char
 
 			/* insert an argument */
 			if (node.has_type("arg")) {
-
+				with_raw_attr(node, "value", [&] (char const *start, size_t length) {
-				Xml_attribute attr = node.attribute("value");
-				attr.with_raw_value([&] (char const *start, size_t length) {
 
 					size_t const size = length + 1; /* for null termination */
 
@@ -72,7 +77,6 @@ static void populate_args_and_env(Libc::Env &env, int &argc, char **&argv, char
 
 					Genode::copy_cstring(argv[arg_i], start, size);
 				});
-
 				++arg_i;
 			}
 			else
@@ -87,17 +91,15 @@ static void populate_args_and_env(Libc::Env &env, int &argc, char **&argv, char
 				check_attr(node, "key");
 				check_attr(node, "value");
 
-				Xml_attribute const key   = node.attribute("key");
-				Xml_attribute const value = node.attribute("value");
-
 				using namespace Genode;
 
 				/*
 				 * An environment variable has the form <key>=<value>, followed
 				 * by a terminating zero.
 				 */
-				size_t const var_size = key  .value_size() + 1
+				size_t var_size = 1 + 1;
-				                      + value.value_size() + 1;
+				with_raw_attr(node, "key",   [&] (char const *, size_t l) { var_size += l; });
+				with_raw_attr(node, "value", [&] (char const *, size_t l) { var_size += l; });
 
 				envp[env_i] = (char*)malloc(var_size);
 
@@ -116,19 +118,18 @@ static void populate_args_and_env(Libc::Env &env, int &argc, char **&argv, char
 					pos += len;
 				};
 
-				key.with_raw_value([&] (char const *start, size_t length) {
+				with_raw_attr(node, "key", [&] (char const *start, size_t length) {
 					append(start, length); });
 
 				append("=", 1);
 
-				value.with_raw_value([&] (char const *start, size_t length) {
+				with_raw_attr(node, "value", [&] (char const *start, size_t length) {
 					append(start, length); });
 
 				++env_i;
 
 			}
 			catch (Xml_node::Nonexistent_sub_node)  { }
-			catch (Xml_node::Nonexistent_attribute) { }
 		});
 
 		/* argv and envp are both NULL terminated */

repos/libports/src/lib/gcov/libc/libc.cc

@@ -293,7 +293,6 @@ extern "C" FILE *fopen(const char *path, const char *mode)
 		gcov_env->fs.close(annotate_file_handle);
 	}
 	catch (Xml_node::Nonexistent_sub_node) { }
-	catch (Xml_attribute::Nonexistent_attribute) { }
 
 	return &gcov_env->file;
 }

repos/libports/src/test/libc_vfs/main.cc

@@ -41,30 +41,21 @@ struct Test_failed : Genode::Exception { };
 	}
 
 
-static void test_write_read(Genode::Xml_node node)
+static void test_write_read(Genode::Xml_node const &config)
 {
-	size_t rounds      = 4;
+	size_t rounds      = 4u;
 	size_t size        = 4*1024*1024;
 	size_t buffer_size = 32*1024;
 
-	try {
+	config.with_optional_sub_node("write-read", [&] (Genode::Xml_node const &node) {
-		Genode::Xml_node config = node.sub_node("write-read");
+		using Num_bytes = Genode::Number_of_bytes;
+		rounds      = node.attribute_value("rounds",      rounds);
+		size        = node.attribute_value("size",        Num_bytes{size});
+		buffer_size = node.attribute_value("buffer_size", Num_bytes{buffer_size});
+	});
 
-		rounds = config.attribute_value("rounds", rounds);
+	void * const buf = malloc(buffer_size);
-
+	char const * const file_name = "write_read.tst";
-		Genode::Number_of_bytes n { };
-		try {
-			config.attribute("size").value(n);
-			size = n;
-		} catch (...) { }
-		try {
-			config.attribute("buffer_size").value(n);
-			buffer_size = n;
-		} catch (...) { }
-	} catch (...) { }
-
-	void *buf = malloc(buffer_size);
-	char const *file_name = "write_read.tst";
 
 	printf("write-read test: %zu rounds of %zu MiB (buffer size %zu)\n",
 	       rounds, size/(1024*1024), buffer_size);
@@ -112,9 +103,8 @@ static void test(Genode::Xml_node node)
 
 	unsigned int iterations = 1;
 
-	try {
+	node.with_optional_sub_node("iterations", [&] (Genode::Xml_node const &iter) {
-		node.sub_node("iterations").attribute("value").value(iterations);
+		iterations = iter.attribute_value("value", iterations); });
-	} catch(...) { }
 
 	for (unsigned int i = 0; i < iterations; i++) {
 

repos/libports/src/test/lwip/udp/server/main.cc

@@ -30,8 +30,6 @@ struct Send_failed       : Genode::Exception { };
 struct Receive_failed    : Genode::Exception { };
 struct Bind_failed       : Genode::Exception { };
 
-struct Read_port_attr_failed : Genode::Exception { };
-
 
 static void test(Libc::Env & env)
 {
@@ -42,12 +40,9 @@ static void test(Libc::Env & env)
 	}
 	/* read server port */
 	unsigned port = 0;
-	env.config([&] (Xml_node config_node) {
+	env.config([&] (Xml_node const &config_node) {
-		try { config_node.attribute("port").value(port); }
+		port = config_node.attribute_value("port", 0u); });
-		catch (...) {
+
-			throw Read_port_attr_failed();
-		}
-	});
 	/* create server socket address */
 	struct sockaddr_in in_addr;
 	in_addr.sin_family = AF_INET;

repos/os/include/vfs/dir_file_system.h

@@ -394,18 +394,7 @@ class Vfs::Dir_file_system : public File_system
 					continue;
 				}
 
-				Genode::error("failed to create <", sub_node.type(), "> VFS node");
+				Genode::error("failed to create VFS node: ", sub_node);
-				try {
-					for (unsigned i = 0; i < 16; ++i) {
-
-						Xml_attribute const attr = sub_node.attribute(i);
-
-						String<64> value { };
-						attr.value(value);
-
-						Genode::error("\t", attr.name(), "=\"", value, "\"");
-					}
-				} catch (Xml_node::Nonexistent_attribute) { }
 			}
 		}
 

repos/os/src/app/sequence/main.cc

@@ -40,12 +40,10 @@ struct Sequence::Child : Genode::Child_policy
 
 	Binary_name _start_binary()
 	{
-		Binary_name name;
+		Binary_name name = _name;
-		try {
+		_start_node.with_optional_sub_node("binary", [&] (Xml_node const &binary) {
-			_start_node.sub_node("binary").attribute("name").value(name);
+			name = binary.attribute_value("name", _name); });
-			return name != "" ? name : _name;
+		return name;
-		}
-		catch (...) { return _name; }
 	}
 
 	Binary_name const _binary_name = _start_binary();

repos/os/src/server/dynamic_rom/main.cc

@@ -205,9 +205,9 @@ class Dynamic_rom::Root : public Genode::Root_component<Session_component>
 		{
 			/* lookup ROM module in config */
 			for (unsigned i = 0; i < _config_node.num_sub_nodes(); i++) {
-				Xml_node node = _config_node.sub_node(i);
+				Xml_node const node = _config_node.sub_node(i);
-				if (node.has_attribute("name")
+
-				 && node.attribute("name").has_value(name.string()))
+				if (node.attribute_value("name", Genode::String<64>()) == name)
 					return node;
 			}
 			throw Nonexistent_rom_module();

repos/os/src/server/nic_router/xml_node.h

@@ -25,14 +25,13 @@ namespace Genode {
 	                           char     const *name,
 	                           uint64_t const  default_sec);
 
-	template <typename FUNC>
+	void xml_node_with_attribute(Xml_node const &node,
-	void xml_node_with_attribute(Xml_node const  node,
 	                             char     const *name,
-	                             FUNC        &&  func)
+	                             auto     const &fn)
 	{
-		if (node.has_attribute(name)) {
+		node.for_each_attribute([&] (Xml_attribute const &attr) {
-			func(node.attribute(name));
+			if (attr.has_type(name))
-		}
+				fn(attr); });
 	}
 }
 

repos/os/src/server/nitpicker/global_keys.cc

@@ -63,7 +63,7 @@ void Global_keys::apply_config(Xml_node config, Session_list &session_list)
 
 			/* assign policy to matching client session */
 			for (Gui_session *s = session_list.first(); s; s = s->next())
-				if (node.attribute("label").has_value(s->label().string()))
+				if (node.attribute_value("label", String<128>()) == s->label().string())
 					policy->client(s);
 		}
 

repos/os/src/server/part_block/main.cc

@@ -327,16 +327,17 @@ class Block::Main : Rpc_object<Typed_root<Session>>,
 				/* sessions are not writeable by default */
 				writeable = policy.attribute_value("writeable", false);
 
-			} catch (Xml_node::Nonexistent_attribute) {
-				error("policy does not define partition number for for '",
-				      label, "'");
-				throw Service_denied();
 			} catch (Session_policy::No_policy_defined) {
 				error("rejecting session request, no matching policy for '",
 				      label, "'");
 				throw Service_denied();
 			}
 
+			if (num == -1) {
+				error("policy does not define partition number for for '", label, "'");
+				throw Service_denied();
+			}
+
 			if (!_partition_table.partition_valid(num)) {
 				error("Partition ", num, " unavailable for '", label, "'");
 				throw Service_denied();

repos/os/src/test/trace/main.cc

@@ -195,7 +195,8 @@ struct Test_tracing
 
 	Constructible<Trace_buffer_monitor> test_monitor { };
 
-	typedef Genode::String<64> String;
+	using String = Genode::String<64>;
+
 	String policy_label  { };
 	String policy_module { };
 	String policy_thread { };
@@ -210,12 +211,13 @@ struct Test_tracing
 
 		log("test Tracing");
 
-		try {
+		config.xml().with_optional_sub_node("trace_policy", [&] (Xml_node const &policy) {
-			Xml_node policy = config.xml().sub_node("trace_policy");
+			policy_label  = policy.attribute_value("label",  String());
-			policy.attribute("label").value(policy_label);
+			policy_module = policy.attribute_value("module", String());
-			policy.attribute("module").value(policy_module);
+			policy_thread = policy.attribute_value("thread", String());
-			policy.attribute("thread").value(policy_thread);
+		});
 
+		try {
 			Rom_connection policy_rom(env, policy_module.string());
 			policy_module_rom_ds = policy_rom.dataspace();