Support transformation between D-Bus errors and exceptions.

doc/tutorial.rst

@@ -332,6 +332,53 @@ See ``help(bus.request_name)`` and ``help(bus.register_object)`` for details.
 
 .. --------------------------------------------------------------------
 
+Error handling
+==============
+
+You can map D-Bus errors to your exception classes for better error handling.
+To handle D-Bus errors, use the ``@map_error`` decorator::
+
+    from pydbus.error import map_error
+
+    @map_error("org.freedesktop.DBus.Error.InvalidArgs")
+    class InvalidArgsException(Exception):
+        pass
+
+    try:
+        ...
+    catch InvalidArgsException as e:
+        print(e)
+
+To register new D-Bus errors, use the ``@register_error`` decorator::
+
+    from pydbus.error import register_error
+
+    @map_error("net.lew21.pydbus.TutorialExample.MyError", MY_DOMAIN, MY_EXCEPTION_CODE)
+    class MyException(Exception):
+        pass
+
+Then you can raise ``MyException`` from the D-Bus method of the remote object::
+
+    def Method():
+        raise MyException("Message")
+
+And catch the same exception on the client side::
+
+    try:
+        proxy.Method()
+    catch MyException as e:
+        print(e)
+
+To handle all unknown D-Bus errors, use the ``@map_by_default`` decorator to specify the default exception::
+
+    from pydbus.error import map_by_default
+
+    @map_by_default
+    class DefaultException(Exception):
+        pass
+
+.. --------------------------------------------------------------------
+
 Data types
 ==========
 

pydbus/error.py

@@ -0,0 +1,97 @@
+from gi.repository import GLib, Gio
+
+
+def register_error(name, domain, code):
+	"""Register and map decorated exception class to a DBus error."""
+	def decorated(cls):
+		error_registration.register_error(cls, name, domain, code)
+		return cls
+
+	return decorated
+
+
+def map_error(error_name):
+	"""Map decorated exception class to a DBus error."""
+	def decorated(cls):
+		error_registration.map_error(cls, error_name)
+		return cls
+
+	return decorated
+
+
+def map_by_default(cls):
+	"""Map decorated exception class to all unknown DBus errors."""
+	error_registration.map_by_default(cls)
+	return cls
+
+
+class ErrorRegistration(object):
+	"""Class for mapping exceptions to DBus errors."""
+
+	_default = None
+	_map = dict()
+	_reversed_map = dict()
+
+	def map_by_default(self, exception_cls):
+		"""Set the exception class as a default."""
+		self._default = exception_cls
+
+	def map_error(self, exception_cls, name):
+		"""Map the exception class to a DBus name."""
+		self._map[name] = exception_cls
+		self._reversed_map[exception_cls] = name
+
+	def register_error(self, exception_cls, name, domain, code):
+		"""Map and register the exception class to a DBus name."""
+		self.map_error(exception_cls, name)
+		return Gio.DBusError.register_error(domain, code, name)
+
+	def is_registered_exception(self, obj):
+		"""Is the exception registered?"""
+		return obj.__class__ in self._reversed_map
+
+	def get_dbus_name(self, obj):
+		"""Get the DBus name of the exception."""
+		return self._reversed_map.get(obj.__class__)
+
+	def get_exception_class(self, name):
+		"""Get the exception class mapped to the DBus name."""
+		return self._map.get(name, self._default)
+
+	def transform_message(self, name, message):
+		"""Transform the message of the exception."""
+		prefix = "{}:{}: ".format("GDBus.Error", name)
+
+		if message.startswith(prefix):
+			return message[len(prefix):]
+
+		return message
+
+	def transform_exception(self, e):
+		"""Transform the remote error to the exception."""
+		if not isinstance(e, GLib.Error):
+			return e
+
+		if not Gio.DBusError.is_remote_error(e):
+			return e
+
+		# Get DBus name of the error.
+		name = Gio.DBusError.get_remote_error(e)
+		# Get the exception class.
+		exception_cls = self.get_exception_class(name)
+
+		# Return the original exception.
+		if not exception_cls:
+			return e
+
+		# Return new exception.
+		message = self.transform_message(name, e.message)
+		exception = exception_cls(message)
+		exception.dbus_name = name
+		exception.dbus_domain = e.domain
+		exception.dbus_code = e.code
+		return exception
+
+
+# Default error registration.
+error_registration = ErrorRegistration()

pydbus/proxy_method.py

@@ -2,6 +2,7 @@
 from .generic import bound_method
 from .identifier import filter_identifier
 from .timeout import timeout_to_glib
+from .error import error_registration
 
 try:
 	from inspect import Signature, Parameter
@@ -69,17 +70,27 @@ def __call__(self, instance, *args, **kwargs):
 				raise TypeError(self.__qualname__ + " got an unexpected keyword argument '{}'".format(kwarg))
 		timeout = kwargs.get("timeout", None)
 
-		ret = instance._bus.con.call_sync(
-			instance._bus_name, instance._path,
-			self._iface_name, self.__name__, GLib.Variant(self._sinargs, args), GLib.VariantType.new(self._soutargs),
-			0, timeout_to_glib(timeout), None).unpack()
-
-		if len(self._outargs) == 0:
-			return None
-		elif len(self._outargs) == 1:
-			return ret[0]
-		else:
-			return ret
+		error = None
+		result = None
+		try:
+			ret = instance._bus.con.call_sync(
+				instance._bus_name, instance._path,
+				self._iface_name, self.__name__, GLib.Variant(self._sinargs, args), GLib.VariantType.new(self._soutargs),
+				0, timeout_to_glib(timeout), None).unpack()
+
+			if len(self._outargs) == 0:
+				result = None
+			elif len(self._outargs) == 1:
+				result = ret[0]
+			else:
+				result = ret
+		except Exception as e:
+			error = error_registration.transform_exception(e)
+
+		if error:
+			raise error
+
+		return result
 
 	def __get__(self, instance, owner):
 		if instance is None:

pydbus/registration.py

@@ -5,6 +5,7 @@
 from .exitable import ExitableWithAliases
 from functools import partial
 from .method_call_context import MethodCallContext
+from .error import error_registration
 import logging
 
 try:
@@ -91,11 +92,16 @@ def call_method(self, connection, sender, object_path, interface_name, method_na
 			logger = logging.getLogger(__name__)
 			logger.exception("Exception while handling %s.%s()", interface_name, method_name)
 
-			#TODO Think of a better way to translate Python exception types to DBus error types.
-			e_type = type(e).__name__
-			if not "." in e_type:
-				e_type = "unknown." + e_type
-			invocation.return_dbus_error(e_type, str(e))
+			if error_registration.is_registered_exception(e):
+				name = error_registration.get_dbus_name(e)
+				invocation.return_dbus_error(name, str(e))
+			else:
+				logger.info("name is not registered")
+				e_type = type(e).__name__
+				if not "." in e_type:
+					e_type = "unknown." + e_type
+
+				invocation.return_dbus_error(e_type, str(e))
 
 	def Get(self, interface_name, property_name):
 		type = self.readable_properties[interface_name + "." + property_name]

tests/error.py

@@ -0,0 +1,67 @@
+from pydbus.error import ErrorRegistration
+
+
+class ExceptionA(Exception):
+	pass
+
+
+class ExceptionB(Exception):
+	pass
+
+
+class ExceptionC(Exception):
+	pass
+
+
+class ExceptionD(Exception):
+	pass
+
+
+class ExceptionE(Exception):
+	pass
+
+
+def test_error_mapping():
+	r = ErrorRegistration()
+	r.map_error(ExceptionA, "net.lew21.pydbus.tests.ErrorA")
+	r.map_error(ExceptionB, "net.lew21.pydbus.tests.ErrorB")
+	r.map_error(ExceptionC, "net.lew21.pydbus.tests.ErrorC")
+
+	assert r.is_registered_exception(ExceptionA("Test"))
+	assert r.is_registered_exception(ExceptionB("Test"))
+	assert r.is_registered_exception(ExceptionC("Test"))
+	assert not r.is_registered_exception(ExceptionD("Test"))
+	assert not r.is_registered_exception(ExceptionE("Test"))
+
+	assert r.get_dbus_name(ExceptionA("Test")) == "net.lew21.pydbus.tests.ErrorA"
+	assert r.get_dbus_name(ExceptionB("Test")) == "net.lew21.pydbus.tests.ErrorB"
+	assert r.get_dbus_name(ExceptionC("Test")) == "net.lew21.pydbus.tests.ErrorC"
+
+	assert r.get_exception_class("net.lew21.pydbus.tests.ErrorA") == ExceptionA
+	assert r.get_exception_class("net.lew21.pydbus.tests.ErrorB") == ExceptionB
+	assert r.get_exception_class("net.lew21.pydbus.tests.ErrorC") == ExceptionC
+	assert r.get_exception_class("net.lew21.pydbus.tests.ErrorD") is None
+	assert r.get_exception_class("net.lew21.pydbus.tests.ErrorE") is None
+
+	r.map_by_default(ExceptionD)
+	assert not r.is_registered_exception(ExceptionD("Test"))
+	assert r.get_exception_class("net.lew21.pydbus.tests.ErrorD") == ExceptionD
+	assert r.get_exception_class("net.lew21.pydbus.tests.ErrorE") == ExceptionD
+
+
+def test_transform_message():
+	r = ErrorRegistration()
+	n1 = "net.lew21.pydbus.tests.ErrorA"
+	m1 = "GDBus.Error:net.lew21.pydbus.tests.ErrorA: Message1"
+
+	n2 = "net.lew21.pydbus.tests.ErrorB"
+	m2 = "GDBus.Error:net.lew21.pydbus.tests.ErrorB: Message2"
+
+	assert r.transform_message(n1, m1) == "Message1"
+	assert r.transform_message(n2, m2) == "Message2"
+	assert r.transform_message(n1, m2) == m2
+	assert r.transform_message(n2, m1) == m1
+
+
+test_error_mapping()
+test_transform_message()