From 69968dec867053e38de0b91d76ac41d5a5735e36 Mon Sep 17 00:00:00 2001
From: Vendula Poncova <vponcova@redhat.com>
Date: Thu, 2 Aug 2018 15:31:56 +0800
Subject: [PATCH 2/2] Support transformation between D-Bus errors and
 exceptions.

Exceptions can be registered with decorators, raised in a remote
method and recreated after return from the remote call.

Upstream-Status: Backport [https://src.fedoraproject.org/cgit/rpms/python-pydbus.git/]

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
---
 pydbus/error.py        | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++
 pydbus/proxy_method.py | 18 ++++++++--
 pydbus/registration.py | 16 ++++++---
 3 files changed, 123 insertions(+), 8 deletions(-)
 create mode 100644 pydbus/error.py

diff --git a/pydbus/error.py b/pydbus/error.py
new file mode 100644
index 0000000..aaa3510
--- /dev/null
+++ b/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()
diff --git a/pydbus/proxy_method.py b/pydbus/proxy_method.py
index 4ea4304..e9496f5 100644
--- a/pydbus/proxy_method.py
+++ b/pydbus/proxy_method.py
@@ -2,6 +2,7 @@ from gi.repository import GLib
 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
@@ -87,9 +88,20 @@ class ProxyMethod(object):
 			call_args += (self._finish_async_call, (callback, callback_args))
 			instance._bus.con.call(*call_args)
 			return None
+
 		else:
-			ret = instance._bus.con.call_sync(*call_args)
-			return self._unpack_return(ret)
+			result = None
+			error = None
+
+			try:
+				result = instance._bus.con.call_sync(*call_args)
+			except Exception as e:
+				error = error_registration.transform_exception(e)
+
+			if error:
+				raise error
+
+			return self._unpack_return(result)
 
 	def _unpack_return(self, values):
 		ret = values.unpack()
@@ -108,7 +120,7 @@ class ProxyMethod(object):
 			ret = source.call_finish(result)
 			return_args = self._unpack_return(ret)
 		except Exception as err:
-			error = err
+			error = error_registration.transform_exception(err)
 
 		callback, callback_args = user_data
 		callback(*callback_args, returned=return_args, error=error)
diff --git a/pydbus/registration.py b/pydbus/registration.py
index f531539..1d2cbcb 100644
--- a/pydbus/registration.py
+++ b/pydbus/registration.py
@@ -5,6 +5,7 @@ from . import generic
 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 @@ class ObjectWrapper(ExitableWithAliases("unwrap")):
 			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]
-- 
2.7.4