Merge pull request #6557 from drew2a/refactoring/maybe_component

Add maybe_component

src/tribler-core/tribler_core/components/base.py

@@ -6,7 +6,7 @@
 from asyncio import Event, create_task, gather, get_event_loop
 from itertools import count
 from pathlib import Path
-from typing import Dict, List, Optional, Set, Type, TypeVar
+from typing import Dict, List, Optional, Set, Type, TypeVar, Union
 
 from tribler_common.simpledefs import STATEDIR_CHANNELS_DIR, STATEDIR_DB_DIR
 
@@ -113,6 +113,7 @@ def _reraise_startup_exception_in_separate_task(self):
         async def exception_reraiser():
             # the exception should be intercepted by event loop exception handler
             raise self._startup_exception
+
         get_event_loop().create_task(exception_reraiser())
 
     def set_startup_exception(self, exc: Exception):
@@ -133,6 +134,11 @@ def __exit__(self, exc_type, exc_val, exc_tb):
 T = TypeVar('T', bound='Component')
 
 
+class NoneComponent:
+    def __getattr__(self, item):
+        return NoneComponent()
+
+
 class Component:
     tribler_should_stop_on_component_error = True
 
@@ -230,6 +236,17 @@ async def get_component(self, dependency: Type[T]) -> Optional[T]:
 
         return dep
 
+    async def maybe_component(self, dependency: Type[T]) -> Union[T, NoneComponent]:
+        """ This method returns instance of the dependency in case this instance can be created
+        otherwise it returns instance of NoneComponent class
+
+        Example of using:
+
+        libtorrent_component = await self.maybe_component(LibtorrentComponent)
+        print(libtorrent_component.download_manager.libtorrent_port) # No NPE exception
+        """
+        return await self.get_component(dependency) or NoneComponent()
+
     def release_component(self, dependency: Type[T]):
         dep = dependency.instance()
         if dep:

src/tribler-core/tribler_core/components/tests/test_base_component.py

@@ -1,6 +1,6 @@
 import pytest
 
-from tribler_core.components.base import Component, MissedDependency, Session, SessionError
+from tribler_core.components.base import Component, MissedDependency, NoneComponent, Session, SessionError
 
 pytestmark = pytest.mark.asyncio
 
@@ -146,7 +146,7 @@ async def shutdown(self):
             assert component.stopped
 
 
-def test_session_context_manager(loop, tribler_config):   # pylint: disable=unused-argument
+def test_session_context_manager(loop, tribler_config):  # pylint: disable=unused-argument
     session1 = Session(tribler_config, [])
     session2 = Session(tribler_config, [])
     session3 = Session(tribler_config, [])
@@ -168,3 +168,22 @@ def test_session_context_manager(loop, tribler_config):   # pylint: disable=unus
 
     with pytest.raises(SessionError, match="Default session was not set"):
         Session.current()
+
+
+async def test_maybe_component(loop, tribler_config):  # pylint: disable=unused-argument
+    class ComponentA(Component):
+        pass
+
+    class ComponentB(Component):
+        pass
+
+    session = Session(tribler_config, [ComponentA()])
+    with session:
+        await session.start()
+        component_a = await ComponentA.instance().maybe_component(ComponentA)
+        component_b = await ComponentA.instance().maybe_component(ComponentB)
+
+        assert isinstance(component_a, ComponentA)
+        assert isinstance(component_b, NoneComponent)
+        assert isinstance(component_b.any_attribute, NoneComponent)
+        assert isinstance(component_b.any_attribute.any_nested_attribute, NoneComponent)