amp.Command.requiresAnswer isn't respected in the failure case, returning failing Deferreds from callRemote when the caller expects none

[twisted-trac]

	@glyph reported
Trac ID	trac#9756
Type	defect
Created	2020-01-09 00:46:27Z

In AMP, there are two kinds of invocations of callRemote: the normal one, where you get a Deferred back and then you have to handle the error from it, and fire-and-forget, where you specify requiresAnswer = False and you get None back, and you don't care if that specific invocation failed.

The distinction is semantically important because unhandled errors on Deferreds get logged, which means if you do this:

#!py
class MyNeatCommand(Command):
    requiresAnswer = False
    ...

self.callRemote(MyNeatCommand)

you can't know a-priori whether the connection is closed or not, so you need this nasty workaround instead:

#!py
result = self.callRemote(MyNeatCommand)
if result is not None:
    result.addErrback(lambda ignored: None)

unless you want your logs to fill up with unexplained ConnectionDone errors.

Instead, BoxDispatcher._sendBoxCommand ought to check requiresAnswer before it checks _failAllReason, and never return a failing Deferred when none is expected.

Searchable metadata

trac-id__9756 9756
type__defect defect
reporter__glyph glyph
priority__high high
milestone__None None
branch__ 
branch_author__ 
status__closed closed
resolution__fixed fixed
component__core core
keywords__None None
time__1578530787791441 1578530787791441
changetime__1579025930222284 1579025930222284
version__None None
owner__glyph glyph

[twisted-trac]

	@glyph commented

#1218

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	@wsanchez set owner to @glyph

reviewed

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	@wsanchez set status to closed