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Re: Implementing "tee" in python asyncio


From: John Snow
Subject: Re: Implementing "tee" in python asyncio
Date: Thu, 27 Jul 2023 12:49:10 -0400



On Thu, Jul 27, 2023, 6:47 AM Daniel P. Berrangé <berrange@redhat.com> wrote:
On Wed, Jul 26, 2023 at 04:25:34PM -0400, John Snow wrote:
> Hi folks,
>
> I'm currently wondering how to take a StreamReader as found on
> https://docs.python.org/3/library/asyncio-subprocess.html#asyncio.subprocess.Process
> and to consume the data while optionally re-streaming it to a
> secondary consumer.
>
> What I'd like to do is create a StreamWatcher class that consumes
> console data while optionally logging to python logging and/or a file;
> but re-buffers the data into an async stream where an additional
> consumer is free to use the "standard asyncio API" to consume console
> data at their leisure in a way that's unsurprising.
>
> What I'd like this *for* is to be able to do aggressive logging of
> stdout/stderr and console data without denying tests the ability to
> consume the data as they see fit for their testing purposes. I want to
> have my cake and eat it too, and we don't do a good job of managing
> this consistently across the board.
>
> I am wondering if there's any way around creating a literal socketpair
> and suffering the creation of a full four StreamReader/StreamWriter
> instances (one pair per socket...) and then just hanging on to the
> "unused" reader/writer per each. It seems kind of foolishly excessive.
> It also seems like it might be a pain in the butt if I want
> cross-platform compatibility with windows for the machine appliance.
>
> Anyone got any bright ideas?

Don't bother with any of the above, just add 'logfile=/path/to/log'
to the -chardev argument.

Part of me feels like it'd be a shame to miss out on the chance to do the logging in the library, but it *would* be a lot easier to just not worry about it.

anyway, this is easy for console, what about stdio? is there a way to run that through a chardev that's just connected to stdio but we attach a logfile? 


With regards,
Daniel
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