glyph@divmod.com wrote:
On 02:13 am, tim@commsecure.com.au wrote:
Having skim-read ticket 638 that JP pointed to in another reply, now I'm not so sure. It's kind of difficult to for me to understand the current state of play, especially since that ticket predates the merge of seemingly-related ticket 3052, but it *seems* to be a battle between the camps of "twistd's logging is limited, it should be infinitely extensible" and "twistd's logging is limited, applications should be allowed to override it". Personally, I think I lean more toward "it should be infinitely extensible" side - but right now I don't really care about the general case of extensibility, I just want more flexible syslog support.
Well, let me first say that your understanding of the issues here is remarkably deep and nuanced, despite your modesty :).
Thank you. :)
I don't believe there are actually different "camps" here, and there isn't a lot of disagreement. At least, I believe all of the core developers have essentially the same perspective, with differences in emphasis, not content.
There are two systems here. Twisted's logging (i.e. twisted.python.log), and twistd's logging (twisted.internet._twistd_unix, twisted.internet._twistw, twisted.python.syslog, among other things). Twisted's logging, while it could certainly be improved, is in reasonable shape. It's extremely simple, and there is a clear and (mostly) well-specified "do anything you want" integration point: addObserver. While there are some tweaks I'd like to see here, I don't think it's what we're talking about.
True; if I had to make a complaint about t.p.log, it would be that this system for arbitrary event-sources to communicate with arbitrary event-observers needs a well-defined interface to facilitate communication. Currently, the only things an event-observer can rely on are the 'isError' and 'system' fields being present, and probably 'message' and 'time'. Any observer winds up either depending on extra fields set by a specific event-source (and hoping that no other event-source happens to use the same field-names for different purposes), or having to treat every event as a raw text event - defeating the point of logging complicated events in the first place. However! That's probably an entirely separate can of worms from the actual problem I'm currently supposed to be working on, so I shall leave it there for now. :)
The ticket which I believe most clearly explains how to fix this issue is #2751. The question of "how do we tell where twistd thinks the logs go" is really just a tiny microcosm of "how do we tell what twistd thinks is going on around here". There is no clear, uniform surface presented to affect twistd's configuration from anywhere, not even internally; let alone in user code.
A kind of document-object-model of application deployment configuration, then?
The first application that needs to do this is twistd itself. The internal APIs of twistd need to be organized such that it is easy to maintain and extend - for example, so that you could do the extension that you are proposing with syslog. Once these APIs are tested, documented, and clearly factored, adding a plugin system to allow users to replace components of the logging system should be relatively straightforward.
Work is underway to do all of this; many of the tickets that we're talking about here have already have work underway.
Your most recent comment on #2571 is a lot more optimistic, it sounds like twistd has most of the stuff it needs already. If I have some free time, I might poke through the twistd code to see if I can understand the architectural issues better.
At any rate, ticket 638 and other related tickets seem to be high-level conceptual arguments, and I don't feel I have the domain-knowledge required to comment intelligibly on them.
I hope that this summary has improved your understanding somewhat. Don't let the depth of the issues here scare you; the best way to resolve major architectural headaches like this is one step at a time, responding to one specific use-case at a time. So, I would recommend that you file a ticket if you haven't already, and simply add syslog facility support to twistd by adding a --syslog-facility command-line option (no, usage.Options won't let you have --foo and --foo=bar options at the same time, sorry...) and a _syslogFacility attribute to the UnixAppLogger object added by the fix to #3052. You would of course need to add this to twisted.python.syslog as well, but I think the way to do that should be pretty straightforward.
Filed as #3300, with patches and explanations.
Also, congratulations on volunteering to maintain Twisted's log subsystem! If you would like to decline, please see David Reid about fighting a bear on your way out. ;-).
Well, we'll see how I go. ;)