[web-devel] Error logging in Yesod

[Michael Snoyman]

@Sven: I agree, database level logging is a *very* nice idea. Timing
could also be very useful. The former will require modifications to
persistent; let's try to think about how that would work (I don't have
any clear ideas immediately). For timing: we could add a nice
combinator on top of the main logging functions:

logTimed :: MonadIO m => (normal params) -> m a -> m a
logTimed (normal params) action = do
    begin <- getCurrentTime
    a <- action
    end <- getCurrentTime
    log (normal params) ++ "; operation took: " ++ show (end - begin)
    return a

@Max: I'm not planning on adding a specific backend like hslogger. I'd
rather make a system that is flexible enough to allow a user to plug
in whatever backend he/she wants. Plus, hslogger in LGPL, which I'm
trying to avoid in yesod-core.

@Greg: I like the idea of adding source. How would you see this, just
another Text argument? As for typeclass/not typeclass: the advantage
to the former is that all subsites will get to piggy-back on what the
master site defines. So I *definitely* think it's worthwhile.

Michael

On Sat, Apr 2, 2011 at 5:48 PM, Greg Weber <greg at gregweber.info> wrote:
> I like Michael's straw man. The only missing aspect I see is specifying a
> source. hslogger has this capability. This is useful for a web framework to
> differentiate between database logging and request logging, etc. It can be
> useful for an application when it grows in size.
> Does logging need to be in the typeclass or does it make send to just import
> it?
> On Sat, Apr 2, 2011 at 3:22 AM, Max Cantor <mxcantor at gmail.com> wrote:
>>
>> Take a look at hslogger.  I know that another dependency is low on the
>> "things we want" list, but its pretty decent.
>>
>> max
>>
>> On Apr 1, 2011, at 3:18 PM, Sven Koschnicke (GFXpro) wrote:
>>
>> > Hello,
>> >
>> > I would add a log level "Debug" which only gets printed to the log when
>> > in development mode. I also found the log output of SQL queries generated by
>> > the database layer quite helpful in development. Another thing is
>> > performance measurements, the time it takes to answer an request. These
>> > ideas are all coming from the way RoR does logging, but I found it very
>> > helpful when developing with Rails, so it should be a nice feature in Yesod,
>> > too. Here is an example:
>> >
>> >  Instrument Load (0.4ms)   SELECT * FROM "instruments" WHERE
>> > ("instruments"."id" = 86) ORDER BY LOWER(instruments.name)
>> > Rendered overview/_notification (2.1ms)
>> >  CACHE (0.0ms)   SELECT * FROM "instruments" WHERE ("instruments"."id" =
>> > 86) ORDER BY LOWER(instruments.name)
>> > Rendered overview/_notification (1.5ms)
>> >  CACHE (0.0ms)   SELECT * FROM "instruments" WHERE ("instruments"."id" =
>> > 90) ORDER BY LOWER(instruments.name)
>> > Rendered overview/_notification (1.4ms)
>> >  CACHE (0.0ms)   SELECT * FROM "instruments" WHERE ("instruments"."id" =
>> > 62) ORDER BY LOWER(instruments.name)
>> > Rendered overview/_notification (1.5ms)
>> >  DepotGroup Load (27.2ms)   SELECT * FROM "depot_groups" ORDER BY
>> > ordinal
>> > Completed in 3530ms (View: 166, DB: 2051) | 200 OK [http://localhost/]
>> >
>> >
>> > Sven
>> >
>> > On 04/01/2011 08:20 AM, Michael Snoyman wrote:
>> >> Hi all,
>> >>
>> >> Hot on the heels of the decision to remove logging from WAI, I would
>> >> like to add it to Yesod. I think (at least to start with), we really
>> >> need two modifications: a new method in the Yesod typeclass that
>> >> specifies what to do with log messages, and a function living in the
>> >> Handler monad that calls that method. I do not have any strong
>> >> opinions on this topic, so I would appreciate input. Here's a strawman
>> >> proposal:
>> >>
>> >> data LogLevel = LevelInfo | LevelWarn | LevelError | LevelOther Text
>> >>
>> >> class Yesod a where
>> >>     messageLogger :: a ->  LogLevel ->  Text ->  IO ()
>> >>     messageLogger _ level msg = formatLogMessage level msg>>=
>> >> Data.Text.Lazy.IO.hPutStrLn System.IO.stderr
>> >>
>> >> formatLogMessage :: LogLevel ->  Text ->  IO Text
>> >> formatLogMessage = ...
>> >> -- print timestamp, log level, message, maybe process ID? to stderr
>> >> -- make sure to expose the
>> >>
>> >> logInfo :: MonadIO m =>  Text ->  GGHandler sub master m ()
>> >> logInfo t = do
>> >>     y<  getYesod
>> >>     liftIO $ messageLogger y LevelInfo t
>> >>
>> >> ... and so on and so forth
>> >>
>> >> This should give completely flexibility to users to send their logs
>> >> anywhere (database, printer, missiles) and in whatever format they
>> >> want.
>> >>
>> >> Other ideas:
>> >>
>> >> * It would be nice to include file/line number information, but I'm
>> >> not sure how easy/possible that will be without requiring the user to
>> >> manually enter CPP macros.
>> >> * Actually, that was my only other idea :)
>> >>
>> >> Michael
>> >>
>> >> _______________________________________________
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>> >> http://www.haskell.org/mailman/listinfo/web-devel
>> >
>> >
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