[web-devel] Error logging in Yesod

Greg Weber greg at gregweber.info
Sat Apr 2 21:25:29 CEST 2011 

On Sat, Apr 2, 2011 at 11:10 AM, Michael Snoyman <michael at snoyman.com>wrote:

> @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.
>
>
in hslogger the source is just another string. That makes it easily
extensible, but the lack of type safety worries me a bit. Maybe we just need
to trust everyone to use a single canonical (Text) string for their sources.
I imagine that for any source one would create a helper function that
applies the source Text argument. Likewise, the default logging function for
Yesod users wouldn't have a source argument.

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
> >> >>
> >> >> _______________________________________________
> >> >> web-devel mailing list
> >> >> web-devel at haskell.org
> >> >> http://www.haskell.org/mailman/listinfo/web-devel
> >> >
> >> >
> >> > _______________________________________________
> >> > web-devel mailing list
> >> > web-devel at haskell.org
> >> > http://www.haskell.org/mailman/listinfo/web-devel
> >>
> >>
> >> _______________________________________________
> >> web-devel mailing list
> >> web-devel at haskell.org
> >> http://www.haskell.org/mailman/listinfo/web-devel
> >
> >
> > _______________________________________________
> > web-devel mailing list
> > web-devel at haskell.org
> > http://www.haskell.org/mailman/listinfo/web-devel
> >
> >
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/web-devel/attachments/20110402/fc51a548/attachment-0001.htm>

More information about the web-devel mailing list