ocharles/logging-effect

Question about adding timestamp to log message

Closed this issue · 8 comments

rikvdkleij commented

I'm really stuck with this problem: I already have a message with severity and want to add timestamp in runLoggingT. Inside runLoggingT I try to do mapLogMessageM timestamp on LoggingT message m a but I do not get it working.

I'm developing Servant application and this is the code with only severity. I am converting custom Servant handler to Servant's default handler. I do not want to add WithTimestamp to the ApiHandler because then I have add timestamp to each separate log. Can you help me further?

type ApiHandler = ReaderT AppEnv (ExceptT ServantErr (LoggingT (WithSeverity PP.Doc) IO))

toHandler :: AppEnv -> Severity -> (ApiHandler :~> ExceptT ServantErr IO)
toHandler env logLevel = Nat toHandler'
  where
    toHandler' :: ApiHandler a -> ExceptT ServantErr IO a
    toHandler' = ExceptT . doLogging logLevel . runExceptT . flip runReaderT env

doLogging :: Severity
         -> LoggingT (WithSeverity PP.Doc) IO (Either ServantErr a)
         -> IO (Either ServantErr a)
doLogging minThreshold body =
  withFDHandler defaultBatchingOptions stdout 0.4 80 $ \stdoutHandler ->
    runLoggingT
      body
      (\message ->
         when (minThreshold >= msgSeverity message) $
           (stdoutHandler . renderWithSeverity PP.pretty) message)
rikvdkleij commented

Another question/issue. Logging to stdout goes fine, when I use withFDHandler with a file handle, no logging appears in log file. Even not when I set flushMaxDelay to 0 or 1.

Hmm, maybe this issue is similar as issue #14 .

ocharles commented
rikvdkleij commented

For the last problem, could you try against master?

I will do that soon.

Will get back to your first question soon!

Thanks! I'm really curious.

rikvdkleij commented

For the last problem, could you try against master?

Yes, master fixes the problem 😄

filterfish commented

@rikvdkleij if you look at the repo I used for verifying #14 it's using timestamps. I should point out that this isn't my code, it came from Jonathan Lange's template, which given I'm a complete newb, I've found incredibly helpful. Even though a lot of it is a bit beyond me ;)

rikvdkleij commented

@filterfish Thanks!
So this is the "trick" is to create this type: type LogM msg m = LoggingT (WithSeverity msg) (LoggingT (WithTimestamp (WithSeverity msg)) m)

Looks a bit weird, nested LoggingT types 😄 I wonder if there is a more simple solution for my case.

ocharles commented

Ah, it's this again. There's some previous discussion here: #6 (comment). Does that help clear things up? I wonder if/where this should be added to the documentation.

rikvdkleij commented

Yeah, it's the same issue/discussion. It helps but it's still difficult to understand because the types are so "abstract" 😄

About the documentation. I think only examples help with clarification.