Add method to format error

[dxuhuang]

@benblack86 @DanSimon @aliyakamercan @jlbelmonte @amotamed

My stab at https://github.com/tumblr/colossus/issues/414

[codecov-io]

Codecov Report

Merging #589 into develop will decrease coverage by 0.06%. The diff coverage is 84%.

@@             Coverage Diff             @@
##           develop     #589      +/-   ##
===========================================
- Coverage    84.94%   84.87%   -0.07%     
===========================================
  Files           99       99              
  Lines         4431     4451      +20     
  Branches       378      379       +1     
===========================================
+ Hits          3764     3778      +14     
- Misses         667      673       +6

Impacted Files	Coverage Δ
...c/main/scala/colossus/service/RequestHandler.scala	88.88% <100%> (ø)	:arrow_up:
...rc/main/scala/colossus/service/ServiceServer.scala	90.83% <83.33%> (-2.17%)	:arrow_down:
...s/src/main/scala/colossus/metrics/Collection.scala	97.43% <0%> (-2.57%)	:arrow_down:
.../scala/colossus/metrics/collectors/Histogram.scala	90.57% <0%> (-0.73%)	:arrow_down:
...sus/src/main/scala/colossus/service/Callback.scala	88.37% <0%> (ø)	:arrow_up:

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[benblack86]

Just trying to think how it would be overriden:

def formatError(error: Throwable): String = {
  error match {
    case DroppedReplyException => "DroppedReplyException"
    case _ => // get stack trace
  }
}

The problem is that it is a bit of work to extract the stack trace since that functionality is contained within the logger. Maybe it would be more useful to be able to indicate whether an error should be logged. There could be three levels:

• don't log
• log name only
• log name and stack trace

It would be great if this stuff can be configurable (like the metrics) so by default the DroppedReplyException would only log name, but everything else would be name and stack trace.

[DanSimon]

I like the general idea. What do you guys think about having formatError also take in the failed request as a parameter, and then using the returned string as the entire error message? That way the formatter has complete control over the error message.

I also agree with what @benblack86 said. Having an ADT like:

sealed trait LogAction
case object DoNotLog extends LogAction
case class Log(message: String, includeStackTrace: Boolean) extends LogAction

or something similar seems like a good idea. Also #414 does mention doing something for exceptions like DroppedReplyException. I'm ok if that's not addressed in this PR, but we should then create another issue for it.

[dxuhuang]

bump. will add stuff in conf soon

[benblack86]

Looks good so far.

[dxuhuang]

bump @DanSimon

[benblack86]

Might be wrong, but I don't think the RequestFormatter is documented. Can you add/update the docs.

[dxuhuang]

bump

[dxuhuang]

bump