Don't emit grok_exporter specific message in tailer package

[virtuald]

I really enjoyed your writeup about the tailer package, and it's definitely the best pure go tail solution out there. The tailer package is immensely useful, it should be it's own project!

But, until that day, one nit is that it has a grok_exporter specific message in it, which is confusing if your application isn't grok_exporter...

Disclaimer: I haven't actually tested this code yet since I don't use grok_exporter itself, but this seems like the right fix.

[coveralls]

Coverage increased (+0.05%) to 69.93% when pulling 465c5bc on virtuald:errmsg into 118f9f6 on fstab:master.

[fstab]

Sounds like a good idea. However, the error is wrapped in the writeError() call in fileTailer.go, so if you call os.IsNotExist() in grok_exporter.go it will always be false. I think the best way to solve this would be to define a custom error type for the tail.Errors() channel. This type could define methods like IsFileNotFound() to get more info on what caused the error.

[virtuald]

Could wrap os.PathError instead of defining a custom error type?

[fstab]

I am not sure. We now have the message "failed to initialize file system watcher..." so the caller knows it's an initialization problem and not a runtime problem. I am not sure how we could keep that message if we use the os.PathError directly in writeError().

[fstab]

I pushed an tailer.Error type where you can call Cause() to get the original error.

[fstab]

Seems that I broke the Windows build. Need to check tomorrow.

[virtuald]

Your solution seems fine to me, thanks!