skel: clean up errors in skel and add some well-known error codes

[mars1024]

ref to #685

[dcbw]

@mars1024 Note that the Spec says Errors must be indicated by a non-zero return code and the following JSON being printed to stdout: so we have to print errors to stdout by design. But they can also be (and probably should?) mirrored to stderr.

[squeed]

Yeah, it would be useful to log the error message to stderr, but I personally don't like logging JSON to stderr.

[jellonek]

👍 for not logging JSON. Also if it's log - it would be nice to have a timestamp at least in it.

[mars1024]

I've updated the aims in issue #685 , and i'm going to update this PR soon ~

[mars1024]

Updated! PTAL, thanks a lot ~ cc @dcbw @squeed @jellonek

[jellonek]

LGTM

[squeed]

This is awesome! Thanks for such a great PR.

To make things easier for plugin authors, we'd like there to be just a bit fewer error codes. Because this is changing the spec, we need to live with it "forever." So don't feel disappointed if we have a lot of suggestions.

[mars1024]

This is awesome! Thanks for such a great PR.

To make things easier for plugin authors, we'd like there to be just a bit fewer error codes. Because this is changing the spec, we need to live with it "forever." So don't feel disappointed if we have a lot of suggestions.

Thanks for your appreciation, I'll update this soon ~

[jellonek]

This looks really good!

[mars1024]

Updated! PTAL, thanks ~

[dcbw]

/lgtm after the 8 -> 11

[jellonek]

Just a note if someone would not understand why we want there 11: http://man7.org/linux/man-pages/man3/errno.3.html and https://www-numi.fnal.gov/offline_software/srt_public_context/WebDocs/Errors/unix_system_errors.html

#define EAGAIN          11      /* Try again */

;)

[mars1024]

Thanks for your suggestion, I've revert index of ErrTryAgainLater to 11, @bboreham @dcbw @jellonek @squeed , PTAL ~

[bboreham]

Thanks!