Logger: skip ANSI color commands if output is not a tty

[aviddiviner]

Here's a little improvement to the default logger so that the output isn't colorised if we're not outputting to a terminal. So, if we run with ./server | tee my.log then instead of my log file looking like this:

[GIN] 2016/11/17 - 16:28:44 |^[[97;42m 200 ^[[0m|   24.459651ms | ::1 |^[[97;44m  ^[[0m GET     /
[GIN] 2016/11/17 - 16:28:44 |^[[97;42m 200 ^[[0m|  1.766299995s | ::1 |^[[97;44m  ^[[0m GET     /ws
[GIN] 2016/11/17 - 16:28:44 |^[[97;42m 200 ^[[0m|   11.265361ms | ::1 |^[[97;44m  ^[[0m GET     /static/favicon.gif

It looks like this:

[GIN] 2016/11/17 - 16:28:44 | 200 |   24.459651ms | ::1 |   GET     /
[GIN] 2016/11/17 - 16:28:44 | 200 |  1.766299995s | ::1 |   GET     /ws
[GIN] 2016/11/17 - 16:28:44 | 200 |   11.265361ms | ::1 |   GET     /static/favicon.gif

The same applies to any pipe. You can see this in action by just running ./server | cat

This does add an extra dependency on golang.org/x/crypto/ssh/terminal but it's pretty widely used and stable. I did consider copying over the IsTerminal function, but there's a bit of tricky syscall magic there and I'd rather they take care of it.

The other change I could think you might want to do, is assume that it's not a terminal if it isn't a valid *os.File, so change line 50 to:

isTerm := false

That might be nice for people funnelling their logs off to other random io.Writers that don't want the ANSI code spam. But I've just kinda left it as it is for now.

Let me know what you think! Thanks 😄

[coveralls]

Coverage increased (+0.02%) to 94.107% when pulling f263a35 on aviddiviner:logger-fix into bb159f9 on gin-gonic:master.

[appleboy]

@aviddiviner Open your pull request against develop not master

[codecov-io]

Current coverage is 93.08% (diff: 100%)

Merging #744 into develop will increase coverage by 0.02%

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  Misses           76         76          
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[aviddiviner]

@appleboy Sure, done.

[aviddiviner]

Any news on this?

[appleboy]

LGTM

[tboerger]

Also LGTM

[appleboy]

@aviddiviner Thanks.

[appleboy]

@aviddiviner we reverted this PR since Google App Engine can't working. Please refer to #752. We need to try another way to resolve this issue.