Support standard log levels

[stevenharman]

It's common amongst log tooling to support various log levels such that you can declaratively say "log the following message, when the level is of appropriate level." This is built into Ruby standard library in the form of the Logger class. e.g.,

logger.level = Logger::WARN

logger.debug("Created logger") #=>
logger.info("Program started") #=>
logger.warn("Nothing to do!")  #=> Nothing to do!

Could we add support for this to L2meter? It would be quite useful to avoid having to invent bespoke logging controls such as:

l2meterlog.log("started", app: 42) if config.verbose_logging?

I could take a shot at a PR to add this, but wanted to see if there was an interest in it first. Please advise.

[rwz]

Well, stdlib logger supports formatter and l2met could be used for this.

We do this in eventbus-pub.

Here's a minimal code to make this happen:

class L2metFormatter
  def initialize(l2meter)
    @l2meter = l2meter
  end

  def call(severity, datetime, progname, msg)
    StringIO.new.tap do |output|
      @l2meter.with_output output do
        @l2meter.log level: severity.downcase, msg: msg
      end
    end.tap(&:rewind).read
  end
end

logger = Logger.new # stdlib
logger.formatter = L2metFormatter.new(L2meter.build.context(component: "Foobar"))

logger.warn "lolwut" # => component=Foobar level=warn msg=lolwut

I thought about including this into the library, but the problem with this approach is that it doesn't seem general enough. Thoughts?

[stevenharman]

it doesn't seem general enough.

Because it means level: and msg: keys (and values) would end up in the log stream?

I) If so, is there a way to make it a little more generic - e.g., msg is "The Object the user passed to the log message; not necessarily a String." And the default Logger::Formatter has a pretty simple way of getting it to a string that could be written out: https://github.com/ruby/ruby/blob/6fbf4e22c83b4504d2d9a4a42216e4306a4e7e38/lib/logger.rb#L607-L617

II) If not... what would you like to be more generic?

Either way, I think providing an out-of-the-box formatter that's compliant with Logger::Formatter would be 💯.