Simplifying the semantic logger formatter

log.rb

#!/usr/bin/env ruby

require 'logger'
require 'semantic_logger'

class KubeFmt < SemanticLogger::Formatters::Json
  # redefine the defaults for log_host and log_application to be false
  def initialize(
      time_format: :iso_8601, log_host: false, log_application: false,
      time_key: :timestamp
  )
    super(
      time_format: time_format, log_host: log_host,
      log_application: log_application, time_key: time_key
    )
  end

  def message
    super
    return if hash[:message]

    # use the exception to form the message is there is none
    return unless log.exception
    hash[:message] = "#{log.exception.class.name}: #{log.exception.message}"
  end

  # redefine process_info to exclude pid and thread
  def process_info
    file, line = log.file_name_and_line
    return unless file

    hash[:file] = file
    hash[:line] = line.to_i
  end

  # eliminate the useless "log_index" field
  def level
    hash[:level] = log.level
  end
end

SemanticLogger.add_appender(io: STDOUT, formatter: KubeFmt.new)
logger = SemanticLogger['poop']
logger.level = :debug
logger.info('poop')
begin
  raise 'WTF'
rescue StandardError => exc
  logger.fatal(exc)
end

out-piped-through-jq.json

{
  "timestamp": "2018-07-26T16:46:06.602569Z",
  "level": "info",
  "name": "poop",
  "message": "poop"
}
{
  "timestamp": "2018-07-26T16:46:06.602623Z",
  "level": "fatal",
  "file": "./app.rb",
  "line": 49,
  "name": "poop",
  "message": "RuntimeError: WTF",
  "exception": {
    "name": "RuntimeError",
    "message": "WTF",
    "stack_trace": [
      "./app.rb:47:in `<main>'"
    ]
  }
}