Contextual Logging with Log4r - ruby-on-rails

Question

Here's how some of my existing logging code with Log4r is working. As you can see in the WorkerX::a_method, any time that I log a message I want the class name and the calling method to be included (I don't want all the caller history or any other noise, which was my purpose behind LgrHelper).
class WorkerX
include LgrHelper
def initialize(args = {})
#logger = Lgr.new({:debug => args[:debug], :logger_type => 'WorkerX'})
end
def a_method
error_msg("some error went down here")
# This prints out: "WorkerX::a_method - some error went down here"
end
end
class Lgr
require 'log4r'
include Log4r
def initialize(args = {}) # args: debug boolean, logger type
#debug = args[:debug]
#logger_type = args[:logger_type]
#logger = Log4r::Logger.new(#logger_type)
format = Log4r::PatternFormatter.new(:pattern => "%l:\t%d - %m")
outputter = Log4r::StdoutOutputter.new('console', :formatter => format)
#logger.outputters = outputter
if #debug then
#logger.level = DEBUG
else
#logger.level = INFO
end
end
def debug(msg)
#logger.debug(msg)
end
def info(msg)
#logger.info(msg)
end
def warn(msg)
#logger.warn(msg)
end
def error(msg)
#logger.error(msg)
end
def level
#logger.level
end
end
module LgrHelper
# This module should only be included in a class that has a #logger instance variable, obviously.
protected
def info_msg(msg)
#logger.info(log_intro_msg(self.method_caller_name) + msg)
end
def debug_msg(msg)
#logger.debug(log_intro_msg(self.method_caller_name) + msg)
end
def warn_msg(msg)
#logger.warn(log_intro_msg(self.method_caller_name) + msg)
end
def error_msg(msg)
#logger.error(log_intro_msg(self.method_caller_name) + msg)
end
def log_intro_msg(method)
msg = class_name
msg += '::'
msg += method
msg += ' - '
msg
end
def class_name
self.class.name
end
def method_caller_name
if /`(.*)'/.match(caller[1]) then # caller.first
$1
else
nil
end
end
end
I really don't like this approach. I'd rather just use the existing #logger instance variable to print the message and be smart enough to know the context. How can this, or similar simpler approach, be done?
My environment is Rails 2.3.11 (for now!).

Answer 1

After posting my answer using extend, (see "EDIT", below), I thought I'd try using set_trace_func to keep a sort of stack trace like in the discussion I posted to. Here is my final solution; the set_trace_proc call would be put in an initializer or similar.
#!/usr/bin/env ruby
# Keep track of the classes that invoke each "call" event
# and the method they called as an array of arrays.
# The array is in the format: [calling_class, called_method]
set_trace_func proc { |event, file, line, id, bind, klass|
if event == "call"
Thread.current[:callstack] ||= []
Thread.current[:callstack].push [klass, id]
elsif event == "return"
Thread.current[:callstack].pop
end
}
class Lgr
require 'log4r'
include Log4r
def initialize(args = {}) # args: debug boolean, logger type
#debug = args[:debug]
#logger_type = args[:logger_type]
#logger = Log4r::Logger.new(#logger_type)
format = Log4r::PatternFormatter.new(:pattern => "%l:\t%d - %m")
outputter = Log4r::StdoutOutputter.new('console', :formatter => format)
#logger.outputters = outputter
if #debug then
#logger.level = DEBUG
else
#logger.level = INFO
end
end
def debug(msg)
#logger.debug(msg)
end
def info(msg)
#logger.info(msg)
end
def warn(msg)
#logger.warn(msg)
end
def error(msg)
#logger.error(msg)
end
def level
#logger.level
end
def invoker
Thread.current[:callstack] ||= []
( Thread.current[:callstack][-2] || ['Kernel', 'main'] )
end
end
class CallingMethodLogger < Lgr
[:info, :debug, :warn, :error].each do |meth|
define_method(meth) { |msg| super("#{invoker[0]}::#{invoker[1]} - #{msg}") }
end
end
class WorkerX
def initialize(args = {})
#logger = CallingMethodLogger.new({:debug => args[:debug], :logger_type => 'WorkerX'})
end
def a_method
#logger.error("some error went down here")
# This prints out: "WorkerX::a_method - some error went down here"
end
end
w = WorkerX.new
w.a_method
I don't know how much, if any, the calls to the proc will affect the performance of an application; if it ends up being a concern, perhaps something not as intelligent about the calling class (like my old answer, below) will work better.
[EDIT: What follows is my old answer, referenced above.]
How about using extend? Here's a quick-and-dirty script I put together from your code to test it out; I had to reorder things to avoid errors, but the code is the same with the exception of LgrHelper (which I renamed CallingMethodLogger) and the second line of WorkerX's initializer:
#!/usr/bin/env ruby
module CallingMethodLogger
def info(msg)
super("#{#logger_type}::#{method_caller_name} - " + msg)
end
def debug(msg)
super("#{#logger_type}::#{method_caller_name} - " + msg)
end
def warn(msg)
super("#{#logger_type}::#{method_caller_name} - " + msg)
end
def error(msg)
super("#{#logger_type}::#{method_caller_name} - " + msg)
end
def method_caller_name
if /`(.*)'/.match(caller[1]) then # caller.first
$1
else
nil
end
end
end
class Lgr
require 'log4r'
include Log4r
def initialize(args = {}) # args: debug boolean, logger type
#debug = args[:debug]
#logger_type = args[:logger_type]
#logger = Log4r::Logger.new(#logger_type)
format = Log4r::PatternFormatter.new(:pattern => "%l:\t%d - %m")
outputter = Log4r::StdoutOutputter.new('console', :formatter => format)
#logger.outputters = outputter
if #debug then
#logger.level = DEBUG
else
#logger.level = INFO
end
end
def debug(msg)
#logger.debug(msg)
end
def info(msg)
#logger.info(msg)
end
def warn(msg)
#logger.warn(msg)
end
def error(msg)
#logger.error(msg)
end
def level
#logger.level
end
end
class WorkerX
def initialize(args = {})
#logger = Lgr.new({:debug => args[:debug], :logger_type => 'WorkerX'})
#logger.extend CallingMethodLogger
end
def a_method
#logger.error("some error went down here")
# This prints out: "WorkerX::a_method - some error went down here"
end
end
w = WorkerX.new
w.a_method
The output is:
ERROR: 2011-07-24 20:01:40 - WorkerX::a_method - some error went down here
The downside is, via this method, the caller's class name isn't automatically figured out; it's explicit based on the #logger_type passed into the Lgr instance. However, you may be able to use another method to get the actual name of the class--perhaps something like the call_stack gem or using Kernel#set_trace_func--see this thread.