Class: ScoutAgent::WireTap

Inherits:
Object
  • Object
show all
Includes:
Severity
Defined in:
lib/scout_agent/wire_tap.rb

Overview

WireTap is a complete replacement for Ruby’s standard Logger class, with a few changes:

  • The code is multi-Process safe

  • Log can be duplicated on a second device

  • The default formatter produces a trimmed down output

  • Severity levels can be dynamically altered (not used in the agent)

The main change was to make the code work for multiple processes. This is done by forcing code to aquire the proper locks during all file interactions. Log rotation also had to be changed to avoid moving an active log file out from under another process. Instead, files are copied and truncated. This also required a seek() to the end of the file before each write to be added to defeat some pos() caching that seemed to be occurring. The end results of all of this is that WireTap is safer than Logger, but slower because of the extra precausions it must take.

The tap=() method on instances of this class, allows you to set a second device input can be copied to.

Defined Under Namespace

Modules: Severity Classes: Error, Formatter, LogDevice, ShiftingError

Constant Summary

Constants included from Severity

Severity::DEBUG, Severity::ERROR, Severity::FATAL, Severity::INFO, Severity::UNKNOWN, Severity::WARN

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(logdev, shift_age = 0, shift_size = 1048576) ⇒ WireTap

Wraps logdev for logging.

You can set shift_age and/or shift_size to setup log rotation. You can pass :daily, :weekly, or :monthly as shift_age to get the named rotation. Alternately, you can set shift_age to the number of log files to keep and shift_size to the byte size at which log files are rotated out.



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# File 'lib/scout_agent/wire_tap.rb', line 356

def initialize(logdev, shift_age = 0, shift_size = 1048576)
  @logdev    = logdev &&
               LogDevice.new( logdev, :shift_age  => shift_age,
                                      :shift_size => shift_size )
  @formatter = Formatter.new
  @level     = min_level
  @progname  = nil
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(method, *args, &block) ⇒ Object

Dynamic level method dispatch. See Severity for details.



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# File 'lib/scout_agent/wire_tap.rb', line 455

def method_missing(method, *args, &block)
  case method.to_s
  when /\A(#{level_re})\?\z/i
    level?($1, *args, &block)
  when /\A(#{level_re})\z/i
    add(levels[$1.upcase], nil, *args, &block)
  else
    super
  end
end

Instance Attribute Details

#formatter ⇒ Object

The Formatter instance being used to format the messages logged by this WireTap instance.



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# File 'lib/scout_agent/wire_tap.rb', line 369

def formatter
  @formatter
end

#level ⇒ Object Also known as: sev_threshold

The current level below which no messages will be logged.



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# File 'lib/scout_agent/wire_tap.rb', line 371

def level
  @level
end

#progname ⇒ Object

The Process name used in messages logged by this instance.



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# File 'lib/scout_agent/wire_tap.rb', line 375

def progname
  @progname
end

Instance Method Details

#<<(message) ⇒ Object

Write’s a raw message to the log without any formatting or preprocessing.



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# File 'lib/scout_agent/wire_tap.rb', line 441

def <<(message)
  @logdev.write(message) unless @logdev.nil?
end

#add(severity, message = nil, progname = nil, &block) ⇒ Object Also known as: log

A low-level way to log a message with severity. You can optionally pass a progname override. You can also choose to pass the message in a block that will be run to build the message only if it would be written.



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# File 'lib/scout_agent/wire_tap.rb', line 416

def add(severity, message = nil, progname = nil, &block)
  severity ||= max_level
  return true if @logdev.nil? or severity < @level
  progname ||= @progname
  if message.nil?
    if block.nil?
      message, progname = progname, @progname
    else
      message = block.call
    end
  end
  output = @formatter.call( level_names[severity] || "ANY",
                            Time.now,
                            progname,
                            message )
  @logdev.write(output)
  tap.write(output) if tap
  true
end

#close ⇒ Object

Closes the underlying log.



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# File 'lib/scout_agent/wire_tap.rb', line 467

def close
  @logdev.close unless @logdev.nil?
end

#datetime_format ⇒ Object

Returns the timestamp format currently in use (or nil if the default is being used) to format messages for this instance.



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# File 'lib/scout_agent/wire_tap.rb', line 389

def datetime_format
  @formatter.datetime_format
end

#datetime_format=(datetime_format) ⇒ Object

Sets a new timestamp format on the Formatter used to format messages for this instance. datetime_format should be a strftime() pattern String.



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# File 'lib/scout_agent/wire_tap.rb', line 381

def datetime_format=(datetime_format)
  @formatter.datetime_format = datetime_format
end

#level?(level) ⇒ Boolean

Returns true if a level message would currently be written.

Returns:

  • (Boolean) 


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# File 'lib/scout_agent/wire_tap.rb', line 407

def level?(level)
  @level <= level_by_name(level)
end

#respond_to?(message, include_private = false) ⇒ Boolean

An override to show the dynamic level methods. See Severity for details.

Returns:

  • (Boolean) 


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# File 'lib/scout_agent/wire_tap.rb', line 446

def respond_to?(message, include_private = false)
  if level_methods.include? message.to_s
    true
  else
    super
  end
end

#tap ⇒ Object

Returns the secondary device messages are being logged to (or nil if none is in use).



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# File 'lib/scout_agent/wire_tap.rb', line 402

def tap
  @tap ||= nil
end

#tap=(logdev) ⇒ Object

Sets a second logdev all messages should be copied to.



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# File 'lib/scout_agent/wire_tap.rb', line 394

def tap=(logdev)
  @tap = logdev && LogDevice.new(logdev)
end