Question

Is it possible to dynamically change the LogDevice of Ruby Logger?

If so, it would allow for some un-obtrusive changes to my existing codebase.

Currently Ruby Logger uses StringIO as the LogDevice:

@logDevice = StringIO.new("", "r+")
@log = Logger.new(@logDevice) // a reference to this is used by many objects
// both are instance vars

...

@log.info('some log') // Logging activity

...

// Before program ends, transmit logs to a server

Can LogDevice be dynamically changed to continue logging to a file?
(dynamic change because initially the filename is not known.)

Or if log device cannot be change can the StringIO object start writing to a file?

Instead of doing the above, I could write to a temporary log file, but wanted to check if the above can be done because it would be a less obstrusive change to the existing codebase.

Answer 1

The object you give to the logger just has to implement the ‘write’ and ‘close’ methods, so you can easily write your own ‘io’:

class MyIO
  def initialize
    @file = nil
    @history = StringIO.new "", "w"
  end

  def file=(filename)
    @file = File.open(filename, 'a+')
    @file.write @history.string if @history
    @history = nil
  end

  def write(data)
    @history.write(data) if @history
    @file.write(data) if @file
  end

  def close
    @file.close if @file
  end

end

create the logger with an instance of that and keep a reference to the instance. Then, whenever you know the filename, just set it with the ‘file=’ method.