From: "lroland@..." <lroland@...>
Date: 2005-11-11T01:07:13+09:00
Subject: Re: Logging vs. Exceptions

Here is parts of the code, newly rewritten from Perl to Ruby. The code
is a basic scanner that uses clamav to scan a file for virus and logs
errors using log4r. The 'scan' method handles the scan result and the
'talk' method speaks to clamav using a socket. The talk method may
throw exceptions but, the scan function tries to grab these, logs
whatever goes wrong and generally tries to be as exception safe as
possible. Also I use a customized exception class that logs all
exceptions using the same log4r object as the rest of the code.

What I would like is to get some opinions/comments on is how to mingle
logging and exception handling together in a usable and yet clean way
(I personally do not feel that the code below is as clean as it could
be but I am  still looking for the correct division of responsibility
between the logging and exception code)

---------
require 'socket'
require 'log4r'
include Log4r

class ClamScanner
  attr_accessor :socket, :result, :logger

  def initialize()
    @logger = Logger['test']
    @socket = '/var/run/clamav/clamd.sock'
  end

  def check()
    res = talk("PING")
    if(res !~ /PONG$/)
	@logger.error("check failed: erroneous clam answer: #{res}")
	return false
    end
    return true
  end

  def scan( path )
    if(@result)
      @logger.info("reusing previous scan result: <#{@result}> of:
<#{path}>")
    else
	begin
          res = talk("SCAN #{path}")
   	  rescue ScannerException
        @logger.error("unable to scan message: #{path}")
   	  return nil
	end

        if(res =~ /: (.*) FOUND$/)
          @logger.info("virus: #{$1} in: #{path}")
          @result = $1;
        elsif(res =~ /: (Zip module failure) ERROR$/)
          @logger.info("broken zip in #{path}")
          @result = 'Broken.ZIP.Archive'
        elsif(res =~ /OK$/)
          @logger.info("no virus detected in: #{path}")
          @result = 'clean'
        else
          @logger.error("unknwon clam resource problem: #{$1}: when
scanning: #{path}")
          return nil
        end
    end

    return @result
  end

  def talk( msg )
    data = nil
    session = nil

    if msg.nil?
      raise ScannerException.new("method called with empty args")
    end
      begin
        session = UNIXSocket.new(@socket)
	session.send(msg,0)
	data = session.recvfrom(512)[0] # [0] ensures we only get clam's
respons
	session.close()
      rescue
        raise ScannerException.new("unable to use socket: #{@socket}")
      end
    return data
  end
end

# exception class that logs using our log4r object
class ScannerException < RuntimeError
  logger = nil
  def initialize( message )
    @logger = Logger['test']
    @logger.error(message)
  end
end

# create logger
logger = Logger.new('test')
outputter = Outputter.stdout
outputter.formatter = PatternFormatter.new(:pattern => "[%l] %d :: %m")
logger.outputters = outputter

# test scanner
clamav = ClamScanner.new();
if !clamav.check()
  logger.error("woop error")
  exit(1)
end

# scan this file
file = '/path/to/test.file'
res = clamav.scan( file )
---------


Regards

Lars Roland