How to setup a generic error/exception handler callback in Ruby?

Question

I’m working on this issue: Rails exception notifier in rake tasks

My question: Is there any function/plugin/gem/whatever to setup a generic error/exception handler callback as in PHP with set_error_handler and set_exception_handler?

I need a way to register a callback function used as a catchall outside any begin .. rescue .. end block. For example:

def my_handler *args
  # exception processing code here
end

some_magic_method my_handler

raise "An Exception" # this will be handled by my_handler

In PHP this could be achieved with the set_exception_handler function. Is there any such function in Ruby/Rails?

If such feature exists I could solve my previous issue in a simple way.

A Rails-only solution would be fine for my needs.

Emily · Accepted Answer · 2011-08-23 22:39:45Z

2

I don't believe Ruby provides a way to do this, either with exceptions or with throw/catch. In general, doing something this way is a code smell and something to avoid. It makes control flow extremely hard to figure out. I would try to find some other way to approach the problem if at all possible.

answered Aug 23, 2011 at 22:39

Emily

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2 Comments

Fabio Over a year ago

I'm agree in part with your point, what I'm asking for is conceptually similar to rescue_from class method used in ActionController but in the top level part of a program. It could be very useful and DRY in some cases.

Emily Over a year ago

Agreed, there are times it's useful. That's why it's a code smell, not an anti-pattern :)

Pedro Rolo · Accepted Answer · 2011-08-23 15:52:21Z

1

If you want to do this in the HTTP Request-handling cycle you may use an around filter in your application controller:

class ApplicationController < ActionController::Base
  around_filter do |controller, action|
    action.call
  rescue ExceptionXPTO
     # ... handle the exception ...
  end
end

answered Aug 23, 2011 at 15:52

Pedro Rolo

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1 Comment

Fabio Over a year ago

I know that, but nice hint. However that won't solve the generic issue.

Fabio · Accepted Answer · 2011-08-24 11:13:19Z

0

I found a partial solution to my issue which works for the simple case I mentioned in the question. However this can not catch the exception, but it can be useful if someone needs only exception logging or reporting.

#!/usr/bin/env ruby

at_exit do
  if $!
    puts "Program ended with an exception #{$!.message}"
    puts $!.backtrace.join("\n")
    # or log the exception here
  end
end

loop do
  value = rand(3)
  puts "Value is #{value}"
  break if value == 2 
  raise "An Exception" if value == 0
end

puts "Program ended normally"

answered Aug 24, 2011 at 11:13

Fabio

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