Where to write begin rescue in Ruby (on Rails)

Question

When I write ruby or (rails), where should I write begin and rescue about http request (or just in general, where to write begin rescue)?

I'm talking about controller, model or module.

For example, I wrote codes like this.

module

module WhateverModule
  def get_list
    http, uri_path, headers = set_request("whatever_api_url")
    http.get(uri_path, headers)
  end

  #codes continue below

end

then, I often time puts begin and rescue code at controller.

controller

begin
  api_list = get_list
rescue => exception
  # do whatever I need to do to handle exceptions
  p "exception happened!"
end

but my PR reviewer keep saying "you should write a code like this"

module

module WhateverModule
  def get_list
    http, uri_path, headers = set_request("whatever_api_url")
    
    begin
      http.get(uri_path, headers)
    rescue => exception
      p "exception happend!"
    end
  end

  #codes continue below

end

My question is, which one is right (or clean or better)? Are there any general consensuses about where to put begin and rescue?

Thanks

user_2483313 · Answer

I would argue that when using rescue blocks it is a common pattern to follow two guidelines:

Put the rescue block only around the lowest number of lines possible. Usually, this should only be one line. That certainly depends on your code but in general, exceptions are raised by specific methods. The rescue block should only be around that block if possible. That makes debugging and refactoring much easier.
When adding a rescue block then name those exceptions that you expect to happen precisely. Otherwise you might catch errors that you didn't expect (syntax errors or method calls on nil). What again makes debugging much harder.

In your example, I agree with the PR reviewer but I would add the specific exceptions that might occur and that I want to handle. for example like this:

def get_list
  http, uri_path, headers = set_request("whatever_api_url")

  begin
    http.get(uri_path, headers)
  rescue Net::HTTPNotFound => e
    # handle page not found
  rescue Net::HTTPForbidden => e
    # handle invalid credentials
  rescue Net::HTTPServerError, Net::HTTPServerException
    # handle server error
  end
end

Of cause, how to handle exceptions and if that is even possible depends on your application. And therefore there is no hard rule but only there guidelines.

Where to write begin rescue in Ruby (on Rails)

1 Answers