From: Joel VanderWerf <joelvanderwerf@...>
Date: 2010-02-23T04:47:37+09:00
Subject: Re: Ruby Idiom To Retry open() Upto N Times Before Giving Up

Dan wrote:
> I write a lot of scripts that I run once or infrequently that uses open-rui. Occasionally I run into a web site that times out or is unavailable for a period of time. My normal solution is to just rerun the script manually at a later time and the problem goes away. What I would like to start doing is rescuing the open() and retrying the open() after a delay. What would be the most idiomatic way to try opening a url say n times before giving up? Here is my crude code for trying twice:
> 
> begin  
>    open("http://www.example.com/foo.html")
>  rescue  
>    begin  
>       open("http://www.example.com/foo.html")
>     rescue  
>       #tried twice - giving up  
>    end  
> end  
> 
> I would like a more general approach using ruby idioms where I could specify the maximum number of attempts and delay before giving up. Thanks for your help.

Another approach (minus the delay part):

$ cat open-with-retry.rb
def open_with_retry uri, tries=3
   catch :success do
     tries.times do |i|
       begin
         throw :success, open(uri)
       rescue => e
         puts "try ##{i}: #{e}"
       end
     end
     raise "Giving up"
   end
end

f = open_with_retry(ARGV[0])
puts f.read

$ ruby open-with-retry.rb readme.txt
this is a file

$ ruby open-with-retry.rb noexist
try #0: No such file or directory - noexist
try #1: No such file or directory - noexist
try #2: No such file or directory - noexist
open-with-retry.rb:10:in `open_with_retry': Giving up (RuntimeError)
	from open-with-retry.rb:2:in `catch'
	from open-with-retry.rb:2:in `open_with_retry'
	from open-with-retry.rb:14