Begin Rescue not catching error

Question

I'm using some ruby code wrapped in a begin - rescue block but somehow it manages to still crash.

the block of code looks like this:

# Retrieve messages from server
def get_messages
  @connection.select('INBOX')
  @connection.uid_search(['ALL']).each do |uid|
    msg = @connection.uid_fetch(uid,'RFC822').first.attr['RFC822']
    begin
      process_message(msg)
      add_to_processed_folder(uid) if @processed_folder
    rescue
       handle_bogus_message(msg)
    end
    # Mark message as deleted 
    @connection.uid_store(uid, "+FLAGS", [:Seen, :Deleted])
  end
end

Given this code i would assume that if process_message or add_to_processed_folder could not execute then rescue would kick in and call handle_bogus_message. That being said I'm running this code in a production environment and sometimes when i "get" an email message (this is run from a rake task) it dies with a SyntaxError.

For a look at the error message check out http://pastie.org/1028479 and not that process_message that it is referring to is the same process_message above. Is there any reason why begin - rescue won't catch this exception?

score 51 · Accepted Answer · edited May 23 '17 at 12:34

51

rescue without a parameter just rescues exceptions that inherit from StandardError. To rescue a SyntaxError use rescue SyntaxError.

To rescue all exceptions you would use rescue Exception, but note that that's a bad idea (which is why it's not the default behavior of rescue) as explained here and here. Especially this part:

Rescuing Interrupt prevents the user from using CTRLC to exit the program.

Rescuing SignalException prevents the program from responding correctly to signals. It will be unkillable except by kill -9.

edited May 23 '17 at 12:34

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answered Jul 02 '10 at 18:23

sepp2k

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The reason `rescue` doesn't rescue `Exception`s by default is that they're usually regarded as too severe to rescue. – Andrew Grimm Jul 06 '10 at 03:16
This still didn't catch SyntaxError for some reason. I am adding extra logging before re-raising the exception. The actual problem on customer side is that they get unescaped RegExp and I get SyntaxError when trying to reproduce the problem. – Human programmer Oct 26 '22 at 16:31

score 3 · Answer 2 · answered Jul 02 '10 at 19:46

rescue without any parameter accepts exceptions raised by StandardError class. Your error type is SyntaxError which is inherited from a different class called ScriptError. All these error classes are subclasses of Exception class. So as sepp2k suggested use rescue Exception to catch all kinds of exceptions.

Begin Rescue not catching error

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