Tutorial :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?


Solution:1

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.


Solution:2

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.


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