rescue_from NoMethodError

Question

My setup: Rails 3.0.9, Ruby 1.9.2

I ran into this Rack bug on Heroku dealing with content-type being sent for non-file fields. Specifically the error I get is

NoMethodError (undefined method `rewind' for "blah":String):

"blah" is the value of a url param I'm passing. I'm thinking it should be possible to ignore this error doing something like this

application_controller.rb

  rescue_from NoMethodError do |exception|
    logger.debug "\n\n==============Rack rewind error=======================\n\n"
  end

How do I only check for NoMethodError rewind method? Or perhaps there is a way to override this Rack method?

Just to clarify, I have no control over calling the rewind method, this is handled in Rack itself, so I cannot use try or fix the error.

Answer 1

I would go and try to fix that error, if at all possible. If not, I don't think Rails lets you re-raise the exception from within rescue_from , but you can call the default error handler instead:

rescue_from NoMethodError do |exception|
  if exception.name == :rewind
    logger.debug "rewind error" 
  else
    rescue_action_without_handler(exception)
  end
end

Answer 2

I had the same problem, a client app written in python needed to upload a file along with couple of other non-file parameters to a Rails back-end. Only parameters with file object worked fine, but Rails raised NoMethodError (undefined method 'rewind' for <String#F3433>): when the python client sent string params. I solved it by applying the this patch by jdelStrother. It just required to comment following:

# elsif !filename && content_type
#   body.rewind
# 
#   # Generic multipart cases, not coming from a form
#   data = {:type => content_type,
#           :name => name, :tempfile => body, :head => head}

and replace them with:

else
    data = body
end

in method parse_multipart in module Rack::Utils::Multipart . just add the patch code in a ruby file in the config/initializers directory.