救援不会在 Rails 中救援

Question

I'm writing a simple app that processes POST ed CSV files and am testing it against invalid input (eg non-CSV files). I'm using the CSV::Reader.parse command to parse the CSV in a controller method, as follows:

@parsed_file = CSV::Reader.parse(params[:file]) rescue []

However, despite the rescue statement, I'm still getting an uncaught CSV::IllegalFormatError when improper submissions are entered. What am I missing here?

Thanks!

Answer 1

You need to pass a file handle to parse:

@parsed_file = CSV::Reader.parse(File.open(params[:file], 'rb')) rescue []

Answer 2

I ended up having to monkey-patch the CSV::Reader class to properly handle the exception. I'm still not sure why it wasn't being caught in the controller, but here's the code I ended up writing:

class CSV
  class Reader
    def each
      while true
        row = []
        parsed_cells = get_row(row) rescue 0 
        if parsed_cells == 0
          break
        end
        yield(row)
      end
      nil
    end
  end
end

Note the rescue 0 after the call to get_row , which isn't present in the original. Definitely an ugly hack, but it'll serve my purposes.

If anyone can explain why the exception wasn't being caught in the controller, I'll gladly give them points for having the correct answer.

Answer 3

It sounds as if your CSV::IllegalFormatError isn't properly subclassing RuntimeError . Or alternatively RuntimeError has been changed to not subclass StandardError .

Only Errors which subclass StandardError are caught by default rescue blocks. To test this theory try

@parsed_file = begin 
  CSV::Reader.parse(params[:file]) 
rescue StandardError
  puts "I caught a StandardError"
  []
rescue Exception => e
  puts "I caught #{e.class}->#{e.class.superclass}->#{e.class.superclass.superclass}"
  []
end

This would explain why I (and probably others) can't repeat this problem.

Whatever the case using Exception explicitly should work, and will be cleaner than a monkey patch.