NoMethodError - undefined method `write' for "":String in custom processor

[kmarsh]

I have a custom processor, using MiniMagick's manipulate! method. Here's a summary of my code:

class PhotoUploader < CarrierWave::Uploader::Base
  include CarrierWave::MiniMagick

  storage :file

  def filename
    "#{model.id}.#{file.extension}"
  end

  def store_dir
    "uploads"
  end  

  version :blurred do
    process :blur
  end

  def blur
    manipulate! do |img|
      img = img.radial_blur 10
    end
  end
end

Problem is, when processing this, CarrierWave throws an error:

NoMethodError - undefined method `write' for "":String:
/Users/kmarsh/.rvm/gems/ruby-1.8.7-p302/gems/carrierwave-0.5.5/lib/carrierwave/processing/mini_magick.rb:246:in `manipulate!'

It seems as though current_path is returning "" for some reason, but I'm not too sure why.

[trevorturk]

Can you provide a sample app that uses the most recent version of CW? A full stack trace would help, too. Here's an example I made to track something down: https://github.com/trevorturk/carrierwave-issue-381

[brewster1134]

i too am struggling with this using mini_magick's resize

  def resize_by_height(height)
    manipulate! do |img|
      img = img.resize("x#{height}")
    end
  end

if i tweak the argument (img.resize("'x#{height}'")) so it throws the CarrierWave::ProcessingError exception, the error is more helpful...

CarrierWave::ProcessingError: Failed to manipulate with MiniMagick, maybe it is not an image? Original Error: Command ("mogrify -resize "'x75'" /var/folders/60/22_1pphd513_xj6j36smvdy80000gn/T/mini_magick20110818-83173-1j425yg.jpg") failed: {:status_code=>1, :output=>"mogrify: invalid argument for option `'x75'': -resize @ error/mogrify.c/MogrifyImageCommand/5423.\n"}

essentially it seems that it is is wrapping the command line arguments in quotes

[brewster1134]

oops. forgot to include yield(img) if block_given?. now its working fine. perhaps its the same issue for @willcodeforfoo

[trevorturk]

@brewster1134 can you provide an example before/after?

[kmarsh]

Didn't seem to make a difference for me, current_path is still "".

@trevorturk: I used your sample Sinatra app posted on the Engine Yard blog recently as a basis for a simple app that demonstrates the issue: https://gist.github.com/1157829

[trevorturk]

This seems to work for me. Maybe you'd be interested in making a wiki page about it?

[trevorturk]

Forgot the link :) https://gist.github.com/5d66897d88d1b5dfbea5

[kmarsh]

That did work! So the keys for processors are:

1. Call method directly on existing img rather than assigning to img
2. Make sure to yield if a block is given, img = yield(img) if block_given?
3. Return img at the end of the processor

lib/carrierwave/processing/mini_magick.rb should probably be edited to reflect this, as it was where I was getting the code from, thinking that img = img.foo would work:

  # Or create your own helpers with the powerful manipulate! method. Check
  # out the ImageMagick docs at http://www.imagemagick.org/script/command-line-options.php for more
  # info
  #
  #     class MyUploader < CarrierWave::Uploader::Base
  #       include CarrierWave::MiniMagick
  #
  #       process :do_stuff => 10.0
  #
  #       def do_stuff(blur_factor)
  #         manipulate! do |img|
  #           img = img.sepiatone
  #           img = img.auto_orient
  #           img = img.radial_blur blur_factor
  #         end
  #       end
  #     end

Would you like a pull request for this change?

I'll see about making a wiki page for custom processing actions.

[trevorturk]

Yeah, pull requests and wiki pages would definitely help. I agree the docs need some work. It was hard for me to tell what was the "right way" to do this :)

[dlindahl]

The details of this Wiki addition should also be reflected in the RDOC output as found here:

http://carrierwave.rubyforge.org/rdoc/classes/CarrierWave/MiniMagick.html

[trevorturk]

http://carrierwave.rubyforge.org/ is no longer updated

[Awea]

I get the same error but for a different processing :

class ImageUploader < CarrierWave::Uploader::Base
  include CarrierWave::MiniMagick

  # S3 Storage
  storage :fog

  def extension_white_list
    %w(jpg jpeg gif png)
  end

  def store_dir
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end

  version :project_list, :if => :is_project_image? do
    process :cropper
  end

  def cropper
    manipulate! do |img|
      if model.crop_x.blank?
        image = MiniMagick::Image.open(current_path)
        model.crop_w = (image[:width] * 0.8).to_i
        model.crop_h = (image[:height] * 0.8).to_i
        model.crop_x = (image[:width] * 0.1).to_i
        model.crop_y = (image[:height] * 0.1).to_i
      end
      img.crop "#{model.crop_w}x#{model.crop_h}+#{model.crop_x}+#{model.crop_y}"
    end 
  end

  def is_project_image?(new_file)
    begin
      return model.model_with_project_image unless model.model_with_project_image.nil?
    rescue
      false
    end
  end
end

I'm missing something or it's a real issue ? ^^