From: Joe Van Dyk <joevandyk@...>
Date: 2005-08-04T11:30:14+09:00
Subject: Re: RMagick problem

On 8/3/05, Joe Van Dyk <joevandyk@gmail.com> wrote:
> On 8/3/05, Tim Hunter <cyclists@nc.rr.com> wrote:
> > Joe Van Dyk wrote:
> >
> > > The following Rails/Ruby code gives me this error: "Zero-length blob
> > > not permitted".
> > >
> > > @magick_image = Magick::Image.from_blob(@file.read).first
> > >
> > > Where @file is a StringIO object or a File object, depending on the
> > > size of the uploaded file.
> > >
> > > @file.read.size returns the expected file size (in bytes).
> > >
> > > Any ideas?
> >
> > Well, it works for me. Here's my attempt to reproduce the problem.
> >
> > require 'RMagick'
> > require 'stringio'
> >
> > file = File.open('Flower_Hat.jpg')
> > img = Magick::Image.from_blob(file.read).first
> > p img
> >
> > blob = IO.read('Flower_Hat.jpg')
> > sio = StringIO.new(blob)
> > img = Magick::Image.from_blob(sio.read).first
> > p img
> >
> >
> > The output is:
> > tim: ~> ruby  test.rb
> >  JPEG 200x250 DirectClass 8-bit 9kb
> >  JPEG 200x250 DirectClass 8-bit 9kb
> 
> Yeah, I tried to do that test last night and it worked fine.
> 
> So I have no idea why the code is failing inside my Image model.

Here's my image model.  Perhaps that will give someone some insight.  

Say, I'm doing the Magick::Image.from_blob call in #after_save. 
Perhaps something weird is happening with @file's lifetime or
something?

class Image < ActiveRecord::Base
  belongs_to :house
  belongs_to :community
  belongs_to :contractor

  FileLocation = "#{RAILS_ROOT}/public/media/"
  DisplayLocation = "/media"
  
def file=(file)
    if file.size > 0
      self.content_type = file.content_type.strip
      @file = file
    end
  end

  # Runs after Image is saved, saves the image to the file system.
  def after_save
    if @file
      @magick_image = Magick::Image.from_blob(@file.read).first
      save_full_image
      save_thumbnail_image
      save_rounded_thumbnail_image
      save_medium_image
      save_large_image
    end
  end

  # If image is already a jpeg, then just write it to a file.
  # If it's not, convert it to a jpeg and then write.
  def save_full_image
    @magick_image.write(full_file)
  end

  # Write a thumbnail to the filesystem
  def save_thumbnail_image
    thumbnailed_magick_image = resize_image_to_exact_size(180,135)
    thumbnailed_magick_image.write(thumbnail_file)
  end

  def save_rounded_thumbnail_image
    thumbnail_image = resize_image_to_exact_size(180, 135)
    color = "#000033"
    corner_width = 15
    corners = Magick::Draw.new
    corners.stroke(color)
    corners.fill_opacity(0)
    corners.stroke_width(15)
    corners.roundrectangle(0, 0, 
                           thumbnail_image.columns, thumbnail_image.rows, 
                           corner_width, corner_width)
    corners.draw(thumbnail_image)
    thumbnail_image.write(rounded_thumbnail_file)
  end

  # Resizes a Magick image to an exact size, keeping the same aspect ratio
  def resize_image_to_exact_size(width, height)
    new_aspect_ratio = width.to_f / height.to_f
    old_aspect_ratio = @magick_image.columns.to_f / @magick_image.rows.to_f

    if old_aspect_ratio < new_aspect_ratio
      # Image too tall, geometry string should restrict height
      geometry_string = "#{width}"
    else
      # Image too wide or just right, geometry string should 
      # restrict width
      geometry_string = "x#{height}"
    end

    # Get the resized image
    resized_image = resize_image(geometry_string)

    # Return the resized, crop image
    resized_image.crop(Magick::CenterGravity, width, height)
  end

  def resize_image(geometry_string)
    logger.debug "resizing image to #{geometry_string}"
    @magick_image.change_geometry(geometry_string) do |w, h, img|
      img.resize(w, h)
    end
  end

  def save_medium_image
    medium_image = resize_image("275")
    medium_image.write(medium_file)
  end

  def save_large_image
    large_image = resize_image("500")
    large_image.write(large_file)
  end



  # Delete images from filesystem
  def after_destroy
    File.delete(full_file) if File.exist? "#{full_file}"
    File.delete(thumbnail_file) if File.exist? "#{thumbnail_file}"
    File.delete(rounded_thumbnail_file) if File.exist?
"#{rounded_thumbnail_file}"
    File.delete(medium_file) if File.exist? "#{medium_file}"
    File.delete(large_file) if File.exist? "#{large_file}"
  end

  # Returns the filesystem location of the image file
  def full_file
    "#{FileLocation}/full/#{id}.jpg"
  end
  def thumbnail_file
    "#{FileLocation}/thumbnail/#{id}.jpg"
  end
  def rounded_thumbnail_file
    "#{FileLocation}/rounded_thumbnail/#{id}.jpg"
  end
  def medium_file
    "#{FileLocation}/medium/#{id}.jpg"
  end
  def large_file
    "#{FileLocation}/large/#{id}.jpg"
  end


  # Returns the location of the image to the browser
  def full
    "#{DisplayLocation}/full/#{id}.jpg"
  end
  def thumbnail
    "#{DisplayLocation}/thumbnail/#{id}.jpg"
  end
  def medium
    "#{DisplayLocation}/medium/#{id}.jpg"
  end
  def large
    "#{DisplayLocation}/large/#{id}.jpg"
  end
  def rounded_thumbnail
    "#{DisplayLocation}/rounded_thumbnail/#{id}.jpg"
  end def resize
    if File.exist? full_file
      @file = File.open full_file
      save
    end
  end
end