A Paperclip adapter to allow attachments to be set using a Mechanize::Download object; the default Paperclip::FileAdapter is incompatible with unlinked Tempfiles which Mechanize returns.

mechanize_download_adapter.rb

require 'paperclip'

module Paperclip
  # Mechanize unlinks its Tempfiles immediately after creating them and some
  # Paperclip functionality relies on an actual file available in the
  # filesystem; not just a reference.
  class MechanizeDownloadAdapter < AbstractAdapter
    def initialize(target)
      @target = target
      cache_current_values
    end

    def cache_current_values
      @original_filename = @target.filename
      @tempfile          = copy_to_tempfile(@target.body_io)
      @content_type      = ContentTypeDetector.new(@original_filename).detect
      @size              = @tempfile.size
    end

    def copy_to_tempfile(src)
      # Download's are either a StringIO or a Tempfile; both respond to read.
      while data = src.read(16*1024)
        destination.write(data)
      end
      destination.rewind
      destination
    end
  end
end

Paperclip.io_adapters.register Paperclip::MechanizeDownloadAdapter do |target|
  target.is_a?(Mechanize::Download)
end

mechanize_download_adapter_spec.rb

require 'spec_helper'
require 'paperclip/mechanize_download_adapter'

describe Paperclip::MechanizeDownloadAdapter do
  let(:filename) { 'chuckg.jpg' }
  let(:body_io)  { StringIO.new('HELLO FRIENDS') } 

  class Mechanize::Download
    # Stub initializer to nothing
    def initialize
    end
  end

  before do
    @download = Mechanize::Download.new 
    @download.stub(:filename).and_return(filename)
    @download.stub(:body_io).and_return(body_io)
  end

  subject { Paperclip.io_adapters.for(@download) }

  it 'sets the original_filename' do
    subject.instance_variable_get(:'@original_filename').should eq(filename)
  end

  it 'sets the tempfile' do
    tempfile = subject.instance_variable_get(:'@tempfile')
    tempfile.should be_a(Tempfile)
    tempfile.length.should > 0
  end

  it 'sets the content_type' do
    subject.instance_variable_get(:'@content_type').should eq('image/jpeg')
  end

  it 'sets the size' do
    subject.instance_variable_get(:'@size').should eq(body_io.size)
  end

  it 'copies the contents of body_io to tempfile' do
    expected = body_io.read
    body_io.rewind
    subject.read.should eq(expected)
  end

end