RESTful file uploads with CarrierWave

问题:

I'm trying to build an API backend for file uploads. I want to be able to upload files with a POST request that has a Base64-encoded string of the file. The server should decode the string, and save the file using CarrierWave. Here's what I have so far:

photo.rb:

class Photo
  include Mongoid::Document
  include Mongoid::Timestamps
  mount_uploader :image_file, ImageUploader
end

image_uploader.rb:

class ImageUploader < CarrierWave::Uploader::Base
  storage :file

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

Rails console: (summary)

ruby-1.8.7-p334 :001 > img = File.open("../image.png") {|i| i.read}
 => "\377���JFIF\000\001\002\001\000H\000H\000\000\377�Photoshop 3.0\0008BIM\003...
ruby-1.8.7-p334 :003 >   encoded_img = Base64.encode64 img
=> 3af8A\nmLpplt5U8q+a7G2...
ruby-1.8.7-p334 :005 >   p = Photo.new
 => #<Photo _id: 4e21b9a31d41c817b9000001, created_at: nil, updated_at: nil, _type: nil, user_id: nil, image_file_filename: nil> 
ruby-1.8.7-p334 :006 > p.user_id = 1
 => 1 
ruby-1.8.7-p334 :007 > p.image_file = Base64.decode64 encoded_img
\255��=\254\200�7u\226���\230�-zh�wT\253%����\036ʉs\232Is�M\215��˿6\247\256\177...
ruby-1.8.7-p334 :008 > p.save
 => true 
ruby-1.8.7-p334 :009 > p.image_file.url
 => nil 

full

The problem appears to be related to the process of converting a Base64-decoded string to a file. CarrierWave seems to expect a File object, and instead I'm giving it a String. So how do I convert that String to a File object. I'd like this conversion not to save anything to the file system, simply create the object and let CarrierWave do the rest.

回答1:

CarrierWave also accepts a StringIO, but it expects a original_filename method, since it needs it for figuring out the file name and doing the extension check. How you do it changed between Rails 2 and 3, here's both methods:

Rails 2

io = StringIO.new(Base64.decode64(encoded_img))
io.original_filename = "foobar.png"

p.image_file = io
p.save

In Rails 3, you need to make a new class and then manually add original_filename back

class FilelessIO < StringIO
    attr_accessor :original_filename
end

io = FilelessIO.new(Base64.decode64(encoded_img))
io.original_filename = "foobar.png"

p.image_file = io
p.save

回答2:

You don't have to monkeypatch StringIO or put any of this in your model. You can override the cache!() method in your uploader definition. Or you can take it a step further and make a module for yourself to include. My file is a serialized string coming from a json document. The object passed in looks like this { :filename => 'something.jpg', :filedata => base64 string }.

Here is my module:

module CarrierWave
  module Uploader
    module BackboneLink  
      def cache!(new_file=sanitized_file)
        #if new_file isn't what we expect just jump to super
        if new_file.kind_of? Hash and new_file.has_key? :filedata
          #this is from a browser, so it has all that 'data:..' junk to cut off.
          content_type, encoding, string = new_file[:filedata].split(/[:;,]/)[1..3]
          sanitized = CarrierWave::SanitizedFile.new( 
            :tempfile => StringIO.new(Base64.decode64(string)), 
            :filename => new_file[:filename], 
            :content_type => content_type 
          )
          super sanitized
        else
          super
        end
      end
    end
  end
end

And then I can include it in an uploader. uploaders/some_uploader.rb:

class SomeUploader < CarrierWave::Uploader::Base

  include CarrierWave::Uploader::BackboneLink

回答3:

class AppSpecificStringIO < StringIO
  attr_accessor :filepath

  def initialize(*args)
    super(*args[1..-1])
    @filepath = args[0]
  end

  def original_filename
    File.basename(filepath)
  end
end

also see the carrierwave wiki https://github.com/carrierwaveuploader/carrierwave/wiki/How-to%3A-Upload-from-a-string-in-Rails-3