Set content type in S3 when attaching via Paperclip 4?

Question

I'm trying to attach CSV files to a Rails3 model using paperclip 4.1.1, but I'm having trouble getting the content-type as reported by S3 to be text/csv (instead I am getting text/plain). When I subsequently download the file from S3, the extension is getting changed to match the content-type instead of preserving the original extension (so test.csv is downloaded as test.txt).

From what I can see, when you upload a file, the FileAdapter will cache the content-type on creation with whatever value was determined by the ContentTypeDetector (which calls file -b --mime filename). Unfortunately, CSV files return text/plain which makes sense, as how can you really distinguish this? Attempts to set the content-type with attachment.instance_write(:content_type, 'text/csv') only set the value in the model and do not affect what gets written to S3.

FileAdapter's content_type initialized here: https://github.com/thoughtbot/paperclip/blob/v4.0/lib/paperclip/io_adapters/file_adapter.rb#L14

Call which creates that io_adapter: https://github.com/thoughtbot/paperclip/blob/v4.0/lib/paperclip/attachment.rb#L98

I really have a generic upload here (so I can't hard-code the content type in the S3 headers definition in has_attached_file), and I don't really want the content-type spoofing protection. Any ideas/suggestions? I would prefer not to downgrade to 3.5 because it would mean just delaying the pain, but if that's the only way, I'll entertain it...

Footgear

Are you using s3 or s3 through fog for your storage provider? You could pass a lambda into the s3_headers to determine if you should overwrite the content_type value, but the fog implementation doesn't have an equivalent :fog_headers option... – Tripod

@Tripod If I use S3 through Fog, do I have any other ways to override the header? – Dresser

@charinten hoping my answer below helps you. – Tripod

Answer 1

If you are using fog then you can do something like this:

has_attached_file :report,
  fog_file: lambda { |attachment|
    {
      content_type: 'text/csv',
      content_disposition: "attachment; filename=#{attachment.original_filename}",
    }
  }

If you are using Amazon S3 as your storage provider, then something like this should work:

has_attached_file :report
  s3_headers: lambda { |attachment|
    { 
      'Content-Type' => 'text/csv',
      'Content-Disposition' => "attachment; filename=#{attachment.original_filename}",
    }
  }

Tripod

In your setup, do you mean that we can only upload 'text/csv'? What about other format? – Dresser

I think you have an extra comma at the end of the 'Content-Disposition' lines. The s3_headers section works fine if using s3 with fog. – Nicolasanicolau

attachment instance here is the model itself, taking the example above - original_filename here is a method or could be an attribute in your model. – Augustusaugy

Almost there... but the attachment is empty entity (before save) when sending to s3, so attachment.original_filename is always nil. How could I access the original filename before it's saved? – Juggernaut

I have the exact same issue. Did you figure out a workaround? – Martinmartina

does anyone know how to fix this? s3_headers lambda gets an attachment which has all the attachment attributes set to nil, the file name, size, content type etc everything is nil when s3_headers lambda gets executed. The lambda is only useful for static headers. – Quintanilla

@Quintanilla others who have encountered empty attachment attributes have found success in adding custom setters to the model like this solution: https://mcmap.net/q/297881/-set-content-type-in-s3-when-attaching-via-paperclip-4 – Tripod

thanks @stereoscott, I've checked it already and also posted a version of my own solution – Quintanilla

Answer 2

Had this problem just recently and both the post process and the lambda don't work so did a work around. Same with others observation, the values of the attachment is empty when calling the s3 lambda headers.

1. add this line to the model

attr_accessor :tmp_content_type, :tmp_file_name

2. override the file assignment method so we could get the file info and store it for later use

 def file=(f)
  set_tmp_values(f.path)
  file.assign(f)
end

def set_tmp_values(file_path)
  self.tmp_file_name = File.basename(file_path)
  self.tmp_content_type = MIME::Types.type_for(file_path).first.content_type
end

2. Use the temp vars

:s3_headers => lambda { |attachment|
  {
    'Content-Type' => attachment.tmp_content_type,
    "Content-Disposition" => "attachment; filename=\"# {attachment.tmp_file_name}\""
  }
}

Choreography

which class' file= method is being overridden in this case? – Quintanilla

figured it out, the file= method is due to the model having has_attached_file :file, so it is being overriden in the model itself – Quintanilla

Answer 3

I'm using Paperclip 6.1.0 with Rails 5.2.3, Ruby 2.6.6, this answer uses the same idea proposed by James Euangel in an existing answer, but it's a bit more generic and uses monkey-patching.

I'll define attr_accessors on the model that uses Paperclip::Attachment for file attachment and use those to set values in the s3_headers options which get passed to has_attached_file macro.

# app/models/concerns/paperclip_attributes_maker.rb
# This concern defines attr_accessors for the paperclip attachment attributes of the ActiveRecord model

module PaperclipAttributesMaker
  extend ActiveSupport::Concern

  def self.included
    base.class_eval do
      base::PAPERCLIP_ATTACHMENT_ATTRS.each do |attachment_attr|
        attr_accessor "paperclip_#{attachment_attr}_content_type"
        attr_accessor "paperclip_#{attachment_attr}_filename"
      end
    end
  end
end

Now, we need to monkey-patch the attachment setter method defined in the Paperclip::HasAttachaedFile class:

# app/initializers/patch_paperclip_has_attached_file.rb
# it patches paperclip/has_attached_file.rb

module Paperclip
  class HasAttachedFile
    def define_setter
      name = @name
      @klass.send :define_method, "#{@name}=" do |file|
        content_type = (file.content_type || MIME::Types.type_for(file.path).first.content_type) rescue nil
        instance_variable_set("@paperclip_#{name}_content_type", content_type)
        instance_variable_set("@paperclip_#{name}_filename", (file.original_filename rescue nil))
        send(name).assign(file)
      end
    end
  end
end

Lastly, we declare the Paperclip attachments(by this I mean how many attachments we got in the ActiveRecord model):

class StudentAttachment < ApplicationRecord
  PAPERCLIP_ATTACHMENT_ATTRS = [:attachment1, :attachment2]
  
  include PaperclipAttributesMaker # should be included after definition of PAPERCLIP_ATTACHMENT_ATTRS
  
  #...other code

  has_attached_file :attachment1, { # other options here
    s3_headers: lambda { |attachment|
      {
        'Content-Type' => attachment.paperclip_attachment1_content_type,
        "Content-Disposition" => "attachment; filename=\"#{attachment.paperclip_attachment1_filename}\""}}
      }

  has_attached_file :attachment2, { # other options here
    s3_headers: lambda { |attachment|
      {
        'Content-Type' => attachment.paperclip_attachment2_content_type,
        "Content-Disposition" => "attachment; filename=\"#{attachment.paperclip_attachment2_filename}\""}}
      }
end

Quintanilla