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...

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}",
    }
  }