Set content type in S3 when attaching via Paperclip 4? - ruby-on-rails-3

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}",
}
}

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.
add this line to the model
attr_accessor :tmp_content_type, :tmp_file_name
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
Use the temp vars
:s3_headers => lambda { |attachment|
{
'Content-Type' => attachment.tmp_content_type,
"Content-Disposition" => "attachment; filename=\"# {attachment.tmp_file_name}\""
}
}