Example Rails model using Paperclip and storing files on S3. This shows how to correctly set a custom header and saving the file in the correct location after it has been directly uploaded to from the users browser.

file_resource.rb

class FileResource < ActiveRecord::Base
  has_attached_file :attachment,
    :storage => :s3,
    :bucket => ENV['S3_BUCKET'],
    :s3_credentials => { :access_key_id => ENV['S3_KEY'],
                         :secret_access_key => ENV['S3_SECRET'] },
    :path => 'files/:id/:filename',
    :url => '/files/:id/:filename'


  validates_attachment_presence :attachment

  after_create :move_upload_from_temp_to_final_resting_place

  protected

  def move_upload_from_temp_to_final_resting_place
    AWS::S3::Base.establish_connection!(
      :access_key_id      => ENV['S3_KEY'],
      :secret_access_key  => ENV['S3_SECRET']
    )

    old_name = "_temp/#{self.attachment_file_name}"
    new_name = self.attachment.path

    AWS::S3::S3Object.rename(old_name, new_name, ENV['S3_BUCKET'], :copy_acl => :true)
    # WARNING: When ever an attachment is reprocessed by paperclip all its headers/metadata is lost! This also applies to the original!
    self.attachment.reprocess! unless self.attachment.styles.empty?
    AWS::S3::S3Object.update(new_name, ENV['S3_BUCKET'], :content_disposition => "attachment; filename=\"#{self.attachment_file_name}\"", :access => :public_read)
  end
end