file_adapter.rb

module Paperclip
  class FileAdapter
    def initialize(target)
      @target = target
      @tempfile = copy_to_tempfile(@target)
    end

    def original_filename
      if @target.respond_to?(:original_filename)
        @target.original_filename
      else
        File.basename(@target.path)
      end
    end

    def content_type
      types = MIME::Types.type_for(original_filename)
      if types.length == 0
        type_from_file_command
      elsif types.length == 1
        types.first.content_type
      else
        best_content_type_option(types)
      end
    end

    def fingerprint
      @fingerprint ||= Digest::MD5.file(path).to_s
    end

    def size
      File.size(@tempfile)
    end

    def nil?
      @target.nil?
    end

    def read(length = nil, buffer = nil)
      @tempfile.read(length, buffer)
    end

    # We don't use this directly, but aws/sdk does.
    def rewind
      @tempfile.rewind
    end

    def eof?
      @tempfile.eof?
    end

    def path
      @tempfile.path
    end

    private

    def copy_to_tempfile(src)
      extension = File.extname(original_filename)
      basename = File.basename(original_filename, extension)
      dest = Tempfile.new([basename, extension])
      dest.binmode
      FileUtils.cp(src.path, dest.path)
      dest
    end

    def best_content_type_option(types)
      types.reject {|type| type.content_type.match(/\/x-/) }.first.content_type
    end

    def type_from_file_command
      # On BSDs, `file` doesn't give a result code of 1 if the file doesn't exist.
      type = (self.original_filename.match(/\.(\w+)$/)[1] rescue "octet-stream").downcase
      mime_type = (Paperclip.run("file", "-b --mime :file", :file => self.path).split(/[:;\s]+/)[0] rescue "application/x-#{type}")
      mime_type = "application/x-#{type}" if mime_type.match(/\(.*?\)/)
      mime_type
    end
  end
end

Paperclip.io_adapters.register Paperclip::FileAdapter do |target|
  File === target || Tempfile === target
end