Rails - Feb 2007 - How to make Rails send a file that is being written

I''m trying to build a simple proxy to Amazon S3 that would allow a
client to request a url that gets mapped to a S3 Object by Rails and
streamed back to the client.
For S3 integration, I use the highly recommended gem AWS::S3
(http://amazon.rubyforge.org/), and to send a file, I simply use the
send_file function.

The concept works BUT the I can''t get the file to be sent as
it''s been
downloaded. Even better would be to download the file to memory instead
of the disk, I''m really not familiar with Ruby''s IO Class
though.. If
anyone has a suggestion..


I first tried this:

  # download the file entirely then uploads it to the client
  send_data AWS::S3::S3Object.value ''object_name'',
''bucket_name''



Then I figured I needed to use the streaming feature of AWS::S3

  # Start a thread that downloads the file in the background
  Thread.start do
    open(''/tmp/tempfile'', ''w'') do |file|
      AWS::S3::S3Object.stream(''object_name'',
''bucket_name'') do |chunk|
        file.write chunk
      end
    end
  end

  ## Then send the file as it''s being written.
  send_file "/tmp/tempfile", :stream => true

This doesn''t work, the sent file is often between 0 and 4 bytes.. not
cool.

I''m guessing I could put it all together, I dont know how.

Here''s the send_file function that could be overwritten:


  def send_file(path, options = {}) #:doc:
    raise MissingFile, "Cannot read file #{path}" unless
File.file?(path) and File.readable?(path)

    options[:length]   ||= File.size(path)
    options[:filename] ||= File.basename(path)
    send_file_headers! options

    @performed_render = false

    if options[:stream]
      render :text => Proc.new { |response, output|
        logger.info "Streaming file #{path}" unless logger.nil?
        len = options[:buffer_size] || 4096
        File.open(path, ''rb'') do |file|
          if output.respond_to?(:syswrite)
            begin
              while true
                output.syswrite(file.sysread(len))
              end
            rescue EOFError
            end
          else
            while buf = file.read(len)
              output.write(buf)
            end
          end
        end
      }
    else
      logger.info "Sending file #{path}" unless logger.nil?
      File.open(path, ''rb'') { |file| render :text =>
file.read }
    end
  end



Please, any idea anyone?

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Remi Gabillet wrote:
> I''m trying to build a simple proxy to Amazon S3 that would allow a
> client to request a url that gets mapped to a S3 Object by Rails and
> streamed back to the client.
> For S3 integration, I use the highly recommended gem AWS::S3
> (http://amazon.rubyforge.org/), and to send a file, I simply use the
> send_file function.
> 
> The concept works BUT the I can''t get the file to be sent as
it''s been
> downloaded. Even better would be to download the file to memory instead
> of the disk, I''m really not familiar with Ruby''s IO Class
though.. If
> anyone has a suggestion..
> ...
> Then I figured I needed to use the streaming feature of AWS::S3
> 
>   # Start a thread that downloads the file in the background
>   Thread.start do
>     open(''/tmp/tempfile'', ''w'') do
|file|
>       AWS::S3::S3Object.stream(''object_name'',
''bucket_name'') do |chunk|
>         file.write chunk
>       end
>     end
>   end
> 
>   ## Then send the file as it''s being written.
>   send_file "/tmp/tempfile", :stream => true
> 
> This doesn''t work, the sent file is often between 0 and 4 bytes..
not
> cool.
Try using a ruby IO.pipe object instead of the tempfile.

-- 
We develop, watch us RoR, in numbers too big to ignore.


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