serve_byte_range

is a small utility for serving HTTP Range responses (partial content responses) from your Rails or Rack app. It will allow you to output partial content in a lazy manner without buffering, and perform correct encoding of multipart/byte-range responses. It will also make serving byte ranges safer because it coalesces the requested byte ranges into larger, consecutive ranges - reducing overhead.

Installation and usage

Add it to your Gemfile:

bundle add serve_byte_range

and use code like this to serve a large File object:

status, headers, body = serve_ranges(env, resource_size: File.size(path_to_large_file)) do |range_in_file, io|
  File.open(path_to_large_file, "rb") do |file|
    file.seek(range_in_file.begin)
    # `io` is an object that responds to `#write` and yields bytes to the Rack-compatible webserver
    IO.copy_stream(file, io, range_in_file.size)
  end
end
[status, headers, body] # And return the Rack response "triplet"

You can also retrieve the range_in_file from an external resource, you can also do it in chunks - whatever you prefer. The important thing is that your response - even for multiple ranges:

• Will be correctly pre-sized with Content-Length
• Will not be generated and buffered eagerly, but will get generated as you serve the content out