HTTP2 Server Push link header generator (Using h2o & mruby, for ictsc-score-server)

h2o.conf

hosts:
  "example.com":
    listen:
      port: 443
      ssl:
        key-file: /etc/h2o/key.pem
        certificate-file: /etc/h2o/cert.pem
    http2-casper: ON
    reproxy: ON
    paths:
      "/":
        mruby.handler: |
          links = []
          {
            "css" => "style",
            "js" => "script"
          }.each do |ext, as|
            Dir.entries("/public/static/#{ext}").each do |file|
              links << "</static/#{ext}/#{file}>; rel=preload; as=#{as}" if file.end_with? ext
            end
          end

          # $stderr.puts links

          lambda do |env|
            if not File.exist?("/public/" + env["PATH_INFO"])
              return [307, {"x-reproxy-url" => "/"}, []]
            end
            return [399, { "link" => links.join("\n") }, []]
          end