rack-mini-profiler + speedscope.app

bookmarklet.js

javascript:void(function(){params=new URLSearchParams(document.location.search.slice(1));params.set("pp","flamegraph");open('https://www.speedscope.app/#profileURL='+encodeURIComponent(`${document.location.origin}${document.location.pathname}?${params.toString()}`))}())

flamegraph.rb

require "zlib"
require "json"
require "stackprof"

module Flamegraph
  def self.generate(filename = nil, opts = {})
    fidelity = opts[:fidelity] || 0.5

    profile = JSON.generate(
      StackProf.run(
        mode: :wall,
        raw: true,
        aggregate: false,
        interval: (fidelity * 1000).to_i
      ) do
        yield
      end
    )

    if filename
      File.open(filename, "w") do |f|
        f.write(profile)
      end
    end

    profile
  end
end

module Rack
  class MiniProfiler
    def flamegraph(graph)
      headers = {
        "Content-Type" => "application/x-download",
        "Content-disposition" => "attachment; filename=\"#{Time.now.to_i}.json.gz\"",
        "Access-Control-Allow-Origin" => "https://www.speedscope.app"
      }
      gz = Zlib::GzipWriter.new(StringIO.new)
      gz << graph
      [200, headers, [gz.close.string]]
    end
  end
end