convert a ruby stackprof file to the format required by pprof

stackprof_to_pprof.rb

# writes protobuf to stdout. Gzip that, and then https://github.com/google/pprof can read it.

require 'stackprof'
require 'pp'
require './profile_pb'

filename = 'profile-web-2020-11-04'
data = Marshal.load(IO.binread(filename)) 

class StringMap
  def initialize()
    @strings = []
    @string_hash = {}
    add("") # spec says string_table[0] must always be "".
  end
  attr_reader :strings
  attr_reader :string_hash

  def add(s)
    i = string_hash[s]
    return i unless i == nil

    i = strings.push(s).length - 1
    string_hash[s] = i
    return i
  end
end

samples = []
locations = []
functions = []
string_map = StringMap.new

data[:frames].each do |location_id, location|
  functions.push(Perftools::Profiles::Function.new(
    :id => location_id,
    :name => string_map.add(location[:name]),
    :filename => string_map.add(location[:file]),
    :start_line => location[:line],
  ))

  line = Perftools::Profiles::Line.new(
    :function_id => location_id,
    :line => location[:line],
  )

  locations.push(Perftools::Profiles::Location.new(
    :id => location_id,
    :line => [line],
  ))
end

raw = data[:raw]
while len = raw.shift
  frames = raw.slice!(0, len)
  frames.reverse!
  weight = raw.shift
  sample = Perftools::Profiles::Sample.new(
    :value => [(weight * data[:interval] * 1e-3).round],
    :location_id => frames,
  )
  samples.push(sample)
end

sample_type = Perftools::Profiles::ValueType.new(
  :type => string_map.add(data[:mode]),
  :unit => string_map.add("ms"),
)

message = Perftools::Profiles::Profile.new(
  :sample_type => [sample_type],
  :sample => samples,
  :string_table => string_map.strings,
  :location => locations,
  :function => functions,
)
STDOUT.write(Perftools::Profiles::Profile.encode(message))