Asset Price Server - debugging edges

Mix.install([
  {:kino, "~> 0.8.0"},
  {:vega_lite, "~> 0.1.6"}
])

Analyze log file

log_file = System.get_env("LB_LOG_FILE")

defmodule LogfileHelp do
  def remove_color_codes(text) do
    text
    |> String.replace(~r|\x1b\[[0-9;]*[mG]|, "")
  end

  def lines(text), do: String.split(text, "\n", trim: true)
end

defmodule AssetPriceServerLogs do
  def into_actions(text) do
    text
    |> Enum.map(fn line ->
      line
      |> String.split("#PID")
      |> Enum.at(1)
      |> String.split("] ")
      |> then(fn [pid, action] ->
        action |> String.split(" ")
        {pid, action}
      end)
    end)
  end

  def into_pid_and_context(text) do
    text
    |> Enum.map(fn line ->
      line
      |> String.split("#PID")
      |> Enum.at(1)
    end)
    |> Enum.reject(&is_nil/1)
    |> Enum.map(fn line ->
      line
      |> String.split("] ")
      |> then(fn [pid, context] ->
        {pid, context}
      end)
    end)
  end

  def group_by_pid(actions) do
    actions
    |> Enum.group_by(&elem(&1, 0))
  end
end

File.read!(log_file)
|> LogfileHelp.remove_color_codes()
|> LogfileHelp.lines()
|> AssetPriceServerLogs.into_pid_and_context()
|> AssetPriceServerLogs.group_by_pid()

These bytes seem to be an issue.

<<73, 9, 92, 8, 251, 255, 255, 254, 202>>

They (currently) parse as

"INSERT 157026555 4294966986"

But based on results from the protohacker check that’s calculating a price that’s way too high.

The problem spec says each of the two 4 byte parts following the query id are 32 bit integers. Maybe something needs to be specially handled there.

> The next 8 bytes are two signed two’s complement 32-bit integers in network byte order (big endian), whose meaning depends on the message type. We’ll refer to these numbers as int32, but note this may differ from your system’s native int32 type (if any), particularly with regard to byte order. — problem spec from protohackers

Aha Elixir defaults to unsigned integers.

https://hexdocs.pm/elixir/1.12/Kernel.SpecialForms.html#%3C%3C%3E%3E/1-sign

> ### Sign > > Integers can be signed or unsigned, defaulting to unsigned. > > > <> = <<-100>> > <<156>> > int > 156 > <> = <<-100>> > <<156>> > int > -100 > > > signed and unsigned are only used for matching binaries (see below) and are only used for integers. > > > <<-100::signed, _rest::binary>> = <<-100, "foo">> > <<156, 102, 111, 111>> > > > ### Endianness > > Elixir has three options for endianness: big, little, and native. The default is big: > > > <> = <<0, 1>> > <<0, 1>> > number > 256 > <> = <<0, 1>> > <<0, 1>> > number > 1 > > > native is determined by the VM at startup and will depend on the host operating system.

bytes = <<73, 9, 92, 8, 251, 255, 255, 254, 202>>

<<"I", timestamp::32, price::32>> = bytes
dbg(timestamp)
dbg(price)

<<"I", timestamp::signed-integer-32, price::signed-integer-32>> = bytes
dbg(timestamp)
dbg(price)

Yeah that’s my problem.

<< "I", timestamp::integer-32, price::integer-32>> = bytes

price: 4294966986

<< "I", timestamp::signed-integer-32, price::signed-integer-32>> = bytes

price: -310