Optimize Cookies.encode by avoiding string interpolation

[preciz]

Assited by: Antigravity CLI : Gemini Flash 3.5

~1.2x-1.7x speedup and same memory usage.

Bench:

Mix.install([
  {:benchee, "~> 1.3"}
])

defmodule OriginalCookieEncoder do
  def encode(key, opts \\ %{}) when is_map(opts) do
    value = Map.get(opts, :value)
    path = Map.get(opts, :path, "/")

    IO.iodata_to_binary([
      "#{key}=#{value}; path=#{path}",
      emit_if(opts[:domain], &["; domain=", &1]),
      emit_if(opts[:max_age], &encode_max_age(&1, opts)),
      emit_if(Map.get(opts, :secure, false), "; secure"),
      emit_if(Map.get(opts, :http_only, true), "; HttpOnly"),
      emit_if(Map.get(opts, :same_site, nil), &encode_same_site/1),
      emit_if(opts[:extra], &["; ", &1])
    ])
  end

  defp encode_max_age(max_age, opts) do
    time = Map.get(opts, :universal_time) || :calendar.universal_time()
    time = add_seconds(time, max_age)
    ["; expires=", rfc2822(time), "; max-age=", Integer.to_string(max_age)]
  end

  defp encode_same_site(value) when is_binary(value), do: "; SameSite=#{value}"

  defp emit_if(value, fun_or_string) do
    cond do
      !value ->
        []

      is_function(fun_or_string) ->
        fun_or_string.(value)

      is_binary(fun_or_string) ->
        fun_or_string
    end
  end

  defp pad(number) when number in 0..9, do: <<?0, ?0 + number>>
  defp pad(number), do: Integer.to_string(number)

  defp rfc2822({{year, month, day} = date, {hour, minute, second}}) do
    [
      weekday_name(:calendar.day_of_the_week(date)),
      ?,,
      ?\s,
      pad(day),
      ?\s,
      month_name(month),
      ?\s,
      Integer.to_string(year),
      ?\s,
      pad(hour),
      ?:,
      pad(minute),
      ?:,
      pad(second),
      " GMT"
    ]
  end

  defp weekday_name(1), do: "Mon"
  defp weekday_name(2), do: "Tue"
  defp weekday_name(3), do: "Wed"
  defp weekday_name(4), do: "Thu"
  defp weekday_name(5), do: "Fri"
  defp weekday_name(6), do: "Sat"
  defp weekday_name(7), do: "Sun"

  defp month_name(1), do: "Jan"
  defp month_name(2), do: "Feb"
  defp month_name(3), do: "Mar"
  defp month_name(4), do: "Apr"
  defp month_name(5), do: "May"
  defp month_name(6), do: "Jun"
  defp month_name(7), do: "Jul"
  defp month_name(8), do: "Aug"
  defp month_name(9), do: "Sep"
  defp month_name(10), do: "Oct"
  defp month_name(11), do: "Nov"
  defp month_name(12), do: "Dec"

  defp add_seconds(time, seconds_to_add) do
    time_seconds = :calendar.datetime_to_gregorian_seconds(time)
    :calendar.gregorian_seconds_to_datetime(time_seconds + seconds_to_add)
  end
end

defmodule OptimizedCookieEncoder do
  def encode(key, opts \\ %{}) when is_map(opts) do
    value = Map.get(opts, :value) || ""
    path = Map.get(opts, :path, "/")

    IO.iodata_to_binary([
      key, ?=, value, "; path=", path,
      emit_if(opts[:domain], &["; domain=", &1]),
      emit_if(opts[:max_age], &encode_max_age(&1, opts)),
      emit_if(Map.get(opts, :secure, false), "; secure"),
      emit_if(Map.get(opts, :http_only, true), "; HttpOnly"),
      emit_if(Map.get(opts, :same_site, nil), &encode_same_site/1),
      emit_if(opts[:extra], &["; ", &1])
    ])
  end

  defp encode_max_age(max_age, opts) do
    time = Map.get(opts, :universal_time) || :calendar.universal_time()
    time = add_seconds(time, max_age)
    ["; expires=", rfc2822(time), "; max-age=", Integer.to_string(max_age)]
  end

  defp encode_same_site(value) when is_binary(value), do: "; SameSite=#{value}"

  defp emit_if(value, fun_or_string) do
    cond do
      !value ->
        []

      is_function(fun_or_string) ->
        fun_or_string.(value)

      is_binary(fun_or_string) ->
        fun_or_string
    end
  end

  defp pad(number) when number in 0..9, do: <<?0, ?0 + number>>
  defp pad(number), do: Integer.to_string(number)

  defp rfc2822({{year, month, day} = date, {hour, minute, second}}) do
    [
      weekday_name(:calendar.day_of_the_week(date)),
      ?,,
      ?\s,
      pad(day),
      ?\s,
      month_name(month),
      ?\s,
      Integer.to_string(year),
      ?\s,
      pad(hour),
      ?:,
      pad(minute),
      ?:,
      pad(second),
      " GMT"
    ]
  end

  defp weekday_name(1), do: "Mon"
  defp weekday_name(2), do: "Tue"
  defp weekday_name(3), do: "Wed"
  defp weekday_name(4), do: "Thu"
  defp weekday_name(5), do: "Fri"
  defp weekday_name(6), do: "Sat"
  defp weekday_name(7), do: "Sun"

  defp month_name(1), do: "Jan"
  defp month_name(2), do: "Feb"
  defp month_name(3), do: "Mar"
  defp month_name(4), do: "Apr"
  defp month_name(5), do: "May"
  defp month_name(6), do: "Jun"
  defp month_name(7), do: "Jul"
  defp month_name(8), do: "Aug"
  defp month_name(9), do: "Sep"
  defp month_name(10), do: "Oct"
  defp month_name(11), do: "Nov"
  defp month_name(12), do: "Dec"

  defp add_seconds(time, seconds_to_add) do
    time_seconds = :calendar.datetime_to_gregorian_seconds(time)
    :calendar.gregorian_seconds_to_datetime(time_seconds + seconds_to_add)
  end
end

inputs = %{
  "Simple cookie" => %{key: "session_id", opts: %{value: "xyz123"}},
  "Nil cookie" => %{key: "session_id", opts: %{}},
  "Complex cookie" => %{key: "session_id", opts: %{value: "xyz123", secure: true, http_only: true, max_age: 3600, same_site: "Lax"}}
}

Benchee.run(
  %{
    "Original (Unoptimized)" => fn %{key: key, opts: opts} -> OriginalCookieEncoder.encode(key, opts) end,
    "Optimized (New)" => fn %{key: key, opts: opts} -> OptimizedCookieEncoder.encode(key, opts) end
  },
  inputs: inputs,
  time: 2,
  warmup: 2,
  memory_time: 1
)

Results on noisy system:

Operating System: Linux
CPU Information: AMD Ryzen 7 8845HS w
Number of Available Cores: 16
Available memory: 54.72 GB
Elixir 1.20.0
Erlang 29.0.1
JIT enabled: true

Benchmark suite executing with the following configuration:
warmup: 2 s
time: 2 s
memory time: 1 s
reduction time: 0 ns
parallel: 1
inputs: Complex cookie, Nil cookie, Simple cookie
Estimated total run time: 30 s
Excluding outliers: false

##### With input Complex cookie #####
Name                             ips        average  deviation         median         99th %
Optimized (New)               1.67 M      600.41 ns  ±1145.56%         501 ns        1373 ns
Original (Unoptimized)        1.40 M      715.00 ns   ±897.61%         601 ns        1502 ns

Comparison:
Optimized (New)               1.67 M
Original (Unoptimized)        1.40 M - 1.19x slower +114.59 ns

Memory usage statistics:

Name                      Memory usage
Optimized (New)                  904 B
Original (Unoptimized)           904 B - 1.00x memory usage +0 B

**All measurements for memory usage were the same**

##### With input Nil cookie #####
Name                             ips        average  deviation         median         99th %
Optimized (New)               6.52 M      153.40 ns  ±5017.02%         120 ns         251 ns
Original (Unoptimized)        3.72 M      268.52 ns  ±2892.86%         181 ns         441 ns

Comparison:
Optimized (New)               6.52 M
Original (Unoptimized)        3.72 M - 1.75x slower +115.12 ns

Memory usage statistics:

Name                      Memory usage
Optimized (New)                  248 B
Original (Unoptimized)           248 B - 1.00x memory usage +0 B

**All measurements for memory usage were the same**

##### With input Simple cookie #####
Name                             ips        average  deviation         median         99th %
Optimized (New)               6.85 M      145.92 ns  ±3391.17%         120 ns         260 ns
Original (Unoptimized)        3.71 M      269.56 ns  ±3417.04%         170 ns        1162 ns

Comparison:
Optimized (New)               6.85 M
Original (Unoptimized)        3.71 M - 1.85x slower +123.64 ns

Memory usage statistics:

Name                      Memory usage
Optimized (New)                  256 B
Original (Unoptimized)           256 B - 1.00x memory usage +0 B

**All measurements for memory usage were the same**

[preciz]

I'm closing this and reopen a better Pull Request on this same code part