Optimize Cookies.encode

[preciz]

Assisted by: Antigravity CLI : Gemini 3.5 Flash

I like the code structure of this pull request.

Bench:

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

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

    key = to_string(key)
    value = to_string(value)
    path = to_string(path)

    acc = [key, ?=, value, "; path=", path]
    acc = if domain = opts[:domain], do: [acc, "; domain=", domain], else: acc
    acc = if max_age = opts[:max_age], do: [acc | encode_max_age(max_age, opts)], else: acc
    acc = if Map.get(opts, :secure, false), do: [acc | "; secure"], else: acc
    acc = if Map.get(opts, :http_only, true), do: [acc | "; HttpOnly"], else: acc
    acc = if same_site = Map.get(opts, :same_site), do: [acc | encode_same_site(same_site)], else: acc
    acc = if extra = opts[:extra], do: [acc, "; ", extra], else: acc

    IO.iodata_to_binary(acc)
  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 pad(n) when n < 10, do: <<?0, ?0 + n>>
  defp pad(n), do: <<?0 + div(n, 10), ?0 + rem(n, 10)>>

  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 = %{
  "Basic cookie" => {"foo", %{value: "bar"}},
  "Full options" => {"foo", %{value: "bar", path: "/baz", domain: "google.com", secure: true, same_site: "Lax", max_age: 60, universal_time: {{2012, 1, 7}, {15, 32, 10}}}},
  "Extra options" => {"foo", %{value: "bar", extra: "SameSite=Lax"}}
}

Benchee.run(
  %{
    "Old encode" => fn {key, opts} -> OldCookies.encode(key, opts) end,
    "New encode" => fn {key, opts} -> NewCookies.encode(key, opts) end
  },
  inputs: inputs,
  time: 2,
  warmup: 1,
  memory_time: 2
)

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: 1 s
time: 2 s
memory time: 2 s
reduction time: 0 ns
parallel: 1
inputs: Basic cookie, Extra options, Full options
Estimated total run time: 30 s
Excluding outliers: false

##### With input Basic cookie #####
Name                 ips        average  deviation         median         99th %
New encode        7.26 M      137.70 ns  ±4224.40%         110 ns         231 ns
Old encode        4.13 M      242.31 ns  ±2428.06%         161 ns         431 ns

Comparison:
New encode        7.26 M
Old encode        4.13 M - 1.76x slower +104.61 ns

Memory usage statistics:

Name          Memory usage
New encode           144 B
Old encode           248 B - 1.72x memory usage +104 B

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

##### With input Extra options #####
Name                 ips        average  deviation         median         99th %
New encode        6.93 M      144.29 ns  ±3214.37%         130 ns         260 ns
Old encode        4.26 M      234.91 ns  ±2437.41%         180 ns         411 ns

Comparison:
New encode        6.93 M
Old encode        4.26 M - 1.63x slower +90.62 ns

Memory usage statistics:

Name          Memory usage
New encode           200 B
Old encode           288 B - 1.44x memory usage +88 B

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

##### With input Full options #####
Name                 ips        average  deviation         median         99th %
New encode        1.90 M      525.63 ns  ±1051.00%         461 ns         891 ns
Old encode        1.47 M      681.61 ns  ±1213.50%         541 ns        1132 ns

Comparison:
New encode        1.90 M
Old encode        1.47 M - 1.30x slower +155.98 ns

Memory usage statistics:

Name          Memory usage
New encode           808 B
Old encode           848 B - 1.05x memory usage +40 B

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

[josevalim]

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