[preciz]

Assisted-by: Antigravity CLI:Gemini 4

Faster and uses less memory.

Bench:

Mix.install([:benchee])

defmodule OldCookies do
  def decode(cookie) when is_binary(cookie) do
    Map.new(decode_kv(cookie, []))
  end

  defp decode_kv("", acc), do: acc
  defp decode_kv(<<h, t::binary>>, acc) when h in [?\s, ?\t], do: decode_kv(t, acc)
  defp decode_kv(kv, acc) when is_binary(kv), do: decode_key(kv, kv, 0, acc)

  defp decode_key(<<h, t::binary>>, _key_rest, _len, acc)
       when h in [?\s, ?\t, ?\r, ?\n, ?\v, ?\f],
       do: skip_until_cc(t, acc)

  defp decode_key(<<?;, t::binary>>, _key_rest, _len, acc), do: decode_kv(t, acc)
  defp decode_key(<<?=, t::binary>>, _key_rest, 0, acc), do: skip_until_cc(t, acc)

  defp decode_key(<<?=, t::binary>>, key_rest, len, acc) do
    key = binary_part(key_rest, 0, len)
    decode_value(t, t, 0, 0, key, acc)
  end

  defp decode_key(<<_, t::binary>>, key_rest, len, acc), do: decode_key(t, key_rest, len + 1, acc)
  defp decode_key(<<>>, _key_rest, _len, acc), do: acc

  defp decode_value(<<?;, t::binary>>, val_rest, len, spaces, key, acc) do
    value = binary_part(val_rest, 0, len - spaces)
    decode_kv(t, [{key, value} | acc])
  end

  defp decode_value(<<?\s, t::binary>>, val_rest, len, spaces, key, acc) do
    decode_value(t, val_rest, len + 1, spaces + 1, key, acc)
  end

  defp decode_value(<<h, t::binary>>, _val_rest, _len, _spaces, _key, acc)
       when h in [?\t, ?\r, ?\n, ?\v, ?\f],
       do: skip_until_cc(t, acc)

  defp decode_value(<<_, t::binary>>, val_rest, len, _spaces, key, acc) do
    decode_value(t, val_rest, len + 1, 0, key, acc)
  end

  defp decode_value(<<>>, val_rest, len, spaces, key, acc) do
    value = binary_part(val_rest, 0, len - spaces)
    [{key, value} | acc]
  end

  defp skip_until_cc(<<?;, t::binary>>, acc), do: decode_kv(t, acc)
  defp skip_until_cc(<<_, t::binary>>, acc), do: skip_until_cc(t, acc)
  defp skip_until_cc(<<>>, acc), do: acc
end

defmodule NewCookies do
  def decode(cookie) when is_binary(cookie) do
    Map.new(decode_kv(cookie, cookie, 0, []))
  end

  defp decode_kv(<<h, t::binary>>, cookie, pos, acc) when h in [?\s, ?\t, ?;],
    do: decode_kv(t, cookie, pos + 1, acc)

  defp decode_kv(<<h, t::binary>>, cookie, pos, acc) when h in [?\r, ?\n, ?\v, ?\f, ?=],
    do: skip_until_cc(t, cookie, pos + 1, acc)

  defp decode_kv(<<_, t::binary>>, cookie, pos, acc), do: decode_key(t, cookie, pos, 1, acc)
  defp decode_kv(<<>>, _cookie, _pos, acc), do: acc

  defp decode_key(<<h, t::binary>>, cookie, pos, len, acc)
       when h in [?\s, ?\t, ?\r, ?\n, ?\v, ?\f],
       do: skip_until_cc(t, cookie, pos + len + 1, acc)

  defp decode_key(<<?;, t::binary>>, cookie, pos, len, acc),
    do: decode_kv(t, cookie, pos + len + 1, acc)

  defp decode_key(<<?=, t::binary>>, cookie, pos, len, acc) do
    key = binary_part(cookie, pos, len)
    decode_value(t, cookie, pos + len + 1, 0, 0, key, acc)
  end

  defp decode_key(<<_, t::binary>>, cookie, pos, len, acc),
    do: decode_key(t, cookie, pos, len + 1, acc)

  defp decode_key(<<>>, _cookie, _pos, _len, acc), do: acc

  defp decode_value(<<?;, t::binary>>, cookie, pos, len, spaces, key, acc) do
    value = binary_part(cookie, pos, len - spaces)
    decode_kv(t, cookie, pos + len + 1, [{key, value} | acc])
  end

  defp decode_value(<<?\s, t::binary>>, cookie, pos, len, spaces, key, acc) do
    decode_value(t, cookie, pos, len + 1, spaces + 1, key, acc)
  end

  defp decode_value(<<h, t::binary>>, cookie, pos, len, _spaces, _key, acc)
       when h in [?\t, ?\r, ?\n, ?\v, ?\f],
       do: skip_until_cc(t, cookie, pos + len + 1, acc)

  defp decode_value(<<_, t::binary>>, cookie, pos, len, _spaces, key, acc) do
    decode_value(t, cookie, pos, len + 1, 0, key, acc)
  end

  defp decode_value(<<>>, cookie, pos, len, spaces, key, acc) do
    value = binary_part(cookie, pos, len - spaces)
    [{key, value} | acc]
  end

  defp skip_until_cc(<<?;, t::binary>>, cookie, pos, acc), do: decode_kv(t, cookie, pos + 1, acc)

  defp skip_until_cc(<<_, t::binary>>, cookie, pos, acc),
    do: skip_until_cc(t, cookie, pos + 1, acc)

  defp skip_until_cc(<<>>, _cookie, _pos, acc), do: acc
end

inputs = %{
  "1. empty" => "",
  "2. single short cookie" => "theme=dark",
  "3. single Phoenix session cookie (~250B)" =>
    "_my_app_key=" <> String.duplicate("SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAY", 5),
  "4. typical browser (5 cookies)" =>
    "_ga=GA1.2.123456789.1234567890; _gid=GA1.2.987654321.1234567890; " <>
      "locale=en_US; theme=dark; _app_session=" <> String.duplicate("a1b2c3d4", 20),
  "5. heavy browser (20 cookies)" =>
    Enum.map_join(1..20, "; ", fn i ->
      "cookie_key_#{i}=#{String.duplicate("val#{i}_", 10)}"
    end),
  "6. many small cookies (50 cookies)" =>
    Enum.map_join(1..50, "; ", fn i -> "k#{i}=v#{i}" end),
  "7. edge: lots of whitespace and trailing spaces" =>
    Enum.map_join(1..15, ";", fn i -> "   \t  key_#{i}=value_#{i}     " end),
  "8. edge: malformed / invalid pairs mixed with valid" =>
    ";;; =only_val; bad key=123; key_without_eq; bad_val=abc\tdef; valid1=ok1; =; \r\ninvalid=2; valid2=ok2;;;"
}

Benchee.run(
  %{
    "old" => fn input -> OldCookies.decode(input) end,
    "new" => fn input -> NewCookies.decode(input) end
  },
  inputs: inputs,
  pre_check: :all_same,
  warmup: 1,
  time: 3,
  memory_time: 2
)

Results:

Operating System: Linux
CPU Information: AMD Ryzen 7 8845HS w
Number of Available Cores: 16
Available memory: 54.72 GB
Elixir 1.20.4
Erlang 29.1.1
JIT enabled: true

Benchmark suite executing with the following configuration:
warmup: 1 s
time: 3 s
memory time: 2 s
reduction time: 0 ns
parallel: 1
inputs: 1. empty, 2. single short cookie, 3. single Phoenix session cookie (~250B), 4. typical browser (5 cookies), 5. heavy browser (20 cookies), 6. many small cookies (50 cookies), 7. edge: lots of whitespace and trailing spaces, 8. edge: malformed / invalid pairs mixed with valid
Estimated total run time: 1 min 36 s
Excluding outliers: false

##### With input 1. empty #####
Name           ips        average  deviation         median         99th %
old        25.13 M       39.79 ns  ±1080.57%          40 ns          50 ns
new        25.00 M       40.00 ns  ±1197.08%          40 ns          51 ns

Comparison: 
old        25.13 M
new        25.00 M - 1.01x slower +0.21 ns

Memory usage statistics:

Name    Memory usage
old             64 B
new             64 B - 1.00x memory usage +0 B

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

##### With input 2. single short cookie #####
Name           ips        average  deviation         median         99th %
new         9.85 M      101.49 ns  ±4066.47%          80 ns         191 ns
old         8.84 M      113.18 ns  ±2382.45%         100 ns         190 ns

Comparison: 
new         9.85 M
old         8.84 M - 1.12x slower +11.69 ns

Memory usage statistics:

Name    Memory usage
new            128 B
old            264 B - 2.06x memory usage +136 B

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

##### With input 3. single Phoenix session cookie (~250B) #####
Name           ips        average  deviation         median         99th %
new         1.97 M      508.78 ns  ±1279.14%         470 ns         671 ns
old         1.73 M      579.36 ns   ±879.54%         541 ns         721 ns

Comparison: 
new         1.97 M
old         1.73 M - 1.14x slower +70.57 ns

Memory usage statistics:

Name    Memory usage
new            128 B
old            288 B - 2.25x memory usage +160 B

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

##### With input 4. typical browser (5 cookies) #####
Name           ips        average  deviation         median         99th %
new         1.32 M      757.18 ns   ±719.72%         711 ns         972 ns
old         1.00 M      995.41 ns   ±555.93%         942 ns        1282 ns

Comparison: 
new         1.32 M
old         1.00 M - 1.31x slower +238.23 ns

Memory usage statistics:

Name    Memory usage
new          0.34 KB
old          1.13 KB - 3.27x memory usage +0.78 KB

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

##### With input 5. heavy browser (20 cookies) #####
Name           ips        average  deviation         median         99th %
new       243.02 K        4.11 μs   ±109.15%        3.99 μs        5.67 μs
old       203.05 K        4.92 μs    ±65.95%        4.79 μs        7.78 μs

Comparison: 
new       243.02 K
old       203.05 K - 1.20x slower +0.81 μs

Memory usage statistics:

Name    Memory usage
new          1.16 KB
old          4.33 KB - 3.72x memory usage +3.16 KB

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

##### With input 6. many small cookies (50 cookies) #####
Name           ips        average  deviation         median         99th %
new       220.33 K        4.54 μs   ±113.50%        4.21 μs        7.20 μs
old       172.45 K        5.80 μs    ±99.43%        5.42 μs        9.43 μs

Comparison: 
new       220.33 K
old       172.45 K - 1.28x slower +1.26 μs

Memory usage statistics:

Name    Memory usage
new          2.63 KB
old         11.38 KB - 4.32x memory usage +8.75 KB

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

##### With input 7. edge: lots of whitespace and trailing spaces #####
Name           ips        average  deviation         median         99th %
new       579.84 K        1.72 μs   ±357.98%        1.64 μs        2.24 μs
old       465.29 K        2.15 μs   ±340.11%        2.04 μs        3.12 μs

Comparison: 
new       579.84 K
old       465.29 K - 1.25x slower +0.42 μs

Memory usage statistics:

Name    Memory usage
new          0.89 KB
old          3.27 KB - 3.67x memory usage +2.38 KB

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

##### With input 8. edge: malformed / invalid pairs mixed with valid #####
Name           ips        average  deviation         median         99th %
new         3.01 M      332.41 ns  ±1413.78%         301 ns         461 ns
old         2.08 M      481.36 ns   ±815.83%         450 ns         662 ns

Comparison: 
new         3.01 M
old         2.08 M - 1.45x slower +148.95 ns

Memory usage statistics:

Name    Memory usage
new         0.180 KB
old          1.50 KB - 8.35x memory usage +1.32 KB

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