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josevalim merged 2 commits into from
Jun 15, 2026
+29 −20
Merged

Optimize cookie parsing #1310

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Optimize cookie parsing
preciz Jun 14, 2026
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preciz Jun 15, 2026
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49 changes: 29 additions & 20 deletions lib/plug/conn/cookies.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -49,40 +49,49 @@ defmodule Plug.Conn.Cookies do

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, "", acc)
defp decode_kv(kv, acc) when is_binary(kv), do: decode_key(kv, kv, 0, acc)

defp decode_key(<<h, t::binary>>, _key, acc) when h in [?\s, ?\t, ?\r, ?\n, ?\v, ?\f],
do: skip_until_cc(t, 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, acc), do: decode_kv(t, acc)
defp decode_key(<<?=, t::binary>>, "", acc), do: skip_until_cc(t, acc)
defp decode_key(<<?=, t::binary>>, key, acc), do: decode_value(t, "", 0, key, acc)
defp decode_key(<<h, t::binary>>, key, acc), do: decode_key(t, <<key::binary, h>>, acc)
defp decode_key(<<>>, _key, acc), do: 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_value(<<?;, t::binary>>, value, spaces, key, acc),
do: decode_kv(t, [{key, trim_spaces(value, spaces)} | 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_value(<<?\s, t::binary>>, value, spaces, key, acc),
do: decode_value(t, <<value::binary, ?\s>>, spaces + 1, key, acc)
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(<<h, t::binary>>, _value, _spaces, _key, 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(<<h, t::binary>>, value, _spaces, key, acc),
do: decode_value(t, <<value::binary, h>>, 0, key, 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(<<>>, value, spaces, key, acc),
do: [{key, trim_spaces(value, spaces)} | acc]
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

defp trim_spaces(value, 0), do: value
defp trim_spaces(value, spaces), do: binary_part(value, 0, byte_size(value) - spaces)

@doc """
Encodes the given cookies as expected in a response header.

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