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Reduce memory pressure when decrypting large binary size #119

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3483916
Optimize Cloak.Tags.Decoder.decode/1
thanabodee-c Jan 3, 2023
d939911
Calculate size before use in pattern matching
thanabodee-c Feb 6, 2023
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31 changes: 12 additions & 19 deletions lib/cloak/tags/decoder.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -16,30 +16,25 @@ defmodule Cloak.Tags.Decoder do
@byte_length 256
@half_byte 128

def decode(message) do
length = tag_length(message)
def decode(<<_type::size(8), len::size(8), rest::binary>> = message) do
tag_length =
if len >= @half_byte do
size = len - @half_byte
<<value::binary-size(size), _::binary>> = rest
@offset + len - @half_byte + value_bytes(:binary.bin_to_list(value))
else
@offset + len
end

case message do
<<tlv::binary-size(length), remainder::binary>> ->
<<tlv::binary-size(tag_length), remainder::binary>> ->
%{tag: tag(tlv), remainder: remainder}

_other ->
:error
end
end

defp tag_length(message) do
<<_type::size(8), len::size(8), rest::binary>> = message

tag_length(len, :binary.bin_to_list(rest))
end

defp tag_length(num, list) when num >= @half_byte do
@offset + num - @half_byte + value_bytes(list, num - @half_byte)
end

defp tag_length(num, _list), do: @offset + num

defp tag(<<_type::size(8), len::size(8), rest::binary>>) when len >= @half_byte do
size = len - @half_byte
<<_value_bytes::binary-size(size), tag::binary>> = rest
Expand All @@ -51,9 +46,7 @@ defmodule Cloak.Tags.Decoder do
tag
end

defp value_bytes(list, num_bytes) do
list
|> Enum.take(num_bytes)
|> Enum.reduce(0, fn value, acc -> acc * @byte_length + value end)
defp value_bytes(list) do
Enum.reduce(list, 0, fn value, acc -> acc * @byte_length + value end)
end
end