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Fix: handle OTP28 uncompressed literals #53

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Fix: handle OTP28 uncompressed literals #53

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15 changes: 14 additions & 1 deletion lib/packbeam.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,20 @@ defmodule ExAtomVM.PackBEAM do
defp uncompress_literals(chunks) do
with {~c"LitT", litt} <- List.keyfind(chunks, ~c"LitT", 0),
<<_header::binary-size(4), data::binary>> <- litt do
litu = :zlib.uncompress(data)
litu =
case data do
# RFC 1950: Valid zlib header when (CMF*256 + FLG) % 31 == 0
<<0x78, flag, _rest::binary>> when rem(0x78 * 256 + flag, 31) == 0 ->
try do
:zlib.uncompress(data)
rescue
_error -> data
end

# OTP 28 compatibility: data is not compressed
_ ->
data
end

chunks
|> List.keyreplace(~c"LitT", 0, {~c"LitU", litu})
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