Stream metadata.config decoding in chunks and increase max size to 1024KB#181
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Stream metadata.config decoding in chunks and increase max size to 1024KB#181
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Decode metadata.config by feeding the binary through safe_erl_term:tokens/2 in 4KB slices, parsing each dot-terminated form as it completes, instead of materializing the whole file as a char list before tokenizing. Peak transient decode memory drops from roughly 17x the binary size to binary + ~64KB. This makes it safe to bump MAX_METADATA_SIZE from 128KB to 1MB. Switches the leex dot rule to end_token so tokens/2 returns one form per call. Atom safety (list_to_existing_atom) and the restricted grammar are preserved. UTF-8 is decoded incrementally with a latin1 fallback restart on invalid bytes.
- Fix infinite loop on trailing incomplete UTF-8 bytes: when no input
bytes remain but the UTF-8 buffer is non-empty, fall back to latin1
rather than spin re-decoding the same buffer.
- Drop overly broad try/catch around erl_parse:parse_term/1; the
function only returns {ok, _} | {error, _} and shouldn't throw.
- Comment in safe_erl_term.xrl explaining why the dot rule emits
end_token instead of token.
- Cover the new chunked path in decode_metadata_test: large
multi-chunk input, UTF-8 char straddling a chunk boundary, latin1
fallback for embedded invalid UTF-8 bytes, the trailing-incomplete-
UTF-8 regression case, and 5000 terms across many chunks.
jeregrine
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May 6, 2026
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Hitting this when we bump to latest Erlang. ❤️
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On OTP28.5 + Elixir 1.19.5 we're hitting this limit already: I'll let you know what library & size we hit. |
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https://hex.pm/packages/phosphor_icons seems to be a package that has a large metadata file that goes over the current limit and breaks. |
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I checked all existing packages and no package hits the limit raised to 1024KB, some outliers are close but I think the fix should be on the package side in that case. |
Adds a `metadata_fields` config option (default `all`) that opts callers into reading only specific top-level keys from metadata.config. When a list is given, the decoder switches to a token-by-token streaming parser: forms whose key is not in the list are discarded with only a bracket-depth counter held in state, so peak memory stays bounded by the chunk size plus one token regardless of how large unwanted forms get.
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