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Marc-André Bombeck
caf68aaea7
The hand-rolled multipart parser consumed the opening boundary marker and
then inspected the next two bytes inline to classify the suffix ("\r\n" for
another part, "--" for the closing boundary). When a stream chunk ended
exactly on that marker, fewer than two bytes were left in the buffer, so the
branch returned while still in the "preamble" state. The next read re-entered
preamble, searched for the marker again — which was already consumed — and
treated the part headers and the entire file body as preamble to discard,
matching only at the closing boundary. The captured file landed on disk
truncated or empty.
A tiny single-chunk upload never tripped it; a multi-megabyte binary arrives
in hundreds of chunks, so a chunk boundary routinely fell in the dead window
and the saved file came up short. The Apple Health export ingest then failed
its ZIP read with "Could not locate ZIP End-Of-Central-Directory record".
Add a dedicated "after-boundary" parser state that buffers until the two-byte
suffix is present instead of falling back to a marker search, route the
post-body separator through the same state, guard the epilogue state against
the body scanner, and tolerate RFC 2046 transport padding after the marker.
The preamble retain window now keeps boundaryMarker.length - 1 bytes so a
marker split across chunks can still complete. Streaming and the size cap are
unchanged — no part of the upload is buffered whole.
Cover the regression with byte-exact round-trip tests over adversarial
chunkings (1/3/7-byte feeds, chunks ending on the marker and inside the
separator, every single and adjacent split offset) plus an end-to-end check
that a streamed export.zip stays a parseable archive.