elixir-mint / hpax / f7d69fc7b33310c4da9165d44ba56cee97df4989

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Add HPAX.protocol_resize/2 for decoding tables (#32)

* Add HPAX.protocol_resize/2 for decoding tables

resize/2 sets both the protocol maximum and the table's own maximum
size. That's right for an encoding context, which takes the whole size
the protocol permits and declares it, but a decoding table's maximum
size is chosen by the peer's encoder and declared with a dynamic table
size update instruction (RFC 7541 4.2). Raising the protocol maximum on
a decoding table kept entries the peer's encoder had evicted, so an
indexed reference to one of them decoded to a stale header instead of
failing.

protocol_resize/2 changes only the maximum the peer is permitted to use
and follows it down when it drops below the maximum the encoder
declared. The encoder then has to declare a size of at most the new
maximum at the start of its next block, which RFC 9113 4.3.1 requires
the receiver to enforce with a COMPRESSION_ERROR, so decode/2 returns
{:error, :missing_size_update} for a block that doesn't start with one.
When the maximum changes more than once before that block, the smallest
of them is the one that has to be declared.

* Return an error tuple for a malformed dynamic table size update

decode/2 parses the size update's integer before the clause that catches
decoding errors, so a block whose integer never ends, such as <<0x3F>>,
threw {:hpax, :bad_integer_encoding} at the caller instead of returning
{:error, :bad_integer_encoding}. Callers that follow the documented
contract don't catch it, so the throw takes down the process decoding
the block.

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