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key the flow table hash with a per-table siphash seed - #2
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The flow table bucketed keys by an unseeded FNV-1a hash masked to the
low bits. Peers choose most of what gets hashed (source ports, IPv6
interface ids, QUIC Initial connection ids), so they could pick keys
that share a bucket and make every lookup walk one long probe chain.
Add a :hash partition with a constexpr streaming SipHash, a 128-bit
hash_seed and random_seed() over getrandom. Keys now feed their
identity to a hasher through hash_append in place of hash_value, and
byte_key feeds its length first so keys built from several fields do
not collide. flow_table::carve takes a seed, or draws one when given
none, and buckets with SipHash-1-3 under it. The load limit drops from
7/8 to 3/4.
std::hash now uses SipHash under a seed drawn once per
process.
Breaking: a custom demux key needs hash_append instead of hash_value.