perf(quic): cache DNS resolutions for a short TTL - #208
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Client::connect() resolved the peer hostname on every attempt, so every connection paid a resolver round trip even though the same small set of hosts is connected to repeatedly, on a path where the latency is visible. Put a TTL cache in front of resolve_dns(), keyed on host, port and the local socket's address family - resolution filters answers by family, so the family is part of what determines the result. Entries expire after DEFAULT_DNS_CACHE_TTL (30s), adjustable per client with with_dns_cache_ttl(); a zero TTL disables caching. Failed lookups are never cached, literal addresses and the explicit SocketAddr argument to connect() bypass the cache entirely, and expired entries are swept on insert so the map stays bounded. Uses only std (HashMap + Mutex), so no new dependency.
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Backport of #203 to draft-14
quic::Client::connect()resolves the peer hostname on every attempt, so each connection pays a resolver round trip even though a client typically connects to the same small set of hosts over and over. This adds a short-lived cache in front ofresolve_dns(), keyed on host, port and the local socket's address family (resolution filters answers by family, so it belongs in the key). Entries expire afterDEFAULT_DNS_CACHE_TTL(30s) and the TTL is adjustable per client viawith_dns_cache_ttl(), with zero disabling the cache; failed lookups are never cached, and literal addresses and the explicitSocketAddrargument toconnect()bypass it entirely. Implemented withHashMap+Mutexfrom std (no new dependency) and covered by unit tests that exercise expiry and keying without touching the network.