feat: add LookupTXTWithTTL to Resolver#75
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Resolver.LookupTXT returns only TXT values and drops the TTL, so a resolver that knows it (such as DNS-over-HTTPS) cannot report it and callers cannot tell how long a record set is valid or when to re-resolve. Correct caching and expiration needs that TTL for both kinds of TXT records this library resolves: - DNSADDR (dnsaddr=): the TTL bounds how long a resolved multiaddr is valid. Multiaddrs increasingly carry rotating /certhash/ segments (AutoTLS WebTransport and WebRTC-direct nodes, including libp2p bootstrappers); without the TTL these cannot be cached or expired correctly, so a peer cannot reliably publish addresses whose certhash changes over time. - DNSLink (dnslink=): the TTL lets an IPFS gateway set Cache-Control max-age for /ipns/<dnslink-host> responses (ipfs/boxo#329). Add LookupTXTWithTTL, which routes to the matched per-domain resolver and returns its TTL when it implements the new TXTWithTTLResolver interface; resolvers without TTL support (such as the OS resolver) report 0 (unknown). LookupTXT and BasicResolver are unchanged, so this is additive.
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The DNS resolver dropped the TXT record TTL, so a gateway could not set Cache-Control max-age for DNSLink (/ipns/<dnslink-host>) responses, and a recursive name was cached for only its final hop's TTL. - add LookupTXTWithTTLFunc and NewDNSResolverWithTTL; LookupTXTFunc and NewDNSResolver keep their signatures and report an unknown TTL (0) - carry the looked-up TTL into AsyncResult.TTL in the DNS resolver - WithDNSResolver detects a resolver implementing multiformats/go-multiaddr-dns#75 TXTWithTTLResolver and propagates the TTL; add WithDNSResolverWithTTL for a TTL-aware lookup - cap a resolved name's TTL to its shortest hop, so a DNSLink or recursive IPNS name is not cached past its earliest-expiring link Refs #329
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Problem
Resolver.LookupTXTroutes to the matched per-domain resolver but returns only the record values, dropping any TTL. A resolver that knows the TTL (such as a DNS-over-HTTPS resolver) has no way to report it, so callers cannot tell how long a TXT record set is valid or when to re-resolve it. Correct caching and expiration needs that TTL for both kinds of TXT records this library resolves:dnsaddr=): the TTL bounds how long a resolved multiaddr is valid. Multiaddrs increasingly carry rotating/certhash/segments (AutoTLS WebTransport / WebRTC-direct nodes, including libp2p bootstrappers). Without the TTL these cannot be cached or expired correctly, so a peer cannot reliably publish addresses whose certhash changes over time: stale certhashes linger and dials fail.dnslink=): the TTL lets an IPFS gateway setCache-Control: max-age=<ttl>for/ipns/<dnslink-host>responses (see Gateway: Cache-Control, max-age=ttl, ETag for /ipns requests ipfs/boxo#329).Fix
TXTWithTTLResolver, an optional interface aBasicResolvermay implement to report the TTL of a TXT record set.Resolver.LookupTXTWithTTL, which routes to the matched per-domain resolver and returns its TTL when that resolver implementsTXTWithTTLResolver. Resolvers without TTL support (such as the default OS resolver) report0, meaning unknown.Resolveritself implementsTXTWithTTLResolver, so aResolverused as a per-domain resolver routes TTL too.LookupTXTand theBasicResolverinterface are unchanged, so this is additive. A DoH resolver that implementsLookupTXTWithTTL(libp2p/go-doh-resolver#33) flows its TTL through to consumers: libp2p address resolution for DNSADDR, and boxo's DNSLink resolution.