feat: resolve /dnsaddr before filtering - #174
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A /dnsaddr carries no transport component, so filter-addrs can neither match it nor exclude it: a ws-speaking peer was dropped by ?filter-addrs=ws, and a quic-only peer survived ?filter-addrs=!quic-v1. Neither is detectable by the client. someguy now resolves before boxo filters, which fixes both directions. See ipfs/specs#542. A filtered request has its /dnsaddr replaced, since keeping it would let a record survive a filter meant to exclude it. The exception is a positive filter naming dnsaddr, the one filter a /dnsaddr matches; the client is asking for indirections, so the /dnsaddr is kept alongside what it resolves to. An unfiltered request gets the resolved addresses added and keeps the /dnsaddr, so it can dial now and re-resolve later. SOMEGUY_DNSADDR_RESOLUTION names what an unfiltered response does with the /dnsaddr: append (default), replace, filtered, or never. Hostnames in provider records are attacker-chosen, and resolution runs inline while the response streams, so it is bounded on four axes: DNS lookups per request, resolved addresses per record, recursion depth, and a per-lookup timeout, which together also cap the delay resolution can add to one response. The per-record limit is threaded through the recursion rather than applied to the finished result: a TXT record that lists itself expands as fan^depth, and re-entering a cached name costs no lookup, so a limit checked at the end still let one request build millions of addresses. - resolve detached from the request context behind a singleflight, so a disconnect cannot cache its own cancellation as a 15 minute failure - shed load once the request is gone rather than spend the rest of its budget on queries nothing will read - keep the original whenever an expansion is not whole, so a failed or throttled lookup does not drop the indirection the rest lives behind - drop a /dnsaddr naming a different peer: nothing it yields can belong to the record carrying it - normalize only the hostname in cache keys, over ASCII: lowering a whole multiaddr folds case-sensitive components together, and Unicode case mapping folds U+0130 and U+212A onto ASCII, which let one record cache a failure under another name's key - skip lookups madns can never satisfy, such as a /p2p-circuit suffix - order addresses by how directly they dial: IP, DNS, dnsaddr, relay last - require go 1.26
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Minor rather than patch: #174 adds SOMEGUY_DNSADDR_RESOLUTION and changes what /routing/v1 returns by default (dnsaddr resolution, address order), and Go 1.26 is now the minimum.
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Problem
A
/dnsaddrcarries no transport component, sofilter-addrscan neither match nor exclude it: a ws-speaking peer behind one vanishes from?filter-addrs=ws, and a quic-only peer survives?filter-addrs=!quic-v1. The client can't detect either case.1Credit to @achingbrain for flagging this gap
Fix
/dnsaddrbefore boxo filters: a filtered request gets it replaced (exceptfilter-addrs=dnsaddr, the one filter that matches it), an unfiltered one keeps it alongside the resolved addressesSOMEGUY_DNSADDR_RESOLUTIONnames what an unfiltered response does with the/dnsaddr:append(default),replace,filtered, orneverdocs/dnsaddr-resolution.mdcarries the rationale/dnsaddr, relays lastThis turned out to not be trivial due to the way things work, and increased surface for abuse, but with enough code/tests should be good to go now.
Footnotes
delegated routing: resolve DNSADDR addresses before filtering specs#542 proposes this behavior for every Delegated Routing implementation. I think there is more nuance, thus this PR provides
SOMEGUY_DNSADDR_RESOLUTIONconfiguration flag. ↩