Feature: Implement DNSADDR Protocol resolves addresses from a TXT record associated with the _dnsaddr subdomain

[acul71]

Feature: Implement DNSADDR Protocol resolves addresses from a TXT record associated with the _dnsaddr subdomain

Overview

The current implementation of the dnsaddr protocol in py-multiaddr does not follow the libp2p specification. The current implementation incorrectly resolves /dnsaddr/ addresses by querying A/AAAA records instead of TXT records, and converts IP addresses to multiaddrs instead of parsing dnsaddr= entries from TXT records.

Current Implementation Issues

❌ What the current implementation does:

1. Queries A and AAAA records from the domain (e.g., example.com)
2. Converts IP addresses to /ip4/ or /ip6/ multiaddrs
3. Ignores TXT records completely
4. Does not parse dnsaddr= entries

✅ What the specification requires:

1. Query TXT records from _dnsaddr.<domain> (e.g., _dnsaddr.example.com)
2. Parse dnsaddr=<multiaddr> entries from TXT records
3. Return the parsed multiaddrs as resolution results
4. Support recursive resolution for nested dnsaddr entries

Specification Reference

According to the libp2p addressing specification:

A libp2p-specific DNS-backed format, /dnsaddr resolves addresses from a TXT record associated with the _dnsaddr subdomain of a given domain.

For example, resolving /dnsaddr/libp2p.io will perform a TXT lookup for _dnsaddr.libp2p.io. If the result contains entries of the form dnsaddr=<multiaddr>, the embedded multiaddrs will be parsed and used.

Example from the specification:

> dig +short _dnsaddr.am6.bootstrap.libp2p.io txt
"dnsaddr=/dns6/am6.bootstrap.libp2p.io/tcp/443/wss/p2p/QmbLHAnMoJPWSCR5Zhtx6BHJX9KiKNN6tpvbUcqanj75Nb"
"dnsaddr=/ip4/147.75.87.27/tcp/4001/p2p/QmbLHAnMoJPWSCR5Zhtx6BHJX9KiKNN6tpvbUcqanj75Nb"

Implementation Plan

1. Update DNS Resolver

Modify multiaddr/resolvers/dns.py to implement proper dnsaddr resolution:

• Query TXT records from _dnsaddr.<hostname>
• Parse dnsaddr=<multiaddr> entries
• Support recursive resolution with depth limiting
• Filter by peer ID if present in original multiaddr

2. Reference Implementation

The JavaScript implementation in js-multiaddr already follows the specification correctly and can serve as a reference:

• File: src/resolvers/dnsaddr.ts
• Queries _dnsaddr.<hostname> for TXT records
• Parses dnsaddr=<multiaddr> entries
• Supports recursive resolution with depth limiting
• Returns parsed multiaddrs, not IP addresses

3. Expected Behavior

For a multiaddr like /dnsaddr/example.com/p2p/QmPeerId:

1. Query TXT records from _dnsaddr.example.com
2. Parse entries starting with dnsaddr=
3. Filter results to include the peer ID QmPeerId
4. Return the matching multiaddrs
5. If any returned multiaddr is itself a /dnsaddr/, recursively resolve it

Benefits

1. Specification Compliance: Aligns with the official libp2p specification
2. Interoperability: Ensures compatibility with other libp2p implementations
3. Correct Functionality: Provides the intended dnsaddr resolution behavior
4. Future-Proof: Follows the established standard for dnsaddr protocol

Testing

The implementation should be tested with real dnsaddr records, such as:

• /dnsaddr/bootstrap.libp2p.io
• /dnsaddr/example.com/p2p/QmPeerId

And should correctly resolve to the multiaddrs specified in the corresponding _dnsaddr.<domain> TXT records.

References

• libp2p Addressing Specification - DNSADDR Links
• JavaScript Implementation Reference

[acul71]

fixed by #81