Module dns 

DNS resolution and caching.

Every verifier resolves DNS records through the backend wrapped by MessageAuthenticator. Exactly one backend is compiled in:

• dns-hickory (default): UDP, TCP or DNS-over-TLS queries through hickory-resolver. Not available on WebAssembly.
• dns-doh: DNS-over-HTTPS queries (RFC 8484) through DohResolver, using either the JSON API or the DNS wire format. Works on WebAssembly.

Lookups can be cached. A cache is supplied per call by wrapping the verifier input in Parameters with Parameters::with_cache. The cache type implements DnsCache, which hands out one ResolverCache per record type (TXT, MX, A, AAAA and PTR). TXT records are cached already parsed, as TxtRecord values. NoCache disables caching and is the default.

Negative answers (RFC 2308) are cached too: a name that does not exist (NXDOMAIN) or has no records of the requested type (NODATA) is stored as TxtRecord::Error in the TXT cache and as Err(Negative) in the other caches, until the negative TTL of the answer expires. That TTL is the SOA-derived value of RFC 2308 Section 5, capped by MessageAuthenticator::with_max_negative_ttl. Answers without an SOA record and resolver failures are never cached.

The lookup helpers on MessageAuthenticator (txt_lookup, mx_lookup, ipv4_lookup, ipv6_lookup, ip_lookup, ptr_lookup, exists) are public so that applications can reuse the resolver and caches for their own queries.

Re-exports

pub use cache::DnsCache;

pub use cache::NoCache;

pub use cache::Parameters;

pub use cache::ResolverCache;

pub use txt::TxtRecord;

pub use txt::TxtRecordParser;

Modules

cache

DNS cache traits and the per-call Parameters wrapper.

Structs

DnsEntry

A raw DNS answer together with the time at which it expires, as returned by MessageAuthenticator::ipv4_lookup_raw and MessageAuthenticator::ipv6_lookup_raw.

Mx

A group of MX records (RFC 5321 Section 5.1) that share a preference value.

Negative

A cached negative answer (RFC 2308): the name does not exist (NXDOMAIN), or it has no records of the requested type (NODATA).

RecordSet

The records returned by a DNS lookup, as stored in a ResolverCache.

Enums

DnssecStatus

DNSSEC validation state of a DNS answer (RFC 4035 Section 4.3).

IpLookupStrategy

Address families queried by MessageAuthenticator::ip_lookup, and in which order.

TxtRecord

A parsed DNS TXT record, as stored in the TXT ResolverCache of a DnsCache.

Traits

ToFqdn

Conversion of a domain name to the fully qualified form used as a DNS query and cache key.

ToReverseName

Conversion of an IP address to the label sequence of its reverse DNS name.

TxtRecordParser

Parser for a record type published in DNS TXT records.

Functions

has_valid_labels

Returns true if domain looks like a valid host name for a DNS query.