Crate hickory_resolver

Expand description

The Resolver is responsible for performing recursive queries to lookup domain names.

This is a 100% in process DNS resolver. It does not use the Host OS’ resolver. If what is desired is to use the Host OS’ resolver, generally in the system’s libc, then the std::net::ToSocketAddrs variant over &str should be used.

Unlike the hickory-client, this tries to provide a simpler interface to perform DNS queries. For update options, i.e. Dynamic DNS, the hickory-client crate must be used instead. The Resolver library is capable of searching multiple domains (this can be disabled by using an FQDN during lookup), dual-stack IPv4/IPv6 lookups, performing chained CNAME lookups, and features connection metric tracking for attempting to pick the best upstream DNS resolver.

This as best as possible attempts to abide by the DNS RFCs, please file issues at https://github.com/hickory-dns/hickory-dns.

§Usage

§Declare dependency

[dependency]
hickory-resolver = "*"

§Using the host system config

On Unix systems, the /etc/resolv.conf can be used for configuration. Not all options specified in the host systems resolv.conf are applicable or compatible with this software. In addition there may be additional options supported which the host system does not. Example:

// Use the host OS'es `/etc/resolv.conf`
let resolver = Resolver::builder_tokio().unwrap().build();
let response = resolver.lookup_ip("www.example.com.").await.unwrap();

§Using the Tokio/Async Resolver

use std::net::*;
use tokio::runtime::Runtime;
use hickory_resolver::Resolver;
use hickory_resolver::name_server::TokioConnectionProvider;
use hickory_resolver::config::*;

// We need a Tokio Runtime to run the resolver
//  this is responsible for running all Future tasks and registering interest in IO channels
let mut io_loop = Runtime::new().unwrap();

// Construct a new Resolver with default configuration options
let resolver = Resolver::builder_with_config(
    ResolverConfig::default(),
    TokioConnectionProvider::default()
).build();

// Lookup the IP addresses associated with a name.
// This returns a future that will lookup the IP addresses, it must be run in the Core to
//  to get the actual result.
let lookup_future = resolver.lookup_ip("www.example.com.");

// Run the lookup until it resolves or errors
let mut response = io_loop.block_on(lookup_future).unwrap();

// There can be many addresses associated with the name,
//  this can return IPv4 and/or IPv6 addresses
let _address = response.iter().next().expect("no addresses returned!");

Generally after a lookup in an asynchronous context, there would probably be a connection made to a server, for example:

let ips = io_loop.block_on(resolver.lookup_ip("www.example.com.")).unwrap();

let result = io_loop.block_on(async {
    let ip = ips.iter().next().unwrap();
    TcpStream::connect((ip, 443))
})
.and_then(|conn| Ok(conn) /* do something with the connection... */)
.unwrap();

It’s beyond the scope of these examples to show how to deal with connection failures and looping etc. But if you wanted to say try a different address from the result set after a connection failure, it will be necessary to create a type that implements the Future trait. Inside the Future::poll method would be the place to implement a loop over the different IP addresses.

§Optional protocol support

The following DNS protocols are optionally supported:

Enable tls for DNS over TLS (DoT)
Enable https-rustls for DNS over HTTP/2 (DoH)
Enable quic for DNS over QUIC (DoQ)
Enable h3 for DNS over HTTP/3 (DoH3)

§Example

Enable the TLS library through the dependency on hickory-resolver:

hickory-resolver = { version = "*", features = ["tls"] }

A default TLS configuration is available for Cloudflare’s 1.1.1.1 DNS service (Quad9 as well):

use hickory_resolver::Resolver;
use hickory_resolver::name_server::TokioConnectionProvider;
use hickory_resolver::config::*;

// Construct a new Resolver with default configuration options
let mut resolver = Resolver::builder_with_config(
    ResolverConfig::cloudflare_tls(),
    TokioConnectionProvider::default(),
).build();

// see example above...

§mDNS (multicast DNS)

Multicast DNS is an experimental feature in Hickory DNS at the moment. Its support on different platforms is not yet ideal. Initial support is only for IPv4 mDNS, as there are some complexities to figure out with IPv6. Once enabled, an mDNS NameServer will automatically be added to the Resolver and used for any lookups performed in the .local. zone.

Re-exports§

pub use hickory_proto as proto;

Modules§

caching_client: Caching related functionality for the Resolver.
config: Configuration for a resolver
dns_lru: An LRU cache designed for work with DNS lookups
lookup: Lookup result from a resolution of ipv4 and ipv6 records with a Resolver.
lookup_ip: LookupIp result from a resolution of ipv4 and ipv6 records with a Resolver.
name_server: A module with associated items for working with nameservers
system_conf: System configuration loading

Structs§

Hosts: Configuration for the local hosts file
Name: A domain name
ResolveError: The error type for errors that get returned in the crate
Resolver: An asynchronous resolver for DNS generic over async Runtimes.
ResolverBuilder: A builder to construct a Resolver.

Enums§

ResolveErrorKind: The error kind for errors that get returned in the crate

Traits§

IntoName: Conversion into a Name

Functions§

version: returns a version as specified in Cargo.toml

Type Aliases§

TokioResolvertokio: A Resolver used with Tokio

Crate hickory_resolverCopy item path