Crate trust_dns_resolver

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 trust-dns client, this tries to provide a simpler interface to perform DNS queries. For update options, i.e. Dynamic DNS, the trust-dns 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.

There are two types for performing DNS queries, Resolver and ResolverFuture. Resolver is the easiest to work with, it is a wrapper around ResolverFuture. ResolverFuture is a Tokio based async resolver, and can be used inside any Tokio based system.

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

Usage

Declare dependency

[dependency]
trust-dns-resolver = "^0.9"

Extern the crate for usage in the library

extern crate trust_dns_resolver;

Using the Synchronous Resolver

This uses the default configuration, which sets the Google Public DNS as the upstream resolvers. Please see their privacy statement for important information about what they track, many ISP's track similar information in DNS.

use std::net::*;
use trust_dns_resolver::Resolver;
use trust_dns_resolver::config::*;

// Construct a new Resolver with default configuration options
let resolver = Resolver::new(ResolverConfig::default(), ResolverOpts::default()).unwrap();

// Lookup the IP addresses associated with a name.
// The final dot forces this to be an FQDN, otherwise the search rules as specified
//  in `ResolverOpts` will take effect. FQDN's are generally cheaper queries.
let response = resolver.lookup_ip("www.example.com.").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!");
if address.is_ipv4() {
    assert_eq!(address, IpAddr::V4(Ipv4Addr::new(93, 184, 216, 34)));
} else {
    assert_eq!(address, IpAddr::V6(Ipv6Addr::new(0x2606, 0x2800, 0x220, 0x1, 0x248, 0x1893, 0x25c8, 0x1946)));
}

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::from_system_conf().unwrap();
let response = resolver.lookup_ip("www.example.com.").unwrap();

Using the Tokio/Async Resolver

For more advanced asynchronous usage, the ResolverFuture is integrated with Tokio. In fact, the ResolverFuture is used by the synchronous Resolver for all lookups.

use std::net::*;
use tokio::runtime::current_thread::Runtime;
use trust_dns_resolver::AsyncResolver;
use trust_dns_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, background) = AsyncResolver::new(
    ResolverConfig::default(),
    ResolverOpts::default()
);
// AsyncResolver::new returns a handle for sending resolve requests and a background task
// that must be spawned on an executor.
io_loop.spawn(background);

// 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!");
if address.is_ipv4() {
    assert_eq!(address, IpAddr::V4(Ipv4Addr::new(93, 184, 216, 34)));
} else {
    assert_eq!(address, IpAddr::V6(Ipv6Addr::new(0x2606, 0x2800, 0x220, 0x1, 0x248, 0x1893, 0x25c8, 0x1946)));
}

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

let result = io_loop.block_on(lookup_future.and_then(|ips| {
                                 let ip = ips.next().unwrap();
                                 TcpStream::connect()
                             }).and_then(|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.

DNS-over-TLS

DNS over TLS is experimental in the Trust-DNS Resolver library. The underlying implementations have been available as addon libraries to the Client and Server, but the configuration is experimental in Trust-DNS Resolver. WARNING The trust-dns developers make no claims on the security and/or privacy guarantees of this implementation.

To use you must compile in support with one of the dns-over-tls features. There are three: dns-over-openssl, dns-over-native-tls, and dns-over-rustls. The reason for each is to make the Trust-DNS libraries flexible for different deployments, and/or security concerns. The easiest to use will generally be dns-over-rustls which utilizes the native Rust library (a rework of the boringssl project), this should compile and be usable on most ARM and x86 platforms. dns-over-native-tls will utilize the hosts TLS implementation where available or fallback to openssl where not. dns-over-openssl will specify that openssl should be used (which is a perfect fine option if required). If more than one is specified, the presidence will be in this order (i.e. only one can be used at a time) dns-over-rustls, dns-over-native-tls, and then dns-over-openssl. NOTICE thetrust-dns developers are not responsible for any choice of library that does not meet required security requirements.

Example

Enable the TLS library through the dependency on trust-dns-resolver:

trust-dns-resolver = { version = "*", features = ["dns-over-rustls"] }

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

use trust_dns_resolver::Resolver;
use trust_dns_resolver::config::*;

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

// see example above...

mDNS (multicast DNS)

Multicast DNS is an experimental feature in Trust-DNS at the moment. It's 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 extern crate trust_dns_proto as proto;

Modules

config	Configuration for a resolver
error	Error types for the crate
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.
lookup_state	Caching related functionality for the Resolver.
system_conf	System configuration loading

Structs

AsyncResolver	A handle for resolving DNS records.
Background	A future that represents sending a request to a background task, waiting for it to send back a lookup future, and then running the lookup future.
Hosts	Configuration for the local hosts file
Name	Them should be through references. As a workaround the Strings are all Rc as well as the array
Resolver	The Resolver is used for performing DNS queries.

Traits

IntoName	Conversion into a Name
TryParseIp	Types of this trait will can be attempted for conversion to an IP address

Functions

version

returns a version as specified in Cargo.toml

Type Definitions

BackgroundLookup	Future returned by lookup requests to the background task.
BackgroundLookupIp	Future returned by LookupIp requests to the background task.
ResolverFuture	Deprecated This is an alias for AsyncResolver, which replaced the type previously called ResolverFuture.