Crate trust_dns_resolver [−] [src]

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 directly. 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 = "^0.5"

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 mut 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 mut 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 mut resolver = Resolver::from_system_conf().unwrap();
let mut 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_core::reactor::Core;
use trust_dns_resolver::ResolverFuture;
use trust_dns_resolver::config::*;

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

// Construct a new Resolver with default configuration options
let mut resolver = ResolverFuture::new(ResolverConfig::default(), ResolverOpts::default(), &io_loop.handle());

// 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.run(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.run(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.

Modules

config	Configuration for a resolver
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

Hosts	Configuration for the local `/etc/hosts`
Resolver	The Resolver is used for performing DNS queries.
ResolverFuture	A Resolver for DNS records.

Functions

version

returns a version as specified in Cargo.toml