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 = "^0.8"
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_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 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 |
error | |
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 |
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 |