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//! An asynchronous stub resolver. //! //! A resolver is the component in the DNS that answers queries. A stub //! resolver does so by simply relaying queries to a different resolver //! chosen from a predefined set. This is how pretty much all user //! applications use DNS. //! //! This module implements a modern, asynchronous stub resolver built on //! top of [tokio-core]. //! //! The module provides ways to create a *resolver* that knows how to //! process DNS *queries*. A query asks for all the resource records //! associated with a given triple of a domain name, resource record type, //! and class (known as a *question*). It is a future resolving to a DNS //! message with the response or an error. Queries can be combined into //! *lookups* that use the returned resource records to answer more //! specific enquiries such as all the IP addresses associated with a given //! host name. The module provides a rich set of common lookups in the //! [lookup] sub-module. //! //! The following gives an introduction into using the resolver. For an //! introduction into the internal design, please have a look at the [intro] //! sub-module. //! //! //! # Creating a Resolver //! //! The resolver is represented by the [`Resolver`] type. When creating a //! value of this type, you create all the parts of an actual resolver //! according to a resolver configuration. Since these parts are handling //! actual network traffic, the resolver needs a handle to a Tokio reactor //! into which these parts will be spawned as futures. //! //! For the resolver configuration, there’s [`ResolvConf`]. While you can //! create a value of this type by hand, the more common way is to use your //! system’s resolver configuration. [`ResolvConf`] implements the `Default` //! trait doing exactly that by reading `/etc/resolv.conf`. //! //! > That probably won’t work on Windows, but, sadly, I have no idea how to //! > retrieve the resolver configuration there. Some help here would be //! > very much appreciated. //! //! Since using the system configuration is the most common case by far, //! [`Resolver`]’s `new()` function does just that. So, the easiest way to //! get a resolver is just this: //! //! ``` //! # extern crate domain; //! # extern crate tokio_core; //! use domain::resolv::Resolver; //! use tokio_core::reactor::Core; //! //! # fn main() { //! let core = Core::new().unwrap(); //! let resolv = Resolver::new(&core.handle()).unwrap(); //! # } //! ``` //! //! If you do have a configuration, you can use the `from_conf()` function //! instead. //! //! //! # Using the Resolver: Queries //! //! As was mentioned above, the [`Resolver`] does’t actually contain the //! networking parts necessary to answer queries. Instead, it only knows how //! to contact those parts. Because of this, you can clone the resolver, //! even pass it to other threads. //! //! Oddly, the one thing you can’t do with a resolver is start a query. //! Instead, you need an intermediary type called [`ResolverTask`]. You’ll //! get one through [`Resolver::start()`] or, more correctly, you get a future //! to one through this method. You then chain on your actual query or //! sequence of queries using combinators such as `Future::and_then()`. //! //! The actual query is started through [`ResolverTask::query()`]. It takes a //! domain name, a resource record type, and a class and returns a future //! that will resolve into either a [`MessageBuf`] with the response to the //! query or an [`Error`]. //! //! As an example, let’s find out the IPv6 addresses for `www.rust-lang.org`: //! //! ``` //! extern crate domain; //! extern crate futures; //! extern crate tokio_core; //! //! use std::str::FromStr; //! use domain::bits::DNameBuf; //! use domain::iana::{Class, Rtype}; //! use domain::rdata::Aaaa; //! use domain::resolv::Resolver; //! use futures::Future; //! use tokio_core::reactor::Core; //! //! fn main() { //! let mut core = Core::new().unwrap(); //! let resolv = Resolver::new(&core.handle()).unwrap(); //! //! let addrs = resolv.start().and_then(|resolv| { //! let name = DNameBuf::from_str("www.rust-lang.org.").unwrap(); //! resolv.query(name, Rtype::Aaaa, Class::In) //! }); //! let response = core.run(addrs).unwrap(); //! for record in response.answer().unwrap().limit_to::<Aaaa>() { //! println!("{}", record.unwrap()); //! } //! } //! ``` //! //! Note the final dot at `"www.rust-lang.org."` making it an absolute domain //! name. Queries don’t know how to deal with relative names and will error //! out if given one. //! //! //! # Complex Queries: Lookups //! //! Most times when you are using DNS you aren’t really interested in a //! bunch of resource records, though, you want an answer to a more direct //! question. For instance, if you want to know the IP addresses for a //! host name, you don’t really care that you have to make a query for the //! `A` records and one for `AAAA` records for that host name. You want the //! addresses. //! //! This is what lookups do. They take a [`ResolverTask`] and some additional //! information and turn that into a future of some specific result. So, //! to do lookups you have to follow the procedure using `start()` as given //! above but instead of calling `query()` inside the closure, you use one //! of the lookup functions from the [lookup] sub-module. //! //! Using [`lookup_host()`], the process of looking up the IP addresses //! becomes much easier. To update above’s example: //! //! ``` //! extern crate domain; //! extern crate futures; //! extern crate tokio_core; //! //! use std::str::FromStr; //! use domain::bits::DNameBuf; //! use domain::resolv::Resolver; //! use domain::resolv::lookup::lookup_host; //! use futures::Future; //! use tokio_core::reactor::Core; //! //! fn main() { //! let mut core = Core::new().unwrap(); //! let resolv = Resolver::new(&core.handle()).unwrap(); //! //! let addrs = resolv.start().and_then(|resolv| { //! let name = DNameBuf::from_str("www.rust-lang.org").unwrap(); //! lookup_host(resolv, name) //! }); //! let response = core.run(addrs).unwrap(); //! for addr in response.iter() { //! println!("{}", addr); //! } //! } //! ``` //! //! No more fiddeling with record types and classes and the result can now //! iterate over IP addresses. And we get both IPv4 and IPv6 addresses to //! boot. //! //! Furthermore, we now can use a relative host name. It will be turned into //! an absolute name according to the rules set down by the configuration we //! used when creating the resolver. //! //! As an aside, the lookup functions are named after the thing they look //! up not their result following the example of the standard library. So, //! when you look for the addresses for the host, you have to use //! [`lookup_host()`], not [`lookup_addr()`]. //! //! Have a look at the [lookup] module for all the lookup functions //! currently available. //! //! //! # The Run Shortcut //! //! If you only want to do a DNS lookup and don’t otherwise use tokio, there //! is a shortcut through the [`Resolver::run()`] associated function. It //! takes a closure from a [`ResolverTask`] to a future and waits while //! driving the future to completing. In other words, it takes away all the //! boiler plate from above: //! //! ``` //! extern crate domain; //! //! use std::str::FromStr; //! use domain::bits::DNameBuf; //! use domain::resolv::Resolver; //! use domain::resolv::lookup::lookup_host; //! //! fn main() { //! let response = Resolver::run(|resolv| { //! let name = DNameBuf::from_str("www.rust-lang.org").unwrap(); //! lookup_host(resolv, name) //! }); //! for addr in response.unwrap().iter() { //! println!("{}", addr); //! } //! } //! ``` //! //! //! [intro]: intro/index.html //! [lookup]: lookup/index.html //! [tokio-core]: https://github.com/tokio-rs/tokio-core //! [`Error`]: error/enum.Error.html //! [`MessageBuf`]: ../bits/message/struct.MessageBuf.html //! [`ResolvConf`]: conf/struct.ResolvConf.html //! [`Resolver`]: struct.Resolver.html //! [`Resolver::start()`]: struct.Resolver.html#method.start //! [`Resolver::run()`]: struct.Resolver.html#method.run //! [`ResolverTask`]: struct.ResolverTask.html //! [`ResolverTask::query()`]: struct.ResolverTask.html#method.query //! [`lookup_addr()`]: lookup/fn.lookup_addr.html //! [`lookup_host()`]: lookup/fn.lookup_host.html //============ Sub-modules =================================================== //--- Re-exports pub use self::conf::ResolvConf; pub use self::error::{Error, Result}; pub use self::query::Query; //--- Public modules pub mod conf; pub mod error; pub mod hosts; pub mod lookup; //--- Private modules mod core; mod query; mod request; mod service; mod tcp; mod transport; mod udp; mod utils; //--- Meta-modules for documentation pub mod intro; //============ Actual Content ================================================ use std::io; use std::ops::Deref; use std::result; use std::sync::Arc; use futures::{BoxFuture, Future, lazy}; use futures::task::TaskRc; use tokio_core::reactor; use ::bits::DName; use ::iana::{Class, Rtype}; use self::conf::ResolvOptions; use self::core::Core; //------------ Resolver ----------------------------------------------------- /// Access to a resolver. /// /// This types collects all information in order to be able to start a DNS /// query on a resolver. You can create a new resolver by calling either /// the `new()` or `from_conf()` functions passing in a handle to a Tokio /// reactor core. Either function will spawn everything necessary for a /// resolver into that core. Existing resolver values can be cloned. Clones /// will refer to the same resolver. /// /// In order to perform a query, you will have to call the `start()` method /// to create a future that will resolve into an intermediary value that /// will than allow calling a `query()` method on it and will also allow /// more complex operations as a complex future. /// /// Alternatively, you can use the `run()` associated function to /// synchronously perfrom a series of queries. #[derive(Clone, Debug)] pub struct Resolver { core: Arc<Core> } impl Resolver { /// Creates a new resolver using the system’s default configuration. /// /// All the components of the resolver will be spawned into the reactor /// referenced by `reactor`. pub fn new(reactor: &reactor::Handle) -> io::Result<Self> { Self::from_conf(reactor, ResolvConf::default()) } /// Creates a new resolver using the given configuration. /// /// All the components of the resolver will be spawned into the reactor /// referenced by `reactor`. pub fn from_conf(reactor: &reactor::Handle, conf: ResolvConf) -> io::Result<Self> { Core::new(reactor, conf) .map(|core| Resolver{core: Arc::new(core)}) } /// Returns a reference to the configuration of this resolver. pub fn conf(&self) -> &ResolvConf { self.core.conf() } /// Returns a reference to the configuration options of this resolver. pub fn options(&self) -> &ResolvOptions { &self.core.conf().options } /// Starts a resolver future atop this resolver. /// /// The method returns a future that will resolve into a [ResolverTask] /// value that can be used to start queries atop this resolver. /// /// Since the future will never error, it is generic over the error type. /// /// [ResolverTask]: struct.ResolverTask.html pub fn start<E>(&self) -> BoxFuture<ResolverTask, E> where E: Send + 'static { let core = self.core.deref().clone(); lazy(move || Ok(ResolverTask{core: TaskRc::new(core)})).boxed() } } /// # Shortcuts /// impl Resolver { /// Synchronously perform a DNS operation atop a standard resolver. /// /// This associated functions removes almost all boiler plate for the /// case that you want to perform some DNS operation on a resolver using /// the system’s configuration and wait for the result. /// /// The only argument is a closure taking a [ResolverTask] for creating /// queries and returning a future. Whatever that future resolves to will /// be returned. pub fn run<R, F>(f: F) -> result::Result<R::Item, R::Error> where R: Future, R::Error: From<io::Error> + Send + 'static, F: FnOnce(ResolverTask) -> R { let mut reactor = try!(reactor::Core::new()); let resolver = try!(Resolver::new(&reactor.handle())); let fut = resolver.start().and_then(f); reactor.run(fut) } pub fn run_with_conf<R, F>(conf: ResolvConf, f: F) -> result::Result<R::Item, R::Error> where R: Future, R::Error: From<io::Error> + Send + 'static, F: FnOnce(ResolverTask) -> R { let mut reactor = try!(reactor::Core::new()); let resolver = try!(Resolver::from_conf(&reactor.handle(), conf)); let fut = resolver.start().and_then(f); reactor.run(fut) } /// Spawn a query. /// /// This method is a shortcut for `self.start().and_then(f).boxed()`. /// Because of the `boxed()` bit, it requires lots of things to be /// `Send + 'static` and because of that isn’t necessarily better than /// the longer way. /// /// I am also not sure if *spawn* is the right name. Probably not since /// it actually returns the future. pub fn spawn<R, F>(&self, f: F) -> BoxFuture<R::Item, R::Error> where R: Future + Send + 'static, R::Error: From<io::Error> + Send + 'static, F: FnOnce(ResolverTask) -> R + Send + 'static { self.start().and_then(f).boxed() } } //------------ ResolverTask -------------------------------------------------- /// A resolver bound to a futures task. /// /// You can use this type within a running future to start a query on top /// of the resolver using the `query()` method. #[derive(Clone)] pub struct ResolverTask { core: TaskRc<Core> } impl ResolverTask { /// Start a DNS query on this resolver. /// /// Returns a future that, if successful, will resolve into a DNS /// message containing a response to a query for resource records of type /// `rtype` associated with the domain name `name` and class `class`. The /// name must be an absolute name or else the query will fail. pub fn query<N: DName>(&self, name: N, rtype: Rtype, class: Class) -> Query { Query::new(self, name, rtype, class) } /// Returns an arc reference to the resolver’s config. pub fn conf(&self) -> Arc<ResolvConf> { self.core.with(|core| core.clone_conf()) } }