third_party/rust_crates/forks/trust-dns-resolver/examples/global_resolver.rs

#![recursion_limit = "128"]

#[macro_use]
extern crate lazy_static;

use std::fmt::Display;
#[cfg(feature = "tokio-runtime")]
use std::io;
#[cfg(feature = "tokio-runtime")]
use std::net::SocketAddr;
use std::task::Poll;

use futures_util::future;

#[cfg(feature = "tokio-runtime")]
use trust_dns_resolver::{IntoName, TryParseIp};
#[cfg(feature = "tokio-runtime")]
use trust_dns_resolver::{TokioAsyncResolver, TokioHandle};

// This is an example of registering a static global resolver into any system.
//
// We may want to create a GlobalResolver as part of the Resolver library
//   in the mean time, this example has the necessary steps to do so.
//
// Thank you to @zonyitoo for the original example.
// TODO: this example can probably be made much simpler with the new
//      `AsyncResolver`.
#[cfg(feature = "tokio-runtime")]
lazy_static! {
    // First we need to setup the global Resolver
    static ref GLOBAL_DNS_RESOLVER: TokioAsyncResolver = {
        use std::sync::{Arc, Mutex, Condvar};
        use std::thread;

        // We'll be using this condvar to get the Resolver from the thread...
        let pair = Arc::new((Mutex::new(None::<TokioAsyncResolver>), Condvar::new()));
        let pair2 = pair.clone();


        // Spawn the runtime to a new thread...
        //
        // This thread will manage the actual resolution runtime
        thread::spawn(move || {
            // A runtime for this new thread
            let runtime = tokio::runtime::Runtime::new().expect("failed to launch Runtime");

            // our platform independent future, result, see next blocks
            let resolver = {

                // To make this independent, if targeting macOS, BSD, Linux, or Windows, we can use the system's configuration:
                #[cfg(any(unix, windows))]
                {
                    // use the system resolver configuration
                    TokioAsyncResolver::from_system_conf(TokioHandle)
                }

                // For other operating systems, we can use one of the preconfigured definitions
                #[cfg(not(any(unix, windows)))]
                {
                    // Directly reference the config types
                    use trust_dns_resolver::config::{ResolverConfig, ResolverOpts};

                    // Get a new resolver with the google nameservers as the upstream recursive resolvers
                    TokioAsyncResolver::new(ResolverConfig::google(), ResolverOpts::default(), runtime.handle().clone())
                }
            };

            let &(ref lock, ref cvar) = &*pair2;
            let mut started = lock.lock().unwrap();

            let resolver = resolver.expect("failed to create trust-dns-resolver");

            *started = Some(resolver);
            cvar.notify_one();
            drop(started);

            runtime.block_on(future::poll_fn(|_cx| Poll::<()>::Pending))
        });

        // Wait for the thread to start up.
        let &(ref lock, ref cvar) = &*pair;
        let mut resolver = lock.lock().unwrap();
        while resolver.is_none() {
            resolver = cvar.wait(resolver).unwrap();
        }

        // take the started resolver
        let resolver = std::mem::replace(&mut *resolver, None);

        // set the global resolver
        resolver.expect("resolver should not be none")
    };
}

/// Provide a general purpose resolution function.
///
/// This looks up the `host` (a `&str` or `String` is good), and combines that with the provided port
///   this mimics the lookup functions of `std::net`.
#[cfg(feature = "tokio-runtime")]
#[cfg_attr(docsrs, doc(cfg(feature = "tokio-runtime")))]
pub async fn resolve<N: IntoName + Display + TryParseIp + 'static>(
    host: N,
    port: u16,
) -> io::Result<Vec<SocketAddr>> {
    // Now we use the global resolver to perform a lookup_ip.
    let name = host.to_string();
    let result = GLOBAL_DNS_RESOLVER.lookup_ip(host).await;
    // map the result into what we want...
    result
        .map_err(move |err| {
            // we transform the error into a standard IO error for convenience
            io::Error::new(
                io::ErrorKind::AddrNotAvailable,
                format!("dns resolution error for {}: {}", name, err),
            )
        })
        .map(move |lookup_ip| {
            // we take all the IPs returned, and then send back the set of IPs
            lookup_ip
                .iter()
                .map(|ip| SocketAddr::new(ip, port))
                .collect::<Vec<_>>()
        })
}

#[cfg(feature = "tokio-runtime")]
fn main() {
    use std::thread;

    // Let's resolve some names, we should be able to do it across threads
    let names = &["www.google.com", "www.reddit.com", "www.wikipedia.org"];

    // spawn all the threads to do the lookups
    let threads = names
        .iter()
        .map(|name| {
            let join = thread::spawn(move || {
                let runtime = tokio::runtime::Runtime::new().expect("failed to launch Runtime");
                runtime.block_on(resolve(*name, 443))
            });

            (name, join)
        })
        .collect::<Vec<_>>();

    // print the resolved IPs
    for (name, join) in threads {
        let result = join
            .join()
            .expect("resolution thread failed")
            .expect("resolution failed");
        println!("{} resolved to {:?}", name, result);
    }
}

#[cfg(not(feature = "tokio-runtime"))]
fn main() {
    println!("tokio-runtime feature must be enabled")
}