refactor: run dns resolution in the same tracing-span as the caller (#134)

This makes it possible to trace the entire request, including DNS
resolution.

The use case for this is to be able to suppress specific requests from
being traced in a situation where the request is used to transmit logs
to a remote server. This would result in an infinite loop of logs being
sent to the remote server. tokio-rs/tokio#6659
has more details.

Author: joshka

src/client/legacy/connect/dns.rs

@@ -31,7 +31,7 @@ use std::{fmt, io, vec};
 
 use tokio::task::JoinHandle;
 use tower_service::Service;
-use tracing::debug;
+use tracing::{debug, debug_span};
 
 pub(super) use self::sealed::Resolve;
 
@@ -118,8 +118,10 @@ impl Service<Name> for GaiResolver {
     }
 
     fn call(&mut self, name: Name) -> Self::Future {
+        let span = debug_span!("resolve", host = %name.host).or_current();
         let blocking = tokio::task::spawn_blocking(move || {
-            debug!("resolving host={:?}", name.host);
+            let _enter = span.enter();
+            debug!(host = name.host, "resolving");
             (&*name.host, 0)
                 .to_socket_addrs()
                 .map(|i| SocketAddrs { iter: i })