refactor(examples): use tokio instead of async-std in relay-server (#…

…5600)

## Description

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Following on issue #4449 
refactor: use tokio instead of async-std in the relay-servert example
and remove unnecessary dependencies
## Notes & open questions

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don't need to go into the final commit message.
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Fails on testing with the [whole punch
tutorial](https://docs.rs/libp2p/0.54.1/libp2p/tutorials/hole_punching/index.html)
possibly because of my networking topology. connection established event
registered.

I will publish the logs and testing information as a comment 

## Change checklist
* Removed unnecessary dependencies on examples/relay-server/Cargo.toml
* Updated tokio version  to "1.37.0"
<!-- Please add a Changelog entry in the appropriate crates and bump the
crate versions if needed. See
<https://github.com/libp2p/rust-libp2p/blob/master/docs/release.md#development-between-releases>-->

- [ ] I have performed a self-review of my own code
- [ ] I have made corresponding changes to the documentation
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] A changelog entry has been made in the appropriate crates

---------

Co-authored-by: David E. Perez Negron R. <david@nethunters.xyz>
Co-authored-by: Guillaume Michel <guillaumemichel@users.noreply.github.com>
Co-authored-by: João Oliveira <hello@jxs.pt>

examples/relay-server/Cargo.toml

@@ -10,10 +10,9 @@ release = false
 
 [dependencies]
 clap = { version = "4.5.6", features = ["derive"] }
-async-std = { version = "1.12", features = ["attributes"] }
-async-trait = "0.1"
+tokio = { version = "1.37.0", features = ["full"] }
 futures = { workspace = true }
-libp2p = { path = "../../libp2p", features = [ "async-std", "noise", "macros", "ping", "tcp", "identify", "yamux", "relay", "quic"] }
+libp2p = { path = "../../libp2p", features = ["tokio", "noise", "macros", "ping", "tcp", "identify", "yamux", "relay", "quic"] }
 tracing = { workspace = true }
 tracing-subscriber = { workspace = true, features = ["env-filter"] }
 

examples/relay-server/src/main.rs

@@ -22,8 +22,7 @@
 #![doc = include_str!("../README.md")]
 
 use clap::Parser;
-use futures::executor::block_on;
-use futures::stream::StreamExt;
+use futures::StreamExt;
 use libp2p::{
     core::multiaddr::Protocol,
     core::Multiaddr,
@@ -35,7 +34,8 @@ use std::error::Error;
 use std::net::{Ipv4Addr, Ipv6Addr};
 use tracing_subscriber::EnvFilter;
 
-fn main() -> Result<(), Box<dyn Error>> {
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error>> {
     let _ = tracing_subscriber::fmt()
         .with_env_filter(EnvFilter::from_default_env())
         .try_init();
@@ -46,7 +46,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     let local_key: identity::Keypair = generate_ed25519(opt.secret_key_seed);
 
     let mut swarm = libp2p::SwarmBuilder::with_existing_identity(local_key)
-        .with_async_std()
+        .with_tokio()
         .with_tcp(
             tcp::Config::default(),
             noise::Config::new,
@@ -81,27 +81,25 @@ fn main() -> Result<(), Box<dyn Error>> {
         .with(Protocol::QuicV1);
     swarm.listen_on(listen_addr_quic)?;
 
-    block_on(async {
-        loop {
-            match swarm.next().await.expect("Infinite Stream.") {
-                SwarmEvent::Behaviour(event) => {
-                    if let BehaviourEvent::Identify(identify::Event::Received {
-                        info: identify::Info { observed_addr, .. },
-                        ..
-                    }) = &event
-                    {
-                        swarm.add_external_address(observed_addr.clone());
-                    }
-
-                    println!("{event:?}")
+    loop {
+        match swarm.next().await.expect("Infinite Stream.") {
+            SwarmEvent::Behaviour(event) => {
+                if let BehaviourEvent::Identify(identify::Event::Received {
+                    info: identify::Info { observed_addr, .. },
+                    ..
+                }) = &event
+                {
+                    swarm.add_external_address(observed_addr.clone());
                 }
-                SwarmEvent::NewListenAddr { address, .. } => {
-                    println!("Listening on {address:?}");
-                }
-                _ => {}
+
+                println!("{event:?}")
+            }
+            SwarmEvent::NewListenAddr { address, .. } => {
+                println!("Listening on {address:?}");
             }
+            _ => {}
         }
-    })
+    }
 }
 
 #[derive(NetworkBehaviour)]