fix: disable async_dht when not using the default features

see: cargo run --no-default-features --example get_immutable 4238af8aff56cf6e0007d9d2003bf23d33eea7c3

Cargo.toml

@@ -29,3 +29,8 @@ futures = "0.3.29"
 [features]
 async = ["flume/async"]
 default = ["async"]
+
+[[example]]
+name = "async_get_immutable"
+path = "examples/async/get_immutable.rs"
+required-features = ["async"]

examples/README.md

@@ -35,3 +35,9 @@ cargo run --example put_mutable <64 bytes hex secret_key> <string>
 ```sh
 cargo run --example get_mutable <40 bytes hex target from put_mutable>
 `````
+
+## Async Get Mutable
+
+```sh
+cargo run --example async_get_mutable <40 bytes hex target from put_mutable>
+`````

examples/async/get_immutable.rs

@@ -0,0 +1,67 @@
+use std::{str::FromStr, time::Instant};
+
+use mainline::{Dht, Id};
+
+use clap::Parser;
+
+#[derive(Parser)]
+#[command(author, version, about, long_about = None)]
+struct Cli {
+    /// Immutable data sha1 hash to lookup.
+    target: String,
+}
+
+async fn async_main() {
+    let cli = Cli::parse();
+
+    let target_parse_result: Result<Id, _> = Id::from_str(cli.target.as_str());
+
+    match target_parse_result {
+        Ok(infohash) => {
+            let dht = Dht::default().as_async();
+
+            let start = Instant::now();
+
+            println!("\nLooking up immutable data: {} ...\n", cli.target);
+
+            let response = &mut dht.get_immutable(infohash).await;
+
+            if let Some(res) = response.next_async().await {
+                println!(
+                    "Got result in {:?} seconds\n",
+                    start.elapsed().as_secs_f32()
+                );
+
+                // No need to stream responses, just print the first result, since
+                // all immutable data items are guaranteed to be the same.
+
+                match String::from_utf8(res.value.to_vec()) {
+                    Ok(string) => {
+                        println!("Got immutable data: {:?} | from: {:?}", string, res.from);
+                    }
+                    Err(_) => {
+                        println!("Got immutable data: {:?} | from: {:?}", res.value, res.from);
+                    }
+                };
+            }
+
+            println!(
+                "\nVisited {:?} nodes, found {:?} closest nodes",
+                response.visited,
+                &response.closest_nodes.len()
+            );
+
+            println!(
+                "\nQuery exhausted in {:?} seconds",
+                start.elapsed().as_secs_f32(),
+            );
+        }
+        Err(err) => {
+            println!("Error: {}", err)
+        }
+    };
+}
+
+fn main() {
+    futures::executor::block_on(async_main());
+}

src/lib.rs

@@ -5,6 +5,7 @@
 //! Rust implementation of read-only BitTorrent Mainline DHT client.
 
 // Public modules
+#[cfg(feature = "async")]
 pub mod async_dht;
 pub mod common;
 pub mod dht;