refactor: introduce constants for default addresses and improve error handling in TCP examples (#7741)

- Added `DEFAULT_ADDR` constant to `chat.rs` and `echo-tcp.rs` for better maintainability.
- Enhanced error logging in `connect-tcp.rs` and `echo-tcp.rs` to include connection addresses.
- Improved peer management in `chat.rs` by automatically cleaning up disconnected peers.

examples/chat.rs

@@ -39,6 +39,8 @@ use std::io;
 use std::net::SocketAddr;
 use std::sync::Arc;
 
+const DEFAULT_ADDR: &str = "127.0.0.1:6142";
+
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn Error>> {
     use tracing_subscriber::{fmt::format::FmtSpan, EnvFilter};
@@ -70,7 +72,7 @@ async fn main() -> Result<(), Box<dyn Error>> {
 
     let addr = env::args()
         .nth(1)
-        .unwrap_or_else(|| "127.0.0.1:6142".to_string());
+        .unwrap_or_else(|| DEFAULT_ADDR.to_string());
 
     // Bind a TCP listener to the socket address.
     //
@@ -88,9 +90,9 @@ async fn main() -> Result<(), Box<dyn Error>> {
 
         // Spawn our handler to be run asynchronously.
         tokio::spawn(async move {
-            tracing::debug!("accepted connection");
+            tracing::debug!("accepted connection from {}", addr);
             if let Err(e) = process(state, stream, addr).await {
-                tracing::info!("an error occurred; error = {:?}", e);
+                tracing::warn!("Connection from {} failed: {:?}", addr, e);
             }
         });
     }
@@ -138,12 +140,26 @@ impl Shared {
 
     /// Send a `LineCodec` encoded message to every peer, except
     /// for the sender.
+    ///
+    /// This function also cleans up disconnected peers automatically.
     async fn broadcast(&mut self, sender: SocketAddr, message: &str) {
-        for peer in self.peers.iter_mut() {
-            if *peer.0 != sender {
-                let _ = peer.1.send(message.into());
+        let mut failed_peers = Vec::new();
+        let message = message.to_string(); // Clone once for all sends
+
+        for (addr, tx) in self.peers.iter() {
+            if *addr != sender {
+                if tx.send(message.clone()).is_err() {
+                    // Receiver has been dropped, mark for removal
+                    failed_peers.push(*addr);
+                }
             }
         }
+
+        // Clean up disconnected peers
+        for addr in failed_peers {
+            self.peers.remove(&addr);
+            tracing::debug!("Removed disconnected peer: {}", addr);
+        }
     }
 }
 
@@ -203,7 +219,10 @@ async fn process(
         tokio::select! {
             // A message was received from a peer. Send it to the current user.
             Some(msg) = peer.rx.recv() => {
-                peer.lines.send(&msg).await?;
+                if let Err(e) = peer.lines.send(&msg).await {
+                    tracing::error!("Failed to send message to {}: {:?}", username, e);
+                    break;
+                }
             }
             result = peer.lines.next() => match result {
                 // A message was received from the current user, we should
@@ -221,6 +240,7 @@ async fn process(
                         username,
                         e
                     );
+                    break;
                 }
                 // The stream has been exhausted.
                 None => break,

examples/connect-tcp.rs

@@ -58,7 +58,7 @@ pub async fn connect(
             //BytesMut into Bytes
             Ok(i) => future::ready(Some(i.freeze())),
             Err(e) => {
-                println!("failed to read from socket; error={e}");
+                eprintln!("failed to read from socket; error={e}");
                 future::ready(None)
             }
         })

examples/echo-tcp.rs

@@ -27,6 +27,9 @@ use tokio::net::TcpListener;
 use std::env;
 use std::error::Error;
 
+const DEFAULT_ADDR: &str = "127.0.0.1:8080";
+const BUFFER_SIZE: usize = 4096;
+
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn Error>> {
     // Allow passing an address to listen on as the first argument of this
@@ -34,7 +37,7 @@ async fn main() -> Result<(), Box<dyn Error>> {
     // 127.0.0.1:8080 for connections.
     let addr = env::args()
         .nth(1)
-        .unwrap_or_else(|| "127.0.0.1:8080".to_string());
+        .unwrap_or_else(|| DEFAULT_ADDR.to_string());
 
     // Next up we create a TCP listener which will listen for incoming
     // connections. This TCP listener is bound to the address we determined
@@ -44,7 +47,7 @@ async fn main() -> Result<(), Box<dyn Error>> {
 
     loop {
         // Asynchronously wait for an inbound socket.
-        let (mut socket, _) = listener.accept().await?;
+        let (mut socket, addr) = listener.accept().await?;
 
         // And this is where much of the magic of this server happens. We
         // crucially want all clients to make progress concurrently, rather than
@@ -55,23 +58,27 @@ async fn main() -> Result<(), Box<dyn Error>> {
         // which will allow all of our clients to be processed concurrently.
 
         tokio::spawn(async move {
-            let mut buf = vec![0; 1024];
+            let mut buf = vec![0; BUFFER_SIZE];
 
             // In a loop, read data from the socket and write the data back.
             loop {
-                let n = socket
-                    .read(&mut buf)
-                    .await
-                    .expect("failed to read data from socket");
-
-                if n == 0 {
-                    return;
+                match socket.read(&mut buf).await {
+                    Ok(0) => {
+                        // Connection closed by peer
+                        return;
+                    }
+                    Ok(n) => {
+                        // Write the data back. If writing fails, log the error and exit.
+                        if let Err(e) = socket.write_all(&buf[0..n]).await {
+                            eprintln!("Failed to write to socket {}: {}", addr, e);
+                            return;
+                        }
+                    }
+                    Err(e) => {
+                        eprintln!("Failed to read from socket {}: {}", addr, e);
+                        return;
+                    }
                 }
-
-                socket
-                    .write_all(&buf[0..n])
-                    .await
-                    .expect("failed to write data to socket");
             }
         });
     }