Use expect() for error handling in task.md (#1639)

The use of conditionals for error handling makes the code look mode
complex than is.

Read the actual port number from the listener instead of hardcoding port
6142 in two places. That also demonstrates how to deal with ephemeral
ports.

---------

Co-authored-by: Dustin J. Mitchell <[email protected]>

Author: proski

src/async/tasks.md

@@ -13,35 +13,22 @@ use tokio::net::TcpListener;
 
 #[tokio::main]
 async fn main() -> io::Result<()> {
-    let listener = TcpListener::bind("127.0.0.1:6142").await?;
-    println!("listening on port 6142");
+    let listener = TcpListener::bind("127.0.0.1:0").await?;
+    println!("listening on port {}", listener.local_addr()?.port());
 
     loop {
         let (mut socket, addr) = listener.accept().await?;
 
         println!("connection from {addr:?}");
 
         tokio::spawn(async move {
-            if let Err(e) = socket.write_all(b"Who are you?\n").await {
-                println!("socket error: {e:?}");
-                return;
-            }
+            socket.write_all(b"Who are you?\n").await.expect("socket error");
 
             let mut buf = vec![0; 1024];
-            let reply = match socket.read(&mut buf).await {
-                Ok(n) => {
-                    let name = std::str::from_utf8(&buf[..n]).unwrap().trim();
-                    format!("Thanks for dialing in, {name}!\n")
-                }
-                Err(e) => {
-                    println!("socket error: {e:?}");
-                    return;
-                }
-            };
-
-            if let Err(e) = socket.write_all(reply.as_bytes()).await {
-                println!("socket error: {e:?}");
-            }
+            let name_size = socket.read(&mut buf).await.expect("socket error");
+            let name = std::str::from_utf8(&buf[..name_size]).unwrap().trim();
+            let reply = format!("Thanks for dialing in, {name}!\n");
+            socket.write_all(reply.as_bytes()).await.expect("socket error");
         });
     }
 }