Add problem 01

problem_01/.gitignore

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+/target/

problem_01/Cargo.toml

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+[package]
+name = "problem_01"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+tokio = { version = "1.27.0", features = ["full"] }

problem_01/src/main.rs

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+use tokio::net::TcpListener;
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let listener = TcpListener::bind("127.0.0.1:4040").await?;
+
+    loop {
+        let (mut socket, _) = listener.accept().await?;
+
+        tokio::spawn(async move {
+            let mut buf = [0; 1024];
+            
+            loop {
+
+                let n = match socket.read(&mut buf).await {
+                    Ok(n) if n == 0 => return,
+                    Ok(n) => n,
+                    Err(e) => {
+                        eprintln!("failed to read from socket; err = {:?}", e);
+                        return;
+                    }
+                };
+
+                if let Err(e) = socket.write_all(&buf[0..n]).await {
+                    eprintln!("failed to write to socket; err = {:?}", e);
+                    return;
+                }
+            }
+        });
+    }
+}