First echo server barebones for problem_04

problem_04/.gitignore

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+/target/
+.idea

problem_04/Cargo.toml

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+[package]
+name = "problem_04"
+version = "0.1.0"
+edition = "2021"
+
+[[bin]]
+name = "server"
+path = "bin/server.rs"
+
+[[bin]]
+name = "client"
+path = "bin/client.rs"
+
+[dependencies]
+tokio = { version = "1.14.0", features = ["full"] }
+tracing = "0.1.37"
+tracing-subscriber = "0.3.17"

problem_04/bin/server.rs

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+use std::io;
+use tokio::net::UdpSocket;
+
+#[tokio::main]
+async fn main() -> io::Result<()> {
+    let sock = UdpSocket::bind("0.0.0.0:8080").await?;
+    let mut buf = [0; 1024];
+    loop {
+        let (len, addr) = sock.recv_from(&mut buf).await?;
+        println!("{:?} bytes received from {:?}", len, addr);
+
+        let len = sock.send_to(&buf[..len], addr).await?;
+        println!("{:?} bytes sent", len);
+    }
+}

problem_04/src/lib.rs

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+fn main() {
+    println!("Hello, world!");
+}