Implement simple listening

Cargo.toml

@@ -4,3 +4,5 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
+thiserror = "2.0.18"
+## Make it easier to generate errors

src/lib.rs

@@ -1,2 +1,23 @@
-#[derive(Default)]
-pub struct Peer {}
+use std::net::{SocketAddr, UdpSocket};
+
+use thiserror::*;
+
+#[derive(Error, Debug)]
+pub enum PeerError {
+    #[error("Error binding to port: {0}")]
+    BindError(std::io::Error),
+}
+
+pub struct Peer {
+    socket: UdpSocket,
+}
+
+impl Peer {
+    /// Bind given port to listen to incoming messages. Creates a new Peer that
+    /// can establish new connections.
+    pub fn listen(port: Option<u16>) -> Result<Peer, PeerError> {
+        let socket = UdpSocket::bind(SocketAddr::from(([0, 0, 0, 0], port.unwrap_or(0))))
+            .map_err(|e| PeerError::BindError(e))?;
+        Ok(Peer { socket })
+    }
+}