add echo server

Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "protohackers"
+version = "0.1.0"

Cargo.toml

@@ -5,4 +5,7 @@ edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
+[[bin]]
+name = "smoke"
+
 [dependencies]

src/bin/smoke.rs

@@ -0,0 +1,27 @@
+use std::{io::{Read, Write}, net::TcpListener};
+
+const PORT: usize = 10000;
+const BUFF_SIZE: usize = 1;
+fn main() -> std::io::Result<()> {
+
+    let listener = TcpListener::bind(format!("127.0.0.1:{PORT}"))?;
+
+    for stream in listener.incoming() {
+        match stream {
+            Ok(mut stream) => {
+                loop {
+                    let mut buf: [u8; BUFF_SIZE] = [0; BUFF_SIZE];
+
+                    if let Ok(_) = stream.read_exact(&mut buf) {
+                        stream.write(&buf)?;
+                    } else {
+                        break;
+                    }
+                }
+            },
+            Err(e) => panic!("{:?}", e)
+        }
+    }
+
+    Ok(())
+}