Refactored runtime (#192)

runtime/src/network.rs

@@ -0,0 +1,8 @@
+use std::net::TcpListener;
+
+/// Returns an available port on the local machine.
+pub fn get_available_port() -> Option<u16> {
+    TcpListener::bind(("127.0.0.1", 0))
+        .map(|listener| listener.local_addr().unwrap().port())
+        .ok()
+}