Create initial version of client

This just connects to the server and does very little else.

client/main.vala

@@ -0,0 +1,82 @@
+using Gtk;
+
+public class Connection {
+	private InetSocketAddress host;
+	public signal void response_received(uint8[] response);
+
+	public Connection() {
+		var loopback = new InetAddress.loopback(SocketFamily.IPV6);
+		host = new InetSocketAddress(loopback, 12888);
+	}
+
+	public async void send(uint8[] message) throws Error {
+		var client = new SocketClient();
+		var conn = yield client.connect_async(host);
+		yield conn.output_stream.write_async(message);
+
+		var response = new uint8[1024];
+		var len = yield conn.input_stream.read_async(response);
+		response_received(response[0:len]);
+	}
+}
+
+public class MainWindow : Gtk.ApplicationWindow {
+	private Connection connection;
+	private Gtk.Label response_label;
+	private Gtk.Button connect_button;
+
+	public MainWindow(Gtk.Application app, Connection connection) {
+		Object(application: app);
+
+		default_width = 600;
+		default_height = 400;
+		title = "Study System Client";
+
+		this.connection = connection;
+		connection.response_received.connect((response) => {
+				response_label.label = "Response: " + (string)response;
+		});
+
+		var box = new Gtk.Box(Gtk.Orientation.VERTICAL, 10);
+		box.margin_start = 10;
+		box.margin_end = 10;
+		box.margin_top = 10;
+		box.margin_bottom = 10;
+
+		connect_button = new Gtk.Button.with_label("Foo");
+		connect_button.clicked.connect(on_connect_clicked);
+		box.append(connect_button);
+
+		response_label = new Gtk.Label("");
+		response_label.wrap = true;
+		box.append(response_label);
+
+		set_child(box);
+						  
+		present();
+	}
+
+	private async void on_connect_clicked() {
+		try {
+			yield connection.send("Bar".data);
+		} catch (Error e) {
+			response_label.label = "Error: " + e.message;
+		}
+	}
+}
+
+public class StudySystemClient : Gtk.Application {
+	public StudySystemClient() {
+		Object(application_id: "sh.wip.study-system-client");
+	}
+
+	protected override void activate() {
+		var connection = new Connection();
+		new MainWindow(this, connection);
+	}
+
+	public static int main(string[] args) {
+		var app = new StudySystemClient();
+		return app.run(args);
+	}
+}

client/meson.build

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+project(
+  'study-system-client',
+  'vala',
+  version : '0.1.0',
+)
+
+# Vala often generates C code that produces warnings, so ignore these
+# to avoid a noisy build output.
+add_project_arguments('-w', language: 'c')
+
+gtk_dep = dependency('gtk4')
+
+exe = executable(
+  'study-system-client',
+  'main.vala',
+  dependencies: [gtk_dep],
+  c_args: ['-w']
+)