Add an option to allow people to join without being invited (requires a public IP address).

Due to the non-obvious technical requirements, I decided to hide it a bit.

fixes #618

src/gui/windows/invite.zig

@@ -9,6 +9,7 @@ const gui = @import("../gui.zig");
 const GuiComponent = gui.GuiComponent;
 const GuiWindow = gui.GuiWindow;
 const Button = @import("../components/Button.zig");
+const CheckBox = @import("../components/CheckBox.zig");
 const Label = @import("../components/Label.zig");
 const TextInput = @import("../components/TextInput.zig");
 const VerticalList = @import("../components/VerticalList.zig");
@@ -59,8 +60,22 @@ fn copyIp(_: usize) void {
 	main.Window.setClipboardString(ipAddress);
 }
 
+fn inviteFromExternal(address: main.network.Address) void {
+	const ip = std.fmt.allocPrint(main.stackAllocator.allocator, "{}", .{address}) catch unreachable;
+	defer main.stackAllocator.free(ip);
+	const user = main.server.User.initAndIncreaseRefCount(main.server.connectionManager, ip) catch |err| {
+		std.log.err("Cannot connect user from external IP {}: {s}", .{address, @errorName(err)});
+		return;
+	};
+	user.decreaseRefCount();
+}
+
+fn makePublic(public: bool) void {
+	main.server.connectionManager.newConnectionCallback.store(if(public) &inviteFromExternal else null, .monotonic);
+}
+
 pub fn onOpen() void {
-	const list = VerticalList.init(.{padding, 16 + padding}, 300, 16);
+	const list = VerticalList.init(.{padding, 16 + padding}, 260, 16);
 	list.add(Label.init(.{0, 0}, width, "Please send your IP to the player who wants to join and enter their IP below.", .center));
 	//                                           255.255.255.255:?65536 (longest possible ip address)
 	ipAddressLabel = Label.init(.{0, 0}, width, "                      ", .center);
@@ -70,6 +85,7 @@ pub fn onOpen() void {
 	list.add(ipAddressEntry);
 	list.add(Button.initText(.{0, 0}, 100, "Invite", .{.callback = &invite}));
 	list.add(Button.initText(.{0, 0}, 100, "Manage Players", gui.openWindowCallback("manage_players")));
+	list.add(CheckBox.init(.{0, 0}, width, "Allow anyone to join (requires a publicly visible IP address+port which may need some configuration in your router)", main.server.connectionManager.newConnectionCallback.load(.monotonic) != null, &makePublic));
 	list.finish(.center);
 	window.rootComponent = list.toComponent();
 	window.contentSize = window.rootComponent.?.pos() + window.rootComponent.?.size() + @as(Vec2f, @splat(padding));

src/network.zig

@@ -126,7 +126,7 @@ pub fn init() void {
 	}
 }
 
-const Address = struct {
+pub const Address = struct {
 	ip: u32,
 	port: u16,
 	isSymmetricNAT: bool = false,
@@ -368,6 +368,7 @@ pub const ConnectionManager = struct { // MARK: ConnectionManager
 
 	mutex: std.Thread.Mutex = .{},
 	waitingToFinishReceive: std.Thread.Condition = std.Thread.Condition{},
+	newConnectionCallback: Atomic(?*const fn(Address) void) = .init(null),
 
 	receiveBuffer: [Connection.maxPacketSize]u8 = undefined,
 
@@ -533,19 +534,25 @@ pub const ConnectionManager = struct { // MARK: ConnectionManager
 				}
 			}
 		}
-		defer self.mutex.unlock();
+		{
-		// Check if it's part of an active request:
+			defer self.mutex.unlock();
-		for(self.requests.items) |request| {
+			// Check if it's part of an active request:
-			if(request.address.ip == source.ip and request.address.port == source.port) {
+			for(self.requests.items) |request| {
-				request.data = main.globalAllocator.dupe(u8, data);
+				if(request.address.ip == source.ip and request.address.port == source.port) {
-				request.requestNotifier.signal();
+					request.data = main.globalAllocator.dupe(u8, data);
-				return;
+					request.requestNotifier.signal();
+					return;
+				}
 			}
+			if(self.online.load(.acquire) and source.ip == self.externalAddress.ip and source.port == self.externalAddress.port) return;
+		}
+		if(self.newConnectionCallback.load(.monotonic)) |callback| {
+			callback(source);
+		} else {
+			// TODO: Reduce the number of false alarms in the short period after a disconnect.
+			std.log.warn("Unknown connection from address: {}", .{source});
+			std.log.debug("Message: {any}", .{data});
 		}
-		if(self.online.load(.acquire) and source.ip == self.externalAddress.ip and source.port == self.externalAddress.port) return;
-		// TODO: Reduce the number of false alarms in the short period after a disconnect.
-		std.log.warn("Unknown connection from address: {}", .{source});
-		std.log.debug("Message: {any}", .{data});
 	}
 
 	pub fn run(self: *ConnectionManager) void {