Use promises to fetch net messages

Refs: #5585

source/gui/CGUI.cpp

@@ -1,4 +1,4 @@
-/* Copyright (C) 2025 Wildfire Games.
+/* Copyright (C) 2026 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -41,6 +41,7 @@
 #include "lib/timer.h"
 #include "lib/utf8.h"
 #include "maths/Size2D.h"
+#include "network/NetClient.h"
 #include "ps/CLogger.h"
 #include "ps/Errors.h"
 #include "ps/Filesystem.h"
@@ -104,7 +105,11 @@ CGUI::CGUI(ScriptContext& context)
 	m_ScriptInterface->LoadGlobalScripts();
 }
 
-CGUI::~CGUI() = default;
+CGUI::~CGUI()
+{
+	if (g_NetClient)
+		g_NetClient->Unregister(*m_ScriptInterface);
+}
 
 InReaction CGUI::HandleEvent(const SDL_Event_* ev)
 {

source/network/NetClient.cpp

@@ -40,6 +40,7 @@
 #include "ps/Profile.h"
 #include "ps/Threading.h"
 #include "scriptinterface/JSON.h"
+#include "scriptinterface/ScriptContext.h"
 #include "scriptinterface/ScriptInterface.h"
 #include "simulation2/Simulation2.h"
 #include "simulation2/system/TurnManager.h"
@@ -49,6 +50,7 @@
 #include <functional>
 #include <iterator>
 #include <js/GCAPI.h>
+#include <js/Promise.h>
 #include <js/TracingAPI.h>
 #include <map>
 #include <memory>
@@ -323,6 +325,7 @@ void CNetClient::Poll()
 
 	CheckServerConnection();
 	m_Session->ProcessPolledMessages();
+	FetchMessage();
 }
 
 void CNetClient::CheckServerConnection()
@@ -357,15 +360,35 @@ void CNetClient::CheckServerConnection()
 	}
 }
 
-JS::Value CNetClient::GuiPoll(const ScriptRequest& rq)
+JSObject* CNetClient::GetNextGUIMessage(const ScriptInterface& guiInterface)
 {
-	if (m_GuiMessageQueue.empty())
-		return JS::UndefinedValue();
+	const ScriptRequest rq{guiInterface};
+	m_GuiMessagePoll.emplace(GuiPollData{guiInterface, {rq.cx, JS::NewPromiseObject(rq.cx, nullptr)}});
 
-	JS::RootedValue ret{rq.cx};
-	Script::ReadStructuredClone(rq, m_GuiMessageQueue.front(), &ret);
+	FetchMessage();
+	return m_GuiMessagePoll.value().promise;
+}
+
+void CNetClient::Unregister(const ScriptInterface& guiInterface)
+{
+	if (m_GuiMessagePoll.has_value() && &m_GuiMessagePoll.value().interface == &guiInterface)
+		m_GuiMessagePoll.reset();
+}
+
+void CNetClient::FetchMessage()
+{
+	if (m_GuiMessageQueue.empty() || !m_GuiMessagePoll.has_value() ||
+		JS::GetPromiseState(m_GuiMessagePoll.value().promise) != JS::PromiseState::Pending)
+	{
+		return;
+	}
+
+	const ScriptRequest rq{m_GuiMessagePoll.value().interface};
+	JS::RootedValue message{rq.cx};
+	Script::ReadStructuredClone(rq, std::move(m_GuiMessageQueue.front()), &message);
 	m_GuiMessageQueue.pop_front();
-	return ret;
+
+	JS::ResolvePromise(rq.cx, m_GuiMessagePoll.value().promise, message);
 }
 
 std::string CNetClient::TestReadGuiMessages()
@@ -375,9 +398,13 @@ std::string CNetClient::TestReadGuiMessages()
 	std::string r;
 	while (true)
 	{
-		JS::RootedValue msg{rq.cx, GuiPoll(rq)};
-		if (msg.isUndefined())
+		JS::RootedObject promise{rq.cx, GetNextGUIMessage(GetScriptInterface())};
+		g_ScriptContext->RunJobs();
+
+		if (JS::GetPromiseState(promise) == JS::PromiseState::Pending)
 			break;
+
+		JS::RootedValue msg{rq.cx, JS::GetPromiseResult(promise)};
 		r += Script::ToString(rq, &msg) + "\n";
 	}
 	return r;

source/network/NetClient.h

@@ -1,4 +1,4 @@
-/* Copyright (C) 2025 Wildfire Games.
+/* Copyright (C) 2026 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -144,19 +144,25 @@ public:
 
 	/**
 	 * Retrieves the next queued GUI message, and removes it from the queue.
-	 * The returned value is in the GetScriptInterface() JS context.
+	 * The returned value is in the JS context of the provided
+	 * @c ScriptInterface.
 	 *
 	 * This is the only mechanism for the networking code to send messages to
-	 * the GUI - it is pull-based (instead of push) so the engine code does not
-	 * need to know anything about the code structure of the GUI scripts.
+	 * the GUI.
 	 *
 	 * The structure of the messages is <code>{ "type": "...", ... }</code>.
 	 * The exact types and associated data are not specified anywhere - the
 	 * implementation and GUI scripts must make the same assumptions.
 	 *
-	 * @return next message, or the value 'undefined' if the queue is empty
+	 * @return a promise resolving to the next message.
 	 */
-	JS::Value GuiPoll(const ScriptRequest& rq);
+	JSObject* GetNextGUIMessage(const ScriptInterface& guiInterface);
+
+	/**
+	 * Has to be called bevore the @c ScriptInterface gets destroied so that
+	 * no future messages are sent to it.
+	 */
+	void Unregister(const ScriptInterface& guiInterface);
 
 	/**
 	 * Add a message to the queue, to be read by GuiPoll.
@@ -305,6 +311,8 @@ private:
 	 */
 	void PostPlayerAssignmentsToScript();
 
+	void FetchMessage();
+
 	CGame *m_Game;
 	CStrW m_UserName;
 
@@ -346,6 +354,18 @@ private:
 	/// Queue of messages for GuiPoll
 	std::deque<Script::StructuredClone> m_GuiMessageQueue;
 
+	struct GuiPollData
+	{
+		const ScriptInterface& interface;
+		/**
+		 * In the context of interface.
+		 * When the promise is pending @see Poll should fill it with a message.
+		 * When there it's fulfilled JavaScript code can take it.
+		 */
+		JS::PersistentRootedObject promise;
+	};
+	std::optional<GuiPollData> m_GuiMessagePoll;
+
 	/// Serialized game state received when joining an in-progress game
 	std::string m_JoinSyncBuffer;
 

source/network/scripting/JSInterface_Network.cpp

@@ -1,4 +1,4 @@
-/* Copyright (C) 2025 Wildfire Games.
+/* Copyright (C) 2026 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -196,9 +196,12 @@ CStr GetPlayerGUID()
 	return g_NetClient->GetGUID();
 }
 
-JS::Value PollNetworkClient(const ScriptRequest& rq)
+JS::Value PollNetworkClient(const ScriptInterface& guiInterface)
 {
-	return g_NetClient ? g_NetClient->GuiPoll(rq) : JS::UndefinedValue();
+	if (!g_NetClient)
+		throw std::logic_error{"Network client not present"};
+
+	return JS::ObjectValue(*g_NetClient->GetNextGUIMessage(guiInterface));
 }
 
 void SendGameSetupMessage(const ScriptInterface& scriptInterface, JS::HandleValue attribs1)

source/ps/GameSetup/GameSetup.cpp

@@ -855,6 +855,7 @@ bool Autostart(const CmdLineArgs& args)
 		while (!shouldQuit)
 		{
 			g_NetClient->Poll();
+			g_ScriptContext->RunJobs();
 			if (!ScriptFunction::Call(rq, global, "onTick", shouldQuit))
 				return false;
 			std::this_thread::sleep_for(std::chrono::microseconds(200));