From eeeba977eac6a43b97e1c0d00eb064d15700e920 Mon Sep 17 00:00:00 2001
From: phosit <phosit@autistici.org>
Date: Thu, 26 Jun 2025 13:31:52 +0200
Subject: [PATCH] Don't crash if rl-interface port is already in use

Replace `ENSURE` with recoverable error handling. Introduce a new error
type so that it's distinguishable from other errors.

When such an error occurs the program exits with `EXIT_FAILURE`.

Fixes: #7475
---
 source/main.cpp                    | 58 ++++++++++++++++++++----------
 source/rlinterface/RLInterface.cpp |  3 +-
 source/rlinterface/RLInterface.h   |  6 ++++
 3 files changed, 47 insertions(+), 20 deletions(-)

diff --git a/source/main.cpp b/source/main.cpp
index a8dc337589..2527be2e90 100644
--- a/source/main.cpp
+++ b/source/main.cpp
@@ -636,6 +636,7 @@ static void RunGameOrAtlas(const PS::span<const char* const> argv)
 	g_frequencyFilter = CreateFrequencyFilter(res, 30.0);
 
 	// run the game
+	bool rlInterfaceError{false};
 	bool firstIteration{true};
 	do
 	{
@@ -687,23 +688,31 @@ static void RunGameOrAtlas(const PS::span<const char* const> argv)
 		else if (!InitNonVisual(args))
 			g_Shutdown = ShutdownType::Quit;
 
-		// MSVC doesn't support copy elision in ternary expressions. So we use a lambda instead.
-		std::optional<RL::Interface> rlInterface{[&]() -> std::optional<RL::Interface>
-			{
-				if (g_Shutdown == ShutdownType::None)
-					return CreateRLInterface(args);
-				else
-					return std::nullopt;
-			}()};
-
-		while (g_Shutdown == ShutdownType::None)
+		try
 		{
-			if (isVisual)
-				Frame(rlInterface ? &*rlInterface : nullptr, fixedFrameFrequency);
-			else if(rlInterface)
-				rlInterface->TryApplyMessage();
-			else
-				NonVisualFrame();
+			// MSVC doesn't support copy elision in ternary expressions. So we use a lambda instead.
+			std::optional<RL::Interface> rlInterface{[&]() -> std::optional<RL::Interface>
+				{
+					if (g_Shutdown == ShutdownType::None)
+						return CreateRLInterface(args);
+					else
+						return std::nullopt;
+				}()};
+
+			while (g_Shutdown == ShutdownType::None)
+			{
+				if (isVisual)
+					Frame(rlInterface ? &*rlInterface : nullptr, fixedFrameFrequency);
+				else if(rlInterface)
+					rlInterface->TryApplyMessage();
+				else
+					NonVisualFrame();
+			}
+
+		}
+		catch (const RL::SetupError&)
+		{
+		      rlInterfaceError = true;
 		}
 
 		ShutdownNetworkAndUI();
@@ -713,6 +722,9 @@ static void RunGameOrAtlas(const PS::span<const char* const> argv)
 
 	} while (g_Shutdown == ShutdownType::Restart);
 
+	if (rlInterfaceError)
+	      throw RL::SetupError{};
+
 #if OS_MACOSX
 	if (g_Shutdown == ShutdownType::RestartAsAtlas)
 		startNewAtlasProcess(g_Mods.GetEnabledMods());
@@ -755,8 +767,16 @@ extern "C" int main(int argc, char* argv[])
 
 	EarlyInit();	// must come at beginning of main
 
-	// static_cast is ok, argc is never negative.
-	RunGameOrAtlas({argv, static_cast<std::size_t>(argc)});
+	int returnValue{EXIT_SUCCESS};
+	try
+	{
+		// static_cast is ok, argc is never negative.
+		RunGameOrAtlas({argv, static_cast<std::size_t>(argc)});
+	}
+	catch (const RL::SetupError&)
+	{
+		returnValue = EXIT_FAILURE;
+	}
 
 	// Shut down profiler initialised by EarlyInit
 	g_Profiler2.Shutdown();
@@ -769,5 +789,5 @@ extern "C" int main(int argc, char* argv[])
 	wutil_Shutdown();
 #endif
 
-	return EXIT_SUCCESS;
+	return returnValue;
 }
diff --git a/source/rlinterface/RLInterface.cpp b/source/rlinterface/RLInterface.cpp
index 2a7f7a1510..f98a4e87c4 100644
--- a/source/rlinterface/RLInterface.cpp
+++ b/source/rlinterface/RLInterface.cpp
@@ -50,7 +50,8 @@ Interface::Interface(const char* server_address)
 		nullptr
 	};
 	m_Context = mg_start(MgCallback, this, options);
-	ENSURE(m_Context);
+	if (!m_Context)
+		throw SetupError{};
 }
 
 Interface::~Interface()
diff --git a/source/rlinterface/RLInterface.h b/source/rlinterface/RLInterface.h
index ef93885d99..c1cc41fd52 100644
--- a/source/rlinterface/RLInterface.h
+++ b/source/rlinterface/RLInterface.h
@@ -22,6 +22,7 @@
 #include "third_party/mongoose/mongoose.h"
 
 #include <condition_variable>
+#include <exception>
 #include <mutex>
 #include <vector>
 
@@ -57,6 +58,11 @@ struct GameMessage
 	std::vector<GameCommand> commands;
 };
 
+struct SetupError : std::exception
+{
+	using std::exception::exception;
+};
+
 /**
  * Implements an interface providing fundamental capabilities required for reinforcement
  * learning (over HTTP).