From d7a4fb7c20b36733c965603b7f70cb0e95db7d46 Mon Sep 17 00:00:00 2001
From: wraitii <wraitii@wildfiregames.com>
Date: Sat, 22 May 2021 08:34:00 +0000
Subject: [PATCH] Try to punch a hole through local firewalls, and fallback to
 localhost.

Fixes (probably rare) regression in 2034136560.

Differential Revision: https://code.wildfiregames.com/D3999
This was SVN commit r25515.
---
 source/lobby/XmppClient.cpp  |  4 ++-
 source/network/NetClient.cpp | 59 ++++++++++++++++++++++++++----------
 source/network/NetClient.h   |  3 +-
 3 files changed, 48 insertions(+), 18 deletions(-)

diff --git a/source/lobby/XmppClient.cpp b/source/lobby/XmppClient.cpp
index 4b7ee097ac..e1279c2dec 100644
--- a/source/lobby/XmppClient.cpp
+++ b/source/lobby/XmppClient.cpp
@@ -862,7 +862,7 @@ bool XmppClient::handleIq(const glooxwrapper::IQ& iq)
 			}
 
 			g_NetClient->SetupServerData(cd->m_Ip.to_string(), stoi(cd->m_Port.to_string()), !cd->m_UseSTUN.empty());
-			g_NetClient->TryToConnect(iq.from().full());
+			g_NetClient->TryToConnect(iq.from().full(), !cd->m_IsLocalIP.empty());
 		}
 		if (gq)
 		{
@@ -995,6 +995,7 @@ bool XmppClient::handleIq(const glooxwrapper::IQ& iq)
 				connectionData->m_Ip = g_NetServer->GetPublicIp();
 				connectionData->m_Port = std::to_string(g_NetServer->GetPublicPort());
 				connectionData->m_UseSTUN = g_NetServer->GetUseSTUN() ? "true" : "";
+				connectionData->m_IsLocalIP = "";
 			}
 			else
 			{
@@ -1004,6 +1005,7 @@ bool XmppClient::handleIq(const glooxwrapper::IQ& iq)
 					connectionData->m_Ip = ip;
 					connectionData->m_Port = std::to_string(g_NetServer->GetLocalPort());
 					connectionData->m_UseSTUN = "";
+					connectionData->m_IsLocalIP = "true";
 				}
 				else
 					connectionData->m_Error = "local_ip_failed";
diff --git a/source/network/NetClient.cpp b/source/network/NetClient.cpp
index 61dda12afd..8f75a32f24 100644
--- a/source/network/NetClient.cpp
+++ b/source/network/NetClient.cpp
@@ -231,7 +231,7 @@ void CNetClient::HandleGetServerDataFailed(const CStr& error)
 	);
 }
 
-bool CNetClient::TryToConnect(const CStr& hostJID)
+bool CNetClient::TryToConnect(const CStr& hostJID, bool localNetwork)
 {
 	if (m_Session)
 		return false;
@@ -245,23 +245,22 @@ bool CNetClient::TryToConnect(const CStr& hostJID)
 		return false;
 	}
 
-	ENetHost* enetClient = nullptr;
+	ENetAddress hostAddr{ ENET_HOST_ANY, ENET_PORT_ANY };
+	ENetHost* enetClient = enet_host_create(&hostAddr, 1, 1, 0, 0);
+
+	if (!enetClient)
+	{
+		PushGuiMessage(
+			"type", "netstatus",
+			"status", "disconnected",
+			"reason", static_cast<i32>(NDR_STUN_PORT_FAILED));
+		return false;
+	}
+
+	CStr ip;
+	u16 port;
 	if (g_XmppClient && m_UseSTUN)
 	{
-		ENetAddress hostAddr{ ENET_HOST_ANY, ENET_PORT_ANY };
-		enetClient = enet_host_create(&hostAddr, 1, 1, 0, 0);
-
-		if (!enetClient)
-		{
-			PushGuiMessage(
-				"type", "netstatus",
-				"status", "disconnected",
-				"reason", static_cast<i32>(NDR_STUN_PORT_FAILED));
-			return false;
-		}
-
-		CStr ip;
-		u16 port;
 		if (!StunClient::FindPublicIP(*enetClient, ip, port))
 		{
 			PushGuiMessage(
@@ -280,11 +279,39 @@ bool CNetClient::TryToConnect(const CStr& hostJID)
 			// Return true anyways - we're on a success path here.
 			return true;
 		}
+	}
+	else if (g_XmppClient && localNetwork)
+	{
+		// We may need to punch a hole through the local firewall, so fetch our local IP.
+		// NB: we'll ignore failures here, and hope that the firewall will be open to connection
+		// if we fail to fetch the local IP (which is unlikely anyways).
+		if (!StunClient::FindLocalIP(ip))
+			ip = "";
+		// Check if we're hosting on localhost, and if so, explicitly use that
+		// (this circumvents, at least, the 'block all incoming connections' setting
+		// on the MacOS firewall).
+		if (ip == m_ServerAddress)
+		{
+			m_ServerAddress = "127.0.0.1";
+			ip = "";
+		}
+		port = enetClient->address.port;
+	}
 
+	LOGMESSAGE("NetClient: connecting to server at %s:%i", m_ServerAddress, m_ServerPort);
+
+	if (!ip.empty())
+	{
+		// UDP hole-punching
+		// Step 0: send a message, via XMPP, to the server with our external IP & port.
 		g_XmppClient->SendStunEndpointToHost(ip, port, hostJID);
 
+		// Step 1b: Wait some time - we need the host to receive the stun endpoint and start punching a hole themselves before
+		// we try to establish the connection below.
 		SDL_Delay(1000);
 
+		// Step 2: Send a message ourselves to the server so that the NAT, if any, routes incoming trafic correctly.
+		// TODO: verify if this step is necessary, since we'll try and connect anyways below.
 		StunClient::SendHolePunchingMessages(*enetClient, m_ServerAddress, m_ServerPort);
 	}
 
diff --git a/source/network/NetClient.h b/source/network/NetClient.h
index ff1200bd82..4af25b8614 100644
--- a/source/network/NetClient.h
+++ b/source/network/NetClient.h
@@ -134,9 +134,10 @@ public:
 	/**
 	 * Connect to the remote networked server using lobby.
 	 * Push netstatus messages on failure.
+	 * @param localNetwork - if true, assume we are trying to connect on the local network.
 	 * @return true on success, false on connection failure
 	 */
-	bool TryToConnect(const CStr& hostJID);
+	bool TryToConnect(const CStr& hostJID, bool localNetwork);
 
 	/**
 	 * Destroy the connection to the server.