From ddab98412f3fc47eedfa74f8a4edafd324e59707 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gabriel=20P=C3=A9rez-Cerezo?= <gabriel@gpcf.eu>
Date: Thu, 28 Nov 2019 12:30:21 +0100
Subject: Add static_save and prevent UDP connect exhaustions

This merges two pull requests from 5.0
---
 src/server.cpp | 78 +++++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 53 insertions(+), 25 deletions(-)

(limited to 'src/server.cpp')

diff --git a/src/server.cpp b/src/server.cpp
index 71a349b08..4b54c2398 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -90,6 +90,15 @@ void *ServerThread::run()
 	DSTACK(FUNCTION_NAME);
 	BEGIN_DEBUG_EXCEPTION_HANDLER
 
+	/*
+	 * The real business of the server happens on the ServerThread.
+	 * How this works:
+	 * AsyncRunStep() runs an actual server step as soon as enough time has
+	 * passed (dedicated_server_loop keeps track of that).
+	 * Receive() blocks at least(!) 30ms waiting for a packet (so this loop
+	 * doesn't busy wait) and will process any remaining packets.
+	 */
+
 	m_server->AsyncRunStep(true);
 
 	while (!stopRequested()) {
@@ -100,7 +109,6 @@ void *ServerThread::run()
 
 			m_server->Receive();
 
-		} catch (con::NoIncomingDataException &e) {
 		} catch (con::PeerNotFoundException &e) {
 			infostream<<"Server: PeerNotFoundException"<<std::endl;
 		} catch (ClientNotFoundException &e) {
@@ -1052,30 +1060,45 @@ void Server::Receive()
 	DSTACK(FUNCTION_NAME);
 	SharedBuffer<u8> data;
 	u16 peer_id;
-	try {
-		NetworkPacket pkt;
-		m_con.Receive(&pkt);
-		peer_id = pkt.getPeerId();
-		ProcessData(&pkt);
-	}
-	catch(con::InvalidIncomingDataException &e) {
-		infostream<<"Server::Receive(): "
-				"InvalidIncomingDataException: what()="
-				<<e.what()<<std::endl;
-	}
-	catch(SerializationError &e) {
-		infostream<<"Server::Receive(): "
-				"SerializationError: what()="
-				<<e.what()<<std::endl;
-	}
-	catch(ClientStateError &e) {
-		errorstream << "ProcessData: peer=" << peer_id  << e.what() << std::endl;
-		DenyAccess_Legacy(peer_id, L"Your client sent something server didn't expect."
-				L"Try reconnecting or updating your client");
-	}
-	catch(con::PeerNotFoundException &e) {
-		// Do nothing
-	}
+	bool first = true;
+	NetworkPacket pkt;
+	for (;;) {	  
+	  pkt.clear();
+	  peer_id = 0;
+	  try {
+	    /*
+	      In the first iteration *wait* for a packet, afterwards process
+	      all packets that are immediately available (no waiting).
+	    */
+	    if (first) {
+	      m_con.Receive(&pkt);
+	      first = false;
+	    } else {
+	      if (!m_con.TryReceive(&pkt))
+		return;
+	    }
+	    
+	    peer_id = pkt.getPeerId();
+	    ProcessData(&pkt);
+
+	  } catch (const con::InvalidIncomingDataException &e) {
+	    infostream << "Server::Receive(): InvalidIncomingDataException: what()="
+		       << e.what() << std::endl;
+	  } catch (const SerializationError &e) {
+	    infostream << "Server::Receive(): SerializationError: what()="
+		       << e.what() << std::endl;
+	  } catch (const ClientStateError &e) {
+	    errorstream << "ProcessData: peer=" << peer_id << " what()="
+			<< e.what() << std::endl;
+	    DenyAccess_Legacy(peer_id, L"Your client sent something server didn't expect."
+			      L"Try reconnecting or updating your client");
+	  } catch (const con::PeerNotFoundException &e) {
+	    // Do nothing
+	  } catch (const con::NoIncomingDataException &e) {
+	    return;
+	  }
+ 	}
+	
 }
 
 PlayerSAO* Server::StageTwoClientInit(u16 peer_id)
@@ -3682,6 +3705,11 @@ void dedicated_server_loop(Server &server, bool &kill)
 	static const float profiler_print_interval =
 			g_settings->getFloat("profiler_print_interval");
 
+	/*
+	 * The dedicated server loop only does time-keeping (in Server::step) and
+	 * provides a way to main.cpp to kill the server externally (bool &kill).
+	 */
+
 	for(;;) {
 		// This is kind of a hack but can be done like this
 		// because server.step() is very light
-- 
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