From 197542c7ec19b41e865be1e84c6c6898de8514d1 Mon Sep 17 00:00:00 2001
From: Perttu Ahola <celeron55@gmail.com>
Date: Mon, 26 Nov 2012 09:49:07 +0200
Subject: [PATCH] New PROTOCOL_VERSION scheme (allow client to support a range
 of versions)

---
 src/client.cpp     |  9 +++++----
 src/clientserver.h | 11 +++++++++--
 src/server.cpp     | 25 ++++++++++++++++++-------
 3 files changed, 32 insertions(+), 13 deletions(-)

diff --git a/src/client.cpp b/src/client.cpp
index f72c4b65..f6e97c52 100644
--- a/src/client.cpp
+++ b/src/client.cpp
@@ -499,8 +499,9 @@ void Client::step(float dtime)
 			// [2] u8 SER_FMT_VER_HIGHEST
 			// [3] u8[20] player_name
 			// [23] u8[28] password (new in some version)
-			// [51] u16 client network protocol version (new in some version)
-			SharedBuffer<u8> data(2+1+PLAYERNAME_SIZE+PASSWORD_SIZE+2);
+			// [51] u16 minimum supported network protocol version (added sometime)
+			// [53] u16 maximum supported network protocol version (added later than the previous one)
+			SharedBuffer<u8> data(2+1+PLAYERNAME_SIZE+PASSWORD_SIZE+2+2);
 			writeU16(&data[0], TOSERVER_INIT);
 			writeU8(&data[2], SER_FMT_VER_HIGHEST);
 
@@ -513,8 +514,8 @@ void Client::step(float dtime)
 			memset((char*)&data[23], 0, PASSWORD_SIZE);
 			snprintf((char*)&data[23], PASSWORD_SIZE, "%s", m_password.c_str());
 			
-			// This should be incremented in each version
-			writeU16(&data[51], PROTOCOL_VERSION);
+			writeU16(&data[51], CLIENT_PROTOCOL_VERSION_MIN);
+			writeU16(&data[53], CLIENT_PROTOCOL_VERSION_MAX);
 
 			// Send as unreliable
 			Send(0, data, false);
diff --git a/src/clientserver.h b/src/clientserver.h
index ba535a66..b7e64d29 100644
--- a/src/clientserver.h
+++ b/src/clientserver.h
@@ -75,8 +75,14 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 		GENERIC_CMD_SET_ATTACHMENT
 */
 
-#define PROTOCOL_VERSION 14
+// Server always only supports one version
+#define SERVER_PROTOCOL_VERSION 14
 
+// Client can support older versions too
+#define CLIENT_PROTOCOL_VERSION_MIN 13
+#define CLIENT_PROTOCOL_VERSION_MAX SERVER_PROTOCOL_VERSION
+
+// Constant that differentiates the protocol from random data and other protocols
 #define PROTOCOL_ID 0x4f457403
 
 #define PASSWORD_SIZE 28       // Maximum password length. Allows for
@@ -350,7 +356,8 @@ enum ToServerCommand
 		[2] u8 SER_FMT_VER_HIGHEST
 		[3] u8[20] player_name
 		[23] u8[28] password (new in some version)
-		[51] u16 client network protocol version (new in some version)
+		[51] u16 minimum supported network protocol version (added sometime)
+		[53] u16 maximum supported network protocol version (added later than the previous one)
 	*/
 
 	TOSERVER_INIT2 = 0x11,
diff --git a/src/server.cpp b/src/server.cpp
index ac243a29..f4da73fa 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -2037,11 +2037,22 @@ void Server::ProcessData(u8 *data, u32 datasize, u16 peer_id)
 			Read and check network protocol version
 		*/
 
-		u16 net_proto_version = 0;
+		u16 min_net_proto_version = 0;
 		if(datasize >= 2+1+PLAYERNAME_SIZE+PASSWORD_SIZE+2)
-		{
-			net_proto_version = readU16(&data[2+1+PLAYERNAME_SIZE+PASSWORD_SIZE]);
-		}
+			min_net_proto_version = readU16(&data[2+1+PLAYERNAME_SIZE+PASSWORD_SIZE]);
+
+		// Use min if version field doesn't exist (backwards compatibility)
+		u16 max_net_proto_version = min_net_proto_version;
+		if(datasize >= 2+1+PLAYERNAME_SIZE+PASSWORD_SIZE+2+2)
+			max_net_proto_version = readU16(&data[2+1+PLAYERNAME_SIZE+PASSWORD_SIZE+2]);
+
+		u16 net_proto_version = max_net_proto_version;
+		if(max_net_proto_version != SERVER_PROTOCOL_VERSION && min_net_proto_version <= SERVER_PROTOCOL_VERSION)
+			net_proto_version = SERVER_PROTOCOL_VERSION;
+
+		verbosestream<<"Server: "<<peer_id<<" Protocol version: min: "
+				<<min_net_proto_version<<", max: "<<max_net_proto_version
+				<<", chosen: "<<net_proto_version<<std::endl;
 
 		getClient(peer_id)->net_proto_version = net_proto_version;
 
@@ -2059,7 +2070,7 @@ void Server::ProcessData(u8 *data, u32 datasize, u16 peer_id)
 		
 		if(g_settings->getBool("strict_protocol_version_checking"))
 		{
-			if(net_proto_version != PROTOCOL_VERSION)
+			if(net_proto_version != SERVER_PROTOCOL_VERSION)
 			{
 				actionstream<<"Server: A mismatched client tried to connect"
 						<<" from "<<addr_s<<std::endl;
@@ -2068,7 +2079,7 @@ void Server::ProcessData(u8 *data, u32 datasize, u16 peer_id)
 						L"Server version is ")
 						+ narrow_to_wide(VERSION_STRING) + L",\n"
 						+ L"server's PROTOCOL_VERSION is "
-						+ narrow_to_wide(itos(PROTOCOL_VERSION))
+						+ narrow_to_wide(itos(SERVER_PROTOCOL_VERSION))
 						+ L", client's PROTOCOL_VERSION is "
 						+ narrow_to_wide(itos(net_proto_version))
 				);
@@ -2310,7 +2321,7 @@ void Server::ProcessData(u8 *data, u32 datasize, u16 peer_id)
 		}
 		
 		// Warnings about protocol version can be issued here
-		if(getClient(peer_id)->net_proto_version < PROTOCOL_VERSION)
+		if(getClient(peer_id)->net_proto_version < SERVER_PROTOCOL_VERSION)
 		{
 			SendChatMessage(peer_id, L"# Server: WARNING: YOUR CLIENT IS OLD AND MAY WORK PROPERLY WITH THIS SERVER!");
 		}