Engine: add new netmsg 'SVC_SetClassVar'

Netmessage SVC_SetClassVar allows the server to change class settings securely on the client. This was implemented due to popular demand, and previous approaches using a combination of ClientCommands (Cbuf and NET_StringCmd) were deemed insecure and unreliable.

src/common/callback.h

@@ -4,6 +4,8 @@ inline bool(*v_SetupGamemode)(const char* pszPlayList);
 
 /* ==== CONCOMMANDCALLBACK ============================================================================================================================================== */
 inline void(*v__Cmd_Exec_f)(const CCommand& args);
+inline bool(*v__setClassVarServer_f)(const CCommand& args);
+inline bool(*v__setClassVarClient_f)(const CCommand& args);
 #ifndef DEDICATED
 inline void(*v__UIScript_Reset_f)();
 #endif // !DEDICATED
@@ -41,6 +43,8 @@ class VCallback : public IDetour
 	{
 		LogFunAdr("SetupGamemode", v_SetupGamemode);
 		LogFunAdr("Cmd_Exec_f", v__Cmd_Exec_f);
+		LogFunAdr("SetClassVarServer_f", v__setClassVarServer_f);
+		LogFunAdr("SetClassVarClient_f", v__setClassVarClient_f);
 #ifndef DEDICATED
 		LogFunAdr("UIScript_Reset_f", v__UIScript_Reset_f);
 #endif // !DEDICATED
@@ -49,6 +53,8 @@ class VCallback : public IDetour
 	{
 		g_GameDll.FindPatternSIMD("40 53 48 83 EC 20 48 8B D9 48 C7 C0 ?? ?? ?? ??").GetPtr(v_SetupGamemode);
 		g_GameDll.FindPatternSIMD("40 55 53 48 8D AC 24 ?? ?? ?? ?? B8 ?? ?? ?? ?? E8 ?? ?? ?? ?? 48 2B E0 48 8B D9").GetPtr(v__Cmd_Exec_f);
+		g_GameDll.FindPatternSIMD("41 56 48 83 EC ?? 8B 05 ?? ?? ?? ?? 4C 8B F1 FF C0").GetPtr(v__setClassVarServer_f);
+		g_GameDll.FindPatternSIMD("4C 8B DC 57 48 81 EC ?? ?? ?? ?? 8B 05").GetPtr(v__setClassVarClient_f);
 #ifndef DEDICATED
 		g_GameDll.FindPatternSIMD("40 55 41 54 48 8D AC 24 ?? ?? ?? ?? 48 81 EC ?? ?? ?? ?? 45 33 E4 48 8D 0D").GetPtr(v__UIScript_Reset_f);
 #endif // !DEDICATED

src/common/netmessages.cpp

@@ -12,6 +12,7 @@
 #include "tier1/cvar.h"
 #include "engine/net.h"
 #include "common/netmessages.h"
+#include "common/callback.h"
 #include "game/shared/usermessages.h"
 
 ///////////////////////////////////////////////////////////////////////////////////
@@ -64,6 +65,37 @@ bool SVC_UserMessage::ProcessImpl()
 	return SVC_UserMessage_Process(this); // Need to return original.
 }
 
+///////////////////////////////////////////////////////////////////////////////////
+// Net message to change class settings vars on the client
+///////////////////////////////////////////////////////////////////////////////////
+bool SVC_SetClassVar::ReadFromBuffer(bf_read* buffer)
+{
+	const bool set = buffer->ReadString(m_szSetting, sizeof(m_szSetting));
+	const bool var = buffer->ReadString(m_szVariable, sizeof(m_szVariable));
+
+	return set && var;
+}
+bool SVC_SetClassVar::WriteToBuffer(bf_write* buffer)
+{
+	const bool set = buffer->WriteString(m_szSetting);
+	const bool var = buffer->WriteString(m_szVariable);
+
+	return set && var;
+}
+bool SVC_SetClassVar::Process(void)
+{
+	const char* pArgs[3] = {
+		"_setClassVarClient",
+		m_szSetting,
+		m_szVariable
+	};
+
+	CCommand command((int)V_ARRAYSIZE(pArgs), pArgs, cmd_source_t::kCommandSrcCode);
+	v__setClassVarClient_f(command);
+
+	return true;
+}
+
 ///////////////////////////////////////////////////////////////////////////////////
 // Below functions are hooked as playlist overrides can be abused from the client.
 // The client could basically manage the server's playlists. Only allow read/write
@@ -122,7 +154,7 @@ bool Base_CmdKeyValues::WriteToBufferImpl(Base_CmdKeyValues* thisptr, bf_write*
 // determine whether or not the message should be copied into the replay buffer,
 // regardless of the 'CNetMessage::m_Group' type.
 ///////////////////////////////////////////////////////////////////////////////////
-bool ShouldReplayMessage(const CNetMessage* msg)
+bool ShouldReplayMessage(const CNetMessage* msg) // todo(amos): rename to 'CanReplayMessage'
 {
 	switch (msg->GetType())
 	{

src/common/netmessages.h

@@ -162,6 +162,15 @@ enum NetMessageType
 	clc_AntiCheat                   = 63,
 	clc_AntiCheatChallenge          = 64,
 	clc_GamepadMsg                  = 65,
+
+	// NOTE: if you make new netmessages, the order should be as follows:
+	// - NET (messages shared between server & client).
+	// - SVC (messages originating from the server).
+	// - CLC (messages originating from the client.
+	// Reorder message indices to retain consistency here.
+	// --------------------------------------------------------------------
+	// From here on, SDK netmessages are enumerated.
+	svc_SetClassVar                 = 66,
 };
 
 //-------------------------------------------------------------------------
@@ -176,10 +185,16 @@ enum NetMessageGroup
 class CNetMessage : public INetMessage
 {
 public:
+	virtual void	SetNetChannel(CNetChan* netchan) { m_NetChannel = netchan; }
+	virtual void	SetReliable(bool state) { m_bReliable = state; }
+	virtual bool	IsReliable(void) const { return m_bReliable; }
+	virtual int		GetGroup(void) const { return m_nGroup; }
+	virtual CNetChan* GetNetChannel(void) const { return m_NetChannel; }
+
 	int m_nGroup;
 	bool m_bReliable;
 	CNetChan* m_NetChannel;
-	INetMessageHandler* m_pMessageHandler;
+	INetChannelHandler* m_pMessageHandler;
 };
 
 ///////////////////////////////////////////////////////////////////////////////////////
@@ -445,6 +460,43 @@ private:
 	bf_write	m_DataOut;
 };
 
+class SVC_SetClassVar : public CNetMessage
+{
+public:
+	SVC_SetClassVar() = default;
+	SVC_SetClassVar(const char* setting, const char* var)
+	{
+		V_strncpy(m_szSetting, setting, sizeof(m_szSetting));
+		V_strncpy(m_szVariable, var, sizeof(m_szVariable));
+
+		m_szSetting[sizeof(m_szSetting) - 1] = '\0';
+		m_szVariable[sizeof(m_szVariable) - 1] = '\0';
+
+		m_nGroup = 2; // must be set to 2 to avoid being copied into replay buffer
+	}
+
+	virtual bool	ReadFromBuffer(bf_read* buffer);
+	virtual bool	WriteToBuffer(bf_write* buffer);
+
+	virtual bool	Process(void);
+
+	virtual int				GetType(void) const { return svc_SetClassVar; };
+	virtual const char*		GetName(void) const { return "svc_SetClassVar"; };
+
+	virtual const char*		ToString(void) const
+	{
+		static char szBuf[4096];
+		V_snprintf(szBuf, sizeof(szBuf), "%s: setting \"%s\", variable \"%s\"", this->GetName(), m_szSetting, m_szVariable);
+
+		return szBuf;
+	};
+
+	virtual size_t			GetSize(void) const { return sizeof(SVC_SetClassVar); }
+
+	char m_szSetting[128];
+	char m_szVariable[128];
+};
+
 ///////////////////////////////////////////////////////////////////////////////////////
 // Client messages:
 ///////////////////////////////////////////////////////////////////////////////////////

src/engine/client/clientstate.cpp

@@ -509,6 +509,7 @@ void CClientState::Reconnect()
 //---------------------------------------------------------------------------------
 void CClientState::RegisterNetMsgs(CNetChan* chan)
 {
+    REGISTER_SVC_MSG(SetClassSettingsVar);
 }
 
 void VClientState::Detour(const bool bAttach) const