fix(chat): prevent input exceeding utf-8 byte limit

Because of the `Send` method, max char limit should be based on utf-8
byte count, not utf-16 chars.

Author: anf3is

src/game/client/hud_basechat.cpp

@@ -466,6 +466,8 @@ CBaseHudChatInputLine::CBaseHudChatInputLine( CBaseHudChat *parent, char const *
 	m_pPrompt = new vgui::Label( this, "ChatInputPrompt", L"Enter text:" );
 	m_pInput = new CBaseHudChatEntry( this, "ChatInput", parent );	
 	m_pInput->SetMaximumCharCount( 127 );
+	// Send converts text to utf-8
+	m_pInput->m_iMaxByteCount = 127;
 }
 
 void CBaseHudChatInputLine::ApplySchemeSettings(vgui::IScheme *pScheme)
@@ -2519,3 +2521,59 @@ void CBaseHudChat::FireGameEvent( IGameEvent *event )
 		ChatPrintf( player->entindex(), CHAT_FILTER_NONE, "(SourceTV) %s", event->GetString( "text" ) );
 	}
 }
+
+// Prevent player from inserting text over utf-8 byte limit
+void CBaseHudChatEntry::InsertChar(wchar_t ch)
+{
+	if ( m_iMaxByteCount == -1 )
+	{
+		BaseClass::InsertChar(ch);
+		return;
+	}
+
+	// single utf-16 char converted to utf-8 is 3 byte long in worst case
+	const int iBufLen = BaseClass::GetTextLength() * 3;
+
+	// Shortcut: fitting max byte count even in worst case
+	if ( iBufLen + 4 <= m_iMaxByteCount )
+	{
+		BaseClass::InsertChar(ch);
+		return;
+	}
+
+	// Count bytes of converted utf-8 str
+	m_szCharBuf.EnsureCapacity( iBufLen );
+	BaseClass::GetText( m_szCharBuf.Base(), m_szCharBuf.Count() );
+	const int iCurrentByteLen = Q_strlen( m_szCharBuf.Base() );
+
+	// Shortcut: average case
+	if ( iCurrentByteLen + 4 <= m_iMaxByteCount )
+	{
+		BaseClass::InsertChar(ch);
+		return;
+	}
+
+	// Edge case: check if current wchar_t will cause Send to truncate message
+	int iCharByteLen; // utf-8
+	if ( ch < 0x80 ) iCharByteLen = 1;
+	else if ( ch < 0x800 ) iCharByteLen = 2;
+	else if ( ch >= 0xD800 && ch <= 0xDBFF ) iCharByteLen = 4; // high surrogate, assume pair
+	else if ( ch >= 0xDC00 && ch <= 0xDFFF ) // low surrogate
+	{
+		// Check if previous wchar was a high surrogate
+		wchar_t wszHigh[2];
+		const int iLast = BaseClass::GetTextLength() - 1;
+		BaseClass::GetTextRange( wszHigh, iLast, 1 );
+		if ( wszHigh[0] >= 0xD800 && wszHigh[0] <= 0xDBFF ) { BaseClass::InsertChar(ch); return; }
+		else return; // it was not a hight surrogate, reject
+	}
+	else iCharByteLen = 3;
+
+	if ( iCurrentByteLen + iCharByteLen <= m_iMaxByteCount )
+	{
+		BaseClass::InsertChar(ch);
+		return;
+	}
+
+	return; // do not insert anything
+}

src/game/client/hud_basechat.h

@@ -324,6 +324,8 @@ class CBaseHudChatEntry : public vgui::TextEntry
 {
 	typedef vgui::TextEntry BaseClass;
 public:
+	int m_iMaxByteCount = -1; // utf-8 string length
+
 	CBaseHudChatEntry( vgui::Panel *parent, char const *panelName, CBaseHudChat *pChat )
 		: BaseClass( parent, panelName )
 	{
@@ -340,6 +342,8 @@ class CBaseHudChatEntry : public vgui::TextEntry
 		SetPaintBorderEnabled( false );
 	}
 
+	virtual	void InsertChar(wchar_t ch);
+
 	virtual void OnKeyCodeTyped(vgui::KeyCode code)
 	{
 		if ( code == KEY_ENTER || code == KEY_PAD_ENTER || code == KEY_ESCAPE )
@@ -371,6 +375,7 @@ class CBaseHudChatEntry : public vgui::TextEntry
 
 private:
 	CBaseHudChat *m_pHudChat;
+	CUtlMemory<char> m_szCharBuf{ 0, 64 }; // tmp buffer
 };
 
 //-----------------------------------------------------------------------------