Fix #11646: Non-thread safe shared buffer returned from GetLogPrefix().

src/console.cpp

@@ -51,10 +51,9 @@ static void IConsoleWriteToLogFile(const std::string &string)
 {
 	if (_iconsole_output_file != nullptr) {
 		/* if there is an console output file ... also print it there */
-		const char *header = GetLogPrefix();
-		if ((strlen(header) != 0 && fwrite(header, strlen(header), 1, _iconsole_output_file) != 1) ||
-				fwrite(string.c_str(), string.size(), 1, _iconsole_output_file) != 1 ||
-				fwrite("\n", 1, 1, _iconsole_output_file) != 1) {
+		try {
+			fmt::print(_iconsole_output_file, "{}{}\n", GetLogPrefix(), string);
+		} catch (const std::system_error &) {
 			fclose(_iconsole_output_file);
 			_iconsole_output_file = nullptr;
 			IConsolePrint(CC_ERROR, "Cannot write to console log file; closing the log file.");

src/debug.cpp

@@ -232,18 +232,16 @@ std::string GetDebugString()
 
 /**
  * Get the prefix for logs; if show_date_in_logs is enabled it returns
- * the date, otherwise it returns nothing.
- * @return the prefix for logs (do not free), never nullptr
+ * the date, otherwise it returns an empty string.
+ * @return the prefix for logs.
  */
-const char *GetLogPrefix()
+std::string GetLogPrefix()
 {
-	static std::string _log_prefix;
+	std::string log_prefix;
 	if (_settings_client.gui.show_date_in_logs) {
-		_log_prefix = fmt::format("[{:%Y-%m-%d %H:%M:%S}] ", fmt::localtime(time(nullptr)));
-	} else {
-		_log_prefix.clear();
+		log_prefix = fmt::format("[{:%Y-%m-%d %H:%M:%S}] ", fmt::localtime(time(nullptr)));
 	}
-	return _log_prefix.c_str();
+	return log_prefix;
 }
 
 /**

src/debug.h

@@ -120,7 +120,7 @@ std::string GetDebugString();
 void ShowInfoI(const std::string &str);
 #define ShowInfo(format_string, ...) ShowInfoI(fmt::format(FMT_STRING(format_string), ## __VA_ARGS__))
 
-const char *GetLogPrefix();
+std::string GetLogPrefix();
 
 void DebugSendRemoteMessages();
 void DebugReconsiderSendRemoteMessages();