Move debug.txt after it grows too big (#8904)

Before opening the file for writing, its file size is tested. If it exceeds 50 MB, it is moved to debut.txt.1, otherwise the log is appended to the old messages. An old debut.txt.1 is removed if it already exists.

builtin/settingtypes.txt

@@ -1319,6 +1319,12 @@ language (Language) enum   ,be,ca,cs,da,de,dv,en,eo,es,et,fr,he,hu,id,it,ja,jbo,
 #    -    verbose
 debug_log_level (Debug log level) enum action ,none,error,warning,action,info,verbose
 
+#    If the file size of debug.txt exceeds the number of megabytes specified in
+#    this setting when it is opened, the file is moved to debug.txt.1,
+#    deleting an older debug.txt.1 if it exists.
+#    debug.txt is only moved if this setting is positive.
+debug_log_size_max (Debug log file size threshold) int 50
+
 #    IPv6 support.
 enable_ipv6 (IPv6) bool true
 

src/defaultsettings.cpp

@@ -385,6 +385,7 @@ void set_default_settings(Settings *settings)
 	settings->setDefault("ignore_world_load_errors", "false");
 	settings->setDefault("remote_media", "");
 	settings->setDefault("debug_log_level", "action");
+	settings->setDefault("debug_log_size_max", "50");
 	settings->setDefault("emergequeue_limit_total", "512");
 	settings->setDefault("emergequeue_limit_diskonly", "64");
 	settings->setDefault("emergequeue_limit_generate", "64");

src/log.cpp

@@ -310,16 +310,32 @@ void Logger::logToOutputs(LogLevel lev, const std::string &combined,
 //// *LogOutput methods
 ////
 
-void FileLogOutput::open(const std::string &filename)
+void FileLogOutput::setFile(const std::string &filename, s64 file_size_max)
 {
-	m_stream.open(filename.c_str(), std::ios::app | std::ios::ate);
+	// Only move debug.txt if there is a valid maximum file size
+	bool is_too_large = false;
+	if (file_size_max > 0) {
+		std::ifstream ifile(filename, std::ios::binary | std::ios::ate);
+		is_too_large = ifile.tellg() > file_size_max;
+		ifile.close();
+	}
+
+	if (is_too_large) {
+		std::string filename_secondary = filename + ".1";
+		actionstream << "The log file grew too big; it is moved to " <<
+			filename_secondary << std::endl;
+		remove(filename_secondary.c_str());
+		rename(filename.c_str(), filename_secondary.c_str());
+	}
+	m_stream.open(filename, std::ios::app | std::ios::ate);
+
 	if (!m_stream.good())
 		throw FileNotGoodException("Failed to open log file " +
 			filename + ": " + strerror(errno));
 	m_stream << "\n\n"
-		   "-------------" << std::endl
-		<< "  Separator" << std::endl
-		<< "-------------\n" << std::endl;
+		"-------------" << std::endl <<
+		"  Separator" << std::endl <<
+		"-------------\n" << std::endl;
 }
 
 

src/log.h

@@ -165,7 +165,7 @@ private:
 
 class FileLogOutput : public ICombinedLogOutput {
 public:
-	void open(const std::string &filename);
+	void setFile(const std::string &filename, s64 file_size_max);
 
 	void logRaw(LogLevel lev, const std::string &line)
 	{

src/main.cpp

@@ -580,9 +580,8 @@ static void init_log_streams(const Settings &cmd_args)
 			"using maximum." << std::endl;
 	}
 
-	verbosestream << "log_filename = " << log_filename << std::endl;
-
-	file_log_output.open(log_filename);
+	file_log_output.setFile(log_filename,
+		g_settings->getU64("debug_log_size_max") * 1000000);
 	g_logger.addOutputMaxLevel(&file_log_output, log_level);
 }