add syslog logging option

Daemon.cpp

@@ -159,7 +159,10 @@ namespace i2p
 			if (isDaemon && (logs == "" || logs == "stdout"))
 				logs = "file";
 
-			if (logs == "file") {
+			if (logs == "syslog") {
+				// use syslog only no stdout
+				StartSyslog();
+			} else if (logs == "file") {
 				if (logfile == "")
 					logfile = i2p::fs::DataDirPath("i2pd.log");
 				StartLog (logfile);

Log.cpp

@@ -11,8 +11,32 @@ static const char * g_LogLevelStr[eNumLogLevels] =
 	"debug"	 // eLogDebug 
 };
 
+/** convert LogLevel enum to syslog priority level */
+static int ToSyslogLevel(LogLevel lvl)
+{
+  switch (lvl) {
+  case eLogError:
+    return LOG_ERR;
+  case eLogWarning:
+    return LOG_WARNING;
+  case eLogInfo:
+    return LOG_INFO;
+  case eLogDebug:
+    return LOG_DEBUG;
+  default:
+    // WTF? invalid log level?
+    return LOG_CRIT;
+  }
+}
+
+
 void LogMsg::Process()
 {
+  if (log && log->SyslogEnabled()) {
+    // only log to syslog
+    syslog(ToSyslogLevel(level), "%s", s.str().c_str());
+    return;
+  }
 	auto stream = log ? log->GetLogStream () : nullptr;
 	auto& output = stream ? *stream : std::cout;	
 	if (log)	
@@ -84,3 +108,20 @@ void Log::SetLogStream (std::shared_ptr<std::ostream> logStream)
 {
 	m_LogStream = logStream;
 }
+
+void Log::StartSyslog(const std::string & ident, const int facility)
+{
+	m_Ident = ident;
+	openlog(m_Ident.c_str(), LOG_PID, facility);
+}
+
+void Log::StopSyslog()
+{
+	closelog();
+	m_Ident.clear();
+}
+
+bool Log::SyslogEnabled()
+{
+	return m_Ident.size() > 0;
+}

Log.h

@@ -8,6 +8,7 @@
 #include <functional>
 #include <chrono>
 #include <memory>
+#include <syslog.h>
 #include "Queue.h"
 
 enum LogLevel
@@ -45,8 +46,13 @@ class Log: public i2p::util::MsgQueue<LogMsg>
 		std::shared_ptr<std::ostream> GetLogStream () const { return m_LogStream; };	
 		const std::string& GetTimestamp ();
 		LogLevel GetLogLevel () { return m_MinLevel; };
-		const std::string& GetFullFilePath () const { return m_FullFilePath; };
-
+	 	const std::string& GetFullFilePath () const { return m_FullFilePath; };
+		/** start logging to syslog */
+		void StartSyslog(const std::string & ident, const int facility = LOG_USER);
+		/** stop logging to syslog */
+		void StopSyslog();
+		/** are we logging to syslog right now? */
+		bool SyslogEnabled();
 	private:
 
 		void Flush ();
@@ -62,6 +68,7 @@ class Log: public i2p::util::MsgQueue<LogMsg>
 #else		
 		std::chrono::steady_clock::time_point m_LastTimestampUpdate;	
 #endif
+		std::string m_Ident;
 };
 
 extern Log * g_Log;
@@ -116,6 +123,18 @@ inline bool IsLogToFile ()
 	return g_Log ? !g_Log->GetFullFilePath ().empty () : false;
 }	
 
+inline void StartSyslog()
+{
+	StartLog("");
+	g_Log->StartSyslog("i2pd");
+}
+
+inline void StopSyslog()
+{
+	if(g_Log)
+		g_Log->StopSyslog();
+}
+
 template<typename TValue>
 void LogPrint (std::stringstream& s, TValue arg) 
 {

docs/i2pd.conf

@@ -16,7 +16,10 @@
 ## Logging configuration section
 ## By default logs go to stdout with level info
 ##
-## Logs destination (stdout, file) 
+## Logs destination (stdout, file, syslog)
+## stdout - print log entries to stdout
+## file - log entries to a file
+## syslog - use syslog, see man 3 syslog
 #log = file
 ## Path to logfile (default - autodetect)
 #logfile = /var/log/i2pd.log
@@ -40,7 +43,7 @@
 ## don't just uncomment this
 #port = 4321
 ##Enable communication through ipv6
-ipv6 
+ipv6 = true
 ## Bandwidth configuration
 ## L limit bandwidth to 32Kbs/sec, O - to 256Kbs/sec, P - unlimited
 ## Default is P for floodfill, L for regular node