Logging format option (#831)

When SYSLOG environment variable set, adopt NO_COLOR behaviour and also strip time from output.
Make the output suitable for use a systemd service where the output is processed by journald. Without this option, logging would have double timestamp.

Author: SnowLeopard71

ethminer/main.cpp

@@ -44,6 +44,7 @@ void help()
 		<< "    -h,--help  Show this help message and exit." << endl
 		<< " Environment variables:" << endl
 		<< "     NO_COLOR - set to any value to disable color output. Unset to re-enable color output." << endl
+		<< "     SYSLOG   - set to any value to strip time and disable color from output, for logging under systemd" << endl
 		;
 	exit(0);
 }
@@ -63,6 +64,11 @@ int main(int argc, char** argv)
 	setenv("GPU_MAX_ALLOC_PERCENT", "100");
 	setenv("GPU_SINGLE_ALLOC_PERCENT", "100");
 
+	if (getenv("SYSLOG"))
+	{
+		g_syslog = true;
+		g_useColor = false;
+	}
 	if (getenv("NO_COLOR"))
 		g_useColor = false;
 #if defined(_WIN32)

libdevcore/Log.cpp

@@ -32,6 +32,7 @@ using namespace dev;
 // Logging
 int dev::g_logVerbosity = 5;
 bool dev::g_useColor = true;
+bool dev::g_syslog = false;
 
 mutex x_logOverride;
 
@@ -66,15 +67,21 @@ LogOutputStreamBase::LogOutputStreamBase(char const* _id, std::type_info const*
 		auto it = s_logOverride.find(_info);
 		if ((it != s_logOverride.end() && it->second) || it == s_logOverride.end())
 		{
-			time_t rawTime = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
-			char buf[24];
-			if (strftime(buf, 24, "%X", localtime(&rawTime)) == 0)
-				buf[0] = '\0'; // empty if case strftime fails
 			static char const* c_begin = "  " EthViolet;
 			static char const* c_sep1 = EthReset EthBlack "|" EthNavy;
 			static char const* c_sep2 = EthReset EthBlack "|" EthTeal;
 			static char const* c_end = EthReset "  ";
-			m_sstr << _id << c_begin << buf << c_sep1 << std::left << std::setw(8) << getThreadName() << c_sep2 << c_end;
+			if (g_syslog) 
+			{
+				c_begin = "  " EthNavy;
+				m_sstr << c_begin << std::left << std::setw(8) << getThreadName() << c_sep2 << c_end;
+			} else {
+				time_t rawTime = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
+				char buf[24];
+				if (strftime(buf, 24, "%X", localtime(&rawTime)) == 0)
+					buf[0] = '\0'; // empty if case strftime fails
+				m_sstr << _id << c_begin << buf << c_sep1 << std::left << std::setw(8) << getThreadName() << c_sep2 << c_end;
+			}
 		}
 	}
 }

libdevcore/Log.h

@@ -49,6 +49,7 @@ void simpleDebugOut(std::string const&);
 /// The logging system's current verbosity.
 extern int g_logVerbosity;
 extern bool g_useColor;
+extern bool g_syslog;
 
 class ThreadContext
 {