[FEATURE] Added support for logging to a file. To enable it, set the …

…QGIS_LOG_FILE environment variable to a writable file on your file system. When using the QGIS Mapserver, you can enable logging by adding a directive such as 'SetEnv QGIS_LOG_FILE /tmp/qgislog.txt' to the cgi-bin section of your apache config file.

src/core/qgslogger.cpp

@@ -18,6 +18,7 @@
 
 #include "qgslogger.h"
 #include <QtDebug>
+#include <QFile>
 
 int QgsLogger::mDebugLevel = -999; // undefined value
 
@@ -38,14 +39,17 @@ void QgsLogger::debug( const QString& msg, int debuglevel, const char* file, con
     if ( file == NULL )
     {
       qDebug( "%s", msg.toLocal8Bit().constData() );
+      logMessageToFile( msg );
     }
     else if ( function == NULL )
     {
       qDebug( "%s: %s", file, msg.toLocal8Bit().constData() );
+      logMessageToFile( msg );
     }
     else if ( line == -1 )
     {
       qDebug( "%s: (%s) %s", file, function, msg.toLocal8Bit().constData() );
+      logMessageToFile( msg );
     }
     else
     {
@@ -54,6 +58,7 @@ void QgsLogger::debug( const QString& msg, int debuglevel, const char* file, con
 #else
       qDebug( "%s(%d) : (%s) %s", file, line, function, msg.toLocal8Bit().constData() );
 #endif
+      logMessageToFile( msg );
     }
   }
 }
@@ -75,14 +80,17 @@ void QgsLogger::debug( const QString& var, int val, int debuglevel, const char*
     if ( file == NULL )
     {
       qDebug( "%s: %d", var.toLocal8Bit().constData(), val );
+      logMessageToFile( QString( "%s: %d" ).arg( var.toLocal8Bit().constData() ).arg( val ) );
     }
     else if ( function == NULL )
     {
       qDebug( "%s: %s: %d", file, var.toLocal8Bit().constData(), val );
+      logMessageToFile( QString( "%s: %s: %d" ).arg( file ).arg( var.toLocal8Bit().constData() ).arg( val ) );
     }
     else if ( line == -1 )
     {
       qDebug( "%s: (%s): %s: %d", file, function, var.toLocal8Bit().constData(), val );
+      logMessageToFile( QString( "%s: (%s): %s: %d" ).arg( file ).arg( function ).arg( var.toLocal8Bit().constData() ).arg( val ) );
     }
     else
     {
@@ -91,6 +99,7 @@ void QgsLogger::debug( const QString& var, int val, int debuglevel, const char*
 #else
       qDebug( "%s: %d: (%s), %s: %d", file, line, function, var.toLocal8Bit().constData(), val );
 #endif
+      logMessageToFile( QString(  "%s: %d: (%s), %s: %d" ).arg( file ).arg( line ).arg( function ).arg( var.toLocal8Bit().constData() ).arg( val ) );
     }
   }
 }
@@ -112,14 +121,17 @@ void QgsLogger::debug( const QString& var, double val, int debuglevel, const cha
     if ( file == NULL )
     {
       qDebug( "%s: %f", var.toLocal8Bit().constData(), val );
+      logMessageToFile( QString( "%s: %f" ).arg( var.toLocal8Bit().constData() ).arg( val ) ); 
     }
     else if ( function == NULL )
     {
       qDebug( "%s: %s: %f", file, var.toLocal8Bit().constData(), val );
+      logMessageToFile( QString( "%s: %s: %f" ).arg( file ).arg( var.toLocal8Bit().constData() ).arg( val ) );
     }
     else if ( line == -1 )
     {
       qDebug( "%s: (%s): %s: %f", file, function, var.toLocal8Bit().constData(), val );
+      logMessageToFile( QString(  "%s: (%s): %s: %f" ).arg( file ).arg( function ).arg( var.toLocal8Bit().constData() ).arg( val ) );
     }
     else
     {
@@ -128,23 +140,27 @@ void QgsLogger::debug( const QString& var, double val, int debuglevel, const cha
 #else
       qDebug( "%s: %d: (%s), %s: %f", file, line, function, var.toLocal8Bit().constData(), val );
 #endif
+      logMessageToFile( QString( "%s: %d: (%s), %s: %f").arg( file ).arg( line ).arg( function ).arg( var.toLocal8Bit().constData() ).arg( val ) );
     }
   }
 }
 
 void QgsLogger::warning( const QString& msg )
 {
   qWarning( "%s", msg.toLocal8Bit().constData() );
+  logMessageToFile( msg );
 }
 
 void QgsLogger::critical( const QString& msg )
 {
   qCritical( "%s", msg.toLocal8Bit().constData() );
+  logMessageToFile( msg );
 }
 
 void QgsLogger::fatal( const QString& msg )
 {
   qFatal( "%s", msg.toLocal8Bit().constData() );
+  logMessageToFile( msg );
 }
 
 int QgsLogger::debugLevel()
@@ -178,6 +194,26 @@ int QgsLogger::debugLevel()
   return mDebugLevel;
 }
 
+const QString QgsLogger::logFile()
+{
+  const QString logFile = getenv( "QGIS_LOG_FILE" );
+  return logFile;
+}
+
+const void QgsLogger::logMessageToFile( QString theMessage )
+{
+  if ( ! logFile().isEmpty() )
+  {
+    //Maybe more efficient to keep the file open for the life of qgis...
+    QFile file( logFile() );
+    file.open(QIODevice::Append);
+    file.write( theMessage.toStdString().c_str() );
+    file.write( "\n" );  
+    file.close();
+  }
+  return;
+}
+
 const char* QgsLogger::debugFile()
 {
   const char* dfile = getenv( "QGIS_DEBUG_FILE" );

src/core/qgslogger.h

@@ -21,6 +21,7 @@
 #include <iostream>
 #include <sstream>
 #include <QString>
+class QFile;
 
 #ifdef QGISDEBUG
 #define QgsDebugMsg(str) QgsLogger::debug(QString(str), 1, __FILE__, __FUNCTION__, __LINE__)
@@ -45,6 +46,9 @@
  * QGIS_DEBUG_FILE may contain a file name. Only the messages from this file are
  * printed (provided they have the right debuglevel). If QGIS_DEBUG_FILE is not
  * set, messages from all files are printed
+ *
+ * QGIS_LOG_FILE may contain a file name. If set, all messages will be appended
+ * to this file rather than to stdout.
 */
 
 class CORE_EXPORT QgsLogger
@@ -107,8 +111,15 @@ class CORE_EXPORT QgsLogger
     static int debugLevel();
 
   private:
+    /**Reads the environment variable QGIS_LOG_FILE. Returns NULL if the variable is not set,
+     * otherwise returns a file name for writing log messages to.*/
+    static const QString logFile();
 
-    /**Reads the environment variable QGIS_DEBUG_FILE. Returns NULL if the variable is not set*/
+    /** Logs the message passed in to the logfile defined in QGIS_LOG_FILE if any. **/
+    static const void logMessageToFile( QString theMessage );
+
+    /**Reads the environment variable QGIS_DEBUG_FILE. Returns NULL if the variable is not set.
+     * If set, only messages from this source file will be sent to logs. */
     static const char* debugFile();
 
     /** current debug level */