The Logging System

Collaboration diagram for The Logging System:

Modules
	The flatlogs log protocol
	Log Entry Types

Classes
struct	MagAOX::logger::logManager< logFileT >
	The standard MagAOX log manager, used for both process logs and telemetry streams. More...

Detailed Description

Logging an event or information

libMagAO-X implements a binary logging system, using the co-developed "flatlogs" format and the "flatbuffers" binary protocol from google. Any class derived from MagAOX::app::MagAOXApp has two log methods defined which can be used as follows.

• To log an event, such as a control loop closing:

  log<loop_closed>(); //an empty log, just an event

• To log information, such as a software error:

  log<software_error>({__FILE__, __LINE__, errno}); //information is logged like this

Here we see that the log system constructs a message from a "brace enclosed initializer list". The system is statically typed, and the list of parameters in the "{}" list depends on the type specified as a template parameter to log. All details, such as the time stamp and log priority, are handled automatically but can be specified/overridden if needed.

Steps to adding a new log type:

To add a log type to the MagAO-X flatlogs logging system, perform the following steps. We will assume that this log is named "log_type" in what follows.

1. If it is an empty log:
   • Create a new file "log_type.hpp" in the logger/types directory. This new file has the following form

     #ifndef logger_types_loop_open_hpp
     #define logger_types_loop_open_hpp
     
      #include "empty_log.hpp"
     
      namespace MagAOX
      {
      namespace logger
      {
     
      /// <add documentation here>
      struct log_type : public empty_log<log_type>
      {
         ///The event code -- This line should appear verbatim
         constexpr static flatlogs::eventCodeT eventCode = eventCodes::LOG_TYPE; //DO NOT EDIT
     
         ///The default level -- edit the default level as desired.
         constexpr static flatlogs::logPrioT defaultLevel = flatlogs::logPrio::LOG_NOTICE; //EDIT PRIORITY AS NEEDED
     
         ///The message string -- edit for this case.
         static const char * msg() {return "specific log_type message";} //EDIT "message" AS NEEDED
      
      };
     
      } //namespace logger
      } //namespace MagAOX
     
      #endif

2. If it is not an empty log:
   • Create a flatbuffer schema in logger/types/schemas
   • Create a new file "log_type.hpp" in the logger/types directory. This new file has the following form

     #ifndef logger_types_log_type_hpp
     #define logger_types_log_type_hpp
     
     #include "generated/log_type_generated.h"  //EDIT THIS FILENAME
     #include "flatbuffer_log.hpp" //DO NOT EDIT
     
     namespace MagAOX
     {
     namespace logger
     {
     
     /// <add documentation here>   
     struct log_type : public flatbuffer_log //Must derive from flatbuffer_log
     {
        ///The type of the message.  Each flatbuffer_log has a messageT struct.
        struct messageT : public fbMessage
        {
           /// c'tor, used to initialize the log.
           messageT( const char * msg ) // EXAMPLE: this log_type takes a string as its contents
           {
              auto _msg = builder.CreateString(msg); // EXAMPLE: pack the contents in the flatbuffer
           
              auto gs = CreateString_log_fb(builder, _msg); // EXAMPLE: finalizing the buffer
              builder.Finish(gs);
           }
        };
     
        ///Each flatbuffer_log must implement this function to format the log for human consumption
        static std::string msgString(void * msgBuffer, flatlogs::msgLenT len)
        {
           static_cast<void>(len); // unused by most log types
        
           auto rgs = GetString_log_fb(msgBuffer); // EXAMPLE: how to work with a flatbuffer
        
           if(rgs->message()) return rgs->message()->c_str(); // EXAMPLE: how to access the message contents.
           else return "";
        }
     
     };
     
     } //namespace logger
     } //namespace MagAOX
     #endif

     For more information about how to write flatbuffer schemas and pack and access data, see the flatbuffer documentation.
3. For completeness you should add the new types/log_type.hpp file to the libMagAOX Makefile INCLUDEDEPS list.
4. Now add the log to "logger/logCodes.dat"
   • Place it in an appropriate section of the file, and in numerical order by the code so future additions can be easily managed.
   • Choose a code <= 65535, that is not already used.
   • Be sure to make the third column the name of the schema (without .fbs attached), which is not necessarily the log type name.
5. Re-compile the logging system by, in the libMagAOX directory (above logger), typing make. This will generate a number of files based on the logCodes.dat entry you have made. Correct any errors from the flatc compiler or the flatlogs code gerator.
6. Now recompile (at least) the app using the log type and the logdump utility.