logging with osip

As I posted before, logging is an important debugging means. In order to be truly useful and convenient, the logging module should at lease have two traits:

1. can be turned on and off globally
2. supports the concept of logging level

osip also comes with a mature logging system. Besides the traits I just mentioned, it also enables we  to configure log output destination, which can be a plain file, syslog, or a function pointer to a custom logging function. The function pointer enables us to save the log to any possible storage we prefer, e.g., across network.
There is a tiny bug which prevents us using the function pointer mechanism on windows platform if we compile the osip as dynamic library. The author forgot export osip_trace_initialize_func in osipparser2.def file. So our application will end in unresolved external symbol error if we use this function. To get around this, I added the line at the very end of osipparser2.def:  osip_trace_initialize_func        @416

To use osip logging, we need to:

1. Compile osip with ENABLE_TRACE macro defined
2. Define ENABLE_TRACE in our application
3. Initialize osip logging module
4. Write log message with:  OSIP_TRACE (osip_trace(__FILE__, __LINE__, OSIP_INFO1, NULL, "log message"));

The wonderful thing is we can easily turn off logging by either undefine ENABLE_TRACE macro, or eliminate the line that initialize osip logging module. We can also trun logging message with specific logging level on and off. Very convenient.

An example of is available here:
http://code.google.com/p/rxwen-blog-stuff/source/browse/trunk/protocol/osip_logging/osip_log.cpp