question about config code

[David Relson]

Gram,

You've overlooked an important detail in the design.  NULL pointers are 
used for two purposes.

Each entry in the parm_desc struct has a "type" field (CP_ALGORITHM, 
CP_INTEGER, etc).  A switch statement branches on the type and either does 
inline processing to get a value and store it (for simple types like 
CP_INTEGER, CP_DOUBLE, etc), or it calls a function to process the 
parameter (for CP_ALGORITHM and CP_WORDLIST).

CP_ALGORITH has a NULL pointer because the work is done by function 
select_method().

That's the first part of what goes on.  There's a second part.

Some options apply to bogofilter as a whole.  Some apply to a particular 
algorithm, but not to the others.  The parm_desc struct in config.c gives 
the handling info for the global parameters.  The algorithm files 
(graham.c, robinson.c, and fisher.c) have their own parm_desc structs for 
their private parameters.

When CP_ALGORITHM is encountered, a method pointer is set and the method's 
parm_desc struct is retrieved (as a pointer) and saved in global variable 
"method".  Having this info, process_config_lines) can be called twice - 
once to see if the option belongs to the algorithm and, it not found, a 
second time to see if it belongs to the global parm_desc.  All options 
should be found during one of these calls to process_config_line().  If 
not, then the option is bogus.

Unfortunately, there's a slight problem with this.  Consider the bogofilter 
admin who's testing the different algorithms and their options.  He/she 
will want to change options as easily as possible, likely by using the 
'-g', '-r', and '-f' command line switches.  He/she will also want a single 
config that has options for all the methods.  If all config.c knows is the 
global options and those that pertain to the selected algorithm, the other 
options will generate warning messages (even though they are valid for a 
different algorithm).  Not good.  To avoid this, config.c has dummy entries 
at the end of its parm_desc struct for the method specific options.  The 4 
options currently there are surrounded by #ifdefs and all have NULL 
pointers.  NULL tells process_config_line() to ignore the value.

I know this is long, but the code is somewhat intricate and tricky.  I'll 
probably edit this message and convert it to some comments in config.c.

Thanks for looking at code, working to understand it, and pointing out a 
piece whose functioning is neither obvious nor documented.

David