16.4. A Gentle Introduction to func_odbc

The very first use of func_odbc, which occurred while its author was still writing it, is also a good introduction to its use. A customer of one of the module’s authors noted that some people calling into his switch had figured out a way to make free calls with his system. While his eventual intent was to change his dialplan to avoid those problems, he needed to blacklist certain caller IDs in the meantime, and the database he wanted to use for this was a Microsoft SQL Server database. With a few exceptions, this is the actual dialplan^[170]:

^[170] This system is unfortunately no longer in service. Thus, any changes have been made for the sake of simplicity, not to conceal the business for which it was designed.

[span3pri]
exten => _50054XX,1,NoOp()
   same => n,Set(CDR(accountcode)=pricall)
   same => n,GotoIf($[${ODBC_ANIBLOCK(${CALLERID(number)})}]?busy)
   same => n(dial),Dial(DAHDI/G1/${EXTEN})
   same => n(busy),Busy(10)
   same => n,Hangup

This dialplan, in a nutshell, passes through all calls to another system for routing purposes, except those calls whose caller IDs are in a blacklist. The calls coming into this system used a block of 100 7-digit DIDs. There is a mystery function in this dialplan, though: ODBC_ANIBLOCK(). This function is defined in another configuration file, func_odbc.conf, at runtime: