A number of worker programs are shipped with xymond, e.g. xymond_filestore(8) xymond_history(8) xymond_alert(8) xymond_rrd(8)
If you want to write your own worker module, a sample worker module is provided as part of the xymond distribution in the xymond_sample.c file. This illustrates how to easily fetch and parse messages.
Note that messages for "logrotate", "shutdown", "drophost", "renamehost", "droptest" and "renametest" are ALWAYS forwarded by xymond_channel, whether or not they match any of the above filters.
Note that if --filter or --metafilter are specified, any message which does NOT pass those matches will be REJECTED. (The presence of --exfilter or --metaexfilter alone does not cause this type of "default denial.")