[SR-Users] Proposal to extend acc/dialog modules in order to log CDRs

Hi all, I'd like to bring forward a proposal for creating CDRs (Call Data Records) from Kamailio by means of extending both acc and dialog modules. Feedback is very welcome. So far, CDR generation requires post-processing of log entries created by the (transaction-based) acc module or some other means. Looking at OpenSIPS (which is already capable of producing CDRs), my idea is to copy the basic notion of tracking dialogs for to-be-accounted calls and log a proper CDR on termination. Creating basic CDRs including start time, end time, and call duration can be accomplished quite easily this way. Apart from this very minimum CDR content, however, one can think of a number of CDR fields that cannot be filled easily. For instance, caller identity isn't always contained in the From header (think of CLIR calls) but need to be determined from other headers depending on the type of call, possibly even involving a database lookup. That's why I'd like to provide a way to pass additional, CDR-specific data from the configuration file to the dialog structure associated with the call. When the dialog is about to terminate, the extended acc module would make sure that the added CDR data associated to the dialog is included in the CDR. This way, users may define CDR fields to their personal needs from the configuration file in a flexible manner. In order to accomplish this, the dialog module would need to be extended such that dialog-specific data may be stored for the duration of a dialog (which is not possible to this day AFAICS). A new setter function attached to the dialog interface (struct dlg_binds) could accept a simple key/value pair for storage purposes. Exporting this function to the configuration file and accompanying it with a corresponding getter function will ensure that dialog-specific data may be written and read generically. Thus, improvements to the dialog module may be leveraged not just for CDR-accounting purposes. Regarding the acc module, a couple of new features need to be implemented: First, the introduction of another module parameter called something like "cdr_fields" that comprises the set of key names designated for CDR inclusion. Hence, a line like modparam("acc", "cdr_fields", "caller, callee, foo, bar") would require Kamailio configurators to store dialog-specific values for the keys "caller", "callee", "foo", and "bar", respectively, during call processing. The values will be fed to the dialog structure employing the new dialog store function explained above. Second, when the acc module is in CDR mode, dialogs shall be tracked from creation to termination using dialog callbacks. On termination of a dialog, values from keys referenced in the "cdr_fields" parameter will be fetched from the terminating dialog structure and associated with the new, fresh CDR. Third, the CDR is persisted to either log file, database, or both. Note that my approach would not touch the existing acc module functionality: CDR mode is supposed to be working in addition to transaction-based accounting as people will likely want to keep transaction logs for debugging or similar needs. A flag would enable and disable CDR generation at will. I have not fully investigated re-usability possibilities but believe that acc's persistence functions may be taken advantage of by the new CDR-producing parts as well. That's it with regards to the basic mode of operation. I am also thinking of having a few other features, such as using a switch to set the call start time to the moment the ACK or OK is seen instead of the INVITE (because users shouldn't be billed for call setup times). Looking forward to seeing your feedback on this proposal. Cheers, --Timo