Hello,
some time ago I created a new branch in GIT named 'daniel/xavp' that includes code for a new pseudo-variable class 'xavp' - name being a shortcut to 'extended attribute value pair'. I collected some design details in wiki:
http://sip-router.org/wiki/devel/xavp
It is not a replacement for current AVP api implementation, although in the future can replace it. In the past we had couple of discussions about the limitations of avps which I tried to overcome. Here are some highlights of xavp design:
- string names only - various tests showed that having the complex addressing scheme with integer id and string name does not pay off performance gains. XAVP computes and integer id for each name that is used to speed up comparison
- possibility to store more data types - AVP allow string and integer data types. More can be handled by XAVP, including a generic data type where you can build your own structure and store it in the list. This is good for example to store custom structures for transaction lifetine -- right now dialog module needs to store reference to dialog structure. Optimizations can be done for any case of serial forking -- uri, dst uri, q, etc can be stored in a structure without a need to parse and build it from an encoded value stored in one or many avps
- possibility to group XAVPs inside another XAVP - practically is building lists of XAVPs. This should overcome issues with naming conflicts between modules - e.g., dispatacher module can group its avps in a list named "dispatacher", lcr module in a list named 'lcrl, then there can be XAVP with name 'uri' in both lists, without the risk of misusage. Another benefit would be reducing the number of parameters, right now each module exports a parameter to set the name for each AVP, with xavp there is need for one parameter to set the name of the list, then inside that list the module is free to use predefined names without the risk of overlapping.
- xavp having value integer or string can be used directly in config, whether they are in a sublist or not
Check the wiki (link above) for more. Looking forward for comments, suggestions and improvements.
Cheers, Daniel
Daniel-Constantin Mierla wrote:
- possibility to store more data types - AVP allow string and integer
data types. More can be handled by XAVP, including a generic data type where you can build your own structure and store it in the list. This is good for example to store custom structures for transaction lifetine -- right now dialog module needs to store reference to dialog structure. Optimizations can be done for any case of serial forking -- uri, dst uri, q, etc can be stored in a structure without a need to parse and build it from an encoded value stored in one or many avps
You could generalize this into only using the generic data value and wrap the other types into these. This requires makeing these generic data values in the script language somehow. For all this, you will need a somewhat more elaborate interface to the type than a free function.
I suppose you could define a struct much like the module struct that contains a bunch of pointers to various functions for various things. An instance of this type then consists of a pair from the pointer to the type struct (which incidentally is uniquely identifying the type and a pointer into shared memory pointing to the value).
- possibility to group XAVPs inside another XAVP - practically is
building lists of XAVPs.
If you wrap this into a generic type, you can have various types for lists and maps and whatnot (although this should really do). There are some questions around references vs. copies here, so this will probably go off into reference counting and stuff.
Although, neatly enough, this can probably made in such a way that XAVPs get auto-magically destroyed when their parent object (the transaction, dialog, etc.) is being destroyed.
Regards, Martin
On 28.07.2009 13:51 Uhr, Martin Hoffmann wrote:
Daniel-Constantin Mierla wrote:
- possibility to store more data types - AVP allow string and integer
data types. More can be handled by XAVP, including a generic data type where you can build your own structure and store it in the list. This is good for example to store custom structures for transaction lifetine -- right now dialog module needs to store reference to dialog structure. Optimizations can be done for any case of serial forking -- uri, dst uri, q, etc can be stored in a structure without a need to parse and build it from an encoded value stored in one or many avps
You could generalize this into only using the generic data value and wrap the other types into these. This requires makeing these generic data values in the script language somehow. For all this, you will need a somewhat more elaborate interface to the type than a free function.
it is an option, but I wanted to have it simple for common data types in the same time to allow dealing with more complex structures. This can be implemented for generic data, so it adds kind of: fromStr and toStr functions, making possible to set/get values from config.
I suppose you could define a struct much like the module struct that contains a bunch of pointers to various functions for various things. An instance of this type then consists of a pair from the pointer to the type struct (which incidentally is uniquely identifying the type and a pointer into shared memory pointing to the value).
- possibility to group XAVPs inside another XAVP - practically is
building lists of XAVPs.
If you wrap this into a generic type, you can have various types for lists and maps and whatnot (although this should really do). There are some questions around references vs. copies here, so this will probably go off into reference counting and stuff.
with current implementation, this is a matter of what free function does for generic data type. For the common types, free is done automatically, being easier for developers.
Although, neatly enough, this can probably made in such a way that XAVPs get auto-magically destroyed when their parent object (the transaction, dialog, etc.) is being destroyed.
Now they are attached to transaction and auto-destroyed when the transaction terminates -- same like with AVP list. The API allow to work with custom xavp lists, therefore developer can attach new lists to different contexts -- will need to extend the interface to config, as the PV export is using the default list bound to sip message/transaction.
Thanks, Daniel
Daniel-Constantin Mierla wrote:
On 28.07.2009 13:51 Uhr, Martin Hoffmann wrote:
You could generalize this into only using the generic data value and wrap the other types into these. This requires makeing these generic data values in the script language somehow. For all this, you will need a somewhat more elaborate interface to the type than a free function.
it is an option, but I wanted to have it simple for common data types in the same time to allow dealing with more complex structures.
Agree. I was actually more thinking into the future and into a Grand Unified Variable kind of thing. Not sure if this should be a service provided by the core or some module. But should we agree that we want such a thing then it might be better to work on that instead of building an interims solution based on AVPs.
This is not to diminish your work in any way, I quite like the possibilities especially with the option for lists. It just may safe you same work that will eventually be superseded by something else.
Regards, Martin
On 29.07.2009 11:52 Uhr, Martin Hoffmann wrote:
Daniel-Constantin Mierla wrote:
On 28.07.2009 13:51 Uhr, Martin Hoffmann wrote:
You could generalize this into only using the generic data value and wrap the other types into these. This requires makeing these generic data values in the script language somehow. For all this, you will need a somewhat more elaborate interface to the type than a free function.
it is an option, but I wanted to have it simple for common data types in the same time to allow dealing with more complex structures.
Agree. I was actually more thinking into the future and into a Grand Unified Variable kind of thing. Not sure if this should be a service provided by the core or some module. But should we agree that we want such a thing then it might be better to work on that instead of building an interims solution based on AVPs.
This is not to diminish your work in any way, I quite like the possibilities especially with the option for lists. It just may safe you same work that will eventually be superseded by something else.
the core has to provide at least the mechanisms to hook up to different contexts (e.g., like now to sip message/transaction). The PV interface implementation is done in pv module, so that is not bound to core at all. Without pv module, xavp cannot be used from config.
To the other matter, I brought this to discussion to find the best solution, therefore all is open. There is no memory penalty as the value is a union, if one uses only the generic data it is not affected by the existence of the other simple data types.
I am not a fan of over-engineering, trying to keep being practical, not getting to something very complex due to nature of variables existing now, in kamailio (at least) there are references inside the sip message, to the proxy and OS environment, to shared and private memory, list of values in share memory (avps), database query result, hash table (local cache), memcached data (distributed cache). What is common to all these is the interface to config file -- each exports set/get function to/from int or str values.
Cheers, Daniel
-
Daniel-Constantin Mierla -
Martin Hoffmann -
Martin Hoffmann