[Kamailio-Devel] [SR-Dev] [Serdev] AVPs

[Andrei Pelinescu-Onciul]

On Dec 16, 2008 at 00:36, Daniel-Constantin Mierla <miconda at gmail.com> wrote:
> Hello,
> 
> On 12/12/08 17:22, Jan Janak wrote:
> > On 12-12 00:25, Daniel-Constantin Mierla wrote:
> >   
> >> Hello,
> >>
> >> I think we need to decide about AVPs. Although not deeply investigated,  
> >> ser seems to have couple of AVPs lists. In kamailio/openser it is one 
> >> list.
> >>
> >> Can a ser developer describe a bit the AVP implementation as it is now  
> >> there?
> >>     
> >
> >   A long time ago we started using AVPs to store all kinds of configuration
> >   information. We needed some sort of general configuration mechanism because
> >   real-world scripts were getting too complex and at that time the AVPs were
> >   readily available.
> >
> >   We started by loading attribute names and value from a database table into
> >   AVPs. This mechanism was/is same as in k. We would always load a set of
> >   attributes this way for a particular user (identified by username and domain
> >   from his/her SIP URI). With this mechanism in place, we were able to load a
> >   generic set of configuration options for a particular user of the server, I
> >   guess you have the same.
> >
> >   To make the AVPs easily accessible from the configuration script, we added
> >   support for AVP identifiers in the config script, so that you can access AVP
> >   with name foo as $foo.
> >
> >   As we migrated more and more configuration options to AVPs, it became clear
> >   that having just one set of AVPs was not enough. Although we could load all
> >   the config options for the caller (From URI) from the database into a set of
> >   AVPs, we could not do the same for the callee (Request-URI) at the same
> >   time. We could not do it because they would conflict with the AVPs of the 
> >   caller as both users could have AVPs with same names but different values.
> >
> >   To get around this issue we added another list of AVPs. The new AVP list
> >   works the same way, it can contain AVPs with same names as AVPs in the
> >   original list and they do not conflict. All functions that work with lists
> >   of AVPs now take the list to work on as parameter.
> >
> >   To make both AVP lists available in the configuration script, we extended
> >   the syntax of AVPs identifiers so the script write can choose the AVP list
> >   to work with. SO instead of just $foo you can write either
> >
> >   $f.foo or $t.foo
> >
> >   $f refers to the original AVP list which is commonly associated with the
> >   caller. The address/uid of the caller is taken from From header, hence the
> >   'f' in the identifier. $t refers to the AVP list which contains
> >   configuration settings of the callee. The address/uid of the calle can be
> >   taken either from the Request-URI or To headers, hence the 't' in the
> >   identifier.
> >
> >   The original syntax without any list identifier is still available, in other
> >   words you can still write $foo, this is defined as a shorthand for
> >   $f.foo. If you do not specify the AVP list to be used then you are referring
> >   to the list containing AVPs of the caller (From).
> >
> >   It also turned out that in some cases we would be having too many attributes
> >   in the database table storing AVPs. This can happen in bigger setups, having
> >   tens or hundreds of thousands users or serving multiple domains. This can
> >   slow the database down and makes SER load too much data. Based on my
> >   observations it is common that a large number of users have AVPs with same
> >   values. If ten thousands of users have attribute named 'foo' with value
> >   'bar' then the attribute will be stored in the database ten thousand times.
> >
> >   As a remedy for this problem, we introduced the concept of AVP levels. The
> >   AVPs described so far and stored in user_attrs table are called user-level
> >   attributes and they store configuration specific to particular users. Then
> >   we added another two AVP lists to store so called domain-level AVPs.
> >
> >   Domain-level AVPs are used to store configuration information that is shared
> >   by a group of users. Domain-level AVPs are stored in a separate database
> >   table, the name of the table is domain_attrs and its contents is cached in
> >   memory by 'domain' SER module. This is an important difference, while
> >   user-level AVPs need to be loaded every time a SIP request is processed,
> >   domain-level AVPs are only loaded when the contents of domain_attrs table
> >   has changed.
> >
> >   The domain-level AVPs are called 'domain' because they are tied to a
> >   particular domain handled by the SIP server. That could be 'iptel.org',
> >   'sip-router.org', and so on. This mainly useful for multi-domain
> >   setups. There are two domain-level AVP lists because it is common that SER
> >   works with two domains at the same time, the domain from From header
> >   (caller's domain) and the domain from Request-URI or To (callee's domain).
> >
> >   Again, we extended the syntax of AVP identifiers in the configuration
> >   file. So you can write:
> >
> >   $fu.foo -- this way you are asking for the value of the user-level foo AVP.
> >   $fd.foo -- This will return the value of the domain-level foo AVP.
> >
> >   And similarly there is $tu and $td for callee's user-level and domain-level
> >   AVPs. If you specify 'u' in the AVP identifiers then SER searches only the
> >   list of user-level attributes. If you specify 'd' then SER searches only the
> >   list of domain-level attributes.
> >
> >   This behavior changes if you do NOT specify the level to be searched. In
> >   that case SER searches the user-level list first and if no match is found
> >   then the domain-level list will be searched. Thus if you write:
> >
> >   $f.foo
> >
> >   then you are telling SER to search for the value of 'foo' AVP in the
> >   user-level list and continue with the domain-level list if no match is
> >   found. In other words, user-level AVPs have higher priority than
> >   domain-level AVPs. With this system you can efficiently set a configuration
> >   option for all users within a domain by creating a domain-level attribute
> >   and yet you can override that option with user-level attributes for
> >   particular users within that domain.
> >
> >   Then there are the global AVPs. Global AVPs can be used to store settings
> >   applicable to the whole SIP server and all domains on that server. Global
> >   AVPs are stored in global_attrs table and the contents of that table is
> >   cached in memory by gflags module. There is only one list of global
> >   AVPs. Global AVPs can be accessed with:
> >
> >   $g.foo
> >
> >   (note that there is no 'f' or 't' in the identifier). The list of global
> >   AVPs is searched after the list of domain-level AVPs. So if you write:
> >
> >   $f.foo
> >
> >   Then SER searches user-level AVPs first, then domain-level and then the
> >   global AVPs.
> >
> >   And finally there are also so called URI-level AVPs. They work just
> >   like user-level AVPs, but a single user can have multiple sets of
> >   uri-level AVPs. They are tied to SIP URIs of that user. Uri-level AVPs are
> >   denoted by 'r' in the AVP identifier, for example:
> >
> >   $fr.foo
> >   
> 
> 
> so, if I understood correctly, there are couple of combinations between 
> the dot, with one or two letters, right?
> 
> Like:
> 
> $xy.name
> 
> where x = f|t|g and y may be missing or u|d|r

x = f|t ("track" in ser avp terminology
y= r|u|d|g ("class")

g is a special case (it cannot be combined with f or t).


Here is the parse_avp_ident() usage comment:

/** parse an avp indentifier.
 *
 * Parses the following avp indentifier forms:
 *       - "i:<number>"  - old form, deprecated  (e.g. i:42)
 *       - "s:<string>"  - old form, deprecated  (e.g. s:foo)
 *       - "<track>.<name>"                      (e.g.: f.bar)
 *       - "<track>.<name>[<index>]"             (e.g.: f.bar[1])
 *       - "<track><class>.<name>"               (e.g:  tu.bar)
 *       - "<track><class>.<name>[<index>]"      (e.g:  fd.bar[2])
 *       - "<string>"                            (e.g.: foo)
 * Where:
 *          <string> = ascii string
 *          <id>   = ascii string w/o '[', ']', '.' and '/'
 *          <name> = <id> | '/' regex '/'
 *                   (Note: regex use is deprecated)
 *          <track> = 'f' | 't'
 *                   (from or to)
 *          <class> = 'r' | 'u' | 'd' | 'g'
 *                    (uri, user, domain or global)
 *          <index> = <number> | '-' <number> | ''
 *                    (the avp index, if missing it means AVP_INDEX_ALL, but
 *                     it's use is deprecated)
 * More examples:
 *       "fr.bar[1]"  - from track, uri class, avp "bar", the value 1.
 *       "tu./^foo/"  - to track,  user class, all avps for which the name
 *                      starts with foo (note RE in avp names are deprecated).
 *        "t.did"     - to track, "did" avp
 *
 * @param name  - avp identifier
 * @param *attr - the result will be stored here
 * @return 0 on success, -1 on error
 */

> 
> Then we can get rid of overlapping in the namespace if we enforce usage 
> of $f.foo for $foo . In K there are couple of PV that use dot in 
> classname (a PV can be $classname or $classname(innername)), but they 
> are proposed to be removed.

For the time being in sip-router this is handled in the following way:

$(...) -> pvar
$foo(...) -> pvar
$foo[...] -> avp
$bar.foo -> avp (if it has a dot in it -> avp)
$foo  (no dot, [] or ()) -> try first to resolve it as pvar and if it
fails consider it an avp.

For the current version I think this is the most compatible way. I'll
use the same approach for ser module fixups (so all ser module that use 
 core fixup functions will be able to use also pvars).
One could also force  kamailio or ser behaviour, by starting the
script with #!KAMAILIO or #!SER.

For future versions we should rethink how everything is accessed.
For example I would use $foo for script variables and some other form
for avps or the current pvar $foo. Also we would have to unify selects
with the select like part of the pvars.
(Note for ser users: pvars in kamailio are used to access script vars,
avps, message headers and something which is kind of similar to ser
selects.).

> 
> In the same idea as in ser, thenK AVPs will map to From list.
> 
[...]


Andrei