Re: [Stox] core: response code mappings

[Daniel-Constantin Mierla <[e-mail]>]

On 8/20/13 12:07 AM, Peter Saint-Andre wrote:
> On 8/19/13 3:44 PM, Daniel-Constantin Mierla wrote:
>> On 8/19/13 10:23 PM, Peter Saint-Andre wrote:
>>> On 8/19/13 2:02 PM, Paul Kyzivat wrote:
>>>> On 8/16/13 10:28 PM, Peter Saint-Andre wrote:
>>>>> The SIP Parameters Registry has a list of SIP response codes:
>>>>>
>>>>> http://www.iana.org/assignments/sip-parameters/sip-parameters.xml#sip-parameters-7
>>>>>
>>>>>
>>>>>
>>>>> A number of those are not specified in RFC 3261. Thus the question
>>>>> arises: for which codes do we need to define mappings? We could define
>>>>> mappings for all of them, but I wonder if that's advisable. Some of the
>>>>> additional codes are specified in RFCs that update RFC 3261 (e.g., code
>>>>> 440 from RFC 5393), whereas other codes are specified in "non-core"
>>>>> RFCs
>>>>> that don't update RFC 3261 (e.g., code 470 from RFC 5360). Would it
>>>>> perhaps make sense to map the "core" codes and not the "non-core"
>>>>> codes?
>>>> I know this is almost a non-answer, but...
>>>>
>>>> The codes that are defined in other RFCs are there to support features
>>>> that are introduced in those RFCs. If there is a mapping of that feature
>>>> to XMPP, then there should be a mapping of the code.
>>> That makes sense.
>>>
>>>> If there is no mapping of the feature, then mapping the code is less
>>>> important, but still perhaps useful in some cases. E.g., it could
>>>> conceivably show up in a Reason code based on signaling that was never
>>>> gatewayed to xmpp. But maybe a default mapping would be sufficient in
>>>> those cases.
>>> I suspect that the default mapping would be fine.
>>>
>>> And in general, there might be more art than science here.
>>>
>>> I have written some proposed text for this section, but it's fairly long
>>> so my inclination is to submit a revised I-D and then folks can review
>>> what I've written and post to the list with feedback.
>> Looking at the latest draft, it seems to bring confusion on mapping from
>> xmpp-to-sip on 400 code. I read this thread and kind of understood that
>> any not-obvious-mapping similar-to-a-4xx case would be handled same as
>> 400 in SIP, but typically the 400 response is given for a malformed sip
>> requests (like broken grammar).
> So your suggestion is that we avoid mapping XMPP error conditions to SIP
> 400 unless the XMPP condition is caused by a malformed request?
Yes, <bad-request/> qualifies for that. Otherwise, could create 
confusion for implementers of sip endpoints - from sip rfc:
21.4.1 400 Bad Request


    The request could not be understood due to malformed syntax.  The
    Reason-Phrase SHOULD identify the syntax problem in more detail, for
    example, "Missing Call-ID header field".



>
>> After quick read, <conflict/> would map more suggestively to 403
>> Forbidden.
> As I said, it's perhaps more art than science. But mapping <conflict/>
> to 403 seems reasonable if we accept your suggestion about not mapping
> to 400 unless we have a good reason to do so.
>
>> Maybe <policy-violation> and <undefined-condition/> could get
>> other mappings as well.
> Well, depending on the policy being violated, <policy-violation/> might
> map to 413, 414, 513, or even 406/606.

I would find more appropriate 500 than 400 for mapping, also because 
these situations are more server related. 500 is the most generic error 
code in sip from my point of view -- is used even for SIP message 
related situations, such as CSeq value in a request within a dialog is 
lower than previous received one.

The section in the draft seems to be a global mapping, it is no 
difference between types of errors in xmpp -- there can be same error 
tag for streams and stanzas. For example <conflict/> for streams says:

4.9.3.3. conflict


    The server either (1) is closing the existing stream for this entity
    because a new stream has been initiated that conflicts with the
    existing stream, or (2) is refusing a new stream for this entity
    because allowing the new stream would conflict with an existing
    stream (e.g., because the server allows only a certain number of
    connections from the same IP address or allows only one server-to-
    server stream for a given domain pair as a way of helping to ensure
    in-order processing as described under Section 10.1).

The second example above can be associated with 'No more channels' in a 
SIP media server/gateway -- 500 is used in this case (at least Asterisk 
did it :-) ).
>
> Given that <undefined-condition/> is something of a catch-all, it's not
> clear to me what we'd map it to in a consistent way. That would probably
> depend on the application-specific element contained in the error stanza.
>
Indeed, could be application/case-to-case specific mapping, but 
otherwise I think 500 should be the catch-all case in sip side.

Daniel

-- 
Daniel-Constantin Mierla - http://www.asipto.com
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda