[asterisk-dev] Problems with the ASTERISK-27206 patch.

[Joshua Colp]

On Wed, Jan 3, 2018, at 3:53 PM, Richard Mudgett wrote:
> On Wed, Jan 3, 2018 at 5:08 AM, Joshua Colp <jcolp at digium.com> wrote:
> 
> > On Wed, Jan 3, 2018, at 12:03 AM, Richard Mudgett wrote:
> > > On Tue, Jan 2, 2018 at 5:41 PM, Joshua Colp <jcolp at digium.com> wrote:
> > >
> > > > On Tue, Jan 2, 2018, at 7:14 PM, Richard Mudgett wrote:
> > > > > The patch for https://issues.asterisk.org/jira/browse/ASTERISK-27206
> > > > which
> > > > > is committed in 7385d1e017e562afe64431606e857e704f86a16d causes a
> > > > > configuration regression by requiring the endpoint and identifier
> > method
> > > > > to agree to match the endpoint.  Doing so is redundant for methods
> > that
> > > > > explicitly specify which endpoints they match.  The redundancy allows
> > > > > configuration errors that cannot be caught when the configuration is
> > > > > loaded.
> > > >
> > > > Can you clarify what the precise regression you are referring to is?
> > Even
> > > > after reading this email I'm still unclear.
> > > >
> > >
> > > The regression is the new requirement for the endpoint identify_by option
> > > to list ip in order for
> > > the type=identify method to be accepted by the endpoint.  This new
> > > requirement is unnecessary
> > > as the type=identify section must specify an endpoint name to know which
> > > endpoint it recognizes.
> > >
> > > More specifically, the change to
> > > res/res_pjsip_endpoint_identifier_ip.c:ip_identify() enforces this
> > > new requirement.
> > >
> > > I should have used the term complexity instead of redundancy.
> > >
> > > The new requirement adds configuration complexity because the endpoint
> > > identify_by option and
> > > the type=identify method must agree to match the endpoint.  The added
> > > complexity doesn't add any
> > > value, can needlessly break existing installations regardless of the note
> > > in CHANGES saying it will,
> > > makes match by ip configuration more error prone, and the error is not
> > > recognizable on configuration
> > > load.
> > >
> > > In addition, as I pointed out, I think the entire ASTERISK-27206 patch
> > was
> > > unnecessary.  Before
> > > the patch, setting the identify_by option to an empty string would
> > disable
> > > the username
> > > identification method from matching the endpoint.
> >
> > I disagree that those are a regression. Those are certainly valid findings
> > and comments, but I don't see a specific regression based on what you've
> > said. If you are trying to state that the regression is "we now require ip
> > to be listed in identify_by in order to match using the IP endpoint
> > identifier" then that was the purpose of the patch itself and is not a
> > regression. I also don't think that the option to set it to an empty string
> > would have been user friendly, that's more of a side effect of how it was
> > coded. Having a specific option for IP only based matching is explicit.
> >
> 
> I accept that defining the identify_by option to list the methods the
> endpoint should be identified by is easy to document and conceptually
> simple.  To comply with that definition, for now, we can just add the "ip"
> value, the "header" value, and any other widget name down the road as
> needed.  Later we need to re-implement it to support dynamically added
> widget names.  I do not accept the unnecessary requirement that the
> type=identify method must be listed in the identify_by value when the user
> must explicitly specify the endpoint name for the type=identify method to
> even work.  The "ip" value in identify_by should just be documentation in
> this case.  Adding a needless source of configuration error by requiring
> the "ip" value to be listed does not help the user experience at all.  That
> requirement is the regression.

Yes, I think having it be dynamic based on the registration of the endpoint identifier would be a nice thing to have long term. I continue to disagree that the requirement is a regression. It's a behavior change and generally the PJSIP configuration is driven around being explicit in things. 
 
> The ASTERISK-27206 reporter's problem was to somehow stop the username
> identification method from recognizing the endpoint.  Setting the
> identify_by value to something that does not include "username" is all that
> is necessary.  Adding the requirement that the type=identify method be
> listed in the identify_by value to accept a match from the type=identify
> method goes too far.  It goes into the negative user experience realm.

The fact that setting it to "something" that does not include username is an implementation detail. I disagree that it's a negative user experience, it's an explicit decision which is easily documented and seen by anyone looking at the configuration.

> >
> >
> > Having a non-explicit option like you mentioned previously for identify_by
> > becomes a free for all on the other endpoint identifiers. If we encounter a
> > scenario where two "other" endpoint identifiers could match but only want
> > to match one then boom - we're back to the same scenario. You've just
> > enforced that two endpoint identifiers that are configurable in some way
> > can never match the same request even if for some reason they did if they
> > fall under the "other" option. If the answer is "don't configure things
> > them that way" then perhaps it isn't possible, we don't know. As well even
> > with your "none" or "other" you'd still need to list it in the identify_by
> > list, so I don't see how that's different than requiring "ip" to be there
> > except being less specific.
> >
> 
> The proposed "other" values are not a free for all and we are not back to
> the same scenario.  It is already known which identifiers do and do not
> need listing in the identify_by value.
> 
> * Adding a new identifier like "my_username" that does not have
> configuration to explicitly identify a specific endpoint has to be listed
> in the identify_by value.  Otherwise, there is no way to restrict which
> endpoints it identifies.  i.e., Which endpoint the "my_username" identifier
> matches is vague.
> 
> * Adding a new identifier like "my_ip" that does have configuration to
> explicitly identify a specific endpoint does not have to be listed in the
> identify_by value.  Listing "my_ip" in the identify_by value would just be
> for documentation purposes.  i.e., Which endpoint the "my_ip" identifier
> matches is specific.  It can match one and only one endpoint.
> 
> The "", "none", or "other" proposed value is a place holder which means not
> "username", "auth_username", or any other "my_username" type identifier.
> The proposed value is only needed if you explicitly did not want to
> identify the endpoint by "username", "auth_username", or any other
> "my_username" type identifier.  i.e., The "", "none", or "other" value
> would be the only thing in the list.  The "" value actually makes that
> point more explicit.

This makes things even more complicated to comprehend and explain to people.
 
> We currently can have many type=identifier identifiers match endpoint foo.
> There is no restriction on that.  However, doing so does point out a
> limitation in
> res/res_pjsip_endpoint_identifier.c:format_ami_endpoint_identify() which
> only handles the first type=identifier identifying endpoint foo.
> 
> 
> >
> > Approaching this from an end-user perspective who knows NOTHING of this
> > stuff having "ip" in the identify_by also makes logical sense. It's
> > explicit, you can understand what it means and you can understand what it
> > does. The use of "other" is vague and requires more thought and
> > investigation. The use of "none" is just downright confusing at first
> > glance unless you dive deeper into things.
> >
> 
> If you have preconceived notions of what the option means and the
> documentation does not disagree then yes it is easier to understand.
> However, until it supports dynamic widget names, that identify_by
> definition requires a third party creating their own identifier module to
> also modify Asterisk modules.

I think long term removing that requirement is a nice thing, but since we have created the PJSIP support no other individual has contributed an endpoint identifier module so I don't see it as a pressing thing or something that is a hindrance.

-- 
Joshua Colp
Digium, Inc. | Senior Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - US
Check us out at: www.digium.com & www.asterisk.org