Re: [netconf] [yang-doctors] Yangdoctors last call review of draft-ietf-netconf-subscribed-notifications-21

[Martin Bjorklund <[e-mail]>]

"Eric Voit (evoit)" <[e-mail]> wrote:
> > From: Martin Bjorklund, January 24, 2019 9:40 AM
> > 
> > "Eric Voit (evoit)" <[e-mail]> wrote:
> > > > From: Martin Bjorklund, January 24, 2019 8:17 AM
> > > >
> > > > "Eric Voit (evoit)" <[e-mail]> wrote:
> > > > > Hi Andy,
> > > > >
> > > > >
> > > > >
> > > > > Thanks very much for the thorough YANG Doctor review.  I have
> > > > > included the
> > > > agreed upon comments, and uploaded to:
> > > > >
> > > > > draft-ietf-netconf-subscribed-notifications-22
> > > > >
> > > > > a summary of the clarifications made is at the end of the document.
> > > > > Let me know if there anything else needed to conclude the YANG
> > > > > doctor review of this document.
> > > > >
> > > > >
> > > > >
> > > > > Also as the result of the ‘error-tag’ discussion with you and
> > > > > Martin, we need to perform the refinement of the ‘error-tag’
> > > > > mapping within both draft-ietf-netconf-netconf-event-notifications
> > Section
> > > > > 7, and draft-ietf-netconf-restconf-notif Section 3.3.   Directly
> > > > > below is some text and proposed error-tag mappings for those
> > > > > documents.
> > > > >
> > > > >
> > > > >
> > > > >     o  An "error-tag" node with the value being a string that
> > > > >
> > > > >        corresponds to an identity associated with the error.  This
> > > > >
> > > > >        "error-tag" will correspond to the error identities within
> > > > >
> > > > >        [I-D.draft-ietf-netconf-subscribed-notifications] section
> > > > >
> > > > >        2.4.6 for general subscription errors:
> > > > >
> > > > >
> > > > >
> > > > >           error identity         uses error-tag
> > > > >
> > > > >           ---------------------- --------------
> > > > >
> > > > >           dscp-unavailable       invalid-value
> > > >
> > > > Ok.  But it is not clear to me when this error is actually supposed
> > > > to be generated?  The leaf and identity have the same if-feature, so
> > > > it isn't a special errro code for "unsupported leaf", which is good!
> > > >
> > > > Then I have to assume it is supposed to be some kind of runtime error?
> > >
> > > Yes.  A publisher, nor the network to which is connects does not have
> > > to:
> > > (a) support all DSCP values, nor
> > > (b) allow a particular value requested by a particular subscriber, So
> > > this condition allows a publisher to reject a request for a DSCP value
> > > where is knows the value will not be respected.
> > 
> > Good explanation, I wish it was part of the "leaf dscp" in the module
> > :)
> > 
> > The dscp-unavailable identity doesn't add any addition value compared
> > to the
> > standard error.
> 
> For NETCONF and RESTCONF, this is the case.

And comi.  The point is, what makes the rpcs in this module so special
that they have to invent a new error reporting scheme?   If we do that
for these rpcs, why not for all other rpc in all other modules?


> > > > Thinking some more, what is supposed to happen if the client on the
> > > > same session sends first an establish-subscription with dscp 42, and
> > > > then another establish-subscription with dscp 10?
> > >
> > > This would be allowed.
> > 
> > On linux at least this is a sockopt, i.e., the option applies to the
> > socket, which
> > means all packets on the session.  So how is this supposed to be
> > implemented if
> > different messages on the session should have different dscp values?
> > Or is the
> > idea that you send the msg, flush all data from ssh/tls to tcp, then
> > flush the tcp
> > buffers (not that easy...)?
> > 
> > Even if there's just one establish-subscription with a dscp value,
> > since it applies
> > to the session it means that all normal rpcs on this session will get
> > the same
> > dscp value.  It is not clear that this is the intention?
> 
> For a NETCONF session, I agree that an implementation need not try to
> attempt to support more than one DSCP for that session.  And the error
> identity dscp-unavailable is a valid response here.

Then that should be explained (preferrably in the leaf dscp).

> For RESTCONF and other transports, there options which can more
> flexibly support different DSCP values.  This is one reason I was
> pushing hard in 2016 to leverage HTTP2.

We're talking about dynamic subscriptions here.  I don't think anyone
has suggested HTTP2 for dynamic subscriptions.

For configured subscriptions, this is not an issue, not even for
NETCONF.


/martin



> 
> Eric
> 
> > /martin
> > 
> > 
> > > The interesting part comes with bundling the event records.  The
> > > initial versions of draft-ietf-netconf-notification-messages required
> > > that all event records in a bundle had a common dscp.  At this point,
> > > that seems overly restrictive to the marshalling process, so for now
> > > that requirement is not in the document.
> > >
> > > > >           encoding-unsupported   invalid-value
> > > >
> > > > Ok.  But this identity doesn't give more information than the
> > > > standard
> > > > error:
> > > >
> > > >   error-tag: invalid-value
> > > >   error-path: /rpc/establish-subscription/encoding
> > > >
> > > >
> > > > >           filter-unavailable     invalid-value
> > > >
> > > > This is a "subscription-terminated-reason", which will never be sent
> > > > in an rpc- error, and thus should not be mapped to an error-tag.
> > >
> > > Yes, forgot to remove those.  It is now out.
> > >
> > > > >          filter-unsupported     invalid-value
> > > >
> > > > Ok.  But this identity doesn't give more information than the
> > > > standard
> > > > error:
> > > >
> > > >   error-tag: invalid-value
> > > >   error-path: /rpc/establish-subscription/stream-xpath-filter
> > > >
> > > >
> > > > >           insufficient-resources resource-denied
> > > >
> > > >
> > > > Ok.  But this identity doens't give more information than the
> > > > standard error in the case of establish-subscription and
> > > > modify-subscription.
> > > >
> > > > >           no-such-subscription   invalid-value
> > > >
> > > > Ok.  But this identity doens't give more information than the
> > > > standard error in the case of establish-subscription and
> > > > modify-subscription.
> > > >
> > > > >           replay-unsupported     operation-not-supported
> > > >
> > > > Ok.  But this identity doesn't give more information than the
> > > > standard error.
> > > >
> > > > >           stream-unavailable     invalid-value
> > > >
> > > > This is a "subscription-terminated-reason", which will never be sent
> > > > in an rpc- error, and thus should not be mapped to an error-tag.
> > >
> > > Yes, forgot to remove those.  It is now out.
> > >
> > > > >           suspension-timeout     operation-failed
> > > >
> > > > This is a "subscription-terminated-reason", which will never be sent
> > > > in an rpc- error, and thus should not be mapped to an error-tag.
> > >
> > > Yes, forgot to remove those.  It is now out.
> > >
> > > > >           unsupportable-volume   too-big
> > > >
> > > > This is a "subscription-terminated-reason", which will never be sent
> > > > in an rpc- error, and thus should not be mapped to an error-tag.
> > >
> > > Yes, forgot to remove those.  It is now out.
> > >
> > > > >        Or this "error-tag" will correspond to the error identities
> > > > >
> > > > >        within [I-D.ietf-netconf-yang-push] Appendix A.1 for
> > > > >
> > > > >        subscription errors specific to YANG datastores:
> > > > >
> > > > >
> > > > >
> > > > >           error identity              uses error-tag
> > > > >
> > > > >           ----------------------      --------------
> > > > >
> > > > >           cant-exclude                operation-not-supported
> > > > >
> > > > >           datastore-not-subscribable  operation-not-supported
> > > >
> > > > I think that this should be invalid-value.
> > >
> > > Ok
> > >
> > > /Eric
> > >
> > > > >           no-such-subscription-resync invalid-value
> > > >
> > > > Ok, but again the value of having this is unclear.
> > > >
> > > > >           on-change-unsupported       operation-not-supported
> > > > >
> > > > >           on-change-sync-unsupported  operation-not-supported
> > > > >
> > > > >           period-unsupported          invalid-value
> > > > >
> > > > >           update-too-big              too-big
> > > > >
> > > > >           sync-too-big                too-big
> > > > >
> > > > >           unchanging-selection        operation-failed
> > > >
> > > >
> > > >
> > > > /martin
> > > >
> > > >
> > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > Do you (or anyone else in this thread) have any suggestions on the
> > > > > text or proposed mappings?  If this turns out to be ok, Alex will
> > > > > need to remove the NETCONF error-tag specifics from
> > > > > draft-ietf-netconf-yang-push Sections 4.4.1 & 4.4.2
> > > > >
> > > > >
> > > > >
> > > > > Also Reshad will have to do some work because he is the YANG
> > > > > doctor of
> > > > netconf-netconf-event-notifications, and he will want to include the
> > > > same information within draft-ietf-netconf-restconf-notif.
> > > > >
> > > > >
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Eric
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > From: Andy Bierman <[e-mail]>
> > > > >
> > > > > Sent: Wednesday, January 23, 2019 12:42 PM
> > > > >
> > > > > To: Eric Voit (evoit) <[e-mail]>
> > > > >
> > > > > Cc: Martin Bjorklund <[e-mail]>; [e-mail];
> > > > > [e-mail];
> > > > > [e-mail]
> > > > >
> > > > > Subject: Re: [yang-doctors] Yangdoctors last call review of
> > > > > draft-ietf-netconf-subscribed-notifications-21
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > On Wed, Jan 23, 2019 at 4:35 AM Eric Voit (evoit)
> > > > > <mailto:[e-mail]>
> > > > wrote:
> > > > >
> > > > > > From: Martin Bjorklund, January 23, 2019 3:32 AM
> > > > >
> > > > > >
> > > > >
> > > > > > Hi,
> > > > >
> > > > > >
> > > > >
> > > > > > "Eric Voit (evoit)" <mailto:[e-mail]> wrote:
> > > > >
> > > > > > > Hi Andy,
> > > > >
> > > > > > >
> > > > >
> > > > > > > Looking at your proposal...  My reading is that it takes the
> > > > > > > transport
> > > > >
> > > > > > > specific error info contained in
> > > > >
> > > > > > > draft-ietf-netconf-netconf-event-notifications section 7, and
> > > > > > > then
> > > > >
> > > > > > > replicates that info within 12 separate description objects of
> > > > > > > the
> > > > >
> > > > > > > transport independent ietf-subscribed-notifications.yang.  The
> > > > > > > value
> > > > >
> > > > > > > you are asserting is that RFCs containing YANG models
> > > > > > > containing the
> > > > >
> > > > > > > rpc-stmt have traditionally document the
> > > > > > > mandatory-to-implement
> > > > >
> > > > > > > "error-tag" field within the model.  And presumably you are
> > > > > > > concerned
> > > > >
> > > > > > > that developers should not have to look elsewhere for this
> > > > >
> > > > > > > information.
> > > > >
> > > > > >
> > > > >
> > > > > > I think that maybe there are two separate issues here.
> > > > >
> > > > > >
> > > > >
> > > > > > The first issue is that for each error identity defined, there
> > > > > > needs to be a
> > > > >
> > > > > > mapping to the protocol-specific error handling.  Andy suggests
> > > > > > that this info is
> > > > >
> > > > > > added to this document, but currently this information is
> > > > > > available in the
> > > > >
> > > > > > protcol-mapping documents (netconf-notif and restconf-notif).
> > > > > > Personally, I
> > > > >
> > > > > > think that the current split of text between documents is fine.
> > > > >
> > > > > >
> > > > >
> > > > > > The second issue is that currently, both netconf-notif and
> > > > > > restconf-notif say
> > > > >
> > > > > > that *all* these errors use the error-tag "operation-failed".
> > > > > > Essentially it means
> > > > >
> > > > > > that we bypass the error handling in the protocols.  As Andy
> > > > > > points out below,
> > > > >
> > > > > > the error "insufficient-resources" should be mapped to
> > > > > > "resource-denied" in
> > > > >
> > > > > > NETCONF and RESTCONF (they mean the same thing).  So it might
> > > > > > make sense
> > > > >
> > > > > > to carefully go through the list of errors and map them to the
> > > > > > correct error-tag
> > > > >
> > > > > > (but specifiy this in the transport drafts).
> > > > >
> > > > >
> > > > >
> > > > > I am completely good with this.   Does this work for you Andy?
> > > > >
> > > > >
> > > > >
> > > > > This is better.
> > > > >
> > > > > I'm glad no other drafts are creating their own error reporting
> > > > > system for
> > > > each rpc-stmt.
> > > > >
> > > > > This is a bad precedent and likely to be skipped in implementations.
> > > > >
> > > > >
> > > > >
> > > > > Eric
> > > > >
> > > > >
> > > > >
> > > > > > /martin
> > > > >
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > > Andy
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > >
> > > > >
> > > > > >
> > > > >
> > > > > >
> > > > >
> > > > > > >
> > > > >
> > > > > > > If the YANG doctors require this, it can be inserted.  A
> > > > > > > similar text
> > > > >
> > > > > > > change would be needed for quite a few error identities within
> > > > > > > YANG
> > > > >
> > > > > > > Push.  Personally I don’t like that YANG models should be
> > > > > > > required to
> > > > >
> > > > > > > embed this information.  But I will make the change if you
> > > > > > > really want
> > > > >
> > > > > > > this, and nobody else objects.
> > > > >
> > > > > > >
> > > > >
> > > > > > > Other than that, I am not aware of any other open issues in
> > > > > > > the YANG
> > > > >
> > > > > > > Doctor review.  Do you know of anything else?
> > > > >
> > > > > > >
> > > > >
> > > > > > > Eric
> > > > >
> > > > > > >
> > > > >
> > > > > > >
> > > > >
> > > > > > > From: Andy Bierman, January 21, 2019 2:26 PM
> > > > >
> > > > > > >
> > > > >
> > > > > > > Hi,
> > > > >
> > > > > > >
> > > > >
> > > > > > > I think the error-tag issue can be resolved by including 1
> > > > > > > extra
> > > > >
> > > > > > > sentence in each error identity.
> > > > >
> > > > > > > I know this is NETCONF and RESTCONF centric but those are the
> > > > > > > only
> > > > > > > 2
> > > > >
> > > > > > > standard protocols supported for the YANG language right now.
> > > > >
> > > > > > >
> > > > >
> > > > > > >        If the 'error-tag' field is used in error reporting,
> > > > >
> > > > > > >        then the value '<correct error-tag>' MUST be used.
> > > > >
> > > > > > >
> > > > >
> > > > > > > For example:
> > > > >
> > > > > > >
> > > > >
> > > > > > >
> > > > >
> > > > > > > OLD:
> > > > >
> > > > > > >
> > > > >
> > > > > > >   identity insufficient-resources {
> > > > >
> > > > > > >     base establish-subscription-error;
> > > > >
> > > > > > >     base modify-subscription-error;
> > > > >
> > > > > > >     base subscription-suspended-reason;
> > > > >
> > > > > > >     description
> > > > >
> > > > > > >       "The publisher has insufficient resources to support the
> > > > >
> > > > > > >        requested subscription.  An example might be that
> > > > > > > allocated CPU
> > > > >
> > > > > > >        is too limited to generate the desired set of
> > > > > > > notification
> > > > >
> > > > > > >        messages.";
> > > > >
> > > > > > >   }
> > > > >
> > > > > > >
> > > > >
> > > > > > >
> > > > >
> > > > > > > NEW:
> > > > >
> > > > > > >
> > > > >
> > > > > > >   identity insufficient-resources {
> > > > >
> > > > > > >     base establish-subscription-error;
> > > > >
> > > > > > >     base modify-subscription-error;
> > > > >
> > > > > > >     base subscription-suspended-reason;
> > > > >
> > > > > > >     description
> > > > >
> > > > > > >       "The publisher has insufficient resources to support the
> > > > >
> > > > > > >        requested subscription.  An example might be that
> > > > > > > allocated CPU
> > > > >
> > > > > > >        is too limited to generate the desired set of
> > > > > > > notification
> > > > >
> > > > > > >        messages. If the 'error-tag' field is used in error
> > > > > > > reporting,
> > > > >
> > > > > > >        then the value 'resource-denied' MUST be used.";
> > > > >
> > > > > > >   }
> > > > >
> > > > > > >
> > > > >
> > > > > > >
> > > > >
> > > > > > > Andy
> > > > >
> > > > > > >
> > > > >
> > > > > > >
> > > > >
> > > > > > > On Fri, Jan 18, 2019 at 11:53 AM Eric Voit (evoit)
> > > > >
> > > > > > > <mailto:[e-mail]<mailto:mailto:[e-mail]>> wrote:
> > > > >
> > > > > > > Hi Andy,
> > > > >
> > > > > > >
> > > > >
> > > > > > > Thanks.  I have incorporated items where there was agreement.
> > > > > > > I have
> > > > >
> > > > > > > removed the items below where you were ok.
> > > > >
> > > > > > >
> > > > >
> > > > > > > Remaining below are the open items, with responses.
> > > > >
> > > > > > >
> > > > >
> > > > > > > > >    Should be clear somewhere that
> > > > >
> > > > > > > > >    suspend is for CPU and other resources, and NACM not
> > > > > > > > > considered
> > > > >
> > > > > > > > >    to be a resource.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > If NACM is active, it needs to be followed.  The text we
> > > > > > > > have for
> > > > >
> > > > > > > > NACM is in Section 5.4.  Do you see something else specific
> > > > > > > > to
> > > > >
> > > > > > > > subscription suspension needed here?  (Maybe I am not
> > > > > > > > getting your
> > > > >
> > > > > > > > point.)
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > No -- OK to leave NACM as terminate-if-loss-of-rights (Is
> > > > > > > > there an
> > > > >
> > > > > > > > error identity for this event?)
> > > > >
> > > > > > >
> > > > >
> > > > > > > The identity which applies here is "stream-unavailable".  This
> > > > > > > is the
> > > > >
> > > > > > > same identity which would be used if a subscriber had never
> > > > > > > sufficient
> > > > >
> > > > > > > permissions in the first place.  I don't believe we would want
> > > > > > > to
> > > > >
> > > > > > > return an identity specific to when NACM when permissions have
> > > > > > > just
> > > > >
> > > > > > > been changed.
> > > > >
> > > > > > >
> > > > >
> > > > > > > > > I3) sec 2.1 para 6:
> > > > >
> > > > > > > > >    Event records MUST NOT be delivered to a receiver in a
> > > > > > > > > different
> > > > >
> > > > > > > > >    order than they were placed onto an event stream.
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >   -- does this apply to subscription-state? Think not,
> > > > > > > > > they are not events
> > > > >
> > > > > > > > >     placed in event stream.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > Agree that they are not on the event stream.  So they do not
> > > > > > > > violate
> > > > >
> > > > > > > > this requirement.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > Additionally there is supporting text in "Section 2.7:
> > > > > > > > subscription
> > > > >
> > > > > > > > state notifications", including...
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > " Instead, they are inserted (as defined in this section)
> > > > > > > > within the
> > > > >
> > > > > > > > sequence of notification messages sent to a particular
> > > > > > > > receiver."
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > >     Need to allow ended or suspended to be sent
> > > > >
> > > > > > > > >     head-of-line whenever state changes
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > I am not sure that suspended should always be sent head-of-line.
> > > > >
> > > > > > > > Consider
> > > > >
> > > > > > > > that implementation might want to let the existing queue of
> > > > > > > > filtered
> > > > >
> > > > > > > > event records be sent if is filter complexity causing the CPU
> > > > > > > > issue.
> > > > >
> > > > > > > > That could be different than if it is a bandwidth issue
> > > > > > > > driving the
> > > > >
> > > > > > > > suspension, and you definitely want the 'subscription-suspended'
> > > > > > > > to
> > > > >
> > > > > > > > be placed at the head of line.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > It is up to the publisher to decide when to stop sending
> > > > > > > > events on a
> > > > >
> > > > > > > > subscription.
> > > > >
> > > > > > > > Obviously the publisher cannot wait until the subscription is
> > > > > > > > idle.
> > > > >
> > > > > > > > The reason it is getting suspended is it is far from idle
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > So also up to the publisher wrt/ what to do with any events
> > > > > > > > that
> > > > >
> > > > > > > > have not been delivered yet on a subscription.  Could delete
> > > > > > > > them or
> > > > >
> > > > > > > > save them for when more bandwidth available (for example)
> > > > >
> > > > > > >
> > > > >
> > > > > > > Agree fully with this.  Is there text required in the draft here?
> > > > >
> > > > > > >
> > > > >
> > > > > > > ...
> > > > >
> > > > > > > > Beyond that it is up to the implementation to decide if some
> > > > >
> > > > > > > > un-transmitted queue of event records should be flushed and
> > > > >
> > > > > > > > reprocessed based on the modification.  I do not expect this
> > > > > > > > would
> > > > >
> > > > > > > > popular, as a replay subscription could accomplish this same
> > > > >
> > > > > > > > functional need.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > Agreed that an implementation can drop at any time and
> > > > > > > > increment the
> > > > >
> > > > > > > > appropriate counters. It will try to to do this, but no
> > > > > > > > requirements
> > > > >
> > > > > > > > except maybe subscription events like 'replay-completed'
> > > > > > > > cannot be
> > > > >
> > > > > > > > dropped
> > > > >
> > > > > > >
> > > > >
> > > > > > > Have put a minor tweak into Section 2.7:
> > > > >
> > > > > > >
> > > > >
> > > > > > > [old]  subscription state change notifications cannot be
> > > > > > > filtered out
> > > > >
> > > > > > >
> > > > >
> > > > > > > [new] subscription state change notifications cannot be
> > > > > > > dropped or
> > > > >
> > > > > > > filtered out
> > > > >
> > > > > > >
> > > > >
> > > > > > > ...
> > > > >
> > > > > > > > Thinking more on your point, it might be worth tweaking a
> > > > > > > > couple
> > > > >
> > > > > > > > words to allow for head-of-line placement of
> > > > >
> > > > > > > > "subscription-suspended".
> > > > >
> > > > > > > >
> > > > >
> > > > > > > >    "Subscribed event records queued for sending after the
> > > > > > > > issuance of
> > > > >
> > > > > > > >    this
> > > > >
> > > > > > > >    subscription state change notification may now be sent."
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > Are you good with this suggested change?
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > Not sure -- it needs to be clear that subscription-suspended
> > > > > > > > is the
> > > > >
> > > > > > > > last event sent before suspending and subscription-resumed
> > > > > > > > is the
> > > > >
> > > > > > > > first event sent after transition from suspended to active.
> > > > >
> > > > > > > > The next event could also be subscription-terminated.
> > > > >
> > > > > > >
> > > > >
> > > > > > > I do think this possibility is covered in the text.  For
> > > > > > > Section
> > > > > > > 2.7.4
> > > > >
> > > > > > > subscription-suspended the current text is:
> > > > >
> > > > > > >
> > > > >
> > > > > > > "No further notification will be sent until the subscription
> > > > > > > resumes
> > > > >
> > > > > > > or is terminated."
> > > > >
> > > > > > >
> > > > >
> > > > > > > And Section 2.7.5 subscription-resumed says":
> > > > >
> > > > > > > "Subscribed event records generated after the issuance of this
> > > > >
> > > > > > > subscription state change notification may now be sent."
> > > > >
> > > > > > >
> > > > >
> > > > > > > Based on the discussion, I can make it:
> > > > >
> > > > > > >
> > > > >
> > > > > > > "Subscribed event records are again permitted to be sent
> > > > > > > following
> > > > >
> > > > > > > this subscription state change notification."
> > > > >
> > > > > > >
> > > > >
> > > > > > > Is this sufficient for you?
> > > > >
> > > > > > >
> > > > >
> > > > > > > ...
> > > > >
> > > > > > > > > I4) sec 2.4.6: RPC Failures
> > > > >
> > > > > > > > >   -- concern about a subscription-specific error reporting
> > > > > > > > > system
> > > > >
> > > > > > > > >      must make sure protocol error reporting system is
> > > > > > > > > used
> > > > >
> > > > > > > > > correctly
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > Yes.  We have done our best to integrate with the embedded
> > > > > > > > NETCONF
> > > > >
> > > > > > > > and RESTCONF mechanisms.  There is much additional
> > > > > > > > information in
> > > > >
> > > > > > > > the transport drafts here.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > >   -- The error-tag value needs to be identified for each
> > > > > > > > >   -- 'reason'
> > > > >
> > > > > > > > > identity
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > This is done in the transport drafts.  E.g., see
> > > > >
> > > > > > > > draft-ietf-netconf-netconf-event-
> > > > >
> > > > > > > > notifications Section 7
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > I do not agree this is a good idea.
> > > > >
> > > > > > > > Each error identity should simply state the required "error-tag"
> > > > >
> > > > > > > > that is associated with the error.  This is expected of
> > > > > > > > protocol
> > > > >
> > > > > > > > operations that are added to NETCONF and RESTCONF.
> > > > >
> > > > > > >
> > > > >
> > > > > > > In draft-ietf-netconf-netconf-event-notifications, section 7,
> > > > > > > the
> > > > >
> > > > > > > required "error-tag" is identified as "operation-failed".  If
> > > > > > > we
> > > > >
> > > > > > > instead placed that "error-tag" information in the YANG model,
> > > > > > > then we
> > > > >
> > > > > > > have tied the YANG model to the RESTCONF and NETCONF transports.
> > > > >
> > > > > > >
> > > > >
> > > > > > > > Both NETCONF and RESTCONF use a compatible error reporting
> > > > > > > > data
> > > > >
> > > > > > > > structure.
> > > > >
> > > > > > > > The "error-tag" is used in both of them.  IMO client
> > > > > > > > developers do
> > > > >
> > > > > > > > not want a different set of error codes for the same error
> > > > > > > > conditions.
> > > > >
> > > > > > >
> > > > >
> > > > > > > draft-ietf-netconf-restconf-notif Section 3.3 also requires an
> > > > >
> > > > > > > "error-tag" node of "operation-failed".  So we used the
> > > > > > > transport
> > > > >
> > > > > > > drafts rather than the YANG model to support the same error
> > > > > > > codes for
> > > > >
> > > > > > > the same error conditions.
> > > > >
> > > > > > >
> > > > >
> > > > > > > > I agree that transport drafts could define their own error
> > > > >
> > > > > > > > identities, which would document the expected error-tag there.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > >    2.  "modify-subscription-stream-error-info": This MUST
> > > > > > > > > be returned
> > > > >
> > > > > > > > >        with the leaf "reason" populated if an RPC error
> > > > > > > > > reason has not
> > > > >
> > > > > > > > >        been placed elsewhere within the transport portion
> > > > > > > > > of a failed
> > > > >
> > > > > > > > >        "modify-subscription" RPC response.  This MUST be
> > > > > > > > > sent if
> > > > >
> > > > > > > > > hints
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >   -- all 3 paragraphs like this; unclear what "placed
> > > > > > > > >   -- elsewhere"
> > > > >
> > > > > > > > >       text means; not appropriate for MUST;
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > Instead of "placed elsewhere", how about: "placed in
> > > > > > > > subscription
> > > > >
> > > > > > > > transport document defined object".  Would this be sufficient?
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > No -- NETCONF and RESTCONF have well-defined error reporting.
> > > > >
> > > > > > > > The server requirements for this error reporting must be
> > documented.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > I agree with the following approach:
> > > > >
> > > > > > > >   - each operation MUST identify the error-tags that are
> > > > > > > > expected for
> > > > >
> > > > > > > >     various error conditions (such s is done in RFC 6241)
> > > > >
> > > > > > > >   - the server MUST return the specified error-tags. If a
> > > > > > > > condition not
> > > > >
> > > > > > > >   - explicitly
> > > > >
> > > > > > > >     defined then the server MUST pick the appropriate
> > > > > > > > error-tag from RFC
> > > > >
> > > > > > > >     6241
> > > > >
> > > > > > > >  - the server MAY include the specified rc:yang-data in the
> > > > >
> > > > > > > > <error-info>
> > > > >
> > > > > > > >  - data
> > > > >
> > > > > > > > structure
> > > > >
> > > > > > > >  - the server MUST use the appropriate rc:yang-data to
> > > > > > > > report hints
> > > > >
> > > > > > > >  - for protocols other than NETCONF and RESTCONF, they can
> > > > > > > > map
> > > > >
> > > > > > > > error-tag
> > > > >
> > > > > > > >  - or
> > > > >
> > > > > > > > ignore it,
> > > > >
> > > > > > > >    but the document defining the protocol operation MUST
> > > > > > > > provide
> > > > >
> > > > > > >
> > > > >
> > > > > > > Functionally, everything you ask for is fully covered when you
> > > > > > > include
> > > > >
> > > > > > > consider draft-ietf-netconf-netconf-event-notifications
> > > > > > > (section
> > > > > > > 7)
> > > > >
> > > > > > > and draft-ietf-netconf-restconf-notif (section 3.3).
> > > > >
> > > > > > >
> > > > >
> > > > > > > My read of the issue is that you believe "error-tag" must be
> > > > > > > specified
> > > > >
> > > > > > > in the YANG model.  I believe that "error-tag" shouldn't be in
> > > > > > > the
> > > > >
> > > > > > > YANG model because that would tie the model to a transport type.
> > > > >
> > > > > > >
> > > > >
> > > > > > > Any thoughts on how we might close this?  If absolutely
> > > > > > > required I
> > > > >
> > > > > > > could place a new comment line in the YANG model under
> > > > >
> > > > > > > /* Identities for RPC and Notification errors */
> > > > >
> > > > > > >
> > > > >
> > > > > > > The comment would be something like:
> > > > >
> > > > > > > /* When used with NETCONF and RESTCONF RPCs:
> > > > >
> > > > > > >     "error-type" node to be used is "application"
> > > > >
> > > > > > >      "error-tag" must be "operation-failed".  */
> > > > >
> > > > > > >
> > > > >
> > > > > > > This seems incongruous.  Just throwing it out as a suggestion.
> > > > >
> > > > > > >
> > > > >
> > > > > > > > In any case, the -v21 wording results from the attempted
> > > > > > > > balancing
> > > > >
> > > > > > > > the WG requests for:
> > > > >
> > > > > > > > * merging with transport protocol error mechanisms
> > > > >
> > > > > > > > * WG leadership guidance to provide requirements for
> > > > > > > > transport
> > > > >
> > > > > > > > documents
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > >      Only 3 fields seem
> > > > >
> > > > > > > > >       to be relevant (error-tag, error-app-tag, error-info).
> > > > >
> > > > > > > > >       Protcol operations are expected to document server
> > > > > > > > > requirements
> > > > >
> > > > > > > > >       for these 3 fields, if applicable.  Only the
> > > > > > > > > error-tag
> > > > >
> > > > > > > > >       is mandatory-to-use.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > Hopefully these are covered sufficiently when this document
> > > > > > > > is
> > > > >
> > > > > > > > coupled with the NETCONF and RESTCONF Notif transport
> > documents.
> > > > >
> > > > > > > > For other transports, the tags you identify about would not
> > > > > > > > be
> > > > >
> > > > > > > > applicable.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > >   -- the error assignments are extremely specific. e.g.,
> > > > > > > > > it is not
> > > > >
> > > > > > > > >      possible for <kill-subscription> to fail with an
> > > > >
> > > > > > > > >      'insufficient-resources' error;
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > This is the intent of the base specification, e.g., we don't
> > > > > > > > believe
> > > > >
> > > > > > > > a
> > > > >
> > > > > > > > kill-
> > > > >
> > > > > > > > subscription should fail for an insufficient-resources reason.
> > > > > > > > But
> > > > >
> > > > > > > > vendors might desire more specificity.  As a result is
> > > > > > > > certainly ok
> > > > >
> > > > > > > > for vendor implementations to add new error identities.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > IMO anything can fail for insufficient resources. That is
> > > > > > > > very
> > > > >
> > > > > > > > implementation-
> > > > >
> > > > > > > > specific.
> > > > >
> > > > > > >
> > > > >
> > > > > > > Instead of implementation specific I would call it application
> > > > >
> > > > > > > specific.  Right now we don't have a catch-all error-identity
> > > > > > > of
> > > > >
> > > > > > > 'other-error'.  We preferred that error conditions beyond the
> > > > > > > current
> > > > >
> > > > > > > ones listed could be included by vendors as needed.  Further
> > > > >
> > > > > > > deployment experience could result in new error identities
> > > > > > > surfacing
> > > > >
> > > > > > > for standardization should this draft catch on.
> > > > >
> > > > > > >
> > > > >
> > > > > > > > >      Do not agree that scoping each
> > > > >
> > > > > > > > >      identity to specific RPC operations is a good idea.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > This level of specificity was not the author's original plans.
> > > > > > > > Nor
> > > > >
> > > > > > > > was this level of specificity part of earlier draft versions
> > > > > > > > up
> > > > >
> > > > > > > > through -v08.  However members of the WG made it clear that
> > > > > > > > such
> > > > >
> > > > > > > > specificity was necessary for draft progression.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > >   -- how are errors in these parameters reported for
> > > > > > > > > configured
> > > > >
> > > > > > > > >      subscriptions when <edit-config> is the RPC that has the
> > > > > > > > >      error?
> > > > >
> > > > > > > > >      How are the yang-data structs used for edit-config or
> > > > > > > > > commit
> > > > errors?
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > None of these yang-data structures are specified for use
> > > > > > > > with
> > > > >
> > > > > > > > <edit-config> operations.  For <edit-config>, the change to
> > > > > > > > a
> > > > >
> > > > > > > > configured subscription would be written to the datastore if
> > > > > > > > it were
> > > > >
> > > > > > > > semantically valid.  At this point the subscription enters
> > > > > > > > the
> > > > >
> > > > > > > > [evaluate] points of Figure 8.  Issues from this point out
> > > > > > > > would be
> > > > >
> > > > > > > > reported with a vendor specific construct such as SYSLOG.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > So how are hints reported for configured subscriptions?
> > > > >
> > > > > > >
> > > > >
> > > > > > > There is nothing in the specification which requires this.  An
> > > > >
> > > > > > > implementation could choose to place these in some form of SYSLOG.
> > > > >
> > > > > > > ...
> > > > >
> > > > > > > > > I6) sec 2.5, para 3:
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >    On a receiver of a
> > > > >
> > > > > > > > >    configured subscription, support for dynamic
> > > > > > > > > subscriptions is
> > > > >
> > > > > > > > >    optional except where replaying missed event records is
> > > > > > > > >    required.
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >   -- confusing because text in 1.3:
> > > > >
> > > > > > > > >      Note that there is no mixing-and-matching of dynamic
> > > > > > > > > and configured
> > > > >
> > > > > > > > >      operations on a single subscription.  Specifically, a
> > > > > > > > > configured
> > > > >
> > > > > > > > >   -- clarify the receiver may have multiple subscriptions
> > > > > > > > > here
> > > > >
> > > > > > > > >   -- not clear what "except where replaying..." text means
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > How about the following tweak:
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > "On a receiver of a configured subscription, support for
> > > > > > > > dynamic
> > > > >
> > > > > > > > subscriptions is optional.  However if replaying missed
> > > > > > > > event
> > > > >
> > > > > > > > records is required for a configured subscription, support
> > > > > > > > for
> > > > >
> > > > > > > > dynamic subscription is highly recommended.  In this case, a
> > > > >
> > > > > > > > separate dynamic subscription can be established to
> > > > > > > > retransmit the
> > > > >
> > > > > > > > missing event records."
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > OK
> > > > >
> > > > > > >
> > > > >
> > > > > > > Change made.
> > > > >
> > > > > > >
> > > > >
> > > > > > > > > I7) leaf stream-xpath-filter: [multiple uses]
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >            The expression is evaluated in the following XPath
> > > > > > > > >            context:
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >              o The set of namespace declarations is the set of
> > > > > > > > >              prefix
> > > > >
> > > > > > > > >                  and namespace pairs for all YANG modules
> > > > > > > > > implemented
> > > > >
> > > > > > > > >                  by the server, where the prefix is the
> > > > > > > > > YANG module
> > > > >
> > > > > > > > >                  name and the namespace is as defined by
> > > > > > > > > the
> > > > >
> > > > > > > > >                  'namespace' statement in the YANG module.
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >   -- This prefix processing is not done anywhere else in
> > > > > > > > > NETCONF
> > > > >
> > > > > > > > >      or RESTCONF.  IMO a bad precedent.  Only the XML
> > > > > > > > > prefixes
> > > > >
> > > > > > > > >      should be required for processing of XML encoding.
> > > > > > > > > YANG
> > > > >
> > > > > > > > >      module prefixes are not required to be unique, unlike
> > > > >
> > > > > > > > >      the prefix mappings in XML
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > This text was proposed by Martin as a result of the "xpath
> > > > >
> > > > > > > > expressions in JSON"
> > > > >
> > > > > > > > thread last October in NETMOD.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > I am happy to incorporate whatever text is appropriate.  I
> > > > > > > > was
> > > > >
> > > > > > > > hoping that the suggested text was sufficient for now.  Kent
> > > > > > > > has
> > > > >
> > > > > > > > already incorporated this as an issue for yang-next
> > > > >
> > > > > > > > https://github.com/netmod-wg/yang-next/issues/55
> > > > >
> > > > > > > > So hopefully there is no final precedent being claimed.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > I do not agree that this YANG module should define a new way
> > > > > > > > to
> > > > >
> > > > > > > > encode XPath into XML instance documents. This will require
> > > > >
> > > > > > > > significant changes to server implementations.  YANG module
> > > > > > > > prefixes
> > > > >
> > > > > > > > are not even required to be unique so the set of prefixes
> > > > > > > > used by
> > > > >
> > > > > > > > the server in XML instance documents may be different, since
> > > > > > > > it must
> > > > >
> > > > > > > > be unique.
> > > > >
> > > > > > >
> > > > >
> > > > > > > See next note
> > > > >
> > > > > > >
> > > > >
> > > > > > > > >   -- NMDA allows the same module to appear in multiple
> > > > > > > > > module-sets
> > > > >
> > > > > > > > >      and different in each datastore. This text about
> > > > > > > > > "implemented by
> > > > >
> > > > > > > > >      the server" does not work for NMDA
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > I am happy to adopt whatever text meets YANG doctor approval.
> > > > > > > > Can
> > > > >
> > > > > > > > you suggest?
> > > > >
> > > > > > > >
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > Remove all text about YANG prefixes and continue using XML
> > > > > > > > encoding
> > > > >
> > > > > > > > without modification
> > > > >
> > > > > > >
> > > > >
> > > > > > > As a different YANG doctor has required the current text
> > > > > > > modification,
> > > > >
> > > > > > > I believe this is a blocker.  What is the process for YANG
> > > > > > > model
> > > > >
> > > > > > > reviews in such a case.  I am happy to accept whatever here.
> > > > > > > Any
> > > > >
> > > > > > > suggestions on next steps?
> > > > >
> > > > > > >
> > > > >
> > > > > > > ...
> > > > >
> > > > > > > > >   -- there should be an example of a configurable encoding
> > > > >
> > > > > > > > > provided
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > I am happy to enhance the definition YANG model's identity
> > > > >
> > > > > > > > definition of "configurable-encoding".  I could do this by
> > > > > > > > adding
> > > > >
> > > > > > > > the following additional text to the description: "An
> > > > > > > > example of a
> > > > >
> > > > > > > > configurable encoding might be a new identity such as
> > > > > > > > 'encode-cbor'.
> > > > >
> > > > > > > > Such an identity could use
> > > > >
> > > > > > > > 'configurable-
> > > > >
> > > > > > > > encoding' as its base.  This would allow a dynamic
> > > > > > > > subscription
> > > > >
> > > > > > > > encoded in JSON [RFC-8259] to request notification messages
> > > > > > > > be
> > > > >
> > > > > > > > encoded via CBOR [RFC- 7049].  Further details for any
> > > > > > > > specific
> > > > >
> > > > > > > > configurable encoding would be explored in a transport
> > > > > > > > document
> > > > >
> > > > > > > > based on this specification."  Does this meet your ask?
> > > > >
> > > > > > > >
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > OK
> > > > >
> > > > > > >
> > > > >
> > > > > > > Added
> > > > >
> > > > > > >
> > > > >
> > > > > > > > > I11) extension subscription-state-notification {
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >        This statement is not for use
> > > > >
> > > > > > > > >        outside of this YANG module.";
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >   -- this text should be removed. There is no value in
> > > > > > > > > limiting
> > > > >
> > > > > > > > >      the scope of this extension.  It prevents even this
> > > > > > > > > WG from
> > > > >
> > > > > > > > >      creating a module that uses the extension again.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > This was the subject of significant debate in the WG.  The
> > > > > > > > authors
> > > > >
> > > > > > > > did not want this restriction either.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > To be allowed to progress the document, we inserted the
> > > > > > > > document.
> > > > >
> > > > > > > > If this really is mandatory-to-remove from a YANG doctor
> > > > >
> > > > > > > > point-of-view, what is the process for quick closure on this
> > > > > > > > issue
> > > > >
> > > > > > > > between WG leadership and the YANG doctors?
> > > > >
> > > > > > > >
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > The YANG language makes no restrictions about exporting
> > statements.
> > > > >
> > > > > > > > I guess I missed that debate so I will just say OK and
> > > > > > > > wonder what
> > > > >
> > > > > > > > problem this is supposed to solve. I guess the WG wants to
> > > > > > > > give YANG
> > > > >
> > > > > > > > Doctors more things to check. (This is what we called a CLR
> > > > > > > > in
> > > > >
> > > > > > > > SNMP-land ;-)
> > > > >
> > > > > > >
> > > > >
> > > > > > > Thanks.  No action taken.
> > > > >
> > > > > > >
> > > > >
> > > > > > > > > I13)   notification subscription-started {
> > > > >
> > > > > > > > >     sn:subscription-state-notification;
> > > > >
> > > > > > > > >     if-feature "configured";
> > > > >
> > > > > > > > >     description
> > > > >
> > > > > > > > >       "This notification indicates that a subscription has
> > > > > > > > > started and
> > > > >
> > > > > > > > >         notifications are beginning to be sent. This
> > > > > > > > > notification shall
> > > > >
> > > > > > > > >        only be sent to receivers of a subscription; it
> > > > > > > > > does not
> > > > >
> > > > > > > > >        constitute a general-purpose notification.";
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >   -- 2nd sentence is confusing; all notifications are sent
> > > > > > > > > to
> > > > >
> > > > > > > > >      receivers of a subscription. last part is redundant
> > > > > > > > > since
> > > > >
> > > > > > > > >      the sn:subscription-state-notification extension is
> > > > > > > > > used
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > There is no issue with removing this second sentence completely.
> > > > > > > > If
> > > > >
> > > > > > > > I did that, would this address your concern?
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > OK
> > > > >
> > > > > > >
> > > > >
> > > > > > > Done
> > > > >
> > > > > > >
> > > > >
> > > > > > > > > I14)   rc:yang-data modify-subscription-stream-error-info {
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >       leaf filter-failure-hint {
> > > > >
> > > > > > > > >         type string;
> > > > >
> > > > > > > > >           description
> > > > >
> > > > > > > > >             "Information describing where and/or why a
> > > > > > > > > provided filter
> > > > >
> > > > > > > > >              was unsupportable for a subscription.";
> > > > >
> > > > > > > > >       }
> > > > >
> > > > > > > > >
> > > > >
> > > > > > > > >   -- rpc-error already allows more precise error reporting
> > > > >
> > > > > > > > >      It uses error-tag, error-path, error-string, and
> > > > > > > > > error-info
> > > > >
> > > > > > > > >      extensions
> > > > >
> > > > > > > > >      to identify which parameters/conditions caused the
> > > > > > > > > RPC to be
> > > > >
> > > > > > > > >      rejected.
> > > > >
> > > > > > > > >      This error reporting will continue to be used, Not
> > > > > > > > > sure this
> > > > >
> > > > > > > > >      failure-hint
> > > > >
> > > > > > > > >      has any standards value. Perhaps real-use example can
> > > > > > > > > be
> > > > >
> > > > > > > > > added
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > Per your thoughts on rpc-error...  For NETCONF and RESTCONF,
> > > > > > > > you
> > > > >
> > > > > > > > point to error structures which historically been used with
> > > > > > > > those
> > > > >
> > > > > > > > transports.
> > > > >
> > > > > > > > Of course
> > > > >
> > > > > > > > we were looking to have all subscription hints supportable
> > > > > > > > across
> > > > >
> > > > > > > > transports via a single portable YANG data structure.  So
> > > > > > > > the value
> > > > >
> > > > > > > > is that a single string object exists so to transport
> > > > > > > > whatever the
> > > > >
> > > > > > > > vendor thinks would be useful as a hint in this case.  I.e.,
> > > > > > > > there
> > > > >
> > > > > > > > has been no attempt to standardize the contents of this string.
> > > > > > > > If
> > > > >
> > > > > > > > operational experiences drive a desire for such structuring,
> > > > > > > > this
> > > > >
> > > > > > > > could provide the basis for a new draft building off of this
> > > > >
> > > > > > > > starting point.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > I guess I do not consider NETCONF and RESTCONF "historic" quite
> > yet.
> > > > >
> > > > > > > > There are many implementations using the rpc-error reporting
> > > > > > > > with no
> > > > >
> > > > > > > > intent to replace it with something else.
> > > > >
> > > > > > > >
> > > > >
> > > > > > > > I was just asking for an example, since I have no idea what
> > > > > > > > an
> > > > >
> > > > > > > > implementor would put in this leaf.
> > > > >
> > > > > > >
> > > > >
> > > > > > > Here is an example from our implementation.  Say you mistype
> > > > > > > an extra
> > > > >
> > > > > > > "\" to an xpath filter:
> > > > >
> > > > > > > /if:interfaces-state/interface[name="GigabitEthernet0/0"]/oper
> > > > > > > -sta
> > > > > > > tus
> > > > >
> > > > > > > As a result, the filter is passed to the publisher is:
> > > > >
> > > > > > > /if:inte\rfaces-state/interface[name="GigabitEthernet0/0"]/ope
> > > > > > > r-st
> > > > > > > atus
> > > > >
> > > > > > >
> > > > >
> > > > > > > What we would return in the failure-hint string is:
> > > > >
> > > > > > > Invalid expression: offset(9) in
> > > > >
> > > > > > > '/if:inte\rfaces-state/interface[name="GigabitEthernet0/0"]/oper-
> > status'
> > > > >
> > > > > > >
> > > > >
> > > > > > > Eric
> > > > >
> > > > > > >
> > > > >
> > > > > > > > Andy