unclear on shared lock support

[John Meissen]

Julian Reschke wrote:
> 
> Joe Orton wrote:
> 
> > On Mon, Nov 03, 2008 at 11:50:08PM -0800, John Meissen wrote:
> >> I consider shared vs exclusive to be a lock attribute. There are other
> >> requested attributes, like timeout, that a server is free to ignore.
> >> I interpreted the RFC as allowing me to ignore the request to make the
> >> lock shared, and permitting me to create the lock in the mode I support
> >> (exclusive), especially since the actual lock characteristics are 
> >> detailed in the response body. Hence there shouldn't be any confusion
> >> on the client's part since it can see what type of lock was created.
> > 
> > Hmmm, interesting.
> > 
> > I agree that neon/litmus should check that the lock returned by LOCK 
> > matches the lock type requested, and fail/skip subsequent shared lock 
> > tests appropriately.
> > 
> > But I don't agree that it's a valid interpretation of 4918 to downgrade 
> > the lock type from exclusive to shared.  There is specific language in 
> > 4918 explaining that the timeout is a "suggestion" made by the client - 
> > there is no such language in the section on the lock type.
> 
> Right.
> 
> > If you can get consensus on the DAV list (w3c-dist-auth at w3.org) that 
> > this behaviour is to be permitted then I'll update litmus to SKIP rather 
> > than FAIL if the shared lock request is downgraded.
> 
> No, I don't think this would be correct.
> 
> If a server doesn't allow shared locks, it should reject the request. 
> That's it.
> 
> And yes, making Litmus smarter with respect to shared lock functionality 
> would be good.
> 
> Best regards, Julian
> 

On the other hand, while there is explicit language detailing what other
conditions constitute failure there is nothing about shared vs exclusive.
And it's not clear to me that any of the listed potential responses would
fit such a failure.

Conceptually, the server is being asked to lock a resource and also allow
other clients to lock it. I'm willing to grant a lock to this client, but
I won't allow other clients to also lock it.

If a client cared about the lock scope they would retrieve the 
lockdiscovery property first to find out whether shared locks are
supported. I suspect that most clients will neither note nor care about 
this distinction, and would only be aware that they were unable to lock
the resource (as I encountered with litmus).

I real-world situations it would seem to me preferrable to grant a lock
of the supported type rather than fail the request. It will almost certainly
make no difference to the requesting client, where to do otherwise has
the potential to break existing applications.

john-