- From: Clemm, Geoff <gclemm@rational.com>
- Date: Mon, 7 Oct 2002 15:17:54 -0400
- To: "'Webdav WG'" <w3c-dist-auth@w3c.org>
- Message-ID: <E4F2D33B98DF7E4880884B9F0E6FDEE25ED471@SUS-MA1IT01>
From: Lisa Dusseault [mailto:lisa@xythos.com] The proposal to require tagged-lists would not fix everything: - The IF header, particularly with URL tagging, is very long and can't be split up over several lines. I'd be happy to extend the syntax of the If header to allow a "," to separate the productions. RFC2518 authors: was it just a blunder (:-) that "," is not the separator, or was there some good reason why it wasn't used? Server writers: what would your server do today if it received multiple If headers in a single request? - If a lock disappears, the request will fail, even if the client wants it to succeed anyway. Round-trip required. As indicated in my previous message, I need to see some explanation for why clients that don't care about merge prevention are using locks in the first place? Why aren't they just using etags? - The client doesn't always know which locks are required (e.g. DELETE a resource in collection with depth-0 lock). Round-trip required. I don't see any connection between this issue and whether or not to use a separate header. If they don't have the right list of tokens in the new header, they will still get a failure and the same extra round-trip is required. Note that if we went with the proposal simply to require tagged lists, then the untagged list production should be 'deprecated', probably by telling clients they MUST NOT use untagged list productions. The untagged syntax becomes useless and should eventually be removed, though servers must continue to support the syntax as long as they want to interoperate with pre-existing clients. If the untagged syntax becomes useless, I'm happy to deprecate it. I'm always happy to delete/deprecate things from the spec if they turned out to not be useful ... that simplifies the spec, rather than making it more complex. I know the proposal to required tagged lists has been considered by client developers, and it was considered inferior to the proposal for a new header. In practice, it's the situation they currently experience - although the specification doesn't say the client MUST use tagged-lists, clients eventually come to that realization. And still, after programming the client to work that way, they find it's complicated and sometimes doesn't work in practice. Why is it complicated to create a tagged list? And I'm not sure what you mean by "in practice". If you mean "against existing servers", then you certainly aren't going to fix things by adding a new header that those servers are not expecting. My impression from what is being reported is that clients aren't aware they should be sending a tagged list, and some servers aren't aware that tagged lists need to be implemented. This is simplest to fix by making clients aware that they should be sending tagged lists, and making servers aware that they should be implementing tagged lists. Client implementers aren't the largest active constituency on this mailing list, and I'm not sure why, because I would guess they are the largest constituency of WebDAV implementers. When we do hear a solid consistent opinion from the client implementers, I believe it should be taken very seriously. For there to be demonstrable solid consistent opinions from client implementers, we need to see it documented in the mailing list, since that is where working group consensus is formed. If client implementers feel this is an important issue, it is imperative that they participate in this discussion. It's like democracy ... you don't get to complain if you don't vote. Cheers, Geoff From: Clemm, Geoff Alternatively, we could just say: "A client MUST submit a tagged-list If header, using the DAV:lock-root of the lock as the tag for that lock token." A simple rule for new clients, that will interoperate with all correctly implemented old and new servers. If any of the tagged-list productions fail, the resource that is no longer locked will be indicated with a 412 in the multistatus return, telling the client to either remove that lock from its table, or request a new lock for that resource. Cheers, Geoff -----Original Message----- From: Jason Crawford [mailto:nn683849@smallcue.com] for compatibility reasons, if the client didn't provide the new submit header, the server prudently can be expected to check the If: header using whatever semantics that it thinks 2518 specifies regarding token submission. Similarly, for compatibility reasons (in addition to any correctness reasons) we might expect the client to continue to submit If headers. For compatibility reasons a production client wouldn't depend on the server checking conditions on resources other than ones the server thinks are pertinent, but we can begin to test interoperability of that. Eventually though clients would only submit the If: header for correctness reasons and will feel free to do checks on any resource it feels is appropriate. > d) all state productions in a If header are checked, not only those that > apply to "affected" resources by the operation. Yes, Initially clients that are spamming the If: header will pay a price for that. But as they eventually move to the new header or stop spamming the If: header, that price will no longer be paid. The tact that can be taken in production systems is... New clients can submit the new header and only the If: clauses that it feels it wants tested. If the LOCKED error code is returned, they can resubmit to check if the error is just a problem with an old server. This means there will be a price for using an old server, but things will still work and it will be an incentive to upgrade. New clients can submit If: clauses for extra resources, but they will not be written to be dependent on submitting extra If: clauses to achieve correctness. Not unless they have a way to verify that the server supports this. I don't see this as a problem since we aren't emphasizing this feature yet. But eventually it becomes a possibility. New servers will know that if a client submits a new header, that it should process that new header. In that case it will also process *all* of the If: header clauses and we can test servers to verify that they support this even if production clients don't exercise this feature. If new servers receive a request that does not have the new header, they will fall back on whatever code they currently use for If: headers submitting lock tokens. That's what productions systems could do. Testing systems and tightly integrated systems could actually fully exercise the new features.
Received on Monday, 7 October 2002 15:18:29 UTC