Re: Getting to Consensus on 1xx Status Codes (#535)

On 2014-07-22 16:33, Cyrus Daboo wrote:
> Hi,
> I wanted to weigh in on one specific use case for 1xx that has come up
> in CalDAV (RFC4791 - a WebDAV based calendaring and scheduling protocol).
> Some CalDAV PUT/POST requests might take a long time to process (of the
> order of several minutes or more). Typically clients (in particular
> mobile clients) implement a client-side response timeout (often 2
> minutes or so). If we know the request is likely to succeed obviously we
> want to keep the client connection alive past their timeout so that the
> response gets through. The original WebDAV spec (RFC2518) defined the
> 102 code for that purpose, but that code was removed (not deprecated) in
> the WebDAV update (RFC4918) because it was not being used.

I'd rephrase this as: it wasn't included in 4918 because we had zero 
implementations (mainly because most WebDAV servers people worked on 
back then were running on the Java servlet API, which didn't provide a 
way to send non-final responses). That means it continues to be defined 
in 2518 (as "proposed standard").

> Well now, some CalDAV servers are using 100-Continue as a keep-alive
> mechanism, and there are a couple of tweaks to that that would be handy
> (e.g., making use of a Prefer header that allows the client to
> communicate to the server what its client-side timeout is). Perhaps we
> should have adopted 102 for this purpose, but 100 seems to work well.
> Some CalDAV implementations also make use of the "Expect: 100-continue"
> mechanism for handling uploads of large event attachments that servers
> often redirect from the "base URI" for attachment uploads.

I'd say that using 100 for this is sort-of ok (it if serves the 
purpose), but it would be good to understand how the implementers that 
chose 100 over 102 came to the conclusion that it's better. It seems we 
have a education problem here; what's relevant for the applicability of 
status codes is how it appears in the IANA registry, after all.

> So as far as HTTP/1.1 goes 100 (and possibly 102) are important for
> CalDAV. In terms of HTTP/2, I presume the PING frame can be used for
> "keep-alive". But I definitely want to see the equivalent of "Expect:
> 100-continue" available in some fashion (either the same as HTTP/1.1 or
> via some new feature specific to HTTP/2).

Best regards, Julian

Received on Tuesday, 22 July 2014 14:47:28 UTC