Here's what's going on, and this is a known problem. Like Apache, when we return an ETag for a resource, if the resource was created in the current second, we return a weak ETag. Past that initial one- second (or less) window, the ETag becomes a strong ETag.
This has been a subject of much debate on the WebDAV mailing lists for a while now. One problem is that the behavior of returning ETag in response to a PUT request isn't specified by HTTP. The actual problem in our case is that we use the time stamp (with a one-second resolution) to compute the ETag, and therefore don't necessarily have a valid ETag in the first second (the file can change again in that second and we'd have no way to know).
So Evolution does a PUT or it does (a GET immediately after a resource is created) and gets back a weak ETag, and it later tries to use that in a PUT, to which the server dutifully that the ETag is now different.
The server behavior in returning the PRECONDITION_FALED response is correct, so this patch isn't. What we probably need to do in web2.dav is stop issuing ETags on PUT at all, given that the HTTP spec doesn't define what this means. We also need a better solution for the first-second problem, which may mean that we omit ETags in responses where we current issue weak tags, or figure out a better way to compute strong tags.
-wsv
On Sep 16, 2006, at 7:34 AM, Guido Guenther wrote:
Hi,when trying to modify an already defined date with evolution 2.6 I get:Evolution: If-Match: W/"5005B-3D3-450BE897" Server: HTTP/1.1 412 Precondition Failed Date: Sat, 16 Sep 2006 13:13:53 GMT DAV: 1, access-control, calendar-access, calendar-schedule Content-Type: text/html Content-Length: 157Server: Twisted/2.4.0 TwistedWeb/[twisted.web2, version 0.2.0] TwistedCalDAV/unknown<html><head><title>Precondition Failed</title></ head><body><h1>Precondition Failed</h1><p>Requested resource does not have a matching ETag.</p></body></html>This is due to the fact that matchEtag fails. The etags match but not the allowWeak flag. This patch lets evolution update entries: --- twisted/web2/http.py.orig 2006-09-16 16:01:13.000000000 +0200 +++ twisted/web2/http.py 2006-09-16 16:23:12.000000000 +0200 @@ -253,7 +255,7 @@ # If either one fails, we return PRECONDITION_FAILED match = request.headers.getHeader("if-match") if match: - if not matchETag(match, False): + if not matchETag(match, True):raise HTTPError(StatusResponse (responsecode.PRECONDITION_FAILED, "Requested resource does not have a matching ETag."))unmod_since = request.headers.getHeader("if-unmodified-since")But I'm not sure that's what's intended. Who's at fault here evo or theserver? Cheers, -- Guido _______________________________________________ calendarserver-users mailing list calendarserver-users@lists.macosforge.org http://lists.macosforge.org/mailman/listinfo/calendarserver-users
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