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Collections and Request-URIs

From: Jim Luther <luther.j@apple.com>
Date: Mon, 17 Jun 2002 16:45:44 -0700
To: w3c-dist-auth@w3c.org
Message-Id: <574F11EC-824C-11D6-9679-0003934B6A22@apple.com>

RFC 2518, section 5.2 says:

"There is a standing convention that when a collection is referred to by 
its name without a trailing slash, the trailing slash is automatically 
appended.  Due to this, a resource may accept a URI without a 
trailing "/" to point to a collection. In this case it SHOULD return a 
content-location header in the response pointing to the URI ending with 
the "/". For example, if a client invokes a method on 
http://foo.bar/blah (no trailing slash), the resource 
http://foo.bar/blah/ (trailing slash) may respond as if the operation 
were invoked on it, and should return a content-location header with 
http://foo.bar/blah/ in it.  In general clients SHOULD use the "/" form 
of collection names."

It looks to me like the "standing convention" doesn't match the BNF. RFC 
2616, section 5.1.2 gives this rule for the Request-URI in the 

	Request-URI 	= "*" | absoluteURI | abs_path | authority

and RFC 2396, section 3 gives these rules for abs_path and path_segments:

	abs_path      = "/"  path_segments
	path_segments = segment *( "/" segment )

So by my reading, abs_path should not have a trailing slash. Did I miss 
something? If not, I think the WebDAV spec should say that servers MUST 
handle Request-URIs to collections without the trail slash.

Anyway, trailing slashes issue causes an interoperability problem for 
our WebDAV file system and Apache 2.0 servers.  Since Mac OS X's WebDAV 
file system doesn't know if the end path component passed to it is a 
collection or non-collection resource, it doesn't put a trailing slash 
on the Request-URI. This works on all servers except for Apache 2 which 
sends us a "301 Moved Permanently" response. We don't redirect because 
the HTTP spec (RFC 2616, section 10.3.2) says:

"If the 301 status code is received in response to a request other than 
GET or HEAD, the user agent MUST NOT automatically redirect the request 
unless it can be confirmed by the user, since this might change the 
conditions under which the request was issued."

Hmmm... WebDAV file system can't confirm it with the user because it's a 
file system which doesn't do user interaction. I guess that I could 
compare the URI in the 301 response to see if it's the same as what I 
sent except for the trailing slash and retry the request. However, that 
would double the number of PROPFIND for collection transactions we send 
to Apache 2 servers and I'm trying to cut the number of transactions 
from our client, not increase them.

Apparently, Microsoft WebFolders had the same problem with Apache 2. 
Here's what we found in httpd.conf:

	# The following directive disables redirects on non-GET requests for
	# a directory that does not include the trailing slash.  This fixes a
	# problem with Microsoft WebFolders which does not appropriately handle
	# redirects for folders with DAV methods.
	BrowserMatch "Microsoft Data Access Internet Publishing Provider" 
	BrowserMatch "^WebDrive" redirect-carefully

So if we add a similar line:

	BrowserMatch "^WebDAVFS" redirect-carefully

to Apache's httpd.conf file to do a redirect-carefully for our 
User-Agent, our client works great with Apache 2 DAV servers.

- Jim Luther
Received on Monday, 17 June 2002 19:45:51 UTC

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