call for participation: roundtripping of WebDAV properties in filesystems

Hi,

I got interested in this issue by some comments in Jim's article "The WebDAV
property design" [1] and discussion on the Subversion mailing list about
NTFS features.

The problem(s):

(a) resources copied to a local file system generally loose their WebDAV
property information, thus they won't round-trip when the resource is PUT
back to a WebDAV server

(b) WebDAV clients mapping servers to filesystems generally can't map the
properties to something a filesystem-based client can take advantage of.

The issues:

(1) Where to store the property information. The only portable solution
involves exposing a second file somewhere else in the namespace (such as by
appending a particular extension). In general, this is ugly due to possible
name collisions, and the fact that the properties will not automatically
move with the base file. Filesystems that offer multiple data streams or
data forks may do better (see below for some information about NTFS data
streams).

(2) Which format to use.


I think there's some hope in getting interoperability if we can get the
client developers (such as MS, Xythos, Apply, davfs Linux developers) to get
together (such as during the Interop event).


Possible solutions:

(1) This problem is hard in general but almost trivial for WIN32 scenarios.
NTFS supports multiple data streams that can be accessed with generic file
syntax (see [2]). All we'd need to do is to agree on a well-known name for
the stream (such as ":dav-properties").

(2) Let's just use the XML serialization of the DAV:prop element from a
PROPFIND/allprop response body.


Proof-of-concept:

Below is a script for Windows Scripting Host that GETs/PROPFINDs a resource
and stores the properties in the named data stream ":dav-properties". You
can see the properties by just opening the data stream like a regular file,
such as

	cat filename:dav-properties

Usage:

cscript davget.js URL destination-file user password


--
// davget.js
// GET a file from an HTTP server, storing it's properties in a NTFS data
stream
// params: URL localfile user password

var fso = new ActiveXObject("Scripting.FileSystemObject");
var http = new ActiveXObject("MSXML2.ServerXMLHTTP.3.0");
var stream = new ActiveXObject("ADODB.Stream");

var url = WScript.Arguments(0);


// PROPFIND

http.open("PROPFIND", url, false, WScript.Arguments(2),
WScript.Arguments(3));
http.setRequestHeader("Depth", "0");
http.send("<propfind xmlns='DAV:'><allprop/></propfind>");

if (http.status != 207) {
  WScript.Echo("unexpected status from PROPFIND: " + http.status);
  WScript.Quit(1);
}

var props = new ActiveXObject("MSXML2.DOMDocument");

http.responseXML.setProperty("SelectionLanguage", "XPath");
http.responseXML.setProperty("SelectionNamespaces", "xmlns:D='DAV:'");

props.appendChild(

http.responseXML.selectSingleNode("/D:multistatus/D:response/D:propstat[cont
ains(D:status,'200')]/D:prop"));

http.open("GET", url, false, WScript.Arguments(2), WScript.Arguments(3));
http.send();

if (http.status != 200) {
  WScript.Echo("unexpected status from GET: " + http.status);
  WScript.Quit(1);
}

stream.open();
stream.Type = 1;
try {
  if (http.responseText.length > 0) {
    stream.Write(http.responseBody);
  }
}
catch (e) {
  WScript.Echo("empty content? " + e);
}

stream.SaveToFile(WScript.Arguments(1), 2);
stream.close();

stream.open();
stream.Type = 1;
props.save(stream);
stream.SaveToFile(WScript.Arguments(1) + ":dav-props", 2);
stream.close();
--

Feedback appreciated,

Julian





[1] <http://www.cs.ucsc.edu/~ejw/papers/spe-whitehead.pdf>
[2] <http://www.sysinternals.com/ntw2k/source/misc.shtml#Streams>

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Received on Friday, 5 September 2003 07:17:42 UTC