WWW Distributed Authoring and Versioning (webdav)B. Korver
Internet-DraftXythos
Intended status: InformationalL. Dusseault
Expires: August 11, 2005OSAF
February 7, 2005

Quota and Size Properties for DAV Collections
draft-ietf-webdav-quota-06

Note: a later version of this document has been published as RFC4331.

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This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668.

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Copyright Notice

Copyright © The Internet Society (2005). All Rights Reserved.

Abstract

WebDAV servers are frequently deployed with quota (size) limitations. This document discusses the properties and minor behaviors needed for clients to interoperate with quota (size) implementations on WebDAV repositories.


Table of Contents

1. Introduction

1.1 Notational Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

1.2 Requirement for quotas

WebDAV servers based on [RFC2518] have been implemented and deployed with quota restrictions on collections and users, so it makes sense to standardize this functionality to improve user experience and client interoperability. This specification requires WebDAV because it requires PROPFIND support and relies on the WebDAV definition of collections and properties, including the definitions for live and protected properties (see section 1.4.2 of [RFC3253] for the definition of protected properties).

The reasons why WebDAV servers frequently have quotas enforced are the same reasons why any storage system comes with quotas.

In order to work best with repositories that support quotas, client software should be able to determine and display the DAV:quota-available-bytes (defined below) on collections. Further, client software should have some way of fairly reliably determining how much storage space is already counted towards that quota.

Support for the properties defined in this document enhances the client experience, because the client has a chance of managing its files to avoid running out of allocated storage space. Clients may not be able to calculate the value as accurately on their own, depending on how total space used is calculated by the server.

2. Solution Overview

The approach to meeting the requirements and scenarios outlined above is to define two live properties. This specification can be met on a server by implementing both DAV:quota-available-bytes and DAV:quota-used-bytes on collections only.

A <DAV:allprop> PROPFIND request SHOULD NOT return any of the properties defined by this document. However, these property names MUST be returned in a <DAV:propname> request for a resource that supports the properties, except in the case of infinite limits which are explained below.

The DAV:quota-available-bytes and DAV:quota-used-bytes definitions below borrow heavily from the quota definitions in the NFS [RFC3530] specification.

3. DAV:quota-available-bytes

Name:
quota-available-bytes
Namespace:
DAV:
Purpose:
Indicates the maximum amount of additional storage available to be allocated to a resource.
DTD:
<!ELEMENT quota-available-bytes (#PCDATA) >

The DAV:quota-available-bytes property value is the value in octets representing the amount of additional disk space beyond the current allocation that can be allocated to this resource before further allocations will be refused. It is understood that this space may be consumed by allocations to other resources.

Support for this property is REQUIRED on collections, and OPTIONAL on other resources. A server SHOULD implement this property for each resource that has the DAV:quota-used-bytes property.

Clients SHOULD expect that as the DAV:quota-available-bytes on a resource approaches 0, further allocations to that resource may be refused. A value of 0 indicates that users will probably not be able to perform operations that write additional information (e.g. a PUT inside a collection), but may be able to replace through overwrite an existing resource of equal size.

Note that there may be a number of distinct but overlapping limits, which may even include physical media limits. When reporting DAV:quota-available-bytes, the server is at liberty to choose any of those limits but SHOULD do so in a repeatable way. The rule may be configured per repository, or may be "choose the smallest number".

If a resource has no quota enforced or unlimited storage ("infinite limits"), the server MAY choose not to return this property (404 Not Found response in Multi-Status), although this specification RECOMMENDS that servers return some appropriate value (e.g. the amount of free disc space). A client cannot entirely assume that there is no quota enforced on a resource that does not have this property, but might as well act as if there is no quota.

The value of this property is protected (see section 1.4.2 of [RFC3253] for the definition of protected properties). A 403 Forbidden response is RECOMMENDED for attempts to write a protected property, and the server SHOULD include an XML error body as defined by DeltaV [RFC3253] with the <DAV:cannot-modify-protected-property/> precondition tag.

4. DAV:quota-used-bytes

Name:
quota-used-bytes
Namespace:
DAV:
Purpose:
Contains the amount of storage counted against the quota on a resource.
DTD:
<!ELEMENT quota-used-bytes (#PCDATA) >

The DAV:quota-used-bytes value is the value in octets representing the amount of space used by this resource and possibly a number of other similar resources, where the set of "similar" meets at least the criterion that allocating space to any resource in the set will count against the DAV:quota-available-bytes. It MUST include the total count including usage derived from sub-resources if appropriate. It SHOULD include metadata storage size if metadata storage is counted against the DAV:quota-available-bytes.

Note that there may be a number of distinct but overlapping sets of resources for which a DAV:quota-used-bytes is maintained (e.g. "all files with a given owner", "all files with a given group owner", etc.). The server is at liberty to choose any of those sets but SHOULD do so in a repeatable way. The rule may be configured per repository.

Support for this property is REQUIRED on collections, and OPTIONAL on other resources. A server SHOULD implement this property for each resource that has the DAV:quota-available-bytes property.

5. Example PROPFIND request and response

 
Request: 

      PROPFIND /~milele/public/ HTTP/1.1
      Depth: 0
      Host: www.example.com
      Content-Type: text/xml
      Content-Length: xxx

      <?xml version="1.0" ?>
      <D:propfind xmlns:D="DAV:">
        <D:prop>
          <D:quota-available-bytes/>
          <D:quota-used-bytes/>
        </D:prop>
      </D:propfind>

Response: 

      HTTP/1.1 207 Multi-Status
      Date: Tue, 16 Oct 2001 22:13:39 GMT
      Content-Length: xxx
      Content-Type: text/xml; charset=UTF-8

      <?xml version="1.0" encoding="utf-8" ?>
      <D:multistatus xmlns:D="DAV:">
      <D:response>
        <D:href>http://www.example.com/~milele/public/</D:href>
        <D:propstat>
          <D:prop>
            <D:quota-available-bytes>596650</D:quota-available-bytes>
            <D:quota-used-bytes>403350</D:quota-used-bytes>
          </D:prop>
          <D:status>HTTP/1.1 200 OK</D:status>
        </D:propstat>
      </D:response>
      </D:multistatus>
                

6. Error reporting

WebDAV [RFC2518] defines the status code 507 (Insufficient Storage). This status code SHOULD be used when a client request (e.g. a PUT, PROPFIND, MKCOL, MOVE or COPY) fails because it would exceed their allotted quota. In order to differentiate the response from other storage problems, the server SHOULD include an XML error body as defined by DeltaV [RFC3253] with the <DAV:quota-not-exceeded/> precondition tag.

Example error response:

   HTTP/1.1 507 Insufficient Storage
   Content-Length: xxx
   Content-Type: text/xml

   <?xml version="1.0">
   <error xmlns="DAV:">
     <quota-not-exceeded/>
   </error>
 

7. Notes

Server implementations store and account for their data in many different ways. Some of the challenges:

Since server storage accounting can vary so much, clients should expect the following:

8. Security Considerations

A hacker may prefer to store files in collections with a large quota. This isn't strictly a security concern because it doesn't make it any easier to store files. On the other hand, the DAV:quota-used-bytes property may make it easier to detect tampering or misuse.

9. Internationalization Considerations

Quota is counted in Arabic numerals expressed in strings. There are no internationalization considerations.

10. IANA Considerations

There are no IANA considerations.

11. Acknowledgements

Stefan Eissing, Geoff Clemm, Jim Luther, Julian Reschke, Jim Whitehead, among others, have provided valuable comments on this document.

12. References

12.1 Normative References

[RFC2119]Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels”, BCP 14, RFC 2119, March 1997.
[RFC2518]Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D. Jensen, “HTTP Extensions for Distributed Authoring -- WebDAV”, RFC 2518, February 1999.
[RFC3253]Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning)”, RFC 3253, March 2002.

12.2 Informative References

[RFC3530]Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame, C., Eisler, M., and D. Noveck, “Network File System (NFS) version 4 Protocol”, RFC 3530, April 2003.

Authors' Addresses

Brian Korver
Xythos Software
One Bush Street
Suite 600
San Francisco, CA 94104
US
Phone: +1 415 248-3800
EMail: briank@xythos.com

Lisa Dusseault
Open Source Applications Foundation
543 Howard Street
5th Floor
San Francisco, CA 94105
US
Phone: +1 415 946-3040
EMail: lisa@osafoundation.org

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