--- 1/draft-ietf-webdav-bind-00.txt 2006-02-05 02:10:26.000000000 +0100 +++ 2/draft-ietf-webdav-bind-01.txt 2006-02-05 02:10:26.000000000 +0100 @@ -1,23 +1,23 @@ INTERNET-DRAFT G. Clemm - draft-ietf-webdav-bind-00 Rational Software + draft-ietf-webdav-bind-01 Rational Software J. Crawford IBM Research J. Reschke Greenbytes J. Slein Xerox E.J. Whitehead U.C. Santa Cruz - Expires April 2, 2002 October 2, 2001 + Expires August 7, 2003 February 7, 2003 Binding Extensions to WebDAV Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of RFC 2026, Section 10. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. @@ -36,59 +36,61 @@ Abstract This specification defines bindings, and the BIND method for creating multiple bindings to the same resource. Creating a new binding to a resource causes at least one new URI to be mapped to that resource. Servers are required to insure the integrity of any bindings that they allow to be created. Clemm, et al. [Page 1] Table of Contents - 1 INTRODUCTION...........................................3 + 1 INTRODUCTION............................................3 1.1 Terminology...........................................4 - 1.2 Rationale for Distinguishing Bindings from URI Mappings6 + 1.2 Rationale for Distinguishing Bindings from URI Mappings + ......................................................6 - 2 OVERVIEW OF BINDINGS...................................6 + 2 OVERVIEW OF BINDINGS....................................6 2.1 Bindings to Collections...............................7 2.2 URI Mappings Created by a new Binding.................7 2.3 DELETE and Bindings...................................8 2.4 COPY and Bindings.....................................9 - 2.5 MOVE and Bindings....................................10 - 2.6 Determining Whether Two Bindings Are to the Same Resource..........10 + 2.5 MOVE and Bindings.....................................9 + 2.6 Determining Whether Two Bindings Are to the Same Resource + .....................................................10 2.7 Discovering the Bindings to a Resource...............11 - 3 PROPERTIES............................................11 - 3.1 DAV:resource-id Property.............................11 + 3 PROPERTIES.............................................11 + 3.1 DAV:resource-id Property.............................12 3.2 DAV:parent-set Property..............................12 - 4 BIND METHOD...........................................12 - 4.1 Example: BIND........................................13 + 4 BIND METHOD............................................12 + 4.1 Example: BIND........................................14 - 5 ADDITIONAL STATUS CODES...............................14 + 5 ADDITIONAL STATUS CODES................................14 5.1 506 Loop Detected....................................14 - 6 SECURITY CONSIDERATIONS...............................15 - 6.1 Privacy Concerns.....................................15 - 6.2 Redirect Loops.......................................15 + 6 SECURITY CONSIDERATIONS................................16 + 6.1 Privacy Concerns.....................................16 + 6.2 Redirect Loops.......................................16 6.3 Bindings, and Denial of Service......................16 6.4 Private Locations May Be Revealed....................16 - 6.5 DAV:parent-set and Denial of Service.................16 + 6.5 DAV:parent-set and Denial of Service.................17 - 7 INTERNATIONALIZATION CONSIDERATIONS...................16 + 7 INTERNATIONALIZATION CONSIDERATIONS....................17 - 8 IANA CONSIDERATIONS...................................16 + 8 IANA CONSIDERATIONS....................................17 - 9 INTELLECTUAL PROPERTY.................................16 + 9 INTELLECTUAL PROPERTY..................................17 10 ACKNOWLEDGEMENTS.....................................17 - 11 REFERENCES...........................................17 + 11 REFERENCES...........................................18 12 AUTHORS' ADDRESSES...................................18 Clemm, et al. [Page 2] 1 INTRODUCTION This specification extends the WebDAV Distributed Authoring Protocol to enable clients to create new access paths to existing resources. This capability is useful for several reasons: @@ -179,24 +181,24 @@ Binding A relation between a single path segment (in a collection) and a resource. A binding is part of the state of a collection. If two different collections contain a binding between the same path segment and the same resource, these are two distinct bindings. So for a collection C, a path segment S, and a resource R, the binding can be thought of as C:(S -> R). Bindings create URI mappings, and hence allow requests to be sent to a single resource from multiple locations in a URI namespace. For example, given a collection C - (accessible through the URI http://www.srv.com/coll/), a path + (accessible through the URI http://www.example.com/coll/), a path segment S (equal to "foo.html"), and a resource R, then creating the binding C: (S -> R) makes it possible to use the URI - http://www.srv.com/coll/foo.html to access R. + http://www.example.com/coll/foo.html to access R. Clemm, et al. [Page 4] Collection A resource that contains, as part of its state, a set of bindings that identify internal member resources. Clemm, et al. [Page 5] Internal Member URI @@ -208,21 +210,21 @@ 1.2 Rationale for Distinguishing Bindings from URI Mappings In [RFC2518], the state of a collection is defined as containing a list of internal member URIs. If there are multiple mappings to a collection, then the state of the collection is different when you refer to it via a different URI. This is undesirable, since ideally a collection's membership should remain the same, independent of which URI was used to reference it. The notion of binding is introduced to separate the final segment - of a URI from its parent collection’s contribution. This done, a + of a URI from its parent collection's contribution. This done, a collection can be defined as containing a set of bindings, thus permitting new mappings to a collection without modifying its membership. The authors of this specification anticipate and recommend that future revisions of [RFC2518] will update the definition of the state of a collection to correspond to the definition in this document. 2 OVERVIEW OF BINDINGS Bindings are part of the state of a collection. They define the @@ -251,22 +253,21 @@ binding. Clemm, et al. [Page 6] 2.1 Bindings to Collections Bindings to collections can result in loops, which servers MUST detect when processing "Depth: infinity" requests. It is sometimes possible to complete an operation in spite of the presence of a loop. However, the 506 (Loop Detected) status code is defined in Section 5 for use in contexts where an operation is terminated - because a loop was encountered. Servers MUST allow loops to be - created. + because a loop was encountered. Creating a new binding to a collection makes each resource associated with a binding in that collection accessible via a new URI, and thus creates new URI mappings to those resources but no new bindings. For example, suppose a new binding CollY is created for collection C1 in the figure below. It immediately becomes possible to access resource R1 using the URI /CollY/x.gif and to access resource R2 using the URI /CollY/y.jpg, but no new bindings for these child @@ -296,54 +297,53 @@ | \ +-------------+ +-------------+ | Resource R1 | | Resource R2 | +-------------+ +-------------+ 2.2 URI Mappings Created by a new Binding Suppose a binding from "Binding-Name" to resource R to be added to a collection, C. Then if C-MAP is the set of URI's that were mapped to C before the BIND request, then for each URI "C-URI" in - - Clemm, et al. [Page 7] C-MAP, the URI "C-URI/Binding-Name" is mapped to resource R following the BIND request. + Clemm, et al. [Page 7] For example, if a binding from "foo.html" to R is added to a collection C, and if the following URI's are mapped to C: - http://www.fuzz.com/A/1/ - http://fuzz.com/A/one/ + http://www.example.com/A/1/ + http://example.com/A/one/ then the following new mappings to R are introduced: - http://www.fuzz.com/A/1/foo.html - http://fuzz.com/A/one/foo.html + http://www.example.com/A/1/foo.html + http://example.com/A/one/foo.html Note that if R is a collection, additional URI mappings are created to the descendents of R. Also, note that if a binding is made in collection C to C itself (or to a parent of C), an infinite number of mappings are introduced. For example, if a binding from "myself" to C is then added to C, the following infinite number of additional mappings to C are introduced: - http://www.fuzz.com/A/1/myself - http://www.fuzz.com/A/1/myself/myself + http://www.example.com/A/1/myself + http://www.example.com/A/1/myself/myself ... and the following infinite number of additional mappings to R are introduced: - http://www.fuzz.com/A/1/myself/foo.html - http://www.fuzz.com/A/1/myself/myself/foo.html + http://www.example.com/A/1/myself/foo.html + http://www.example.com/A/1/myself/myself/foo.html ... 2.3 DELETE and Bindings The DELETE method was originally defined in [RFC2616]. This section redefines the behavior of DELETE in terms of bindings, an abstraction not available when writing [RFC2616]. [RFC2616] states that "the DELETE method requests that the origin server delete the resource identified by the Request-URI." Because [RFC2616] did not distinguish between bindings and resources, the intent of its @@ -352,25 +352,24 @@ The DELETE method requests that the server remove the binding between the resource identified by the Request-URI and the binding name, the last path segment of the Request-URI. The binding MUST be removed from its parent collection, identified by the Request-URI minus its trailing slash (if present) and final segment. Once a resource is unreachable by any URI mapping, the server MAY reclaim system resources associated with that resource. If DELETE removes a binding to a resource, but there remain URI mappings to - - Clemm, et al. [Page 8] that resource, the server MUST NOT reclaim system resources associated with the resource. + Clemm, et al. [Page 8] Although [RFC2518] allows a DELETE to be a non-atomic operation, the DELETE operation defined here is atomic. In particular, a DELETE on a hierarchy of resources is simply the removal of a binding to the collection identified by the Request-URI, and so is a single (and therefore atomic) operation. Section 8.6.1 of [RFC2518] states that during DELETE processing, a server "MUST remove any URI for the resource identified by the Request-URI from collections which contain it as a member." Servers that support bindings MUST NOT follow this requirement. @@ -403,27 +402,28 @@ +---------------------+ +------------------------+ It might be thought that a COPY request with "Depth: 0" on a collection would duplicate its bindings, since bindings are part of the collection's state. This is not the case, however. The definition of Depth in [RFC2518] makes it clear that a "Depth: 0" request does not apply to a collection's members. Consequently, a COPY with "Depth: 0" does not duplicate the bindings contained by the collection. - Clemm, et al. [Page 9] 2.5 MOVE and Bindings The MOVE method has the effect of creating a new binding to a resource (at the Destination), and removing an existing binding (at the Request-URI). The name of the new binding is the last path segment of the Destination header, and the new binding is added to + + Clemm, et al. [Page 9] its parent collection, identified by the Destination header minus its trailing slash (if present) and final segment. As an example, suppose that a MOVE is issued to URI 3 for resource R below (which is also mapped to URI 1 and URI 2), with the Destination header set to URIX. After successful completion of the MOVE operation, a new binding has been created which creates at least the URI mapping between URIX and resource R (although other URI mappings may also have been created). The binding corresponding to the final segment of URI 3 has been removed, which @@ -450,28 +450,37 @@ +---------------------+ Although [RFC2518] allows a MOVE on a collection to be a non-atomic operation, the MOVE operation defined here MUST be atomic. Even when the Request-URI identifies a collection, the MOVE operation involves only removing one binding to that collection and adding another. There are no operations on bindings to any of its children, so the case of MOVE on a collection is the same as the case of MOVE on a non-collection resource. Both are atomic. + 2.5.1Additional MOVE Semantics + + Additional Preconditions: + + (DAV:cycle-allowed): If the request-URL identifies a collection, + and the parent of the Destination is that collection or is a member + of that collection, the server MUST support cycles in the URL + namespace. + + Clemm, et al. [Page 10] 2.6 Determining Whether Two Bindings Are to the Same Resource It is useful to have some way of determining whether two bindings are to the same resource. Two resources might have identical contents and properties, but not be the same resource (e.g. an update to one resource does not affect the other resource). - Clemm, et al. [Page 10] The REQUIRED DAV:resource-id property defined in Section 3.1 is a resource identifier, which MUST be unique across all resources for all time. If the values of DAV:resource-id returned by PROPFIND requests through two bindings are identical, the client can be assured that the two bindings are to the same resource. The DAV:resource-id property is created, and its value assigned, when the resource is created. The value of DAV:resource-id MUST NOT be changed. Even after the resource is no longer accessible through any URI, that value MUST NOT be reassigned to another @@ -502,28 +511,27 @@ whether to support the DAV:parent-set property, server implementers / administrators should balance the benefits it provides against the cost of maintaining the property and the security risks enumerated in Sections 6.4 and 6.5. 3 PROPERTIES The bind feature introduces the following properties for a resource. + Clemm, et al. [Page 11] 3.1 DAV:resource-id Property The DAV:resource-id property is a REQUIRED property that enables clients to determine whether two bindings are to the same resource. The value of DAV:resource-id is a URI, and may use any registered URI scheme that guarantees the uniqueness of the value across all - - Clemm, et al. [Page 11] resources for all time (e.g. the opaquelocktoken: scheme defined in [RFC2518]). 3.2 DAV:parent-set Property The DAV:parent-set property is an OPTIONAL property that enables clients to discover what collections contain a binding to this resource (i.e. what collections have that resource as an internal @@ -558,164 +566,182 @@ request MUST fail. Note that it is especially difficult to maintain the integrity of cross-server bindings. Unless the server where the resource resides knows about all bindings on all servers to that resource, it may unwittingly destroy the resource or make it inaccessible without notifying another server that manages a binding to the resource. For example, if server A permits creation of a binding to a resource on server B, server A must notify server B about its binding and must have an agreement with B that B will not destroy the resource while A's binding exists. Otherwise server B may receive a DELETE request that it thinks removes the + + Clemm, et al. [Page 12] last binding to the resource and destroy the resource while A's binding still exists. Status code 507 (Cross-server Binding Forbidden) is defined in Section 5.1 for cases where servers fail cross-server BIND requests because they cannot guarantee the integrity of cross-server bindings. - Clemm, et al. [Page 12] By default, if there already is a binding for the specified segment in the collection, the new binding replaces the existing binding. This default binding replacement behavior can be overridden using the Overwrite header defined in Section 9.6 of [RFC2518]. Marshalling: The request MAY include an Overwrite header. The request body MUST be a DAV:bind XML element. + If the request succeeds, the server MUST return 201 (Created) when + a new binding was created and 204 (No Content) when an existing + binding was replaced. + If a response body for a successful request is included, it MUST be a DAV:bind-response XML element. Note that this document does not define any elements for the BIND response body, but the DAV:bind- response element is defined to ensure interoperability between future extensions that do define elements for the BIND response body. Preconditions: (DAV:bind-into-collection): The Request-URL MUST identify a collection. + (DAV:bind-source-exists): The DAV:href element MUST identify a + resource. + + (DAV:binding-allowed): The resource identified by the DAV:href + supports multiple bindings to it. + (DAV:cross-server-binding): If the resource identified by the DAV:href element in the request body is on another server from the collection identified by the request-URL, the server MUST support cross-server bindings. + (DAV:name-allowed): The name specified by the DAV:segment is + available for use as a new binding name. + (DAV:can-overwrite): If the collection already contains a binding with the specified path segment, and if an Overwrite header is included, the value of the Overwrite header MUST be "T". + Clemm, et al. [Page 13] + (DAV:cycle-allowed): If the DAV:href element identifies a + collection, and if the request-URL identifies a collection that is + a member of that collection, the server MUST support cycles in the + URL namespace. + Postconditions: (DAV:new-binding): The collection MUST have a binding that maps the segment specified in the DAV:segment element in the request body, to the resource identified by the DAV:href element in the request body. 4.1 Example: BIND >> Request: BIND /coll HTTP/1.1 - Host: www.somehost.com + Host: www.example.com Content-Type: text/xml; charset="utf-8" Content-Length: xxx - - Clemm, et al. [Page 13] bar.html - http://www.somehost.com/coll + http://www.example.com/coll/foo.html >> Response: - HTTP/1.1 201 Created + HTTP/1.1 200 OK The server added a new binding to the collection, - "http://www.somehost.com/coll", associating "bar.html" with the + "http://www.example.com/coll", associating "bar.html" with the resource identified by the URL - "http://www.somehost.com/coll/foo.html". Clients can now use the - URL "http://www.somehost.com/coll/bar.html", to submit requests to + "http://www.example.com/coll/foo.html". Clients can now use the + URL "http://www.example.com/coll/bar.html", to submit requests to that resource. 5 ADDITIONAL STATUS CODES 5.1 506 Loop Detected The 506 (Loop Detected) status code indicates that the server terminated an operation because it encountered an infinite loop while processing a request with "Depth: infinity". When this status code is the top-level status code for the operation, it indicates that the entire operation failed. + Clemm, et al. [Page 14] When this status code occurs inside a multi-status response, it indicates only that a loop is being terminated, but does not indicate failure of the operation as a whole. For example, consider a PROPFIND request on /Coll (bound to collection C), where the members of /Coll are /Coll/Foo (bound to resource R) and /Coll/Bar (bound to collection C). >> Request: PROPFIND /Coll/ HTTP/1.1 - Host: www.somehost.com + Host: www.example.com Depth: infinity Content-Type: text/xml; charset="utf-8" Content-Length: xxx >> Response: HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset="utf-8" - - Clemm, et al. [Page 14] Content-Length: xxx - http://www.somehost.com/Coll/ + http://www.example.com/Coll/ Loop Demo HTTP/1.1 200 OK - http://www.somehost.com/Coll/Foo + http://www.example.com/Coll/Foo Bird Inventory HTTP/1.1 200 OK - http://www.somehost.com/Coll/Bar + http://www.example.com/Coll/Bar HTTP/1.1 506 Loop Detected + Clemm, et al. [Page 15] 6 SECURITY CONSIDERATIONS This section is provided to make WebDAV applications aware of the security implications of this protocol. All of the security considerations of HTTP/1.1 and the WebDAV Distributed Authoring Protocol specification also apply to this protocol specification. In addition, bindings introduce several new security concerns and increase the risk of some existing threats. These issues are detailed below. @@ -726,22 +752,20 @@ bindings on a trusted server may make it possible for a hostile agent to induce users to send private information to a target on a different server. 6.2 Redirect Loops Although redirect loops were already possible in HTTP 1.1, the introduction of the BIND method creates a new avenue for clients to create loops accidentally or maliciously. If the binding and its target are on the same server, the server may be able to detect - - Clemm, et al. [Page 15] BIND requests that would create loops. Servers are required to detect loops that are caused by bindings to collections during the processing of any requests with "Depth: infinity". 6.3 Bindings, and Denial of Service Denial of service attacks were already possible by posting URLs that were intended for limited use at heavily used Web sites. The introduction of BIND creates a new avenue for similar denial of service attacks. If cross-server bindings are supported, clients @@ -750,20 +774,21 @@ 6.4 Private Locations May Be Revealed If the DAV:parent-set property is maintained on a resource, the owners of the bindings risk revealing private locations. The directory structures where bindings are located are available to anyone who has access to the DAV:parent-set property on the resource. Moving a binding may reveal its new location to anyone with access to DAV:parent-set on its resource. + Clemm, et al. [Page 16] 6.5 DAV:parent-set and Denial of Service If the server maintains the DAV:parent-set property in response to bindings created in other administrative domains, it is exposed to hostile attempts to make it devote resources to adding bindings to the list. 7 INTERNATIONALIZATION CONSIDERATIONS All internationalization considerations mentioned in [RFC2518] also @@ -776,22 +801,20 @@ 9 INTELLECTUAL PROPERTY The following notice is copied from RFC 2026, Section 10.4, and describes the position of the IETF concerning intellectual property claims made against this document. The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use other technology described in - - Clemm, et al. [Page 16] this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the procedures of the IETF with respect to rights in standards- track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF Secretariat. @@ -802,20 +825,22 @@ this standard. Please address the information to the IETF Executive Director. 10 ACKNOWLEDGEMENTS This draft is the collaborative product of the authors and Tyson Chihaya, Jim Davis, and Chuck Fay. This draft has benefited from thoughtful discussion by Jim Amsden, Peter Carlson, Steve Carter, Ken Coar, Ellis Cohen, Dan Connolly, Bruce Cragun, Spencer Dawkins, Mark Day, Rajiv Dulepet, David Durand, Roy Fielding, Yaron Goland, + + Clemm, et al. [Page 17] Fred Hitt, Alex Hopmann, James Hunt, Marcus Jager, Chris Kaler, Manoj Kasichainula, Rohit Khare, Daniel LaLiberte, Steve Martin, Larry Masinter, Jeff McAffer, Surendra Koduru Reddy, Max Rible, Sam Ruby, Bradley Sergeant, Nick Shelness, John Stracke, John Tigue, John Turner, Kevin Wiggen, and other members of the WebDAV working group. 11 REFERENCES [RFC2026] S.Bradner, "The Internet Standards Process", RFC 2026, @@ -831,24 +856,23 @@ Resource Identifiers (URI): Generic Syntax." RFC 2396, August 1998. [RFC2518] Y.Goland, E.Whitehead, A.Faizi, S.R.Carter, D.Jensen, "HTTP Extensions for Distributed Authoring - WEBDAV", RFC 2518, February 1999. [RFC2616] R.Fielding, J.Gettys, J.C.Mogul, H.Frystyk, L.Masinter, P.Leach, and T.Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. - Clemm, et al. [Page 17] [XML] T. Bray, J. Paoli, C.M. Sperberg-McQueen, "Extensible Markup - Language (XML)." World Wide Web Consortium Recommendation REC-xml- - 19980210. http://www.w3.org/TR/1998/REC-xml-19980210. + Language (XML) 1.0 (Second Edition)" W3C Recommendation 6 October + 2000. http://www.w3.org/TR/2000/REC-xml-20001006. 12 AUTHORS' ADDRESSES Geoffrey Clemm Rational Software Corporation 20 Maguire Road Lexington, MA 02173-3104 Email: geoffrey.clemm@rational.com Jason Crawford @@ -856,22 +880,23 @@ P.O. Box 704 Yorktown Heights, NY 10598 Email: ccjason@us.ibm.com Julian F. Reschke greenbytes GmbH Salzmannstrasse 152 Muenster, NW 48159, Germany Email: julian.reschke@greenbytes.de + Clemm, et al. [Page 18] Judy Slein Xerox Corporation 800 Phillips Road, 105-50C Webster, NY 14580 Email: jslein@crt.xerox.com Jim Whitehead UC Santa Cruz, Dept. of Computer Science 1156 High Street, Santa Cruz, CA 95064 Email: ejw@cse.ucsc.edu - Clemm, et al. [Page 18] + Clemm, et al. [Page 19]