URI Design and Ownership
draft-ietf-appsawg-uri-get-off-my-lawn-02
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (appsawg WG) | |
|---|---|---|---|
| Author | Mark Nottingham | ||
| Last updated | 2014-04-02 | ||
| Replaces | draft-nottingham-uri-get-off-my-lawn | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text xml htmlized pdfized bibtex | ||
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| Stream | WG state | Waiting for WG Chair Go-Ahead | |
| Document shepherd | Martin Thomson | ||
| Shepherd write-up | Show Last changed 2014-01-28 | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
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draft-ietf-appsawg-uri-get-off-my-lawn-02
appsawg M. Nottingham
Internet-Draft April 3, 2014
Updates: 3986 (if approved)
Intended status: BCP
Expires: October 5, 2014
URI Design and Ownership
draft-ietf-appsawg-uri-get-off-my-lawn-02
Abstract
RFC3986 Section 3.1 defines URI syntax as "a federated and extensible
naming system my further restrict the syntax and semantics of
identifiers using that scheme." In other words, the structure of a
URI is defined by its scheme. While it is common for schemes to
further delegate their substructure to the URI's owner, publishing
standards that mandate particular forms of URI substructure is
inappropriate, because the effectively usurps ownership.
This document is intended to prevent this practice (sometimes called
"URI Squatting") in standards, but updating RFC3986 to indicate where
it is acceptable.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 5, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Who This Document Is For . . . . . . . . . . . . . . . . . 4
1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 4
2. Best Current Practices for Standardizing Structured URIs . . . 4
2.1. URI Schemes . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. URI Authorities . . . . . . . . . . . . . . . . . . . . . . 5
2.3. URI Paths . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4. URI Queries . . . . . . . . . . . . . . . . . . . . . . . . 5
2.5. URI Fragment Identifiers . . . . . . . . . . . . . . . . . 6
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . . 6
5.2. Informative References . . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 7
Appendix B. Alternatives to Specifying Structure in URIs . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
URIs [RFC3986] very often include structured application data. This
might include artifacts from filesystems (often occurring in the path
component), and user information (often in the query component). In
some cases, there can even be application-specific data in the
authority component (e.g., some applications are spread across
several hostnames to enable a form of partitioning or dispatch).
Furthermore, constraints upon the structure of URIs can be imposed by
an implementation; for example, many Web servers use the filename
extension of the last path segment to determine the media type of the
response. Likewise, pre-packaged applications often have highly
structured URIs that can only be changed in limited ways (often, just
the hostname and port they are deployed upon).
Because the owner of the URI (as defined in [webarch] Section
2.2.2.1) is choosing to use the server or the software, this can be
seen as reasonable delegation of authority. When such conventions
are mandated by a party other than the owner, however, it can have
several potentially detrimental effects:
o Collisions - As more conventions for URI structure become
standardized, it becomes more likely that there will be collisions
between such conventions (especially considering that servers,
applications and individual deployments will have their own
conventions).
o Dilution - When the information added to a URI is ephemeral, this
dilutes its utility by reducing its stability (see [webarch]
Section 3.5.1), and can cause several alternate forms of the URI
to exist (see [webarch] Section 2.3.1).
o Rigidity - Fixed URI syntax often interferes with desired
deployment patterns. For example, if an authority wishes to offer
several applications on a single hostname, it becomes difficult to
impossible to do if their URIs do not allow the required
flexibility.
o Operational Difficulty - Supporting some URI conventions can be
difficult in some implementations. For example, specifying that a
particular query parameter be used precludes the use of Web
servers that serve the response from a filesystem. Likewise, an
application that fixes a base path for its operation (e.g., "/v1")
makes it impossible to deploy other applications with the same
prefix on the same host.
o Client Assumptions - When conventions are standardized, some
clients will inevitably assume that the standards are in use when
those conventions are seen. This can lead to interoperability
problems; for example, if a specification documents that the "sig"
URI query parameter indicates that its payload is a cryptographic
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signature for the URI, it can lead to undesirable behavior.
Publishing standards that constrain URI structure in ways which
aren't explicitly allowed by [RFC3986] (e.g., by defining it in the
URI scheme) is usually inappropriate, because the structure of a URI
needs to be firmly under the control of its owner, and the IETF (as
well as other organizations) should not usurp it.
This document explains best current practices for establishing URI
structures, conventions and formats in standards. It also offers
strategies for specifications to avoid violating these guidelines in
Appendix B.
1.1. Who This Document Is For
This document's requirements primarily target a few different types
of specifications:
o Protocol Extensions ("extensions") - specifications that offer new
capabilities to potentially any identifier, or a large subset;
e.g., a new signature mechanism for 'http' URIs, or metadata for
any URI.
o Applications Using URIs ("applications") - specifications that use
URIs to meet specific needs; e.g., a HTTP interface to particular
information on a host.
Requirements that target the generic class "Specifications" apply to
all specifications, including both those enumerated above and others.
Note that this specification ought not be interpreted as preventing
the allocation of control of URIs by parties that legitimately own
them, or have delegated that ownership; for example, a specification
might legitimately define the semantics of a URI on the IANA.ORG Web
site as part of the establishment of a registry.
1.2. 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].
2. Best Current Practices for Standardizing Structured URIs
Best practices differ depending on the URI component.
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2.1. URI Schemes
Applications and extensions MAY require use of specific URI
scheme(s); for example, it is perfectly acceptable to require that an
application support 'http' and 'https' URIs. However, applications
SHOULD NOT preclude the use of other URI schemes in the future,
unless they are clearly specific to the nominated schemes.
A specification that defines substructure within a URI scheme MUST do
so in the defining document for the URI scheme in question, or by
modifying [RFC4395].
2.2. URI Authorities
Scheme definitions define the presence, format and semantics of an
authority component in URIs; all other specifications MUST NOT
constrain, define structure or semantics for URI authorities, unless
they update the scheme registration itself.
For example, an extension or application cannot say that the "foo"
prefix in "foo_app.example.com" is meaningful or triggers special
handling.
2.3. URI Paths
Scheme definitions define the presence, format, and semantics of a
path component in URIs; all other specifications MUST NOT constrain,
define structure or semantics for any path component.
The only exception to this requirement is registered "well-known"
URIs, as specified by [RFC5785]. See that document for a description
of the applicability of that mechanism.
For example, an application cannot specify a fixed URI path "/myapp",
since this usurps the host's control of that space. Specifying a
fixed path relative to another (e.g., {whatever}/myapp) is also bad
practice, since it "locks" the URIs in use; while doing so might
prevent collisions, it does not avoid the other issues discussed.
2.4. URI Queries
The presence, format and semantics of the query component of URIs is
dependent upon many factors, and MAY be constrained by a scheme
definition. Often, they are determined by the implementation of a
resource itself.
Applications SHOULD NOT directly specify the syntax of queries, as
this can cause operational difficulties for deployments that do not
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support a particular form of a query.
Extensions MUST NOT specify the format or semantics of queries.
For example, an extension cannot be minted that indicates that all
query parameters with the name "sig" indicate a cryptographic
signature.
2.5. URI Fragment Identifiers
Media type definitions (as per [RFC6838]) SHOULD specify the fragment
identifier syntax(es) to be used with them; other specifications MUST
NOT define structure within the fragment identifier, unless they are
explicitly defining one for reuse by media type definitions.
3. Security Considerations
This document does not introduce new protocol artifacts with security
considerations. It prohibits some practices that might lead to
vulnerabilities; for example, if a security-sensitive mechanism is
introduced by assuming that a URI path component or query string has
a particular meaning, false positives might be encountered (due to
sites that already use the chosen string). See also [RFC6943].
4. IANA Considerations
There are no direct IANA actions specified in this document.
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI Schemes", BCP 35,
RFC 4395, February 2006.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
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RFC 6838, January 2013.
5.2. Informative References
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785,
April 2010.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570, March 2012.
[RFC6943] Thaler, D., "Issues in Identifier Comparison for Security
Purposes", RFC 6943, May 2013.
[webarch] Jacobs, I. and N. Walsh, "Architecture of the World Wide
Web, Volume One", December 2004,
<http://www.w3.org/TR/2004/REC-webarch-20041215>.
Appendix A. Acknowledgments
Thanks to David Booth, Dave Crocker, Tim Bray, Anne van Kesteren,
Martin Thomson, Erik Wilde and Dave Thaler for their suggestions and
feedback.
Appendix B. Alternatives to Specifying Structure in URIs
Given the issues above, the most successful strategy for applications
and extensions that wish to use URIs is to use them in the fashion
they were designed; as links that are exchanged as part of the
protocol, rather than statically specified syntax. Several existing
specifications can aid in this.
[RFC5988] specifies relation types for Web links. By providing a
framework for linking on the Web, where every link has a relation
type, context and target, it allows applications to define a link's
semantics and connectivity.
[RFC6570] provides a standard syntax for URI Templates that can be
used to dynamically insert application-specific variables into a URI
to enable such applications while avoiding impinging upon URI owners'
control of them.
[RFC5785] allows specific paths to be 'reserved' for standard use on
URI schemes that opt into that mechanism ('http' and 'https' by
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default). Note, however, that this is not a general "escape valve"
for applications that need structured URIs; see that specification
for more information.
Specifying more elaborate structures in an attempt to avoid
collisions is not adequate to conform to this document. For example,
prefixing query parameters with "myapp_" does not help, because the
prefix itself is subject to the risk of collision (since it is not
"reserved").
Author's Address
Mark Nottingham
Email: mnot@mnot.net
URI: http://www.mnot.net/
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