< draft-ietf-appsawg-uri-get-off-my-lawn-00.txt   draft-ietf-appsawg-uri-get-off-my-lawn-01.txt >
Network Working Group M. Nottingham appsawg M. Nottingham
Internet-Draft September 17, 2013 Internet-Draft January 30, 2014
Updates: 3986 (if approved) Updates: 3986 (if approved)
Intended status: BCP Intended status: BCP
Expires: March 21, 2014 Expires: August 3, 2014
Standardising Structure in URIs URI Design and Ownership
draft-ietf-appsawg-uri-get-off-my-lawn-00 draft-ietf-appsawg-uri-get-off-my-lawn-01
Abstract Abstract
Sometimes, it is attractive to add features to protocols or Sometimes, it is attractive to add features to protocols or
applications by specifying a particular structure for URIs (or parts applications by specifying a particular structure for URIs (or parts
thereof). This document cautions against this practice in standards thereof). However, publishing standards that mandate URI structure
(sometimes called "URI Squatting"). is inappropriate because the structure of a URI needs to be firmly
under the control of its owner, and the IETF (as well as other
organisations) should not usurp this 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 Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 21, 2014. This Internet-Draft will expire on August 3, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Who This Document Is For . . . . . . . . . . . . . . . . . 4 1.1. Who This Document Is For . . . . . . . . . . . . . . . . . 4
1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 5 1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 4
2. Best Current Practices for Standardising Structured URIs . . . 5 2. Best Current Practices for Standardising Structured URIs . . . 5
2.1. URI Schemes . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. URI Schemes . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. URI Authorities . . . . . . . . . . . . . . . . . . . . . . 5 2.2. URI Authorities . . . . . . . . . . . . . . . . . . . . . . 5
2.3. URI Paths . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3. URI Paths . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4. URI Queries . . . . . . . . . . . . . . . . . . . . . . . . 5 2.4. URI Queries . . . . . . . . . . . . . . . . . . . . . . . . 5
2.5. URI Fragment Identifiers . . . . . . . . . . . . . . . . . 6 2.5. URI Fragment Identifiers . . . . . . . . . . . . . . . . . 6
3. Alternatives to Specifying Static URIs . . . . . . . . . . . . 6 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.1. Normative References . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . . 7 5.2. Informative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . . 7 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 8 Appendix B. Alternatives to Specifying Structure in URIs . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
URIs [RFC3986] very often include structured application data. This URIs [RFC3986] very often include structured application data. This
might include artifacts from filesystems (often occurring in the path might include artifacts from filesystems (often occurring in the path
component), and user information (often in the query component). In component), and user information (often in the query component). In
some cases, there can even be application-specific data in the some cases, there can even be application-specific data in the
authority component (e.g., some applications are spread across authority component (e.g., some applications are spread across
several hostnames to enable a form of partitioning or dispatch). several hostnames to enable a form of partitioning or dispatch).
skipping to change at page 3, line 31 skipping to change at page 3, line 31
Because the owner of the URI is choosing to use the server or the Because the owner of the URI is choosing to use the server or the
software, this can be seen as reasonable delegation of authority. software, this can be seen as reasonable delegation of authority.
When such conventions are mandated by standards, however, it can have When such conventions are mandated by standards, however, it can have
several potentially detrimental effects: several potentially detrimental effects:
o Collisions - As more conventions for URI structure become o Collisions - As more conventions for URI structure become
standardised, it becomes more likely that there will be collisions standardised, it becomes more likely that there will be collisions
between such conventions (especially considering that servers, between such conventions (especially considering that servers,
applications and individual deployments will have their own applications and individual deployments will have their own
conventions). conventions).
o Dilution - Adorning URIs with extra information to support new o Dilution - When the information added to a URI is ephemeral, this
standard features dilutes their usefulness as identifiers when dilutes its utility by reducing its stability (see [webarch]
that information is ephemeral (as URIs ought to be stable; see Section 3.5.1), and can cause several alternate forms of the URI
[webarch] Section 3.5.1), or its inclusion causes several to exist (see [webarch] Section 2.3.1).
alternate forms of the URI to exist (see [webarch] Section 2.3.1). o Rigidity - Fixed URI syntax often interferes with desired
o Brittleness - A standard that specifies a static URI cannot change deployment patterns. For example, if an authority wishes to offer
its form in future revisions. 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 o Operational Difficulty - Supporting some URI conventions can be
difficult in some implementations. For example, specifying that a difficult in some implementations. For example, specifying that a
particular query parameter be used precludes the use of Web particular query parameter be used precludes the use of Web
servers that serve the response from a filesystem. Likewise, an servers that serve the response from a filesystem. Likewise, an
application that fixes a base path for its operation (e.g., "/v1") application that fixes a base path for its operation (e.g., "/v1")
makes it impossible to deploy other applications with the same makes it impossible to deploy other applications with the same
prefix on the same host. prefix on the same host.
o Client Assumptions - When conventions are standardised, some o Client Assumptions - When conventions are standardised, some
clients will inevitably assume that the standards are in use when clients will inevitably assume that the standards are in use when
those conventions are seen. This can lead to interoperability those conventions are seen. This can lead to interoperability
problems; for example, if a specification documents that the "sig" problems; for example, if a specification documents that the "sig"
URI query parameter indicates that its payload is a cryptographic URI query parameter indicates that its payload is a cryptographic
signature for the URI, it can lead to false positives. signature for the URI, it can lead to undesirable behaviour.
While it is not ideal when a server or a deployed application While it is not ideal when a server or a deployed application
constrains URI structure (indeed, this is not recommended practice, constrains URI structure (indeed, this is not recommended practice,
but that discussion is out of scope for this document), publishing but that discussion is out of scope for this document), publishing
standards that mandate URI structure is inappropriate because the standards that mandate URI structure (beyond those allowed by
structure of a URI needs to be firmly under the control of its owner, [RFC3986]) is inappropriate because the structure of a URI needs to
and the IETF (as well as other organisations) should not usurp this be firmly under the control of its owner, and the IETF (as well as
ownership; see [webarch] Section 2.2.2.1. other organisations) should not usurp this ownership; see [webarch]
Section 2.2.2.1.
This document explains best current practices for establishing URI This document explains best current practices for establishing URI
structures, conventions and formats in standards. It also offers structures, conventions and formats in standards. It also offers
strategies for specifications to avoid violating these guidelines in strategies for specifications to avoid violating these guidelines in
Section 3. Appendix B.
1.1. Who This Document Is For 1.1. Who This Document Is For
These guidelines are IETF Best Current Practice, and are therefore This document's requirements specifically target a few different
binding upon IETF standards-track documents, as well as submissions
to the RFC Editor on the Independent and IRTF streams. See [RFC2026]
and [RFC4844] for more information.
Other Open Standards organisations (in the sense of [RFC2026]) are
encouraged to adopt them. Questions as to their applicability ought
to be handled through the liaison relationship, if present.
Ad hoc efforts are also encouraged to adopt them, as this RFC
reflects Best Current Practice.
This document's requirements specifically targets a few different
types of specifications: types of specifications:
o URI Scheme Definitions ("scheme definitions") - specifications o URI Scheme Definitions ("scheme definitions") - specifications
that define and register URI schemes, as per [RFC4395]. that define and register URI schemes, as per [RFC4395].
o Protocol Extensions ("extensions") - specifications that offer new o Protocol Extensions ("extensions") - specifications that offer new
capabilities to potentially any identifier, or a large subset; capabilities to potentially any identifier, or a large subset;
e.g., a new signature mechanism for 'http' URIs, or metadata for e.g., a new signature mechanism for 'http' URIs, or metadata for
any URI. any URI.
o Applications Using URIs ("applications") - specifications that use o Applications Using URIs ("applications") - specifications that use
URIs to meet specific needs; e.g., a HTTP interface to particular URIs to meet specific needs; e.g., a HTTP interface to particular
information on a host. information on a host.
Requirements that target the generic class "Specifications" apply to Requirements that target the generic class "Specifications" apply to
all specifications, including both those enumerated above above and all specifications, including both those enumerated above above and
others. others.
Note that this specification ought not be interpreted as preventing Note that this specification ought not be interpreted as preventing
the allocation of control of URIs by parties that legitimately own the allocation of control of URIs by parties that legitimately own
them, or have delegated that ownership; for example, a specification them, or have delegated that ownership; for example, a specification
might legitimately specify the semantics of a URI on the IANA.ORG Web might legitimately define the semantics of a URI on the IANA.ORG Web
site as part of the establishment of a registry. site as part of the establishment of a registry.
1.2. Notational Conventions 1.2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Best Current Practices for Standardising Structured URIs 2. Best Current Practices for Standardising Structured URIs
Different components of a URI have differing practices recommended. Best practices differ depending on the URI component.
2.1. URI Schemes 2.1. URI Schemes
Applications and extensions MAY require use of specific URI Applications and extensions MAY require use of specific URI
scheme(s); for example, it is perfectly acceptable to require that an scheme(s); for example, it is perfectly acceptable to require that an
application support 'http' and 'https' URIs. However, applications application support 'http' and 'https' URIs. However, applications
SHOULD NOT preclude the use of other URI schemes in the future, to SHOULD NOT preclude the use of other URI schemes in the future,
promote reuse, unless they are clearly specific to the nominated unless they are clearly specific to the nominated schemes.
schemes.
Specifications MUST NOT define substructure within URI schemes, A specification that defines substructure within a URI scheme MUST do
unless they do so by modifying [RFC4395], or they are the so in a registration document for the URI scheme in question, or by
registration document for the URI scheme(s) in question. modifying [RFC4395].
2.2. URI Authorities 2.2. URI Authorities
Scheme definitions define the presence, format and semantics of an Scheme definitions define the presence, format and semantics of an
authority component in URIs; all other specifications MUST NOT authority component in URIs; all other specifications MUST NOT
constrain, define structure or semantics for them. constrain, define structure or semantics for URI authorities.
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 2.3. URI Paths
Scheme definitions define the presence, format, and semantics of a Scheme definitions define the presence, format, and semantics of a
path component in URIs; all other specifications MUST NOT constrain, path component in URIs; all other specifications MUST NOT constrain,
define structure or semantics for any path component. define structure or semantics for any path component.
The only exception to this requirement is registered "well-known" The only exception to this requirement is registered "well-known"
URIs, as specified by [RFC5785]. See that document for a description URIs, as specified by [RFC5785]. See that document for a description
of the applicability of that mechanism. 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 2.4. URI Queries
The presence, format and semantics of the query component of URIs is The presence, format and semantics of the query component of URIs is
dependent upon many factors, and MAY be constrained by a scheme dependent upon many factors, and MAY be constrained by a scheme
definition. Often, they are determined by the implementation of a definition. Often, they are determined by the implementation of a
resource itself. resource itself.
Applications SHOULD NOT directly specify the syntax of queries, as Applications SHOULD NOT directly specify the syntax of queries, as
this can cause operational difficulties for deployments that do not this can cause operational difficulties for deployments that do not
support a particular form of a query. support a particular form of a query.
Extensions MUST NOT specify the format or semantics of queries. In Extensions MUST NOT specify the format or semantics of queries.
particular, extensions MUST NOT assume that all HTTP(S) resources are
capable of accepting queries in the format defined by [HTML4], For example, an extension cannot be minted that indicates that all
Section 17.13.4. query parameters with the name "sig" indicate a cryptographic
signature.
2.5. URI Fragment Identifiers 2.5. URI Fragment Identifiers
Media type definitions (as per [RFC6838] SHOULD specify the fragment Media type definitions (as per [RFC6838] SHOULD specify the fragment
identifier syntax(es) to be used with them; other specifications MUST identifier syntax(es) to be used with them; other specifications MUST
NOT define structure within the fragment identifier, unless they are NOT define structure within the fragment identifier, unless they are
explicitly defining one for reuse by media type definitions. explicitly defining one for reuse by media type definitions.
3. Alternatives to Specifying Static URIs 3. Security Considerations
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 run-time artifacts that are exchanged as part
of the protocol, rather than statically specified syntax.
For example, if a specific URI needs to be known to interact with an
application, its "shape" can be determined by interacting with the
application's more general interface (in Web terms, its "home page")
to learn about that URI.
[RFC5988] describes a framework for identifying the semantics of a
link in a "link relation type" to aid this. [RFC6570] provides a
standard syntax for "link 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
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.
4. Security Considerations
This document does not introduce new protocol artifacts with security This document does not introduce new protocol artifacts with security
considerations. 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).
5. IANA Considerations 4. IANA Considerations
This document clarifies appropriate registry policy for new URI This document clarifies appropriate registry policy for new URI
schemes, and potentially for the creation of new URI-related schemes, and potentially for the creation of new URI-related
registries, if they attempt to mandate structure within URIs. There registries, if they attempt to mandate structure within URIs. There
are no direct IANA actions specified in this document. are no direct IANA actions specified in this document.
6. References 5. References
6.1. Normative References 5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005. RFC 3986, January 2005.
[RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and [RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI Schemes", BCP 35, Registration Procedures for New URI Schemes", BCP 35,
RFC 4395, February 2006. RFC 4395, February 2006.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, Specifications and Registration Procedures", BCP 13,
RFC 6838, January 2013. RFC 6838, January 2013.
6.2. Informative References 5.2. Informative References
[HTML4] Jacobs, I., Le Hors, A., and D. Raggett, "HTML 4.01
Specification", December 1999,
<http://www.w3.org/TR/REC-html40/>.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC4844] Daigle, L. and Internet Architecture Board, "The RFC
Series and RFC Editor", RFC 4844, July 2007.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785, Uniform Resource Identifiers (URIs)", RFC 5785,
April 2010. April 2010.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010. [RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M., [RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570, March 2012. and D. Orchard, "URI Template", RFC 6570, March 2012.
[webarch] Jacobs, I. and N. Walsh, "Architecture of the World Wide [webarch] Jacobs, I. and N. Walsh, "Architecture of the World Wide
Web, Volume One", December 2004, Web, Volume One", December 2004,
<http://www.w3.org/TR/2004/REC-webarch-20041215>. <http://www.w3.org/TR/2004/REC-webarch-20041215>.
Appendix A. Acknowledgments Appendix A. Acknowledgments
Thanks to David Booth, Anne van Kesteren and Erik Wilde for their Thanks to David Booth, Dave Crocker, Tim Bray, Anne van Kesteren,
suggestions and feedback. Martin Thomson and Erik Wilde 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
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 Author's Address
Mark Nottingham Mark Nottingham
Email: mnot@mnot.net Email: mnot@mnot.net
URI: http://www.mnot.net/ URI: http://www.mnot.net/
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