Network Working Group J. Holsten Internet-Draft Intended status: Standards Track L. Hunt Expires: June 2, 2011 Opera Software, ASA. November 29, 2010 The 'about' URI scheme draft-holsten-about-uri-scheme-06 Abstract A URI using the "about:" scheme, henceforth referred to as an "about" URI, is designed to be used internally by applications for almost any desired purpose. Such URIs have commonly been used by web browsers for providing access to built-in functionality, such as application information, preferences, settings, or "easter eggs". Editorial Note (To be removed by RFC Editor) Discussion of this draft should take place on the URI Review mailing list (uri-review@ietf.org). 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 June 2, 2011. Copyright Notice Copyright (c) 2010 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 (http://trustee.ietf.org/license-info) in effect on the date of Holsten & Hunt Expires June 2, 2011 [Page 1] Internet-Draft The 'about' URI scheme November 2010 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. 1. Introduction An "about" URI is designed to be used internally by applications for almost any desired purpose. Such URIs have commonly been used by web browsers for providing access to built-in functionality, such as application information, preferences, settings, or "easter eggs". 2. Terminology 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]. 3. URI Syntax The general syntax of an "about" URI is defined below using ABNF [RFC5234]: abouturi = "about:" segment [ "?" query ] where "segment" and "query" are defined in [RFC3986]. 4. Encoding Considerations Because many characters are not permitted with this syntax, the "segment" and "query" elements MAY contain characters from the Unicode Character Set [UCS] as suggested by URI [RFC3986], by first encoding those characters as octets to the UTF-8 character encoding [RFC3629]; then only those octets that do not correspond to characters in the unreserved set [RFC3986] SHOULD be percent-encoded. By using UTF-8 encoding, there are no known compatibility issues with mapping Internationalized Resource Identifiers to "about" URIs according to [RFC3987]. Since "about" URIs do not use domain names, "ireg-name" conversion is unnecessary. 5. Resolving "about" URIs A reserved "about" URI is one that is defined by a specification for a specific purpose, which MAY also be defined to be resolvable. Holsten & Hunt Expires June 2, 2011 [Page 2] Internet-Draft The 'about' URI scheme November 2010 An unreserved "about" URI is any other "about" URI that is not defined by a specification for a specific purpose, but which MAY be recognized by an application. An unrecognized "about" URI is an "about" URI that is not recognized by an application. 5.1. Reserved "about" URIs Other specifications MAY reserve "about" URIs. Applications attempting to resolve reserved "about" URIs that are not defined to be resolvable, MAY treat such URIs as being unreserved. 5.1.1. about:blank The "about" URI with the segment equal to "blank" and no query component is reserved by this specification. i.e. "about:blank". Applications resolving the URI "about:blank" MUST return a resource of zero length, containing no data, with the media type "text/html" and the character encoding "UTF-8". Note: If a query component is provided with "about:blank", such as "about:blank?" or "about:blank?foo", then the URI is not considered to be reserved by this specification. 5.2. Unreserved "about" URIs Applications MAY resolve any unreserved "about" URI to any resource, either internal or external, or redirect to an alternative URI. Note: As "about" URIs are designed to be internal to each application, there is no expectation of any unreserved URI returning the same resource among different applications. However, it is worth noting that some conventions have arisen for providing particular functionality via common "about" URIs. 5.3. Unrecognized "about" URIs Applications SHOULD resolve unrecognized "about" URIs in the same way as "about:blank". 5.4. Examples The following examples illustrate some known URIs supported by existing applications. They are not guaranteed to be resolvable by every application. Holsten & Hunt Expires June 2, 2011 [Page 3] Internet-Draft The 'about' URI scheme November 2010 about:config Commonly provides access to application preferences and settings about:cache Commonly provides access to information about resources stored in the browsers cache. Current Mozilla Firefox implementations also accept a query string to specify a specific device to show more information about. e.g. about: cache?device=offline provides details about the offline cache. about:plugins Commonly provides access to information about installed plugins about:mozilla An easter egg supported by Mozilla showing a passage from the fictional Book of Mozilla Applications are also permitted to redirect such URIs. For example, Opera redirects all "about" URIs, with the exception of "about:blank", to the equivalent URI using their internal "opera:" scheme. e.g. "about:config" redirects to "opera:config". This is not an exhaustive list. Many more are supported by numerous applications. For more examples, consult Wikipedia's entry on the "about: URI Scheme" [wikiabout]. 6. Normalization "about" URIs use the standard URI normalization rules [RFC3986], specifically Simple String Comparison, Case Normalization, and Percent-Encoding Normalization. For example, "about:blank", "about:blan%6B" and "about:blan%6b" are equivalent, though the percent-encoded forms are discouraged. Due to the structure of "about" URIs, some normalizations do not apply, specifically Syntax- Based Normalization, Scheme-Based Normalization, and Protocol-Based Normalization. For example, "about:blank" is not equivalent to "about:BLANK", "about:blank?" or "about:blank:", each MAY represent a different resource. Similarly, "about:blank%3F" is not equivalent to "about:blank?". 7. Security Considerations "about" URIs might identify resources that reveal sensitive information. Applications SHOULD ensure appropriate restrictions are in place to protect such information from access or modification by untrusted sources. Implementations SHOULD also take note of the security considerations described by [RFC3986]. In particular, the following issues SHOULD be considered: Holsten & Hunt Expires June 2, 2011 [Page 4] Internet-Draft The 'about' URI scheme November 2010 Reliability and Consistency: Implementations are responsible for the reliability and consistency of the resources returned. However, implementations SHOULD take care with "about" URIs that might redirect to, or otherwise return a resource that might subsequently access, remote resources, which might not be reliable or consistent. Malicious Construction: Implementations SHOULD take care to prevent the construction of "about" URIs that might inadvertently perform damaging local or remote operations, such as the modification of data, or leaking of data to untrusted resources. For example, incorporating unsanitised data provided by the user via the query string into the resulting page could allow attackers to inject scripts into pages, similar to a cross-site scripting (XSS) attack. Sensitive Information: Implementations SHOULD avoid including sensitive information, such as passwords, within "about" URIs. The security considerations for Rare IP Address Formats and Semantic Attacks, as discussed by [RFC3986] do not apply to about URIs, as they do not contain either IP addresses nor userinfo components. 8. IANA Considerations This specification requests the IANA provisionally register the "about" URI scheme as specified in this document and summarized in the following template, per [RFC4395]: URI scheme name: about Status: Permanent URI scheme syntax: See RFCXXXX, Section 3 URI scheme semantics: See RFCXXXX, Section 1 Encoding considerations: Percent-encoding is allowed in "segment" and "query" components. Internationalization is handled by IRI processing. See Section 4. Intended usage: An "about" URI is designed to be used internally by applications for almost any desired purpose. See RFCXXXX, Section 1 Holsten & Hunt Expires June 2, 2011 [Page 5] Internet-Draft The 'about' URI scheme November 2010 Applications and/or protocols that use this URI scheme name: Any applications that use URIs as identifiers for private resources, such as web browsers. Interoperability considerations: Applications are only REQUIRED to support "about:blank", and MAY choose to interpret other "about" URIs differently. Security considerations: Applications SHOULD ensure appropriate restrictions are in place to protect sensitive information that might be revealed by "about" URIs from access or modification by untrusted sources. See RFCXXXX, Section 7. Relevant publications: RFCXXXX Contact: Joseph Holsten (joseph@josephholsten.com) Author/Change controller: W3C 9. Acknowledgements This document was made possible thanks to the input of Henri Sivonen, Ian Hickson, Larry Masinter, Bjoern Hoehrmann and Julian Reschke. 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource Identifiers (IRIs)", RFC 3987, January 2005. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. [UCS] International Organization for Standardization, "Information Technology - Universal Multiple-Octet Coded Character Set (UCS)", ISO/IEC Standard 10646, December 2003. Holsten & Hunt Expires June 2, 2011 [Page 6] Internet-Draft The 'about' URI scheme November 2010 10.2. Informative References [RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and Registration Procedures for New URI Schemes", BCP 35, RFC 4395, February 2006. [wikiabout] Wikipedia, The Free Encyclopedia, "About: URI scheme". Authors' Addresses Joseph Anthony Pasquale Holsten EMail: joseph@josephholsten.com URI: http://josephholsten.com Lachlan Hunt Opera Software, ASA. EMail: lachlan.hunt@lachy.id.au URI: http://lachy.id.au/ Holsten & Hunt Expires June 2, 2011 [Page 7]