Network Working Group S. Harhalakis Internet-Draft TEI of Thessaloniki Intended status: Standards Track April 8, 2008 Expires: October 10, 2008 Timezone Information in HTTP draft-sharhalakis-httptz-03.txt Status of this Memo 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 becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 10, 2008. Harhalakis Expires October 10, 2008 [Page 1] Internet-Draft Timezone Information in HTTP April 2008 Abstract This document defines a HTTP header for clients to provide timezone information to web servers. An ABNF description of the corresponding header is provided. Harhalakis Expires October 10, 2008 [Page 2] Internet-Draft Timezone Information in HTTP April 2008 Discussion Discussion about this document takes place in http-wg mailing list (ietf-http-wg@w3.org). Please CC v13@v13.gr too. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Requirements . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.4. Considerations . . . . . . . . . . . . . . . . . . . . . . 5 2. Definition . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Client support . . . . . . . . . . . . . . . . . . . . . . 7 2.2. Server support . . . . . . . . . . . . . . . . . . . . . . 7 2.3. Proxy considerations . . . . . . . . . . . . . . . . . . . 8 3. Security Considerations . . . . . . . . . . . . . . . . . . . 9 3.1. Client side . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Server side . . . . . . . . . . . . . . . . . . . . . . . 9 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 12 6.2. Informative . . . . . . . . . . . . . . . . . . . . . . . 12 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 13 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 15 Harhalakis Expires October 10, 2008 [Page 3] Internet-Draft Timezone Information in HTTP April 2008 1. Introduction 1.1. Purpose Many web based applications could benefit from knowing the timezone of their visiting clients. Most of the dynamic content provider applications depend on user accounts to display time and date in the client's native timezone. Even this is not always adequate since people may travel across timezone boundaries and they currently need to update their web accounts to reflect their actual timezone information. Furthermore, this is also the case for all HTTP-like or HTTP based protocols that make use of timestamps. This document addresses this need by describing a header to be used by HTTP [RFC2616] so that interested clients may provide their current timezone information to web servers and thus to web based applications. 1.2. Requirements 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]. An implementation is not compliant if it fails to satisfy one or more of the MUST or REQUIRED level requirements. An implementation that satisfies all the MUST or REQUIRED level and all the SHOULD level requirements is said to be "unconditionally compliant"; one that satisfies all the MUST level requirements but not all the SHOULD level requirements is said to be "conditionally compliant". 1.3. Terminology This document uses the following terms: HTTP client Every client of the HTTP protocol. Commonly referred to as a web browser. Timezone string A timezone string as described in this document. HTTP header An HTTP header as described in [RFC2616]. The HTTP header specification of this document is presented in the augmented Backus-Naur Form that is described in [RFC2616]. Harhalakis Expires October 10, 2008 [Page 4] Internet-Draft Timezone Information in HTTP April 2008 1.4. Considerations Because of the variety of systems on the Internet and the non- technical nature of timezone, there is no simple method for a client to provide timezone information to HTTP servers. During the writing of this document the following were considered: o Simplicity is a must. The specification needs to be as simple as possible or allow for partial handling in a simple manter. o There is a variety of timezone styles. Some countries don't experience Daylight Saving Time (DST). Other countries have very unstable DST. o Politics affect DST. This makes it a moving target. o DST settings may change from year to year. o Complete past and future timezone information cannot be described using a simple string. o End user systems may have an invalid timezone configured. o There are systems without timezone information. o Not all systems have a time source. This document tries to provide adequate data for applications that can take advantage of the Timezone information to fulfill their needs. There are different levels of requirements that applications may have and HTTP clients may be able to satisfy. Thus this document introduces a way for HTTP clients to provide: o The current client time. o The current time offset. o The current year's timezone information. o Complete timezone information. depending on their abilities. Simple server side applications may just use the current time offset and hope that it is correctly set. More advanced applications (like calendars) need to know when a DST change will occur to correctly represent future or past times. Even more advanced applications may need to know the exact client timezone which can only be described Harhalakis Expires October 10, 2008 [Page 5] Internet-Draft Timezone Information in HTTP April 2008 using a reference to a timezone database entry. Finally, applications may choose to use the client's current time as reference time and optionally ignore client timezone information. Paragraph 4.4 of [RFC3339] "Unqualified Local Time" considers systems with invalid timezone information as inappropriate for Internet communications. Harhalakis Expires October 10, 2008 [Page 6] Internet-Draft Timezone Information in HTTP April 2008 2. Definition 2.1. Client support HTTP clients MAY provide local timezone information to visiting web sites. This information is sent using the client-timezone HTTP header: client-timezone = "Timezone" ":" tzdescr tzdescr = rfctime [ ";" posixtz [ ";" tznames ] ] rfctime = posixtz = tznames = tzname *( "," tzname ) tzname = Where: rfctime A local time string as specified in [RFC3339]. It includes the current time offset. posixtz A POSIX 1003.1 timezone string as specified in [POSIXTZ]. tzname A timezone name. Many systems use a timezone name from a timezone database. This is one such string. More than one such strings may be provided. All of them MUST identify the same timezone. HTTP clients SHOULD provide all three parts of the header unless they aren't able to do so or they are configured not to send timezone information. Clients that don't have a clock source MUST use zeroes for all digits of the datetime string except from the offset. "Z" MUST by used when the offset is also unavailable. 2.2. Server support Compliant servers MAY validate the format of the provided information. Timezone strings that are not in a valid format MAY not be accepted. Validation checks MUST NOT be performed on the content of the Timezone string by servers. Only the format of the string may be checked. This way outdated servers will not filter out proper Harhalakis Expires October 10, 2008 [Page 7] Internet-Draft Timezone Information in HTTP April 2008 information. 2.3. Proxy considerations HTTP proxy servers MUST NOT alter this information. Server side scripts that produce customized results based on the timezone information MUST return an appropriate "Vary" header as specified in paragraph 14.44 of [RFC2616]. Harhalakis Expires October 10, 2008 [Page 8] Internet-Draft Timezone Information in HTTP April 2008 3. Security Considerations 3.1. Client side Timezone information may consist personal information regarding the location of a person. HTTP clients MUST NOT provide this information without letting the user prevent it. Clients must either ask users or provide an option for enabling/disabling this feature. The later is RECOMMENDED. In most cases, Timezone information will not disclose more personal information than an IP address. HTTP clients MAY default in enabling this to imporve user experience. 3.2. Server side Web based applications MUST treat this information as user input that can be invalid and/or malicious. Harhalakis Expires October 10, 2008 [Page 9] Internet-Draft Timezone Information in HTTP April 2008 4. IANA Considerations This specification requires registration of a Message Header Field for HTTP [RFC3864]. Header field: Timezone Applicable protocol: HTTP Status: Experimental Author/change controller: IETF (iesg@ietf.org) Internet Engineering Task Force Specification document: [ this document ] Harhalakis Expires October 10, 2008 [Page 10] Internet-Draft Timezone Information in HTTP April 2008 5. Acknowledgements Timezone information in HTTP was also proposed by David Robinson in an email at HTTP Working Group back in 1995 but the replies he got were negative. It was believed that timezone information should be handled by CGI scripts and not by the Hypertext Transfer Protocol. The discussion can be found at http-wg mailing list archives: . This document was properly formed thanks to the remarks of Julian Reschke. Harhalakis Expires October 10, 2008 [Page 11] Internet-Draft Timezone Information in HTTP April 2008 6. References 6.1. Normative [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, July 2002. [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration Procedures for Message Header Fields", BCP 90, RFC 3864, September 2004. [POSIXTZ] IEEE, The Open Group, "IEEE Std 1003.1", 2004. 6.2. Informative [I-D.rfc-editor-rfc2223bis] Reynolds, J. and R. Braden, "Instructions to Request for Comments (RFC) Authors", draft-rfc-editor-rfc2223bis-08 (work in progress), July 2004. Harhalakis Expires October 10, 2008 [Page 12] Internet-Draft Timezone Information in HTTP April 2008 Appendix A. Examples A complete timezone information header: Current time is 12:00, Jul 30, 1977. time offset is +2 hours. The full timezone string is EET2EEST3,M3.2.0/02:00,M11.1.0/02:00. The timezone database identifier string is Europe/Athens. Timezone: 1977-07-30T12:00+0200; EET2EEST3,M3.2.0/02:00,M11.1.0/02:00; Europe/Athens A partial one: GMT/UTC timezone is noted as Z(ulu). Timezone: 2007-06-12T23:48Z A header from a clock-less client without current offset information: Timezone: 0000-00-00T00:00Z; EET2EEST3,M3.2.0/02:00,M11.1.0/02:00; Europe/Athens Harhalakis Expires October 10, 2008 [Page 13] Internet-Draft Timezone Information in HTTP April 2008 Author's Address Stefanos Harhalakis Technological Educational Institute of Thessaloniki Department of Information Technology Thessaloniki, Greece GR Email: v13@v13.gr, v13@it.teithe.gr Harhalakis Expires October 10, 2008 [Page 14] Internet-Draft Timezone Information in HTTP April 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat 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 on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment This document was produced using xml2rfc v1.33 (of http://xml.resource.org/) from a source in RFC-2629 XML format. Harhalakis Expires October 10, 2008 [Page 15]