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
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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.
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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
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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].
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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
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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.
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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 = <local time>
posixtz = <a POSIX 1003.1 timezone string>
tznames = tzname *( "," tzname )
tzname = <a timezone string from a timezone database>
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
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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].
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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.
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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 ]
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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: <http:/
/www.hpl.hp.com/personal/ange/archives/archives-95/http-wg-archive/
0521.html>.
This document was properly formed thanks to the remarks of Julian
Reschke.
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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.
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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
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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
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This document was produced using xml2rfc v1.33 (of
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