Subject: Timezone information in HTTP

From: Stefanos Harhalakis <[email-masked]>
Date: Fri, 8 Jun 2007 01:32:13 +0300

Hello there,

  Following a suggestion from Julian Reschke I'm sending the attached proposed 
I-D here for discussion. I'd like to know whether you believe that this is 
usefull.

  I'd also appreciate some hints about the timezone format. Julian suggested 
that the format should be changed to the one described in RFC3339 (+OFFSET).  
My original though was that it could be usefull to have the full timezone 
specification as described in POSIX, which includes DST information too. I 
now believe that this should be changed to RFC3339 format in favour of 
simplicity just like Julian suggested.

---

From: Bjoern Hoehrmann <[email-masked]>
Date: Fri, 08 Jun 2007 00:45:36 +0200

>I-D here for discussion. I'd like to know whether you believe that this is 

Could you elaborate on why you think a new HTTP request header would
best address this problem? For example, why would this be better than
improved client-side support for time information rendering?
-- 
Björn Höhrmann · mailto:[email-masked] · http://bjoern.hoehrmann.de
Weinh. Str. 22 · Telefon: +49(0)621/4309674 · http://www.bjoernsworld.de
68309 Mannheim · PGP Pub. KeyID: 0xA4357E78 · http://www.websitedev.de/

---

From: Stefanos Harhalakis <[email-masked]>
Date: Fri, 8 Jun 2007 02:01:42 +0300

On Friday 08 June 2007, Bjoern Hoehrmann wrote:
> >  Following a suggestion from Julian Reschke I'm sending the attached
> > proposed I-D here for discussion. I'd like to know whether you believe
> > that this is usefull.
>

  You mean something like an HTML tag that would instruct browsers to display 
their local time? If so, then I believe that this is practically impossible 
since time is tied to date. For example there can be Friday on one place and 
Saturday on another. Since the date (and time) string cannot be rendered by 
the browser (localization, format etc), the proposal would help. Also, there 
are cases where the time/date information is embedded as a graphic in an 
image that is dynamically created. Think of all network monitoring graphs 
like mrtg. Finally, time is not only a matter of displaying it to web 
clients. For example, think of a web based fax sending application which 
would need to include the sender time in the sending pages.

  I hope that this answers your question...

---

From: Stefanos Harhalakis <[email-masked]>
Date: Fri, 8 Jun 2007 02:33:37 +0300

Just realized that caching proxies should consider documents that were 
returned for different timezones as different. In other words, two requests 
with different Timezone headers should be considered different. This 
introduces an issue where two clients with different timezones ask for a 
document. Either the cache need to record the request TZ or the server side 
must return a header like 'Requested-Timezone' where the request timezone 
would be included. 

  I believe that both need to work on this. The server side should return a 
header indicating the timezone the page was created for. This means that 
pages that don't support the timezone information will not affect caches. The 
cache should intercept the returned header and hold a different copy of 
the 'same' document regarding the request. Non compliant caches would only 
loose their ability to cache timezone related documents but this is what one 
should expect.

  example:

Request #1:
Timezone: +0200

Reply #1:
Requested-Timezone: +0200
....

Request #2:
Timezone: +0300

Reply #2:
Requested-Timezone: +0300
....

Cache intercepts the 'Requested-Timezone' header and considers 'Reply #1' 
and 'Reply #2' as different documents that may be cached.

---

From: Julian Reschke <[email-masked]>
Date: Fri, 08 Jun 2007 06:43:47 +0200

Stefanos Harhalakis wrote:
> ...

Vary: Timezone

Best regards, Julian

---

From: Henrik Nordstrom <[email-masked]>
Date: Sat, 09 Jun 2007 02:17:27 +0200

fre 2007-06-08 klockan 02:33 +0300 skrev Stefanos Harhalakis:
> returned for different timezones as different.

Only if the response is timezone dependent, indicated by carrying an
"Vary: Timezone" response header.

Regards
Henrik

---

From: Stefanos Harhalakis <[email-masked]>
Date: Sat, 9 Jun 2007 14:23:56 +0300

On Friday 08 June 2007, Julian Reschke wrote:
> > returned for different timezones as different. In other words, two
> > requests with different Timezone headers should be considered different.
> > This introduces an issue where two clients with different timezones ask
> > for a document. Either the cache need to record the request TZ or the
> > server side must return a header like 'Requested-Timezone' where the
> > request timezone would be included.
> > ...
>
> Vary: Timezone

Thank you (and Henrik) about this. I didn't knew about the Vary header. I 
added this to the draft. Since there was no further feedback I changed the 
timezone string from POSIX to RFC3339 time-zone, as you suggested.

I've some more questions:

a) What is the proper procedure for working on this draft? Should this be 
submitted by the WG instead of me?
b) I've added you to the Acknowledgement section. Is this correct or should 
you be listed in the authors?
c) Should I try to send this somewhere else to get more feedback?

Thank you for your time,
Harhalakis Stefanos

---

From: Bjoern Hoehrmann <[email-masked]>
Date: Sat, 09 Jun 2007 13:41:18 +0200

>submitted by the WG instead of me?

There is currently no HTTP Working Group and I don't think there is any
other working group chartered to work on this problem so you should sub-
mit this as individual submission. http://www.ietf.org/ID.html links to
the relevant resources.

>you be listed in the authors?

That the question arises is a very strong indication that listing him as
Author would be inappropriate. Listing Julian as Author would indicate,
essentially, that you and Julian submit the document, rather than just
you alone.

>c) Should I try to send this somewhere else to get more feedback?

At this point this is up to you. If you have specific things you want to
get feedback on, you could tell us and we might be able to suggest lists
for those issues.
-- 
Björn Höhrmann · mailto:[email-masked] · http://bjoern.hoehrmann.de
Weinh. Str. 22 · Telefon: +49(0)621/4309674 · http://www.bjoernsworld.de
68309 Mannheim · PGP Pub. KeyID: 0xA4357E78 · http://www.websitedev.de/

---

From: Stefanos Harhalakis <[email-masked]>
Date: Sat, 9 Jun 2007 15:07:14 +0300

> mit this as individual submission. http://www.ietf.org/ID.html links to

That's what I thought. I've already read the documentation/RFCs about ID 
authoring, submission and procedures.

> get feedback on, you could tell us and we might be able to suggest lists

I'm currently considering posting a request for comments about this to php and 
firefox/konqueror mailing lists.

Thanks...

---

From: Julian Reschke <[email-masked]>
Date: Mon, 11 Jun 2007 09:49:09 +0200

> submitted by the WG instead of me?

There is no WG (yet), and even if there would be one it probably 
wouldn't be in scope of the charter.

But it *is* good to discuss it here. For instance, I'm not convinced 
it's the right approach; HTML5 is adding markup to allow user agents to 
do smarter things with time information.

> you be listed in the authors?

No, that's fine. I just tryng to by helpful to get the format and the 
editorial issues right.

Here's another one: I think currently the spec is not clear about 
whether it uses the RFC2616 or the RFC4234 ABNF format...

Best regards, Julian

---

From: Stefanos Harhalakis <[email-masked]>
Date: Mon, 11 Jun 2007 18:08:05 +0300

> do smarter things with time information.

  I'm willing to discuss this for as long as it takes to persuade everyone 
about its usefullness or someone persuade me that it is not required :-)

  I also want to talk about this as much as possible (but not to annoy you).

  I see that HTML 5 has markup for date, time and offsets. Perhaps the time 
offset could be embedded in the html tags. Something like:
<time offset="+0200">02:00:00</time> but this is still not what one should 
expect from HTML. Since HTML is a markup language, it may only tag the text 
and not transform it. The '02:00:00' will always be a string.

  Examples from HTML 5 draft:

<time datetime="2006-09-23">a saturday</time>
<time datetime="2006-09-24 05:00 -7">5am the next morning</time>
<time>08:00</time>

  Should it be possible for browsers to change 08:00 to their local time, 
supposing that TZ information is embedded in <time> ?

  Finally, this doesn't solve the problem of server side generated graphics, 
metadata, files etc (content that is not HTML) that include time information 
in them. Consider the MRTG and FAX examples that were mentioned in a previous 
email.

> whether it uses the RFC2616 or the RFC4234 ABNF format...

It uses the RC2616 ABNF format. In paragraph 1.3 it says:

   The HTTP header specification of this document is presented in the
   augmented Backus-Naur Form that is described in [RFC2616].

But your point is correct. I will remove RFC4234 from the informative 
references.