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draft-holtman-http-safe-00.txt

From: Koen Holtman <koen@win.tue.nl>
Date: Thu, 10 Oct 1996 12:03:21 +0200 (MET DST)
Message-Id: <199610101003.MAA05724@wsooti09.win.tue.nl>
To: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Cc: Koen Holtman <koen@win.tue.nl>

Larry requested an internet draft to progress the
REPOST/Idempotent/Redo-Safe/Safe issue, so I made one.

Happy reading!

Koen.

----snip---

HTTP Working Group                                     Koen Holtman, TUE
Internet-Draft
Expires: April 10, 1997                                 October 10, 1996


                       The Safe Response Header

                     draft-holtman-http-safe-00.txt


STATUS OF THIS MEMO

        This document is an Internet-Draft. Internet-Drafts are
        working documents of the Internet Engineering Task Force
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ABSTRACT

   This document proposes a HTTP response header called Safe, which
   can be used to label the corresponding POST request as being safe.
   This labeling will allow user agents to present services which use
   safe POSTs in a more user-friendly way.  Improving the
   user-friendliness of safe POSTs is considered important, because
   web internationalization will depend for a large part on the use of
   safe POSTs.


1  Introduction

 This document proposes a HTTP response header called Safe, which can
 be used to label the corresponding POST request as being safe.  This
 labeling will allow user agents to present services which use safe
 POSTs in a more user-friendly way.  Improving the user-friendliness
 of safe POSTs is considered important, because web
 internationalization will depend for a large part on the use of safe
 POSTs.


2 Background

 According to Section 9.1.1 (Safe Methods) of the HTTP/1.1 draft
 specification [1], POST requests are assumed to be `unsafe' by
 default.  `Unsafe' means `causes side effects for which the user will
 be held accountable'.

 If the POST request is unsafe, explicit user confirmation is
 necessary before the request is repeated.  User agents will repeat
 POST requests when the user presses the RELOAD button while a POST
 result is displayed, or when the history function is used to
 redisplay a POST result which is no longer in the history buffer.

 The necessary confirmation dialog often takes the form of a `repost
 form data?'  dialog box.  The dialog is confusing to many users, and
 slows down navigation in any case.

 In theory, if the repeated POST request is safe, the user-unfriendly
 confirmation dialog can be omitted.  However, up till now, HTTP has
 no mechanism by which agents can tell if POST requests are safe.
 This proposal adds such a mechanism.

 Many content authors have managed to avoid the confirmation dialog
 problem by using GETs for form submission instead of safe POSTs.
 However, this escape is not possible for forms

    a) which are (sometimes) used to submit large amounts of data
    b) which are (sometimes) used to submit data in a charset other
       than ISO-8859-1.

 Case b) will be the increasingly common; web internationalization [2]
 makes it necessary to use the POST method for form submission.

 It is therefore considered important to eliminate the unnecessary
 confirmation dialogs for safe POSTs as soon as possible.  They are a
 counter-incentive to the upgrading of GET based forms services (like
 search engines) to internationalized POST based forms services.


3 The Safe response header

 This header is proposed as an addition to the HTTP/1.x suite.

 The Safe response header field indicates whether the corresponding
 request is safe in the sense of Section 9.1.1 (Safe Methods) of the
 HTTP/1.1 draft specification [1].

   Safe        = "Safe" ":" safe-nature
   safe-nature = "yes" | "no"

 An example of the field is:

       Safe: yes

 If the Safe header is absent, the corresponding request must be
 considered unsafe, unless it is a GET or HEAD request.  GET and HEAD
 requests are safe by definition, user agents must ignore a `Safe: no'
 header field in GET and HEAD responses.

    Note: User agents can use the received information about safety
    when repeating an earlier request.  If the request is known to be
    safe, it can be silently repeated without asking for user
    confirmation.


4 Smooth upgrade path

 That the Safe header provides a smooth upgrade path; if a service
 switches from GETs to safe POSTs, existing browsers will still be
 able to access the service.  Its use requires little re-coding effort
 for service authors and user agent authors, and is optional in any
 case.


5 About syntax

 This document mainly intends to recommend a _mechanism_; the syntax
 of the corresponding header is considered less important.  One
 alternative to the addition of a Safe header would be the addition of
 a `safe' response directive to the Cache-Control header.


6 Security considerations

 This proposal adds no new HTTP security considerations.


7 References

   [1] Fielding et al, Hypertext Transfer Protocol -- HTTP/1.1.
       Internet-Draft draft-ietf-http-v11-spec-07.txt, HTTP Working
       Group, August 12, 1996

   [2] Yergeau et al, Internationalization of the Hypertext Markup
       Language, Internet-Draft draft-ietf-html-i18n-05.txt, Network
       Working Group, August 7, 1996


8 Author's address

   Koen Holtman
   Technische Universiteit Eindhoven
   Postbus 513
   Kamer HG 6.57
   5600 MB Eindhoven (The Netherlands)
   Email: koen@win.tue.nl


Expires: April 10, 1997
Received on Thursday, 10 October 1996 03:10:03 EDT

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