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Versions: 00                                                            
Network Working Group                                           R. Polli
Internet-Draft                         Team Digitale, Italian Government
Intended status: Standards Track                            9 March 2020
Expires: 10 September 2020


                        Retry-Scope header field
                       draft-polli-retry-scope-00

Abstract

   This document defines the Retry-Scope header field for HTTP thus
   allowing a server to communicate the scope of the returned Retry-
   After header field.

Note to Readers

   _RFC EDITOR: please remove this section before publication_

   Discussion of this draft takes place on the HTTP working group
   mailing list (ietf-http-wg@w3.org), which is archived at
   https://lists.w3.org/Archives/Public/ietf-http-wg/
   (https://lists.w3.org/Archives/Public/ietf-http-wg/).

   The source code and issues list for this draft can be found at
   https://github.com/ioggstream/draft-polli-Retry-Scope
   (https://github.com/ioggstream/draft-polli-Retry-Scope).

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 https://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 10 September 2020.







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Copyright Notice

   Copyright (c) 2020 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 (https://trustee.ietf.org/
   license-info) in effect on the date of 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Header Specifications . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Retry-Scope . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
     3.1.  Role of intermediaries  . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Retry-Scope Header Field Registration . . . . . . . . . .   4
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   5
   FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Change Log  . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The Retry-After header defined in Section 7.1.3 of [SEMANTICS] allows
   a server to indicate how long the user agent ought to wait before
   making a follow-up request.

   While Retry-After applies to the issued request, it may be useful for
   the server to communicate to the user agent that the conditions that
   lead to returning Retry-After are broader in scope than a single
   request.

   This proposal allows a server to convey that scope in the Retry-Scope
   response header field, and ask the client to temporarily refrain from
   making other requests to the same resource, or even to all resources
   on the same server.






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1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.  These words may also appear in this
   document in lower case as plain English words, absent their normative
   meanings.

   This document uses the Augmented BNF defined in [RFC5234] and updated
   by [RFC7405] along with the "#rule" extension defined in Section 7 of
   [MESSAGING] and the URI-reference rule defined in Section 2.7 of
   [MESSAGING].

   The terms "intermediaries" and "target URI" are to be interpreted as
   described in [MESSAGING].

2.  Header Specifications

   The following header is defined

2.1.  Retry-Scope

   The Retry-Scope response header field indicates that the conditions
   that lead to returning Retry-After are broader in scope than a single
   request.

      Retry-Scope = URI-reference

   Two examples of Retry-Scope:

      Retry-Scope: /books
      Retry-Scope: https://api.example/

   A user agent receiving the Retry-Scope header field in conjunction
   with a Retry-After header field ought to wait before making further
   request to the resource identified by the Retry-Scope field value.

   This header MUST NOT be repeated; if a user agent receives multiple
   Retry-Scope header fields, then it SHOULD ignore them.

   Intermediaries aware of the Retry-Scope semantics (eg. reverse
   proxies) MAY modify the Retry-Scope in order to help the user agent
   to correctly identify the scope and ensure that the field value
   matches the target URI, like they would have done for the Location
   header field defined in Section 7.1.2 of [SEMANTICS].




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3.  Security Considerations

3.1.  Role of intermediaries

   An intermediary, by chance or purpose, might alter the scope of the
   Retry-Scope thus causing the user agent to refrain contacting other
   server resource.

   When the server originating the Retry-Scope is behind one or more
   intermediaries it is possible that the field value is not consistent
   with the target URI.

4.  IANA Considerations

4.1.  Retry-Scope Header Field Registration

   This section registers the "Retry-Scope" header field in the
   "Permanent Message Header Field Names" registry ([RFC3864]).

   Header field name: "Retry-Scope"

   Applicable protocol: http

   Status: standard

   Author/Change controller: IETF

   Specification document(s): Section 2.1 of this document

5.  Normative References

   [MESSAGING]
              Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              DOI 10.17487/RFC3864, September 2004,
              <https://www.rfc-editor.org/info/rfc3864>.





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   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC7405]  Kyzivat, P., "Case-Sensitive String Support in ABNF",
              RFC 7405, DOI 10.17487/RFC7405, December 2014,
              <https://www.rfc-editor.org/info/rfc7405>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [SEMANTICS]
              Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

Appendix A.  Acknowledgements

   This specification was born from a thread created by Martin Thomson,
   and the subsequent discussion.

FAQ

   Q: Why not using link relations?  This solution is simpler and was
      previously discussed here (https://github.com/httpwg/http-core/
      pull/317#issuecomment-585868767).

Change Log

   RFC EDITOR PLEASE DELETE THIS SECTION.

Author's Address

   Roberto Polli
   Team Digitale, Italian Government

   Email: robipolli@gmail.com











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