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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 7231 (Obsoleted by RFC 9110) -- Obsolete informational reference (is this intentional?): RFC 7234 (Obsoleted by RFC 9111) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group E. Wilde 3 Internet-Draft CA Technologies 4 Intended status: Standards Track August 3, 2017 5 Expires: February 4, 2018 7 The Sunset HTTP Header 8 draft-wilde-sunset-header-03 10 Abstract 12 This specification defines the Sunset HTTP response header field, 13 which indicates that a URI is likely to become unresponsive at a 14 specified point in the future. 16 Note to Readers 18 This draft should be discussed on the ART mailing list 19 (). 21 Online access to all versions and files is available on GitHub 22 (). 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on February 4, 2018. 41 Copyright Notice 43 Copyright (c) 2017 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 59 1.1. Temporary Resources . . . . . . . . . . . . . . . . . . . 2 60 1.2. Migration . . . . . . . . . . . . . . . . . . . . . . . . 3 61 1.3. Retention . . . . . . . . . . . . . . . . . . . . . . . . 3 62 1.4. Deprecation . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 3. The Sunset HTTP Response Header . . . . . . . . . . . . . . . 3 65 4. Sunset and Caching . . . . . . . . . . . . . . . . . . . . . 4 66 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 67 5.1. The Sunset Response Header . . . . . . . . . . . . . . . 4 68 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 69 7. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 70 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 71 8.1. Normative References . . . . . . . . . . . . . . . . . . 6 72 8.2. Informative References . . . . . . . . . . . . . . . . . 6 73 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 75 1. Introduction 77 As a general rule, URIs should be stable and persistent, so that 78 applications can use them as stable and persistent identifiers for 79 resources. However, there are many scenarios where for a variety of 80 reasons, URIs have a limited lifetime. In some of these scenarios, 81 this limited lifetime is known in advance. In this case, it can be 82 useful for clients if resources make this information about their 83 limited lifetime known. This specification defines the Sunset HTTP 84 response header field, which indicates that a URI is likely to become 85 unresponsive at a specified point in the future. 87 Possible scenarios for known lifetimes of resources include, but are 88 not limited to the following scenarios. 90 1.1. Temporary Resources 92 Some resources may have a limited lifetime by definition. For 93 example, a pending order represented by a resource may already list 94 all the details of the order, but may only exist for a limited time 95 unless it is confirmed and only then becomes permanent. In such a 96 case, the service managing the pending order can make this limited 97 lifetime explicit, allowing clients to understand that the pending 98 order, unless confirmed, will disappear at some point in time. 100 1.2. Migration 102 If resources are changing identity because a service migrates them, 103 then this may be known in advance. While it may not yet be 104 appropriate to use HTTP redirect status codes (3xx), it may be 105 interesting for clients to learn about the service's plan to take 106 down the original resource. 108 1.3. Retention 110 There are many cases where regulation or legislation require that 111 resources are kept available for a certain amount of time. However, 112 in many cases there also is a requirement for those resources to be 113 permanently deleted after some period of time. Since the deletion of 114 the resource in this scenario is governed by well-defined rules, it 115 could be made explicit for clients interacting with the resource. 117 1.4. Deprecation 119 For Web APIs one standard scenario is that an API or specific subsets 120 of an API may get deprecated. If this is planned in advance, then 121 for the time before the actual deprecation is rolled out, the 122 resources that will be affected by the deprecation can make the date 123 of their deprecation known. This allows consumers of the API to be 124 notified of the upcoming deprecation. 126 2. Terminology 128 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 129 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 130 document are to be interpreted as described in RFC 2119 [RFC2119]. 132 3. The Sunset HTTP Response Header 134 The Sunset HTTP response header field allows a server to communicate 135 the fact that a resource is expected to become unresponsive at a 136 specific point in time. It provides information for clients which 137 they can use to control their usage of the resource. 139 The Sunset header contains a single timestamp which advertises the 140 point in time when the resource is expected to become unresponsive. 141 The Sunset value is an HTTP-date timestamp, as defined in 142 Section 7.1.1.1 of [RFC7231]. 144 Sunset = HTTP-date 145 For example 147 Sunset: Sat, 31 Dec 2018 23:59:59 GMT 149 Clients SHOULD treat Sunset timestamps as hints: It is not guaranteed 150 that the resource will in fact be available until that time, and will 151 not be available after that time. However, since this information is 152 provided by the resource itself, it does have some credibility. 154 After the Sunset time has arrived, it is likely that interactions 155 with the resource will result in client-side errors (HTTP 4xx status 156 codes), redirect responses (HTTP 3xx status codes), or the client 157 might not be able to interact with the resource at all. The Sunset 158 header does not expose any information about which of those behaviors 159 can be expected. 161 Clients not interpreting an existing Sunset header field can operate 162 as usual and simply may experience the resource becoming unavailable 163 without getting any notification about it beforehand. 165 4. Sunset and Caching 167 It should be noted that the Sunset HTTP response header field serves 168 a different purpose than HTTP caching [RFC7234]. HTTP caching is 169 concerned with making resource representations (i.e., represented 170 resource state) reusable, so that they can be more efficiently used. 171 This is achieved by using header fields that allow clients and 172 intermediaries to better understand when a resource representation 173 can be reused, or when resource state (and thus the representation) 174 may have changed. 176 The Sunset header field is not concerned with resource state at all. 177 It only signals that a resource is expected to become unavailable at 178 a specific point in time. There are no assumptions about if, when, 179 or how often a resource may change state in the meantime. 181 For these reasons, the Sunset header field and HTTP caching should be 182 seen as complementary, and not as overlapping in scope and 183 functionality. 185 5. IANA Considerations 187 5.1. The Sunset Response Header 189 The Sunset response header should be added to the permanent registry 190 of message header fields (see [RFC3864]), taking into account the 191 guidelines given by HTTP/1.1 [RFC7231]. 193 Header Field Name: Sunset 195 Applicable Protocol: Hypertext Transfer Protocol (HTTP) 197 Status: Standard 199 Author/Change controller: IETF 201 Specification document(s): RFC XXXX 203 6. Security Considerations 205 The Sunset header field should be treated as a resource hint, meaning 206 that the resource is indicating its potential unavailability. The 207 definitive test whether or not the resource in fact is available or 208 not will be to attempt to interact with it. Applications should 209 never treat an advertised Sunset date as a definitive prediction that 210 is going to happen at the specified point in time. The Sunset 211 indication may have been inserted by an intermediary, or the 212 advertised date may get changed or withdrawn by the resource owner. 214 The main purpose of the Sunset header field is to signal intent, so 215 that applications using resources may get a warning ahead of time and 216 can react accordingly. What an appropriate reaction is (such as 217 switching to a different resource or service), what it will be based 218 on (such as machine-readable formats that allow the switching to be 219 done automatically), and when it will happen (such as ahead of the 220 advertised date or only when the resource in fact becomes 221 unavailable) is outside the scope of this specification. 223 7. Example 225 Assuming that a resource has been created in an archive that for 226 management or compliance reasons only stores resources for two years, 227 and permanently deletes them afterwards, then the Sunset header field 228 can be used to expose this information. If such a resource has been 229 created on November 11, 2014, then the following header field can be 230 included in responses: 232 Sunset: Fri, 11 Nov 2018 11:11:11 GMT 234 This allows clients that are aware of the Sunset header field to 235 understand that the resource likely will become unavailable at the 236 specified point in time. Clients can decide to ignore this 237 information, adjust their own behavior accordingly, or alert 238 applications or users about this timestamp. 240 Even though the Sunset header information is made available by the 241 resource itself, there is no guarantee that the resource indeed will 242 become unavailable, and if so, how the response will look like for 243 requests made after that timestamp. In case of the archive used as 244 an example here, the resource indeed may be permanently deleted, and 245 requests for the URI after the Sunset timestamp may receive a "410 246 Gone" HTTP response. (This is assuming that the archive keeps track 247 of the URIs that it had previously assigned; if not, the response may 248 be a more generic "404 Not Found".) 250 8. References 252 8.1. Normative References 254 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 255 Requirement Levels", RFC 2119, March 1997. 257 [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration 258 Procedures for Message Header Fields", BCP 90, RFC 3864, 259 September 2004. 261 [RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 262 (HTTP/1.1): Semantics and Content", RFC 7231, June 2014. 264 8.2. Informative References 266 [RFC7234] Fielding, R., Nottingham, M., and J. Reschke, "Hypertext 267 Transfer Protocol (HTTP/1.1): Caching", RFC 7234, June 268 2014. 270 Author's Address 272 Erik Wilde 273 CA Technologies 275 Email: erik.wilde@dret.net 276 URI: http://dret.net/netdret/