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Nottingham 3 Internet-Draft Akamai Technologies 4 Expires: March 23, 2001 September 22, 2000 6 HTTP Cache Control Extensions for Direct Cache Manipulation 7 draft-nottingham-cache-extensions-00 9 Status of this Memo 11 This document is an Internet-Draft and is in full conformance with 12 all provisions of Section 10 of RFC2026. 14 Internet-Drafts are working documents of the Internet Engineering 15 Task Force (IETF), its areas, and its working groups. Note that 16 other groups may also distribute working documents as 17 Internet-Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six 20 months and may be updated, replaced, or obsoleted by other documents 21 at any time. It is inappropriate to use Internet-Drafts as reference 22 material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at 25 http://www.ietf.org/ietf/1id-abstracts.txt 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html. 30 This Internet-Draft will expire on March 23, 2001. 32 Copyright Notice 34 Copyright (C) The Internet Society (2000). All Rights Reserved. 36 Abstract 38 HTTP/1.1 provides for extensions to Cache-Control headers, which 39 provide new methods of controlling caches. This document specifies 40 extensions which allow content providers more precise control over 41 shared caches. 43 1. Introduction 45 Shared caches are sometimes deployed into the Internet with the 46 participation of the providers of content which will be flowing 47 through them. For example, a content provider may use a surrogate 48 HTTP server to improve performance. Likewise, an access provider who 49 controls both the origin servers and caching proxies in their 50 network may wish to optimize the relationship between them. 52 Although HTTP/1.1 provides mechanisms for controlling caches, it 53 does not provide an efficient means of controlling objects already 54 in cache. In the situations outlined above, it would be useful to 55 allow content providers to manipulate cached objects. 57 This document provides simple mechanisms to do so, by use of 58 Cache-Control request header extensions. 60 It should be noted that because of their nature, the extensions lose 61 efficiency when used with a large number of shared caches. 63 1.1 Requirements 65 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 66 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 67 document are to be interpreted as described in RFC 2119[2]. 69 An implementation is not compliant if it fails to satisfy one or 70 more of the MUST or REQUIRED level requirements. An implementation 71 that satisfies all the MUST or REQUIRED level and all the SHOULD 72 level requirements is said to be "unconditionally compliant"; one 73 that satisfies all the MUST level requirements but not all the 74 SHOULD level requirements is said to be "conditionally compliant". 76 2. Direct Cache Manipulation Extensions 78 This section specifies Cache-Control request header extensions which 79 allow specification of cache operations, as allowed for in 80 HTTP/1.1[1]. 82 These extensions are intended for the manipulation of shared caches; 83 they MUST NOT be interpreted by non-shared caches. 85 Upon receiving one of these extension headers, an implementation 86 will perform the operation specified, and then MUST return a 87 response; the type of response returned is dependent on the nature 88 of the operation. 90 Such responses MUST NOT have an entity body included. If the status 91 code returned would normally have a body, a 'Content-Length: 0' 92 header MUST be included. 94 2.1 Prefetch 96 The prefetch extension allows content providers to insert an object 97 into the cache without incurring the expense of a complete round 98 trip for the object body. 100 prefetch-extension = "prefetch" 102 For example, if the resource "http://www.example.com/largeobject" 103 were requested from a DCM-capable shared cache, with a 104 "Cache-Control: prefetch" header, the intermediate would operate 105 exactly as it normally does, except that the response would not 106 contain an entity body. 108 This avoids the inefficiency of transporting the object both to the 109 cache and then to the device which made the request, which is 110 frequently near the origin server. 112 Implementations SHOULD support validation, server-driven content 113 negotiation and other HTTP mechanisms in conjunction with this 114 mechanism. 116 The prefetch extension MUST NOT be forwarded by implementations. 118 2.2 Eject 120 This extension enables the eviction of objects from the cache. When 121 an implementation receives this directive, it MUST evict the object 122 identified by the resource, so that the next request for the 123 resource is unconditional (unless the request itself is conditional). 125 eject-extension = "eject" 127 When ejecting objects, implementations MUST eject all variants of 128 the resource identified. 130 Requests containing the eject extension MUST NOT be forwarded by 131 implementations. 133 3. Security Considerations 135 This document does not address security-related issues, but the 136 mechanisms it describes should be used in conjuction with 137 appropriate authentication and authorization control. Such control 138 may be implementation-specific, although there are defined 139 mechanisms in the HTTP and elsewhere that may be appropriate. 141 In particular, unauthorized use of these mechanisms may lead to 142 reduced cache efficiency, denial of service to the intermediate, and 143 may make other security issues in the intermediate more readily 144 exploitable. 146 References 148 [1] Fielding, R., Gettys, J., Mogul, J. C., Frystyk, H., Masinter, 149 L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol 150 - HTTP/1.1", RFC 2616, June 1999. 152 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement 153 Levels", RFC 2119, March 1997. 155 Author's Address 157 Mark Nottingham 158 Akamai Technologies 159 Suite 703, 1400 Fashion Island Bvld 160 San Mateo, CA 94404 161 US 163 EMail: mnot@akamai.com 164 URI: http://www.mnot.net/ 166 Full Copyright Statement 168 Copyright (C) The Internet Society (2000). All Rights Reserved. 170 This document and translations of it may be copied and furnished to 171 others, and derivative works that comment on or otherwise explain it 172 or assist in its implementation may be prepared, copied, published 173 and distributed, in whole or in part, without restriction of any 174 kind, provided that the above copyright notice and this paragraph 175 are included on all such copies and derivative works. However, this 176 document itself may not be modified in any way, such as by removing 177 the copyright notice or references to the Internet Society or other 178 Internet organizations, except as needed for the purpose of 179 developing Internet standards in which case the procedures for 180 copyrights defined in the Internet Standards process must be 181 followed, or as required to translate it into languages other than 182 English. 184 The limited permissions granted above are perpetual and will not be 185 revoked by the Internet Society or its successors or assigns. 187 This document and the information contained herein is provided on an 188 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 189 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 190 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 191 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 192 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 194 Acknowledgement 196 Funding for the RFC editor function is currently provided by the 197 Internet Society.