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Freed 3 Internet-Draft Sun Microsystems 4 Expires: September 20, 2007 March 19, 2007 6 Sieve Email Filtering: Ihave Extension 7 draft-freed-sieve-ihave-00 9 Status of this Memo 11 By submitting this Internet-Draft, each author represents that any 12 applicable patent or other IPR claims of which he or she is aware 13 have been or will be disclosed, and any of which he or she becomes 14 aware will be disclosed, in accordance with Section 6 of BCP 79. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt. 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 This Internet-Draft will expire on September 20, 2007. 34 Copyright Notice 36 Copyright (C) The IETF Trust (2007). 38 Abstract 40 This document describes the "ihave" extension to the Sieve email 41 filtering language. The "ihave" extension provides a means to write 42 scripts that can take advantage of optional Sieve features but can 43 still run when those optional features are not available. 45 Change History (to be removed prior to publication as an RFC 47 Changed the comparator used in the ihave test from "i;ascii-casemap" 48 to "i;octet". 50 Updated the IANA registration template 52 Simplified the semantics of ihave to be independent of block 53 structure. 55 Moved the environment extension to a separate document so the 56 standards status of the two extensions can be different. 58 1. Introduction 60 Sieve [I-D.ietf-sieve-3028bis] is a language for filtering email 61 messages at or around the time of final delivery. It is designed to 62 be implementable on either a mail client or mail server. It is 63 suitable for running on a mail server where users may not be allowed 64 to execute arbitrary programs, such as on black box Internet Message 65 Access Protocol [RFC3501] servers, as it has no user-controlled loops 66 or the ability to run external programs. 68 A large number of sieve extensions have already been defined and more 69 are sure to be created over time. Sieve's require clause is used to 70 specify the extensions a particular sieve needs; an error results if 71 the script's require clause calls for an extension that isn't 72 available. This mechanism is sufficient in most situations. 73 However, there can be cases where a script may be able to take 74 advantage of an extension if it is available but can still function 75 if it is not, possibly with some degradation of capabilities. 77 The "ihave" extension provides a means to write scripts that make use 78 of other extensions only when they are actually available. Ihave 79 defines a new ihave test that takes a list of capability names as an 80 argument and succeeds if all of the those capabilities are present. 81 Additionally, specification of the "ihave" extension in the require 82 clause disables parse-time checking of extension use in scripts; run- 83 time checking must be used instead. 85 2. Conventions used in this document 87 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 88 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 89 document are to be interpreted as described in RFC 2119 [RFC2119]. 91 The terms used to describe the various components of the Sieve 92 language are taken from [I-D.ietf-sieve-3028bis] section 1.1. 94 3. Capability Identifiers 96 The capability string associated with the extension defined in this 97 document is "ihave". 99 4. Ihave Test 101 Usage: ihave 103 The ihave test provides a means for Sieve scripts to test for the 104 existence of a given extension prior to actually using it. The 105 capabilities argument to ihave is the same as the similarly-named 106 argument to the require control statement: It specifies the names of 107 one or more Sieve extensions or comparators. 109 Unlike most Sieve tests, ihave accepts no match or comparator 110 arguments. The type of match for ihave is always ":is" and the 111 comparator is always "i;octet". 113 The strings in the capabilities list are constant strings in context 114 of Sieve variables [I-D.ietf-sieve-variables]. It is an error to 115 pass a non-constant string as an argument to ihave. 117 The Sieve base specification demands that that all Sieve extensions 118 used in a given script be specified in the initial require control 119 statement. It is an error for a script to call for extensions the 120 interpreter doesn't support or to attempt to use extensions that have 121 not been listed in the script's require clause. Use of ihave changes 122 Sieve interpreter behavior and the underlying requirements in the 123 following ways: 125 1. Use of a given extension is allowed subsequent to the successful 126 evaluation of an ihave test on that extension. The extension 127 then operates just as if it had been specified in the script's 128 require clause. The extension cannot be used prior to the 129 evaluation of such a test and a runtime error MUST be generated 130 if such usage is attempted. 132 2. Sieve interpreters normally have the option of checking extension 133 use at either parse time or execution time. The specification of 134 "ihave" in a script's require clause changes this behavior: 135 Scripts MUST either defer extension checking to run time or else 136 take the presence of ihave tests into account at parse time. 137 Note that since ihave can be used inside of anyof, allof, and not 138 tests full parse time checking of ihave may be very difficult to 139 implement. 141 3. Although it makes little sense to do so, an extension can be 142 specified in both the require control statement and in an ihave 143 test. If this is done and the extension has been implemetned the 144 extension can be used anywhere in the script and ihave test of 145 that extension will always return true. 147 4. Using ihave to set a variable to a particular value and then 148 testing that variable in another block is not permitted as it 149 unduly complicates parse time analysis of scripts. 151 Ihave is designed to be used with extensions that add tests, actions, 152 or comparators. It MUST NOT be used with extensions that change how 153 the content of Sieve scripts are interpreted such as the variables 154 extension [I-D.ietf-sieve-variables] 156 5. Security Considerations 158 The ihave extension is essentially a more flexible variant of Sieve's 159 existing require mechanism. As such, it has no real effect on the 160 security considerations associated with the use of Sieve. Of course 161 all of the security considerations given in the base Sieve 162 specification are still relevant. 164 6. IANA Considerations 166 The following template specifies the IANA registration of the Sieve 167 extension specified in this document: 169 To: iana@iana.org 170 Subject: Registration of new Sieve extension 172 Capability name: ihave 173 Description: The "ihave" extension provides a means to write 174 scripts that make use of other extensions only 175 when they are actually available. 176 RFC number: RFC XXXX 177 Contact address: Ned Freed 179 This information should be added to the list of sieve extensions 180 given on http://www.iana.org/assignments/sieve-extensions. 182 7. References 183 7.1. Normative references 185 [I-D.ietf-sieve-3028bis] 186 Guenther, P. and T. Showalter, "Sieve: An Email Filtering 187 Language", draft-ietf-sieve-3028bis-12 (work in progress), 188 February 2007, . 191 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 192 Requirement Levels", BCP 14, RFC 2119, March 1997. 194 7.2. Informative references 196 [I-D.ietf-sieve-variables] 197 Homme, K., "Sieve Mail Filtering Language: Variables 198 Extension", draft-ietf-sieve-variables-08 (work in 199 progress), December 2005, . 202 [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 203 4rev1", RFC 3501, March 2003. 205 Author's Address 207 Ned Freed 208 Sun Microsystems 209 3401 Centrelake Drive, Suite 410 210 Ontario, CA 92761-1205 211 USA 213 Phone: +1 909 457 4293 214 Email: ned.freed@mrochek.com 216 Full Copyright Statement 218 Copyright (C) The IETF Trust (2007). 220 This document is subject to the rights, licenses and restrictions 221 contained in BCP 78, and except as set forth therein, the authors 222 retain all their rights. 224 This document and the information contained herein are provided on an 225 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 226 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 227 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 228 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 229 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 230 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 232 Intellectual Property 234 The IETF takes no position regarding the validity or scope of any 235 Intellectual Property Rights or other rights that might be claimed to 236 pertain to the implementation or use of the technology described in 237 this document or the extent to which any license under such rights 238 might or might not be available; nor does it represent that it has 239 made any independent effort to identify any such rights. 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