Network Working Group Arnt Gulbrandsen Internet-Draft Oryx Mail Systems GmbH Intended Status: Proposed Standard April 16, 2008 IMAP Response Codes draft-gulbrandsen-imap-response-codes-02.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet- Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft expires in August 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract IMAP responses consist of a response type (OK, NO, BAD), an optional machine-readable response code and a human-readable text. This document collects and documents a variety of machine-readable response codes, for better interoperation and error reporting. Gulbrandsen Expires October 2008 [Page 1] Internet-draft April 2008 1. Conventions Used in This Document Formal syntax is defined by [RFC5234] as modified by [RFC3501]. Example lines prefaced by "C:" are sent by the client and ones prefaced by "S:" by the server. "[...]" means elision. 2. Introduction [RFC3501] section 7.1 defines a number of response codes which can help tell an IMAP client why a command failed. However, experience has shown that more codes are useful. For example, it is useful for a client to know that an authentication attempt failed because of a server problem as opposed to a password problem. Currently many IMAP servers use English-language human-readable text to describe these errors, and a few IMAP clients attempt to translate this text into the user's language. This document names a variety of errors as response codes. It is based on errors checked and reported in some IMAP server implementations, and on needs in some IMAP clients. This document doesn't require any servers to test for these errors, or any clients to test for these names. It only names errors for better reporting and handling. 3. Response Codes This section defines all the new response codes. Each definition is followed by one or more examples. UNAVAILABLE Temporary failure because a subsystem is down. For example, an IMAP server which uses an LDAP or Radius server for authentication might use this when the LDAP/Radius server is down. C: a LOGIN "fred" "foo" S: a NO [UNAVAILABLE] User's backend down for maintenance AUTHENTICATIONFAILED Authentication failed for some reason which the server is not willing to elaborate. Typically this includes "unknown user" and "bad password". This is the same as not sending any response code, except that when a client sees AUTHENTICATIONFAILED, it knows Gulbrandsen Expires October 2008 [Page 2] Internet-draft April 2008 that the problem wasn't e.g. UNAVAILABLE, so there's no point in trying the same login/password again later. C: b LOGIN "fred" "foo" S: b NO [AUTHENTICATIONFAILED] Authentication failed AUTHORIZATIONFAILED Authentication succeeded, but authorization failed. This is only applicable when the authentication and authorization identities are different. C: c AUTHENTICATE PLAIN [...] S: c NO [AUTHORIZATIONFAILED] No such auth-ID EXPIRED Authentication succeeded or the server didn't have the necessary data any more, but access is no longer permitted using that passphrase. The client or user should get a new passphrase. C: d login "fred" "foo" S: d NO [EXPIRED] That password isn't valid any more CONTACTADMIN The user should contact the system administrator or support desk. CONTACTADMIN may include suitable contact details (a telephone number, email address, a Jabber/XMPP address, or any combination). C: e login "fred" "foo" S: e OK [CONTACTADMIN] ACL The access control system (e.g. ACL, see [RFC4314]) does not permit this user to carry out an operation, such as selecting or creating a mailbox. C: f select "/archive/projects/experiment-iv" S: f NO [ACL] Access denied INUSE An operation has not been carried out because it involves sawing off a branch someone else is sitting on. Someone else may be holding an exclusive lock needed for this operation, or it may involve deleting a resource someone else is using, typically a mailbox. The operation may succeed if the client tries again later. Gulbrandsen Expires October 2008 [Page 3] Internet-draft April 2008 C: g remove "/archive/projects/experiment-iv" S: g NO [INUSE] Mailbox in use EXPUNGEISSUED Someone else has issued an EXPUNGE for the same mailbox. The client may want to issue NOOP soon. [RFC2180] discusses this subject in depth. C: h search from fred@example.com S: * SEARCH 1 2 3 5 8 13 21 42 S: h OK [EXPUNGEISSUED] Search completed CORRUPTION The server discovered that some relevant data (e.g. the mailbox) are corrupt. May be followed by the name of the relevant mailbox. C: i select "/archive/projects/experiment-iv" S: i NO [CORRUPTION] Cannot open mailbox SERVERBUG The server encountered a bug in itself or violated one of its own invariants. C: j select "/archive/projects/experiment-iv" S: j NO [SERVERBUG] This should not happen CLIENTBUG The server has detected a client bug. This can accompany all of OK, NO and BAD, depending on what the client bug is. C: k1 select "/archive/projects/experiment-iv" [...] S: k1 OK [READONLY] Done C: k2 status "/archive/projects/experiment-iv" [...] S: k2 OK [CLIENTBUG] Done NOBODYPART The specified bodypart does not exist. (This seems unjustified. It will be removed before IETF LC unless I learn a sensible use case before then.) CANNOT The operation violates some invariant of the server and can never succeed. C: l create "///////" S: l NO [CANNOT] Unsupported name LIMIT The operation ran up against an implementation limit of some kind, such as the number of flags on a single Gulbrandsen Expires October 2008 [Page 4] Internet-draft April 2008 message or number of flags used in a mailbox. C: m store 42 FLAGS f1 f2 f3 f4 f5 ... f250 S: m NO [LIMIT] At most 32 flags in one mailbox supported OVERQUOTA The user is or would be over quota after the operation. (The user may or may not be over quota already.) C: n1 uid copy 1:* oldmail S: n1 NO [OVERQUOTA] Sorry C: n2 uid copy 1:* oldmail S: n2 OK [OVERQUOTA] You are now over your soft quota ALREADYEXISTS The operation attempts to create something which already exists, such as when the CREATE or RENAME directories attempt to create a mailbox and there is one of that name. C: o RENAME this that S: o NO [ALREADYEXISTS] Mailbox "that" already exists NONEXISTENT The operation attempts to delete something which does not exist. Similar to ALREADYEXISTS. C: p RENAME this that S: p NO [NONEXISTENT] No such mailbox 4. Formal Syntax The following syntax specification uses the Augmented Backus-Naur Form (ABNF) notation as specified in [RFC5234]. [RFC3501] defines the non-terminal "resp-text-code". Except as noted otherwise, all alphabetic characters are case- insensitive. The use of upper or lower case characters to define token strings is for editorial clarity only. Implementations MUST accept these strings in a case-insensitive fashion. resp-text-code =/ "UNAVAILABLE" / "AUTHENTICATIONFAILED" / "AUTHORIZATIONFAILED" / "EXPIRED" / "CONTACTADMIN" *contact-details / "ACL" / "INUSE" / "EXPUNGEISSUED" / "CORRUPTION" / "SERVERBUG" / "CLIENTBUG" / "NOBODYPART" / "CANNOT" / "LIMIT" / "OVERQUOTA" / "ALREADYEXISTS" / "NONEXISTENT" Gulbrandsen Expires October 2008 [Page 5] Internet-draft April 2008 contact-detail = SP ( "EMAIL" / "XMPP" / "TEL" ) SP string 5. Security considerations Revealing information about a passphrase to unauthenticated IMAP clients has bad karma. Response codes are easier to parse than human-readable text. This can amplify the consequences of an information leak. For example, selecting a mailbox can fail because the mailbox doesn't exist, because the user doesn't have the "l" right (right to know the mailbox exists) or "r" (right to read the mailbox). If the server sent different responses in the first two cases in the past, only malevolent clients would discover it. With response codes it's possible, perhaps probable, that benevolent clients forward the leaked information to the user. Server authors are encouraged to be particularly careful with the ACL and authentication-related responses. 6. IANA considerations The IANA is requested to create a new registry, tentatively named imap-response-codes, and populate it as follows: REFERRAL RFC 2221 ALERT RFC 3501 BADCHARSET RFC 3501 PARSE RFC 3501 PERMANENTFLAGS RFC 3501 READ-ONLY RFC 3501 READ-WRITE RFC 3501 TRYCREATE RFC 3501 UIDNEXT RFC 3501 UIDVALIDITY RFC 3501 UNSEEN RFC 3501 UNKNOWN-CTE RFC 3516 UIDNOTSTICKY RFC 4315 APPENDUID RFC 4315 COPYUID RFC 4315 URLMECH RFC 4467 TOOBIG RFC 4469 BADURL RFC 4469 HIGHESTMODSEQ RFC 4551 NOMODSEQ RFC 4551 MODIFIED RFC 4551 COMPRESSIONACTIVE RFC 4978 Gulbrandsen Expires October 2008 [Page 6] Internet-draft April 2008 CLOSED RFC 5162 UNAVAILABLE RFC (this) AUTHENTICATIONFAILED RFC (this) AUTHORIZATIONFAILED RFC (this) EXPIRED RFC (this) CONTACTADMIN RFC (this) ACL RFC (this) INUSE RFC (this) EXPUNGEISSUED RFC (this) CORRUPTION RFC (this) SERVERBUG RFC (this) CLIENTBUG RFC (this) NOBODYPART RFC (this) CANNOT RFC (this) LIMIT RFC (this) OVERQUOTA RFC (this) ALREADYEXISTS RFC (this) NONEXISTENT RFC (this) Further, two drafts in the RFC-editor's queue define new response codes. Presumably they will have RFC numbers when this document is processed, but their draft names are given here: BADCOMPARATOR (draft-ietf-imapext-i18n-15.txt) ANNOTATE TOOBIG (draft-ietf-imapext-annotate-16.txt) ANNOTATE TOOMANY (draft-ietf-imapext-annotate-16.txt) ANNOTATIONS (draft-ietf-imapext-annotate-16.txt) The RFC editor is requested to delete this entire text, and insert a sentence mentioning the registrly's URL instead. 7. Acknowledgements Peter Coates, Mark Crispin, Philip Guenther, Philip Van Hoof, Alexey Melnikov, Ken Murchison and Dale Wiggins helped with this document. 8. Normative References [RFC3501] Crispin, "Internet Message Access Protocol - Version 4rev1", RFC 3501, University of Washington, June 2003. [RFC5234] Crocker, Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 5234, Brandenburg Internetworking, THUS plc, January 2008. Gulbrandsen Expires October 2008 [Page 7] Internet-draft April 2008 9. Informative References [RFC2180] Gahrns, "IMAP4 Multi-Accessed Mailbox Practice", RFC 2180, Microsoft, July 1997. [RFC4314] Melnikov, "IMAP4 Access Control List (ACL) Extension", RFC 4314, December 2005. 10. Author's Address Arnt Gulbrandsen Oryx Mail Systems GmbH Schweppermannstr. 8 D-81671 Muenchen Germany Fax: +49 89 4502 9758 Email: arnt@oryx.com Gulbrandsen Expires October 2008 [Page 8] Internet-draft April 2008 11. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Gulbrandsen Expires October 2008 [Page 9] Internet-draft April 2008 (RFC Editor: Please delete everything after this point) Open Issues I took TOOWEAK out since it doesn't seem to have real purpose: "The server requires a stronger authentication mechanism. If the connection is not encrypted, the client could also try the same mechanism via an encrypted connection." But now I remember why it was there: The server may offer e.g. AUTH=CRAM-MD5, but not be able to carry that out for every user. Maybe it should be returned with a better name. I'd like to hear whether anyone actually does this. READ-ONLY is misspelled in one case. Changes since -00 - CHILDMAILBOXEXISTS merged into INUSE. - ACCESSDENIED renamed ACL to clarify its scope. - NOBODYPART scheduled for deletion if noone minds. - EXISTS renamed ALREADYEXISTS to avoid confusion with the EXISTS response. Mustn't overload developer brains. (Do unto others.) - Added a security note about how response codes makes some information leaks worse. - A couple of open issues. Changes since -01 - Two people independently argued that merging ALREADYEXISTS and NONEXISTENT was bad because of RENAME. Open issue closed. - An example for each response code. - EXPUNGED renamed, see EXISTS above. - EXPUNGEISSUED semantics changed to be 2180-neutral. It should now be equally useful no matter which part of 2180 the server implements. - CONTACTADMIN vs. ALERT, an open issue. Gulbrandsen Expires October 2008 [Page 10] Internet-draft April 2008 - Added an IANA considerations section registering every (?) response code defined so far. - Added contact details to CONTACTADMIN, by request. - Resolved the CA/SB/C issue: The three responses may be handled similarly by some clients, but they may equally well be handled differently, so they should not be folded. Gulbrandsen Expires October 2008 [Page 11]