]" command. The type of the object may be determined with a "UID FETCH BODYS- TRUCTURE" command and locating the appropriate part in the result- ing BODYSTRUCTURE. Note that unsafe characters in [isection] MUST be encoded as described in [URI-GEN]. The [ipartial] field is optional. If present, it effectively appends "<>" to the end of the UID FETCH BODY.PEEK[

] command constructed as described in the previ- ous paragraph. In other words it allows the client to request a byte range of the message/message part. 6.1 URLAUTH authorized URL URLAUTH authorized URLs are only supported by an IMAP server adver- tising the URLAUTH IMAP capability [URLAUTH]. 6.1.1. Concepts 6.1.1.1. URLAUTH The URLAUTH is a component, appended at the end of a URL, which conveys authorization to access the data addressed by that URL. It Newman & Co Expires: July 2007 FORMFEED[Page 7] INTERNET DRAFT IMAP URL Scheme January 2007 contains an authorized access identifier, an authorization mecha- nism name, and an authorization token. The authorization token is generated from the URL, the authorized access identifer, authoriza- tion mechanism name, and a mailbox access key. (Note that currently this specification only allows for the URLAUTH component in IMAP URLs describing a message or its part.) 6.1.1.2. Mailbox Access Key The mailbox access key is a random string with at least 128 bits of entropy. It is generated by software (not by the human user), and MUST be unpredictable. Each user has a table of mailboxes and an associated mailbox access key for each mailbox. Consequently, the mailbox access key is per- user and per-mailbox. In other words, two users sharing the same mailbox each have a different mailbox access key for that mailbox, and each mailbox accessed by a single user also has a different mailbox access key. 6.1.1.3. Authorized Access Identifier The authorized access identifier restricts use of the URLAUTH authorized URL to certain users authorized on the server, as described in section 6.1.2. 6.1.1.4. Authorization Mechanism The authorization mechanism is the algorithm by which the URLAUTH is generated and subsequently verified, using the mailbox access key. 6.1.1.5. Authorization Token The authorization token is a deterministic string of at least 128 bits which an entity with knowledge of the secret mailbox access key and URL authorization mechanism can use to verify the URL. Newman & Co Expires: July 2007 FORMFEED[Page 8] INTERNET DRAFT IMAP URL Scheme January 2007 6.1.2. URLAUTH extensions to IMAP URL A specific message or message part IMAP URL can optionally contain ";EXPIRE=" and/or ";URLAUTH=::". When ";EXPIRE=" is used, this indicates the latest date and time that the URL is valid. After that date and time, the URL has expired and server implementations MUST reject the URL. If ";EXPIRE=" is not used, the URL has no expiration, but still can be revoked using the RESETKEY command [URLAUTH]. The URLAUTH takes the form ";URLAUTH=::", and MUST be at the end of the URL. It is composed of three parts. The portion provides the authorized access identifiers which may constrain the operations and users that are permitted to use this URL. The portion provides the authorization mechanism used by the IMAP server to generate the authorization token that follows. The portion provides authorization token, which can be generated using the GENURLAUTH command [URLAUTH]. The "submit+" access identifier prefix, followed by a userid, indi- cates that only a userid authorized as a message submission entity on behalf of the specified userid is permitted to use this URL. The IMAP server does not validate the specified userid but does validate that the IMAP session has an authorization identity that is authorized as a message submission entity. The authorized mes- sage submission entity MUST validate the userid prior to contacting the IMAP server. The "user+" access identifier prefix, followed by a userid, indi- cates that use of this URL is limited to IMAP sessions which are logged in as the specified userid (that is, have authorization identity as that userid). Note: if a SASL mechanism which provides both authorization and authentication identifiers is used to authenticate to the IMAP server, the "user+" access identifier MUST match the authoriza- tion identifier. If the SASL mechanism can't transport the authorization identifier, the "user+" access identifier MUST match the authorization identifier derived from the authentica- tion identifier (see [SASL]). The "authuser" access identifier indicates that use of this URL is limited to IMAP sessions which are logged in as an authorized user (that is, have authorization identity as an authorized user) of that IMAP server. Use of this URL is prohibited to anonymous IMAP sessions. Newman & Co Expires: July 2007 FORMFEED[Page 9] INTERNET DRAFT IMAP URL Scheme January 2007 The "anonymous" access identifier indicates that use of this URL is not restricted by session authorization identity; that is, any IMAP session in authenticated or selected state (as defined in [IMAP4]), including anonymous sessions, may issue a URLFETCH [URLAUTH] using this URL. The authorization token is represented as an ASCII-encoded hexadec- imal string, which is used to authorize the URL. The length and the calculation of the authorization token depends upon the mecha- nism used; but, in all cases, the authorization token is at least 128 bits (and therefore at least 32 hexadecimal digits). 7. Relative IMAP URLs Relative IMAP URLs are permitted and are resolved according to the rules defined in [URI-GEN]. In particular in IMAP URLs, parameters are treated as part of the normal path with respect to relative URL resolution. The following observations are also important: The grammar element is considered part of the user name for purposes of resolving relative IMAP URLs. This means that unless a new login/server specification is included in the relative URL, the authentication mechanism is inherited from a base IMAP URL. URLs always use "/" as the hierarchy delimiter for the purpose of resolving paths in relative URLs. IMAP4 permits the use of any hierarchy delimiter in mailbox names. For this reason, relative mailbox paths will only work if the mailbox uses "/" as the hierar- chy delimiter. Relative URLs may be used on mailboxes which use other delimiters, but in that case, the entire mailbox name MUST be specified in the relative URL or inherited as a whole from the base URL. If an IMAP server allows for mailbox names starting with "./" or "../", ending with "/." or "/..", or containing sequences "/../" or "/./", then such mailbox names MUST be encoded as described in [URI-GEN]. Otherwise they would be misinterpreted as dot-segments (see Section 3.3 of [URI-GEN]), which are processed specially dur- ing relative path resolution process. 7.1. absolute-path References A relative reference that begins with a single slash character is termed an absolute-path reference [URI-GEN]. If an IMAP server Newman & Co Expires: July 2007 FORMFEED[Page 10] INTERNET DRAFT IMAP URL Scheme January 2007 permits mailbox names with a leading "/", then the leading "/" MUST be encoded as described in [URI-GEN]. Otherwise the produced abso- lute-path reference URI will be misinterpreted as a network-path reference [URI-GEN]. 7.2. relative-path References A relative reference that does not begin with a slash character is termed a relative-path reference [URI-GEN]. Implementations SHOULD NOT generate or accept relative-path IMAP references. See also section 4.2 of [URI-GEN] for restrictions on relative-path references. 8. Multinational Considerations IMAP4 [IMAP4] section 5.1.3 includes a convention for encoding non- US-ASCII characters in IMAP mailbox names. Because this convention is private to IMAP, it is necessary to convert IMAP's encoding to one that can be more easily interpreted by a URL display program. For this reason, IMAP's modified UTF-7 encoding for mailboxes MUST be converted to UTF-8 [UTF-8]. Since 8-bit characters are not per- mitted in URLs, the UTF-8 characters are encoded as required by the URL specification [URI-GEN], section 2.1. Sample code is included in Appendix A to demonstrate this conversion. IMAP usernames are UTF-8 strings and MUST be encoded as required by the URL specification [URI-GEN], section 2.1. Also note that IMAP SEARCH criteria can contain non US-ASCII char- acters. 8-bit octets in those strings MUST be encoded as required by the URL specification [URI-GEN], section 2.1. 9. Examples The following examples demonstrate how an IMAP4 client program might translate various IMAP4 URLs into a series of IMAP4 commands. Commands sent from the client to the server are prefixed with "C:", and responses sent from the server to the client are prefixed with "S:". Newman & Co Expires: July 2007 FORMFEED[Page 11] INTERNET DRAFT IMAP URL Scheme January 2007 The URL: Results in the following client commands: C: A001 LOGIN ANONYMOUS sheridan@babylon5.example.org C: A002 SELECT gray-council C: A003 UID FETCH 20 BODY.PEEK[]<0.1024> The URL: Results in the following client commands: C: A001 LOGIN ANONYMOUS bester@psycop.psicorp.example.org C: A002 SELECT ~peter/&ZeVnLIqe-/&U,BTFw- The URL: Results in the following client commands: C: A001 AUTHENTICATE GSSAPI C: A002 SELECT gray-council C: A003 UID FETCH 20 BODY.PEEK[1.2] <> If the following relative URL is located in that body part: <;section=1.4> This could result in the following client commands: C: A004 UID FETCH 20 (BODY.PEEK[1.2.MIME] Newman & Co Expires: July 2007 FORMFEED[Page 12] INTERNET DRAFT IMAP URL Scheme January 2007 BODY.PEEK[1.MIME] BODY.PEEK[HEADER.FIELDS (Content-Location)]) C: A005 UID FETCH 20 BODY.PEEK[1.4] The URL: Could result in the following: C: A001 CAPABILITY S: * CAPABILITY IMAP4rev1 AUTH=DIGEST-MD5 S: A001 OK C: A002 AUTHENTICATE DIGEST-MD5 S: A002 OK user lennier authenticated C: A003 SELECT "gray council" ... C: A004 SEARCH SUBJECT shadows S: * SEARCH 8 10 13 14 15 16 S: A004 OK SEARCH completed C: A005 FETCH 8,10,13:16 ALL ... NOTE: In this final example, the client has implementation depen- dent choices. The authentication mechanism could be anything, including PREAUTH. And the final FETCH command could fetch more or less information about the messages, depending on what it wishes to display to the user. The URL: shows that 8-bit data can be sent using non-synchronizing literals [LITERAL+]. This could result in the following: C: A001 CAPABILITY S: * CAPABILITY IMAP4rev1 LITERAL+ AUTH=DIGEST-MD5 S: A001 OK C: A002 AUTHENTICATE DIGEST-MD5 Newman & Co Expires: July 2007 FORMFEED[Page 13] INTERNET DRAFT IMAP URL Scheme January 2007 S: A002 OK user john authenticated C: A003 SELECT babylon5/personel ... C: A004 SEARCH CHARSET UTF-8 SUBJECT {14+} C: XXXXXXXXXXXXXX S: * SEARCH 7 10 12 S: A004 OK SEARCH completed C: A005 FETCH 7,10,12 ALL ... Where XXXXXXXXXXXXXX is 14 bytes of UTF-8 encoded data as specified in the URL above. 9.1. Examples of relative URLs The following absolute-path reference is the same as I.e. both of them reference the mailbox "foo". The following relative-path reference <;UID=20> references a message with UID in the mailbox specified by the Base URI. <..;UIDVALIDITY=385759045/;UID=20> <> 10. Security Considerations Security considerations discussed in the IMAP specification [IMAP4] and the URI specification [URI-GEN] are relevant. Security consid- erations related to authenticated URLs are discussed in section 3 of this document. Many email clients store the plain text password for later use after logging into an IMAP server. Such clients MUST NOT use a stored password in response to an IMAP URL without explicit Newman & Co Expires: July 2007 FORMFEED[Page 14] INTERNET DRAFT IMAP URL Scheme January 2007 permission from the user to supply that password to the specified host name. 10.1. Security Consideration specific to URLAUTH authorized URL The "user+" access identifier limits resolution of that URL to a particular userid, whereas the "submit+" access identifier is more general and simply requires that the session be authorized by a user that has been granted a "submit" role within the authentication system. Use of either of these access identifiers makes it impossible for an attacker, spying on the session, to use the same URL, either directly or by submission to a message submission entity. The "authuser" and "anonymous" access identifiers do not have this level of protection. These access identifiers are primarily useful for public export of data from an IMAP server, without requiring that it be copied to a web or anonymous FTP server. The decision to use the "authuser" access identifier should be made with caution. An "authuser" access identifier can be used by any authorized user of the IMAP server; and therefore use of this access identifier should be limited to content which may be disclosed to any authorized user of the IMAP server. The decision to use the "anonymous" access identifier should be made with extreme caution. An "anonymous" access identifier can be used by anyone; and therefore use of this access identifier should be limited to content which may be disclosed to anyone. Many IMAP servers do not permit anonymous access; in the case of such servers the "anonymous" access identifer is equivalent to "authuser", but this MUST NOT be relied upon. Newman & Co Expires: July 2007 FORMFEED[Page 15] INTERNET DRAFT IMAP URL Scheme January 2007 11. ABNF for IMAP URL scheme Formal syntax is defined using ABNF [ABNF], extending the ABNF rules in section 9 of [IMAP4]. Elements not defined here can be found in the [ABNF], [IMAP4], [IMAPABNF] or [URI-GEN]. Strings are not case sensitive and free insertion of linear-white-space is not permitted. sub-delims-sh = "!" / "$" / "'" / "(" / ")" / "*" / "+" / "," ;; <> bchar = achar / ":" / "@" / "/" enc-auth-type = 1*achar ; %-encoded version of [IMAP4] "auth-type" enc-mailbox = 1*bchar ; %-encoded version of [IMAP4] "mailbox" enc-search = 1*bchar ; %-encoded version of [IMAPABNF] ; "search-program". Note that IMAP4 ; literals may not be used in ; a "search-program", i.e. only ; quoted or non-synchronizing ; literals (if the server supports ; LITERAL+ [LITERAL+]) are allowed. enc-section = 1*bchar ; %-encoded version of [IMAP4] "section-spec" enc-user = 1*achar ; %-encoded version of [IMAP4] authorization ; identity or "userid". imapurl = "imap://" iserver ipath-query ; Defines an absolute IMAP URL ipath-query = ["/" [ icommand ]] Newman & Co Expires: July 2007 FORMFEED[Page 16] INTERNET DRAFT IMAP URL Scheme January 2007 ; <> ; Corresponds to "path-abempty [ "?" query ]" ; in [URI-GEN] Generic syntax for relative URLs is defined in Section 4.2 of [URI-GEN]. For ease of implementation, the relative IMAP URL syntax is defined below: imapurl-rel = inetwork-path / iabsolute-path / irelative-path / ipath-empty inetwork-path = "//" iserver ipath-query ; Corresponds to '"//" authority path-abempty ; [ "?" query ]' in [URI-GEN] iabsolute-path = "/" [ icommand ] ; icommand, if present, MUST NOT start with '/'. ; ; Corresponds to 'path-absolute [ "?" query ]' ; in [URI-GEN] irelative-path = imessagelist / ( imsg-or-part [iurlauth] ) ; Corresponds to 'path-noscheme [ "?" query ]' ; in [URI-GEN] <> imsg-or-part = ( imailbox-ref "/" iuid-only ["/" isection-only] ["/" ipartial-only] ) / ( iuid-only ["/" isection-only] ["/" ipartial-only] ) / ( isection-only ["/" ipartial-only] ) / ipartial-only ipath-empty = 0 ; Zero characters. ; Corresponds to the relative form of "an IMAP server" ; URL The following 3 rules are only used in the presence of the IMAP [URLAUTH] extension: authimapurl = "imap://" iserver "/" imessagepart Newman & Co Expires: July 2007 FORMFEED[Page 17] INTERNET DRAFT IMAP URL Scheme January 2007 ; Same as "imapurl" when "[icommand]" is ; "imessagepart" authimapurlfull = authimapurl iurlauth ; Same as "imapurl" when "[icommand]" is ; "imessagepart iurlauth" authimapurlrump = authimapurl iurlauth-rump <> enc-urlauth = 32*HEXDIG iurlauth = iurlauth-rump iua-verifier iua-verifier = ":" uauth-mechanism ":" enc-urlauth iurlauth-rump = [expire] ";URLAUTH=" access access = ("submit+" enc-user) / ("user+" enc-user) / "authuser" / "anonymous" expire = ";EXPIRE=" date-time ; date-time defined in [DATETIME] uauth-mechanism = "INTERNAL" / 1*(ALPHA / DIGIT / "-" / ".") ; Case-insensitive. ; New mechanisms MUST be registered with IANA. ; <> iauth = ";AUTH=" ( "*" / enc-auth-type ) icommand = imessagelist / imessagepart [iurlauth] imailbox-ref = enc-mailbox [uidvalidity] ; <> imessagelist = imailbox-ref [ "?" enc-search ] ; "enc-search" is [URI-GEN] "query". imessagepart = imailbox-ref iuid [isection] [ipartial] Newman & Co Expires: July 2007 FORMFEED[Page 18] INTERNET DRAFT IMAP URL Scheme January 2007 ipartial = "/" ipartial-only ipartial-only = ";PARTIAL=" partial-range ; <> isection = "/" isection-only isection-only = ";SECTION=" enc-section ; <> iserver = [iuserinfo "@"] host [ ":" port ] ; This is the same as "authority" defined ; in [URI-GEN]. See [URI-GEN] for "host" ; and "port" definitions. iuid = "/" iuid-only iuid-only = ";UID=" nz-number ; <> ; See [IMAP4] for "nz-number" definition iuserinfo = enc-user [iauth] / [enc-user] iauth ; conforms to the generic syntax of ; "userinfo" as defined in [URI-GEN]. list-type = "LIST" / "LSUB" partial-range = number ["." nz-number] ; partial fetch uidvalidity = ";UIDVALIDITY=" nz-number ; See [IMAP4] for "nz-number" definition 12. IANA Considerations IANA is requested to update "imap" definition in the "Uniform Resource Identifier scheme registry" to point to this document. The registration template (as per [URI-REG]) is specified in sec- tion 13.1 of this document. 12.1. IANA Registration of imap: URI Scheme This section provides the information required to register the imap: URI scheme. Newman & Co Expires: July 2007 FORMFEED[Page 19] INTERNET DRAFT IMAP URL Scheme January 2007 URI scheme name: imap Status: permanent URI scheme syntax: See section 12 of [RFCXXXX]. URI scheme semantics: The imap: URI scheme is used to designate IMAP servers, mail- boxes, messages, MIME bodies [MIME] and their parts, and search programs on Internet hosts accessible using the IMAP protocol. There is no MIME type associated with this URI. Encoding considerations: See Section 9 of [RFCXXXX]. Applications/protocols that use this URI scheme name: The imap: URI is intended to be used by applications that might need access to IMAP mailstore. Such applications may include (but not limited to) IMAP-capable web browsers; IMAP clients that wish to access a mailbox, message, or edit a message on the server using [CATENATE]; [SUBMIT] clients and servers that are requested to assemble a complete message on submission using [BURL]. Interoperability considerations: A widely deployed IMAP client Mozilla/Thubderbird/Seamonkey use a different imap: scheme internally. Security considerations: See Security Considerations (Section 11) of [RFCXXXX]. Contact: Alexey Melnikov Author/Change controller: IESG References: [RFCXXXX] and [IMAP4]. Newman & Co Expires: July 2007 FORMFEED[Page 20] INTERNET DRAFT IMAP URL Scheme January 2007 13. References 13.1. Normative References [KEYWORDS] Bradner, "Key words for use in RFCs to Indicate Require- ment Levels", BCP 14, RFC 2119, Harvard University, March 1997. [IMAP4] Crispin, M., "Internet Message Access Protocol - Version 4rev1", RFC 3501, University of Washington, March 2003. [IMAPABNF] Melnikov, A., and C. Daboo, "Collected extensions to IMAP4 ABNF", RFC 4466, April 2006. [ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, October 2005. [MIME] Freed, N., Borenstein, N., "Multipurpose Internet Mail Extensions", RFC 2045, November 1996. [URI-GEN] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", RFC 3986, January 2005. [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [NAMESPACE] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342, May 1998. [LITERAL+] Myers, J., "IMAP4 non-synchronizing literals", RFC 2088, January 1997. [ANONYMOUS] Zeilenga, K. (Ed.), "Anonymous Simple Authentication and Security Layer (SASL) Mechanism", RFC 4505, June 2006. [DATETIME] Klyne, G., and Newman, C., "Date and Time on the Inter- net: Timestamps", RFC 3339, July 2002. [URLAUTH] Crispin, M., "Internet Message Access Protocol (IMAP) - URLAUTH Extension", RFC 4467, May 2006. 13.2. Informative References Newman & Co Expires: July 2007 FORMFEED[Page 21] INTERNET DRAFT IMAP URL Scheme January 2007 [SUBMIT] Gellens, R. and J. Klensin, "Message Submission for Mail", RFC 4409, April 2006. [BURL] Newman, C. "Message Submission BURL Extension", RFC 4468, May 2006. [CATENATE] Resnick, P., "Internet Message Access Protocol (IMAP) CATENATE Extension", RFC 4469, April 2006. [SASL] Melnikov, A. and K. Zeilenga, "Simple Authentication and Security Layer (SASL)", RFC 4422, June 2006. [GSSAPI] Melnikov, A., "The Kerberos V5 ("GSSAPI") Simple Authenti- cation and Security Layer (SASL) Mechanism", RFC 4752, November 2006. [DIGEST-MD5] Leach, P. and C. Newman, "Using Digest Authentication as a SASL Mechanism", RFC 2831, May 2000. [URI-REG] Hansen, T., Hardie, T. and L. Masinter, "Guidelines and Registration Procedures for New URI Schemes", BCP 115, RFC 4395, February 2006. 14. Author's Address Chris Newman Sun Microsystems 3401 Centrelake Dr., Suite 410 Ontario, CA 91761 EMail: chris.newman@sun.com Alexey Melnikov (Editor) Isode Limited 5 Castle Business Village 36 Station Road Hampton, Middlesex TW12 2BX, UK Email: Alexey.Melnikov@isode.com URI: http://www.melnikov.ca/ Stephane H. Maes (Editor) Oracle Corporation 500 Oracle Parkway M/S 4op634 Redwood Shores, CA 94065 USA Phone: +1-650-607-6296 Newman & Co Expires: July 2007 FORMFEED[Page 22] INTERNET DRAFT IMAP URL Scheme January 2007 Email: stephane.maes@oracle.com Appendix A. Sample code Here is sample C source code to convert between URL paths and IMAP mail- box names, taking into account mapping between IMAP's modified UTF-7 [IMAP4] and hex-encoded UTF-8 which is more appropriate for URLs. This code has not been rigorously tested nor does it necessarily behave rea- sonably with invalid input, but it should serve as a useful example. This code just converts the mailbox portion of the URL and does not deal with parameters, query or server components of the URL. <> #include #include /* hexadecimal lookup table */ static char hex[] = "0123456789ABCDEF"; /* URL unsafe printable characters */ static char urlunsafe[] = " \"#%&+:;<=>?@[\\]^`{|}"; /* UTF7 modified base64 alphabet */ static char base64chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,"; #define UNDEFINED 64 /* UTF16 definitions */ #define UTF16MASK 0x03FFUL #define UTF16SHIFT 10 #define UTF16BASE 0x10000UL #define UTF16HIGHSTART 0xD800UL #define UTF16HIGHEND 0xDBFFUL #define UTF16LOSTART 0xDC00UL #define UTF16LOEND 0xDFFFUL /* Convert an IMAP mailbox to a URL path * dst needs to have roughly 4 times the storage space of src * Hex encoding can triple the size of the input * UTF-7 can be slightly denser than UTF-8 * (worst case: 8 octets UTF-7 becomes 9 octets UTF-8) */ void MailboxToURL(char *dst, char *src) { unsigned char c, i, bitcount; Newman & Co Expires: July 2007 FORMFEED[Page 23] INTERNET DRAFT IMAP URL Scheme January 2007 unsigned long ucs4, utf16, bitbuf; unsigned char base64[256], utf8[6]; /* initialize modified base64 decoding table */ memset(base64, UNDEFINED, sizeof (base64)); for (i = 0; i < sizeof (base64chars); ++i) { base64[base64chars[i]] = i; } /* loop until end of string */ while (*src != '\0') { c = *src++; /* deal with literal characters and &- */ if (c != '&' || *src == '-') { if (c < ' ' || c > '~' || strchr(urlunsafe, c) != NULL) { /* hex encode if necessary */ dst[0] = '%'; dst[1] = hex[c >> 4]; dst[2] = hex[c & 0x0f]; dst += 3; } else { /* encode literally */ *dst++ = c; } /* skip over the '-' if this is an &- sequence */ if (c == '&') ++src; } else { /* convert modified UTF-7 -> UTF-16 -> UCS-4 -> UTF-8 -> HEX */ bitbuf = 0; bitcount = 0; ucs4 = 0; while ((c = base64[(unsigned char) *src]) != UNDEFINED) { ++src; bitbuf = (bitbuf << 6) | c; bitcount += 6; /* enough bits for a UTF-16 character? */ if (bitcount >= 16) { bitcount -= 16; utf16 = (bitcount ? bitbuf >> bitcount : bitbuf) & 0xffff; /* convert UTF16 to UCS4 */ if (utf16 >= UTF16HIGHSTART && utf16 <= UTF16HIGHEND) { ucs4 = (utf16 - UTF16HIGHSTART) << UTF16SHIFT; continue; } else if (utf16 >= UTF16LOSTART && utf16 <= UTF16LOEND) { ucs4 += utf16 - UTF16LOSTART + UTF16BASE; Newman & Co Expires: July 2007 FORMFEED[Page 24] INTERNET DRAFT IMAP URL Scheme January 2007 } else { ucs4 = utf16; } /* convert UTF-16 range of UCS4 to UTF-8 */ if (ucs4 <= 0x7fUL) { utf8[0] = ucs4; i = 1; } else if (ucs4 <= 0x7ffUL) { utf8[0] = 0xc0 | (ucs4 >> 6); utf8[1] = 0x80 | (ucs4 & 0x3f); i = 2; } else if (ucs4 <= 0xffffUL) { utf8[0] = 0xe0 | (ucs4 >> 12); utf8[1] = 0x80 | ((ucs4 >> 6) & 0x3f); utf8[2] = 0x80 | (ucs4 & 0x3f); i = 3; } else { utf8[0] = 0xf0 | (ucs4 >> 18); utf8[1] = 0x80 | ((ucs4 >> 12) & 0x3f); utf8[2] = 0x80 | ((ucs4 >> 6) & 0x3f); utf8[3] = 0x80 | (ucs4 & 0x3f); i = 4; } /* convert utf8 to hex */ for (c = 0; c < i; ++c) { dst[0] = '%'; dst[1] = hex[utf8[c] >> 4]; dst[2] = hex[utf8[c] & 0x0f]; dst += 3; } } } /* skip over trailing '-' in modified UTF-7 encoding */ if (*src == '-') ++src; } } /* terminate destination string */ *dst = '\0'; } /* Convert hex coded UTF-8 URL path to modified UTF-7 IMAP mailbox * dst should be about twice the length of src to deal with non-hex * coded URLs */ void URLtoMailbox(char *dst, char *src) { unsigned int utf8pos, utf8total, i, c, utf7mode, bitstogo, utf16flag; unsigned long ucs4, bitbuf; Newman & Co Expires: July 2007 FORMFEED[Page 25] INTERNET DRAFT IMAP URL Scheme January 2007 unsigned char hextab[256]; /* initialize hex lookup table */ memset(hextab, 0, sizeof (hextab)); for (i = 0; i < sizeof (hex); ++i) { hextab[hex[i]] = i; if (isupper(hex[i])) hextab[tolower(hex[i])] = i; } utf7mode = 0; utf8total = 0; bitstogo = 0; while ((c = *src) != '\0') { ++src; /* undo hex-encoding */ if (c == '%' && src[0] != '\0' && src[1] != '\0') { c = (hextab[src[0]] << 4) | hextab[src[1]]; src += 2; } /* normal character? */ if (c >= ' ' && c <= '~') { /* switch out of UTF-7 mode */ if (utf7mode) { if (bitstogo) { *dst++ = base64chars[(bitbuf << (6 - bitstogo)) & 0x3F]; } *dst++ = '-'; utf7mode = 0; } *dst++ = c; /* encode '&' as '&-' */ if (c == '&') { *dst++ = '-'; } continue; } /* switch to UTF-7 mode */ if (!utf7mode) { *dst++ = '&'; utf7mode = 1; } /* Encode US-ASCII characters as themselves */ if (c < 0x80) { ucs4 = c; utf8total = 1; } else if (utf8total) { /* save UTF8 bits into UCS4 */ ucs4 = (ucs4 << 6) | (c & 0x3FUL); Newman & Co Expires: July 2007 FORMFEED[Page 26] INTERNET DRAFT IMAP URL Scheme January 2007 if (++utf8pos < utf8total) { continue; } } else { utf8pos = 1; if (c < 0xE0) { utf8total = 2; ucs4 = c & 0x1F; } else if (c < 0xF0) { utf8total = 3; ucs4 = c & 0x0F; } else { /* NOTE: can't convert UTF8 sequences longer than 4 */ utf8total = 4; ucs4 = c & 0x03; } continue; } /* loop to split ucs4 into two utf16 chars if necessary */ utf8total = 0; do { if (ucs4 >= UTF16BASE) { ucs4 -= UTF16BASE; bitbuf = (bitbuf << 16) | ((ucs4 >> UTF16SHIFT) + UTF16HIGHSTART); ucs4 = (ucs4 & UTF16MASK) + UTF16LOSTART; utf16flag = 1; } else { bitbuf = (bitbuf << 16) | ucs4; utf16flag = 0; } bitstogo += 16; /* spew out base64 */ while (bitstogo >= 6) { bitstogo -= 6; *dst++ = base64chars[(bitstogo ? (bitbuf >> bitstogo) : bitbuf) & 0x3F]; } } while (utf16flag); } /* if in UTF-7 mode, finish in ASCII */ if (utf7mode) { if (bitstogo) { *dst++ = base64chars[(bitbuf << (6 - bitstogo)) & 0x3F]; } *dst++ = '-'; } Newman & Co Expires: July 2007 FORMFEED[Page 27] INTERNET DRAFT IMAP URL Scheme January 2007 /* tie off string */ *dst = '\0'; } Appendix B. List of changes since RFC 2192 <> Updated boilerplate, list of editor's, etc. Updated references. Updated ABNF not to use _, to use SP instead of SPACE, etc. Updated example domains to use example.org. Fixed ABNF error in "imessagelist" non-terminal. Updated ABNF, due to changes in RFC 3501, RFC 4466 and RFC 3986. Renamed "iuserauth" non-terminal to "iuserinfo". Clarified that the userinfo component describes both authorization identity and mailbox naming scope. Allow for non-synchronizing literals in "enc-search". Added "ipartial" specifier that denotes a partial fetch. Moved URLAUTH text from RFC 4467 to this document. Clarified how relative-path references are constructed. Added more examples demonstrating relative-path references. Updated ABNF for the whole server to allow missing trailing "/" (e.g. "imap://imap.example.com" is now valid and is the same as "imap://imap.example.com/") Added rules for relative URLs and restructured ABNF as the result. Removed text on use of relative URLs in MHTML. Added examples demonstrating security considerations when resolving URLs. Removed some advices about connection reuse, which were incorrect. Removed URLs referencing a list of mailboxes. Appendix C. Acknowledgments Text describing URLAUTH was lifted from [URLAUTH] by Mark Crispin. Editors would like to thank Mark Crispin, Ken Murchison, Dave Crid- land for the time they devoted to reviewing of this document and/or for the comments received. Newman & Co Expires: July 2007 FORMFEED[Page 28] INTERNET DRAFT IMAP URL Scheme January 2007 Intellectual Property 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 (2007). 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. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Newman & Co Expires: July 2007 FORMFEED[Page 29]