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INTERNET-DRAFT                                            M. Yevstifeyev
Intended Status: Standards Track                            May 27, 2011
Updates: 959, 1738 (if approved)
Expires: November 28, 2011

                          The 'ftp' URI Scheme
                  draft-yevstifeyev-ftp-uri-scheme-01

Abstract

   This document specifies the 'ftp' Uniform Resource Identifier (URI)
   scheme, that is used to refer to resources accessible via File
   Transfer Protocol (FTP).  It updates RFC 959 and RFC 1738.


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html


Copyright and License Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  URI Scheme Specification . . . . . . . . . . . . . . . . . . .  3
     2.1. URI Scheme Syntax . . . . . . . . . . . . . . . . . . . . .  3
     2.2. URI Scheme Semantics  . . . . . . . . . . . . . . . . . . .  4
       2.2.1. The <user-pass> Part  . . . . . . . . . . . . . . . . .  4
       2.2.2. The <host-port> Part  . . . . . . . . . . . . . . . . .  5
       2.2.3. The <ftp-path> Part . . . . . . . . . . . . . . . . . .  5
         2.2.3.1. A Note on <typecode-part> Part  . . . . . . . . . .  7
       2.2.4. Errors Handling . . . . . . . . . . . . . . . . . . . .  7
         2.2.4.1. Handling 4xx Errors . . . . . . . . . . . . . . . .  7
         2.2.4.2. Handling 5xx Errors . . . . . . . . . . . . . . . .  7
         2.2.4.3. Handling 6xx Errors . . . . . . . . . . . . . . . .  8
     2.3. Encoding Considerations . . . . . . . . . . . . . . . . . .  8
   3.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     5.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Appendix A.  List of Changes since RFC 1738  . . . . . . . . . . . 11
   Appendix B.  Acknowledgments . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12


1  Introduction

   File Transfer Protocol (FTP) is a standard network protocol used to
   copy a file from one host to another over a TCP-based network.  It
   has had a very long history; the protocol is rooted in the early
   1970s, the times of ARPANET, with the first specification being RFC
   114 [RFC0114]; the most current FTP specification is RFC 959
   [RFC0959].  (Also visit Section 4 of RFC 1123 [RFC1123] for
   "narrative" description of FTP.)

   Historically, there has been a Uniform Resource Identifier (URI)
   scheme for referencing resources accessible via FTP - 'ftp' URI
   scheme.  The first mention of it appears in RFC 1630 [RFC1630] - pre-
   Standard Track RFC on URIs.  Later, RFC 1738 [RFC1738], Section 3.2
   specified this scheme on IETF Standards Track.  Subsequently, RFC
   1738 was formally obsoleted by RFC 4248 [RFC4248] and RFC 4266
   [RFC4266]; in fact RFC 2396 [RFC2396] and its successor - RFC 3986



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   [RFC3986] - replaced and deprecated it (formally they both updated
   RFC 1738).  Currently, almost all of URI schemes specified in RFC
   1738 have been given a separate specification; one of the rare
   exceptions is the 'ftp' URI scheme.  This document removes this
   uncertainty; it gives the 'ftp' URI scheme an official, Standard
   Track documentation.  It updates RFC 959 [RFC0959] and RFC 1738
   [RFC1738].

   Please note that this document does not attempt to make radical
   changes to the existing 'ftp' URI scheme specification (even though
   they are considered necessary), but rather address various major and
   minor issues in it as well as copies its definition from obsoleted
   RFC 1738 to allow it to remain on Standard Track.

   Generic URI syntax is described in RFC 3986 [RFC3986]; registration
   procedures for new URI schemes - in RFC 4395 [RFC4395].

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].


2.  URI Scheme Specification

2.1. URI Scheme Syntax

   The 'ftp' URI takes the form of <ftp-uri> rule below, specified using
   Augmented Backus-Naur Form (ABNF) [RFC5234]:

     ftp-uri       = "ftp:" ftp-hier-part
     ftp-hier-part = "//" [ user-pass "@" ] host-port [ ftp-path ]
     user-pass     = user [ ":" pass ]
     user          = *usp-char
     pass          = *usp-char
     usp-char      = *( unreserved / pct-encoded / sub-delims )
     host-port     = host [ ":" port ]
     ftp-path      = path-abempty [ typecode-part ]
     typecode-part = ";typecode=" typecode
     typecode      = "a" / "i" / "d"

   where the <host>, <port>, <unreserved>, <pct-encoded>, <sub-delims>
   and <path-abempty> rules are defined in RFC 3986 [RFC3986], Appendix
   A.  Section 2.2.3 of this document gives the <ftp-path> another ABNF
   definition, which is, though, compatible with the aforementioned.




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   The semantics of each part are defined below, in Section 2.2.

2.2. URI Scheme Semantics

   The 'ftp' URI specifies either a FTP server for establishing a
   connection (when <ftp-path> is omitted) or a resource on such FTP
   server (when <ftp-path> is present).

   The application resolving the 'ftp' URI SHALL follow the following
   algorithm:

   o Request the password, if not supplied in the URI (per Section
     2.1.1);

   o Establish the Transmission Control Protocol (TCP) [RFC0793]
     connection to the resource identified by the <host> on the port
     identified by the <port> (or 21, if not supplied there);

   o Authenticate itself to the server, using either the credentials of
     the URI, those requested from the user or anonymous FTP [RFC1635],
     if the authentication is requested by it;

   o Perform a series of commands according to <ftp-path> part (see
     Section 2.2.3), if it is present.

   'ftp' URIs may also be used for other operations; for instance, it is
   possible to update or remove a file on a remote file server.  The
   mechanism for doing so is not specified in this document.

     Note:  The 'ftp' URI scheme supports FTP over TCP only; such
     derivations as FTP over User Datagram Protocol (UDP) [RFC0768] are
     not supported by it.

     Note:  The 'ftp' and the 'file' URI are not the same, even though
     they both may refer to the resource on the local host.

   More detailed description of each URI's parts' semantics is below.

2.2.1. The <user-pass> Part

   The <user> part of the 'ftp' URI specifies the user name that will be
   used for FTP authentication; <pass> part - the password.  The user
   name and password SHALL be transmitted using the "USER" and "PASS"
   FTP commands, respectively, defined in RFC 959 [RFC0959], when
   requested by the server.

   The user name and password are delimited by the colon (":") character
   (ASCII [ASCII] character 0x3A).  The <user-pass> part is not intended



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   to define information which should be used if the authentication is
   performed using the AUTH command or other mechanism spelled out in
   RFC 2228 [RFC2228]; see Section 3 of this document.

   The <user-pass> part is OPTIONAL in 'ftp' URIs.  Thus, if the whole
   <user-pass> part is omitted, the following "anonymous FTP" convention
   [RFC1635] SHOULD be used:

   (1) the user name "anonymous"; and

   (2) the password that is an e-mail address [RFC5322] of the client is
       supplied.

   However, the user may choose to denote authentication credentials by
   themselves; thus the FTP clients SHALL provide a way to choose
   whether anonymous FTP will be used.

   The <pass> part in the <user-path> is OPTIONAL as well.  Therefore,
   if there is a user name but no password supplied in the 'ftp' URI, it
   SHALL be requested from the user.

   The <user> and <pass> parts of the URI are composed of the characters
   of <usp-char> ABNF production; any other characters SHALL be percent-
   encoded, if occur in these parts.  The <usp-chair> rule includes
   characters allowed in RFC 3986 <userinfo> production, excluding the
   colon (":") character, whose use is explicitly specified above.

   RFC 3986 deprecated the use of "user:pass" pair in the <userinfo>
   part of URIs.  However, for some historical reasons, the benefits of
   the use of such construction for denoting the user information are
   valuable enough to overlook this issue.

2.2.2. The <host-port> Part

   The <host-port> part specifies the FTP server the resource identified
   by a particular 'ftp' URI is located on.

   If the <port> (in the <host> part) in couple with the preceding colon
   (":") character is omitted, the port SHALL default to 21, as
   registered in [IANA-PORTREG].

2.2.3. The <ftp-path> Part

   The <ftp-path> part, which is OPTIONAL, has the following non-
   normative syntax:

     <cwd1>/<cwd2>/.../<cwdN>/<name>;type=<typecode>




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   where ";type=<typecode>" is OPTIONAL as well.  Each of the <cwd>
   parts MAY be null, as allowed by RFC 3986 syntax for <path-abempty>
   ABNF production.  In the <cwd> and <name> parts any ";" characters
   SHALL be escaped by percent-encoding.

   The <ftp-path> part can be described in the ABNF as follows:

     ftp-path      =/ [ ( [ cwd-part ] [ name ] ) ] [ typecode-part ]
     cwd-part      =  *( "/" cwd )
     cwd           = segment
     name          = segment-nz
     typecode-part = <specified in Section 2.1>

   where the <segment> and <segment-nz> rules are defined in RFC 3986
   [RFC3986], Appendix A.  The ";" character, even allowed by RFC 3986
   is the aforementioned productions, SHALL be escaped by percent
   encoding.  This syntax is compatible with the <ftp-path> definition
   of Section 2.1 and <path-abempty> production of RFC 3986, modulo
   scheme-specific <typecode-part> part.

   The <ftp-path> part SHALL be interpreted as follows:

   (1a) each of <cwd> parts are consistently supplied as arguments to
        the CWD (change working directory) FTP command after
        establishing the FTP connection to the server identified by the
        <host-port> part of the URI;

   (1b) the whole <cwd-part> is submitted as an argument to the
        aforementioned command under the same circumstances;

     Note:  Any null <cwd> parts, allowed above, MUST NOT cause sending
     CWD comands, since they might be erroneously interpreted by some
     FTP servers.

     Note:  The step (1b) below is NOT RECOMMENDED for action by this
     specification; it is only included for compatibility with some FTP
     clients.  FTP servers SHOULD support both variants and MUST support
     the (1a) behavior.

   (2a) if the <typecode> is equal to "d", the NLST (name list) FTP
        command (see Section 4.1.3 of RFC 959 [RFC0959]) with <name> as
        the argument is sent out;

   (2b) otherwise, the TYPE FTP command (see Section 3.1.1 of RFC 959
        [RFC0959]) with the <typecode> as an argument is performed;

     Note:  If the <cwd-part> is absent in the URI, but there is a
     <typecode-part>, the typecode denoted by it concerns the root FTP



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     directory on the <host>.

    (3) access the file identified by the <name> in an appropriate way,
        eg. using the RETR command.

2.2.3.1. A Note on <typecode-part> Part

   The <typecode-part> part has rarely been seen in the wide
   development.  It is not often used in 'ftp' URIs and is included in
   this specification for historical reasons.  Thus, if the <typecode-
   part> is omitted, the client program interpreting the URI SHOULD
   guess the appropriate mode to use.

2.2.4. Errors Handling

   During processing the 'ftp' URI, some errors might occur with the
   server.  This section specifies the client's behavior under such
   circumstances.

2.2.4.1. Handling 4xx Errors

   If the client receives either 421, 426 or 434 response codes, which
   stand for "service not available", "connection closed" and "host not
   available", respectively, it SHALL stop handling the 'ftp' URI,
   notify the user and take no further actions.

   If the client receives either 425, 450, 451 or 452 response codes,
   which stand for "cannot open data connection", "file action not
   taken", "requested action aborted per local problems" and "file
   currently unavailable", respectively, upon processing the <ftp-path>,
   it SHALL stop processing the 'ftp' URI, notify the user and retain
   the most currently accessed directory active to allow them to decide
   on further actions.

   If the client receives the 430 response code, which stands for "user
   name or password invalid" upon processing the <user-pass> part, it
   SHALL suspend handling the 'ftp' URI, either request another
   credentials from the user or allow them to use anonymous FTP, proceed
   not authenticated or terminate the connection.

2.2.4.2. Handling 5xx Errors

   If the client receives either 501, 502, 503 or 504 response code,
   which stand for "syntax error", "command not implemented", "bad
   sequence of commands" and "command not implemented for a particular
   parameter", respectively, it SHALL stop processing the 'ftp' URI,
   notify the user and retain the most currently accessed directory
   active to allow them to decide on further actions.



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   If the client receives the 530 response code, which stands for "not
   logged on", it SHALL suspend handling the 'ftp' URI and first try to
   authenticate itself using the credentials in it, if they are present.
    If the credentials are omitted, they SHALL be requested from the
   user; unless the FTP client is authenticated using them, it SHALL act
   as specified in Section 2.2.4.1 for the case of 430 response code
   received.

   If the client receives either 550, 551, 552 or 553 response codes,
   which stand for "file unavailable", "requested action aborted",
   "exceeded storage allocation" and "file name not allowed",
   respectively, upon processing the <ftp-path>, it SHALL stop
   processing the 'ftp' URI, notify the user and retain the most
   currently accessed directory active to allow them to decide on
   further actions.

2.2.4.3. Handling 6xx Errors

   6xx errors, introduced by RFC 2228 [RFC2228], are truly believed not
   to occur during handling the 'ftp' URIs, since they concern mechanism
   specified in the aforementioned document, whose use cannot be denoted
   by 'ftp' URI; see Section 3 of this document.

2.3. Encoding Considerations

   The 'ftp' URIs may contain characters form the Universal Character
   Set (UCS) [UCS], encoded using UTF-8 character encoding [RFC3629], as
   suggested by RFC 3986 [RFC3986].  Those octets that do not correspond
   to the characters in the unreserved set of RFC 3986 SHALL be percent-
   encoded.  In fact, there are no other encoding considerations for
   'ftp' URIs not addressed in Section 2 of RFC 3986.

   Please visit RFC 3536 [RFC3536] for definitions of the terms related
   to encoding and internalization.


3.  Security Considerations

   Generic security considerations for URIs are discussed in Section 7
   of RFC 3986 [RFC3986].

   Security considerations for FTP are addressed in RFC 2577 [RFC2577].
   RFC 2228 [RFC2228] and RFC 4217 [RFC4217] provided a bunch of ways
   for securing FTP.  However, the 'ftp' URI does not allow to denote
   whether any of these ways should be used.


4.  IANA Considerations



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   IANA is asked to update the registration of the 'ftp' URI scheme with
   the reference to this document using the following template, per RFC
   4395 [RFC4395]:

   o URI scheme name: ftp

   o Status: Permanent

   o URI scheme syntax: see Section 2.1 of RFC xxxx

   o URI scheme semantics: see Section 2.2 of RFC xxxx

   o URI scheme encoding considerations: see Section 2.3 of RFC xxxx

   o Protocols that use the scheme: File Transfer Protocol (FTP)
     [RFC0959]

   o Security considerations: see Section 3 of RFC xxxx

   o Contact: IESG <iesg@ietf.org>

   o Author/Change controller: IETF <ietf@ietf.org>

   o References: see Section 5 of RFC xxxx

   [RFC Editor: Please replace xxxx with assigned RFC number]


5.  References

5.1.  Normative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

   [RFC0959]  Postel, J. and J. Reynolds, "File Transfer Protocol", STD
              9, RFC 959, October 1985.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.




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   [RFC5234]  Crocker, D., Ed., and P. Overell, "Augmented BNF for
              Syntax Specifications: ABNF", STD 68, RFC 5234, January
              2008.

5.2.  Informative References

   [ASCII]    American National Standards Institute (ANSI), "Coded
              Character Set -- 7-bit American Standard Code for
              Information Interchange", ANSI X3.4, 1986.

   [IANA-PORTREG]
              Internet Assigned Numbers Authority (IANA), "Port
              Numbers". <http://www.iana.org/assignments/port-numbers>

   [RFC0114]  Bhushan, A., "File Transfer Protocol", RFC 114, April
              1971.

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              August 1980.

   [RFC1123]  Braden, R., Ed., "Requirements for Internet Hosts -
              Application and Support", STD 3, RFC 1123, October 1989.

   [RFC1630]  Berners-Lee, T., "Universal Resource Identifiers in WWW: A
              Unifying Syntax for the Expression of Names and Addresses
              of Objects on the Network as used in the World-Wide Web",
              RFC 1630, June 1994.

   [RFC1635]  Deutsch, P., Emtage, A., and A. Marine, "How to Use
              Anonymous FTP", FYI 24, RFC 1635, May 1994.

   [RFC1738]  Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
              Resource Locators (URL)", RFC 1738, December 1994.

   [RFC2228]  Horowitz, M. and S. Lunt, "FTP Security Extensions",
              RFC 2228, October 1997.

   [RFC2396]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifiers (URI): Generic Syntax", RFC 2396,
              August 1998.

   [RFC2577]  Allman, M. and S. Ostermann, "FTP Security
              Considerations", RFC 2577, May 1999.

   [RFC3536]  Hoffman, P., "Terminology Used in Internationalization in
              the IETF", RFC 3536, May 2003.

   [RFC4217]  Ford-Hutchinson, P., "Securing FTP with TLS", RFC 4217,



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              October 2005.

   [RFC4248]  Hoffman, P., "The telnet URI Scheme", RFC 4248, October
              2005.

   [RFC4266]  Hoffman, P., "The gopher URI Scheme", RFC 4266, November
              2005.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 35,
              RFC 4395, February 2006.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.

   [UCS]      International Organization for Standardization (ISO),
              "Information Technology - Universal Multiple-Octet Coded
              Character Set (UCS)", ISO/IEC Standard 10646, December
              2003.


Appendix A.  List of Changes since RFC 1738

   The first specification of the 'ftp' URI is RFC 1738.  This appendix
   lists main changes since that document.

     Updated syntax specification to use ABNF.
     Specification changed to suit RFC 3986.
     Given more detailed description of <user-pass> semantics.
     Clarified the <ftp-path> syntax.
     Given detailed algorithm of handling <ftp-path>.
     Clarified client's handling null <cwd>s in <ftp-path>.
     Specified rules for handling errors.
     Clarified encoding considerations.
     Various editorial changes/corrections.
     Added appropriate IANA Considerations section.


Appendix B.  Acknowledgments

   The authors of RFC 1738 were Tim Berners-Lee, Larry Masinter and Mark
   McCahill, who worked on the initial 'ftp' URI scheme definition.
   Another attempts to specify this URI scheme were undertaken by Paul
   Hoffman, {who else?}.

   Considerable input to this document was provided by (in alphabetical
   order) John Klensin and Daniel Stenberg.




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Authors' Addresses

   Mykyta Yevstifeyev
   8 Kuzovkov St., flat 25
   Kotovsk
   Ukraine

   EMail: evnikita2@gmail.com











































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