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
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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
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include Simplified BSD License text as described in Section 4.e of
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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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