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Network Working Group                                         P. Hoffman
Internet-Draft                                            VPN Consortium
Expires: April 20, 2005                                 October 20, 2004


                           The ftp URI Scheme
                      draft-hoffman-ftp-uri-02.txt

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Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document specifies the ftp Uniform Resource Identifier (URI)
   scheme that was originally specified in RFC 1738.  The purpose of
   this document is to allow RFC 1738 to be moved to historic while
   keeping the information about the scheme on standards track.

1.  Introduction

   URIs are were previously defined in RFC 2396 [RFC2396], which was



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   updated by draft-fielding-uri-rfc2396bis [2396bis].  Those documents
   also specify how to define schemes for URIs.

   The first definition for many URI schemes appeared in RFC 1738
   [RFC1738].  Because that document has been moved to Historic status,
   this document copies the ftp URI scheme from it to allow that
   material to remain on standards track.

2.  Scheme Definition

   The FTP URL scheme is used to designate files and directories on
   Internet hosts accessible using the FTP protocol described in STD 9
   [FTP], RFC 959.

   A FTP URL follows the standard syntax described in
   draft-fielding-uri-rfc2396bis [2396bis].  If :<port> is omitted, the
   port defaults to 21.

2.1  FTP Name and Password

   A user name and password may be supplied; they are used in the ftp
   "USER" and "PASS" commands after first making the connection to the
   FTP server.  If no user name or password is supplied and one is
   requested by the FTP server, the conventions for "anonymous" FTP are
   to be used, as follows:

   o  The user name "anonymous" is supplied.

   o  The password is supplied as the Internet e-mail address of the end
      user accessing the resource.

   If the URL supplies a user name but no password, and the remote
   server requests a password, the program interpreting the FTP URL
   should request one from the user.

2.2  FTP url-path

   The url-path of a FTP URL has the following syntax:

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

   <cwd1> through <cwdN> and <name> are (possibly encoded) strings and
   <typecode> is one of the characters "a", "i", or "d".  The <cwdx> and
   <name> parts may be empty.  The part ";type=<typecode>" may be
   omitted.  In fact, the whole url-path may be omitted, including the
   "/" delimiting it from the prefix containing user, password, host,
   and port.




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   The url-path is interpreted as a series of FTP commands as follows:

   o  Each of the <cwd> elements is to be supplied, sequentially, as the
      argument to a CWD (change working directory) command.

   o  If the typecode is "d", perform a NLST (name list) command with
      <name> as the argument, and interpret the results as a file
      directory listing.

   o  Otherwise, perform a TYPE command with <typecode> as the argument,
      and then access the file whose name is <name> (for example, using
      the RETR command.)

   Within a name or CWD component, the characters "/" and ";" are
   reserved and must be encoded.  The components are decoded prior to
   their use in the FTP protocol.  In particular, if the appropriate FTP
   sequence to access a particular file requires supplying a string
   containing a "/" as an argument to a CWD or RETR command, it is
   necessary to encode each "/".

   Historical note: Most FTP client implementations precede the <cwd1>
   with a "/" before sending the CWD command.  This is arguably in
   conflict with RFC 1738, although the practice is quite widespread.
   Thus, a client that is presented with the URL
   <URL:ftp://myname@example.com/abc/def> might send the two commands
   "CWD /abc" and "RETR def" or it might send the two commands "CWD abc"
   and "RETR def".  Server implementers should be aware of these two
   different interpretations of the same URL.

   FTP URLs may also be used for other operations; for example, it is
   possible to update a file on a remote file server, or infer
   information about it from the directory listings.  The mechanism for
   doing so is not spelled out here.

2.3  FTP Typecode is Optional

   The entire ;type=<typecode> part of a FTP URL is optional and is
   rarely used.  Historically, the typecode option was rarely
   implemented and in practice, dereferencing is done by guessing.  If
   the typecode is omitted, the client program interpreting the URL must
   guess the appropriate mode to use.  In general, the data content type
   of a file can only be guessed from the name, such as from the suffix
   of the name; the appropriate type code to be used for transfer of the
   file can then be deduced from the data content of the file.

2.4  Hierarchy

   For some file systems, the "/" used to denote the hierarchical



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   structure of the URL corresponds to the delimiter used to construct a
   file name hierarchy, and thus, the filename will look similar to the
   URL path.  This does NOT mean that the URL is a filename in the Unix
   or similar filesystems.

2.5  Optimization

   Clients accessing resources via FTP may employ additional heuristics
   to optimize the interaction.  For some FTP servers, for example, it
   may be reasonable to keep the control connection open while accessing
   multiple URLs from the same server.  However, there is no common
   hierarchical model to the FTP protocol, so if a directory change
   command has been given, it is impossible in general to deduce what
   sequence should be given to navigate to another directory for a
   second retrieval, if the paths are different.  The only reliable
   algorithm is to disconnect and reestablish the control connection.

3.  Security Considerations

   There are many security considerations for URI schemes discussed in
   draft-fielding-uri-rfc2396bis [2396bis].

4  Informative References

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

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

   [2396bis]  Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
              Resource Identifiers (URI): Generic Syntax", work in
              progress, draft-fielding-uri-rfc2396bis-nn.txt.

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


Author's Address

   Paul Hoffman
   VPN Consortium
   127 Segre Place
   Santa Cruz, CA  95060
   US

   EMail: paul.hoffman@vpnc.org



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