Network Working Group P. Hoffman
Internet-Draft VPN Consortium
Expires: July 2, 2005 January 2005
The file URI Scheme
draft-hoffman-file-uri-03.txt
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. 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 become aware will be disclosed, in accordance with
RFC 3668.
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 will expire on July 2, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document specifies the file Uniform Resource Identifier (URI)
scheme that was originally specified in RFC 1738. The purpose of
this document is to allow RFC 1738 to be made obsolete while keeping
the information about the scheme on standards track.
1. Introduction
URIs were previously defined in RFC 2396 [RFC2396], which was updated
Hoffman Expires July 2, 2005 [Page 1]
Internet-Draft The file URI Scheme January 2005
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 made obsolete, this
document copies the file URI scheme from it to allow that material to
remain on standards track.
2. Scheme Definition
The file URL scheme is used to designate files accessible on a
particular host computer. This scheme, unlike most other URL
schemes, does not designate a resource that is universally accessible
over the Internet.
The file URL scheme has historically had little or no
interoperability between platforms. Further, implementers on a
single platform have often disagreed on the syntax to use for a
particular filesystem. This document does not try to resolve those
problems, only to show what has been commonly seen in use on the
Internet.
Note that the file: and ftp: URIs are not the same, even when the
target of the ftp: URI is the local host.
A file URL takes the form:
file://<host>/<path>
where <host> is the fully qualified domain name of the system on
which the <path> is accessible, and <path> is a hierarchical
directory path of the form <directory>/<directory>/.../<name>.
As a special case, <host> can be the string "localhost" or the empty
string; this is interpreted as "the machine from which the URL is
being interpreted". However, this part of the syntax has been
ignored on many systems. That is, for some systems, the following
are considered equal, while on others they are not:
file://localhost/path/to/file.txt
file:///path/to/file.txt
Some systems allow URLs to point to directories. In this case, there
is usually (but not always) a terminating "/" character, such as in:
file://usr/local/bin/
On systems running some versions of Microsoft Windows, the local
Hoffman Expires July 2, 2005 [Page 2]
Internet-Draft The file URI Scheme January 2005
drive specification is sometimes preceded by a "/" character. Thus,
for a file called "example.ini" in the "windows" directory on the
"c:" drive, the URL might be:
file:///c:/windows/example.ini
For Windows shares, there is an additional "/" prepended to the name.
Thus, the file "example.doc" on the shared directory "department"
would have the URL:
file:////department/example.doc
The file URL scheme is unusual in that it does not specify an
Internet protocol or access method for such files; as such, its
utility in network protocols between hosts is limited.
3. Implementation Notes
3.1 Hierarchical Structure
Most implementations of the file URI scheme do a reasonable job of
mapping the hierarchical part of a directory structure into the "/"
delimited hierarchy of the URI syntax, independent of what the native
platform delimiter is.
For example, on Windows platforms, it is typical that the file system
presents backslash "\" as the file delimeter for file names, yet the
URI's forward slash "/" can be used in file: URIs. Similarly, on
(some) Macintosh OS versions, at least in some contexts, the colon
(":") is used as the delimiter in the native presentation of file
path names. Unix systems natively use the same forward slash "/"
delimiter for hierarchy, so there is a closer mapping between file
paths and native path names.
3.2 Drives, drive letters, mount points, file system root
There is considerable difference, in practice, for handling of the
syntax for the "top" of the hierarchy. The file URI syntax provides
one simple place for designating the root of the file hierachy, and
implementations have diverged, even on the same platform, sometimes
even within a single application.
For example, DOS- and Windows-based systems support the notion of a
"drive letter", a single character which represents a (virtual)
drive, mount point, or device. Native representations of file paths
start with the drive letter, a colon, and then the path; e.g.,
"c:\tmp\test.txt".
Hoffman Expires July 2, 2005 [Page 3]
Internet-Draft The file URI Scheme January 2005
Drive letters are mapped into the top of a file URI in various ways,
depending on the implementation; some applications substitute
vertical bar ("|") for the colon after the drive letter, yielding
"file:///c|/tmp/test.txt". In some cases, the colon is left
unchanged, as in "file:///c:/tmp/test.txt". In other cases, the
colon is simply omitted, as in "file:///c/tmp/test.txt".
3.3 Use of hostname and host name checking
The file URI specification calls for using the actual host name as
the name authority and allowing it to be omitted. This practice is
rarely followed, and frequently is not checked. Some applications
generate URIs with no authority component at all, such as
"file:/this/is/the/path".
3.4 Character sets and encodings
Local file systems sometimes use many different encodings for
representing file names. For interoperability sake, it would be
preferable for file: URI libraries to translate the native character
encoding for file names to and from Unicode.
4. Security Considerations
There are many security considerations for URI schemes discussed in
[2396bis].
File access and the granting of privileges for specific operations
are complex topics, and the use of file: URIs can complicate the
security model in effect for file privileges. Under no circumstance
should software using file: URIs grant greater access than would be
available for other file access methods.
5 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.
Hoffman Expires July 2, 2005 [Page 4]
Internet-Draft The file URI Scheme January 2005
Author's Address
Paul Hoffman
VPN Consortium
127 Segre Place
Santa Cruz, CA 95060
US
EMail: paul.hoffman@vpnc.org
Hoffman Expires July 2, 2005 [Page 5]
Internet-Draft The file URI Scheme January 2005
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.
Disclaimer of Validity
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 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.
Copyright Statement
Copyright (C) The Internet Society (2005). 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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Hoffman Expires July 2, 2005 [Page 6]
