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]