The file URI Scheme

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Author Matthew Kerwin 
Last updated 2013-06-24
Replaced by RFC 8089, RFC 8089
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Network Working Group                                          M. Kerwin
Intended status: Standards Track                           June 24, 2013
Expires: December 26, 2013

                          The file URI Scheme


   This document specifies the file Uniform Resource Identifier (URI)
   scheme that was originally specified in [RFC1738].  The purpose of
   this document is to keep the information about the scheme on
   standards track, since [RFC1738] has been made obsolete.

Status of This Memo

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   This Internet-Draft will expire on December 26, 2013.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Terminology . . . . . . . . . . . . . . .   2
   2.  History . . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Scheme Definition . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Implementation Notes  . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Hierarchical Structure  . . . . . . . . . . . . . . . . .   5
     4.2.  Drives, drive letters, mount points, file system root . .   5
     4.3.  Character sets and encodings  . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7

1.  Introduction

   URIs were previously defined in [RFC1738], which was updated by
   [RFC3986].  Those documents also specify how to define schemes for

   The first definition for many URI schemes appeared in [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.

1.1.  Conventions and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  History

   The file URI scheme was first defined in [RFC1630], and informational
   RFC which does not specify an Internet standard of any kind.  The
   definition was standardised in [RFC1738], and the scheme was
   registered with IANA, however the latter definition omitted certain
   language from former that clarified aspects such as:

   o  the use of slashes to donate boundaries between directory levels
      of a hierarchical file system

   o  the requirement that client software convert the file URL into a
      file name in the local file name conventions

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   o  a justification for defining the scheme.

   The Internet draft [I-D.draft-hoffman-file-uri] was written in an
   effort to keep the file URI scheme on standards track, but it expired
   in 2005.  That draft enumerated concerns arising from the various,
   often conflicting implementations.

   Despite lacking a living standard, the file URI scheme is used by way
   of example in [RFC3986] three times:

   1.  section 1.1 [p6] uses "file:///etc/hosts" as an example

   2.  section 1.2.3 [p10] mentions the "file" scheme regarding relative

   3.  section 3.2.2 [p21] says that '...the "file" URI scheme is
       defined so that no authority, an empty host, and "localhost" all
       mean the end-user's machine...'.

   Finally the WHATWG defines a living URL standard [WHATWG], which
   includes algorithms for interpreting file URIs.

3.  Scheme Definition

   The file URI scheme is used to designate files accessible on a
   particular host computer.  This scheme, unlike most other URI
   schemes, does not designate a resource that is universally accessible
   over the Internet.

   The file URI 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

   Note that file: and ftp: URIs are not the same, even when the target
   of the ftp: URI is the local host.

   A file URI conforms with the generic syntax presented in [RFC3986],
   with the following components:

   scheme name  The literal value "file"

   authority  If present, either the fully qualified domain name of the
      system on which the file is accessible; or one of the special
      values "localhost" or the empty string, in which case it is
      interpreted as "the machine from which the URI is being

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      interpreted".  An absent authority component SHOULD be interpreted
      as if it were present and had the value "localhost".

   path  The hierarchical directory path to the file, using the slash
      character ("/") to separate directories.

   Some systems allow URIs to point to directories.  In this case, there
   is usually (but not always) a terminating slash character, such as


   On systems running some versions of Microsoft Windows, the local
   drive specification is sometimes specified with a colon character
   (":") and sometimes with a pipe ("|").  The two SHOULD be considered
   equivalent.  For example:


   Note that some systems running some versions of Microsoft Windows are
   known to omit the slash before the drive letter.

   For Windows shares, there is an additional slash prepeded to the
   path.  Thus, the file "example.doc" on the shared directory
   "departments" would have the URI


   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.

3.1.  Examples

   For example, a VMS file


   might become


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   On a Windows system, the file


   might become


   On a Linux system, the file


   could be referred to by any of the following equivalent URIs:


4.  Implementation Notes

4.1.  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.

4.2.  Drives, drive letters, mount points, file system root

   Historically there has been 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.

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   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.,

   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".

4.3.  Character sets and encodings

   Local file systems sometimes use many different encodings for
   representing file names.  The URI syntax defined in [RFC3986]
   provides a method of encoding data, presumably for the sake of
   identifying a resource, as a sequence of characters.  The URI
   characters are, in turn, frequently encoded as octets for transport
   or presentation.  This specification does not mandate any particular
   character encoding for mapping between URI characters and the octets
   used to store or transmit those characters, however for
   interoperability sake, it would be preferable for file: URI libraries
   to translate the native character encoding for file names to and from

5.  Security Considerations

   There are many security considerations for URI schemes discussed in

   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.

6.  IANA Considerations

   This document does not modify the existing entry in the URI Schemes
   registry [IANA], except by updating its reference RFC.

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7.  References

7.1.  Normative References

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

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

7.2.  Informative References

              Hoffman, P., "The file URI Scheme", draft-hoffman-file-
              uri-03 (work in progress), January 2005.

   [IANA]     IANA, "Uniform Resource Identifier (URI) Schemes
              registry", June 2013, <

   [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.

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

   [WHATWG]   WHATWG, "URL Living Standard", May 2013,

Author's Address

   Matthew Kerwin


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