The file URI scheme is a URI scheme specified in RFC 1630 and RFC 1738, typically used to retrieve files from within one's own computer.

Format[link]

A file URL takes the form of

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. If host is omitted, it is taken to be "localhost", the machine from which the URL is being interpreted. Note that when omitting host you do not omit the slash ("file:///foo.txt" is okay, while "file://foo.txt" is not, although some interpreters manage to handle the latter).

Meaning of slash character[link]

The slash character (/), depending on its position, is used in different meanings in a file URL.

• The // after the file: is part of the general syntax of URLs. (The double slash // should always appear in a file URL according to the specification, but in practice many Web browsers allow you to omit it, in some cases at least.)
• The single slash between host and path is part of the syntax of file URLs.
• And the slashes in path separate directory names in a hierarchical system of directories and subdirectories. In this usage, the slash is a general, system-independent way of separating the parts, and in a particular host system it might be used as such in a pathname (as in Unix systems).

Examples[link]

Unix[link]

Here are two Unix examples pointing to the same /etc/fstab file:

file://localhost/etc/fstab
file:///etc/fstab

Windows[link]

Here are some examples which may be accepted by some applications on Windows systems, referring to the same, local file c:\WINDOWS\clock.avi

file://localhost/c|/WINDOWS/clock.avi
file:///c|/WINDOWS/clock.avi
file://localhost/c:/WINDOWS/clock.avi

Here is the correct URI as understood by the Windows Shell API:

file:///c:/WINDOWS/clock.avi

For a local file, the last is the most obvious and human-readable, and also the canonical one understood by the operating system [1].

Things to consider[link]

Windows[link]

On Microsoft Windows systems, the normal colon (:) after a device letter has sometimes been replaced by a vertical bar (|) in file URLs. This reflected the original URL syntax, which made the colon a reserved character in a path part.

Since Internet Explorer 4, file URIs have been standardized on Windows, and should follow the following scheme. This applies to all applications which use URLMON or SHLWAPI for parsing, fetching or binding to URIs. To convert a path to a URL, use UrlCreateFromPath, and to convert a URL to a path, use PathCreateFromUrl. [2]

To access a file "the file.txt", the following might be used.

For a network location:

file://hostname/path/to/the%20file.txt

Or for a local file, the hostname is omitted, but the slash is not (note the third slash):

file:///c:/path/to/the%20file.txt

This is not the same as providing the string "localhost" or the dot "." in place of the hostname. The string "localhost" will attempt to access the file as \\localhost\c:\path\to\the file.txt, which will not work since the colon is not allowed in a share name. The dot "." results in the string being passed as \\.\c:\path\to\the file.txt, which will work for local files, but not shares on the local system. For example file://./sharename/path/to/the%20file.txt will not work, because it will result in sharename being interpreted as part of the DOSDEVICES namespace, not as a network share.

The following outline roughly describes the requirements.

• The colon should be used, and should not be replaced with a vertical bar.
• Forward slashes should be used to delimit paths. note that while DOS requires backslashes, the Win32 API will accept either a forward or back slash.
• Characters such as the hash (#) or question mark (?) which are part of the filename should be percent-encoded.
• Characters which are not allowed in URIs, but which are allowed in filenames, must also be percent-encoded. For example, any of "{}`^ " and all control characters. In the example above, the space in the filename is encoded as %20.
• Characters which are allowed in both URIs and filenames must NOT be percent-encoded.
• Must not use legacy ACP encodings. (ACP code pages are specified by DOS CHCP or Windows Control Panel language setting.)
• Unicode characters outside of the ASCII range must be UTF-8 encoded, and those UTF-8 encodings must be percent-encoded.

Use the provided functions if you can. If you must create a URL programmatically and you cannot access SHLWAPI.dll (for example from script, or another programming environment where the equivalent functions are not available) the above outline will help.

Legacy URLs[link]

To aid the installed base of legacy applications, the PathCreateFromUrl recognizes certain URLs which do not meet these criteria, and treats them uniformly. These are called "legacy" file URLs as opposed to "healthy" file URLs. [3]

In the past, A variety of other applications have used other systems. Some added an additional two slashes. For example, \\remotehost\share\dir\file.txt, would become file:////remotehost/share/dir/file.txt instead of the "healthy" file://remotehost/share/dir/file.txt.

Web pages[link]

File URLs are rarely used in Web pages on the Internet, since they make the assumption that such a file exists on the client's computer. The host specifier can be used to retrieve a file from an external source, although no specific file-retrieval protocol is specified; and using it should result in a message that informs the user that no mechanism to access that machine is available.

Mozilla[link]

Mozilla browsers refuse to follow file URLs on a page that it has fetched with the HTTP protocol (i.e. the page's own URL is an http URL). When you click on such a link, nothing happens. The purpose is security: to prevent a remote page from executing a program on the visitor's computer. File links work on Mozilla on pages that are local files on the user's disk. It is not a surprise that Firefox 3.5.3 does nothing when requesting a file on a remote host:

file:////remotehost/share/dir/file.txt 

However, it successfully opens:

file://localhost///remotehost/share/dir/file.txt

or its equivalent:

file://///remotehost/share/dir/file.txt 

as it is referred to as a file on the local host.

Mozilla browsers can be configured to override this security restriction as detailed in Mozillazine's "Links to Local Pages Don't Work".

Mozilla browsers also treat file URLs similarly to the Gopher protocol in the way a directory is represented textually (i.e. the source) and graphically.

Internet Explorer[link]

Internet Explorer browsers, prior to version 7, will attempt to access file: URLs even if they reside on pages fetched over HTTP.^{[citation needed]}

Other[link]

The original Web browser, WorldWideWeb, provided editing of resources in file space [4]. Amaya still has this ability.

External links[link]

• File URLs

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2009)

In the field of computer networking, a URI scheme is the top level of the uniform resource identifier (URI) naming structure. All URIs and absolute URI references are formed with a scheme name, followed by a colon character (":"), and the remainder of the URI called (in the outdated RFCs 1738 and 2396, but not the current STD 66/RFC 3986) the scheme-specific part. The syntax and semantics of the scheme-specific part are left largely to the specifications governing individual schemes, subject to certain constraints such as reserved characters and how to "escape" them.

URI schemes are frequently erroneously referred to as "protocols", or specifically as URI protocols or URL protocols, since most were originally designed to be used with a particular protocol, and often have the same name. The http scheme, for instance, is generally used for interacting with Web resources using HyperText Transfer Protocol. Today, URIs with that scheme are also used for other purposes, such as RDF resource identifiers and XML namespaces, that are not related to the protocol. Furthermore, some URI schemes are not associated with any specific protocol (e.g. "file") and many others do not use the name of a protocol as their prefix (e.g. "news").

URI schemes should be registered with IANA, although non-registered schemes are used in practice. RFC 4395 describes the procedures for registering new URI schemes.

Generic syntax[link]

Internet standard STD 66 (also RFC 3986) defines the generic syntax to be used in all URI schemes. Every URI is defined as consisting of four parts, as follows:

<scheme name> : <hierarchical part> [ ? <query> ] [ # <fragment> ]

The scheme name consist of a sequence of characters beginning with a letter and followed by any combination of letters, digits, plus ("+"), period ("."), or hyphen ("-"). Although schemes are case-insensitive, the canonical form is lowercase and documents that specify schemes must do so with lowercase letters. It is followed by a colon (":").

The hierarchical part of the URI is intended to hold identification information hierarchical in nature. Usually this part begins with a double forward slash ("//"), followed by an authority part and an optional path.

• The authority part holds an optional user-information part, terminated with "@" (e.g. username:password@); a hostname (e.g., domain name or IP address); and an optional port number, preceded by a colon ":".

• The path part is a sequence of segments (conceptually similar to directories, though not necessarily representing them) separated by a forward slash ("/"). Each segment can contain parameters separated from it using a semicolon (";"), though this is rarely used in practice.

The query is an optional part, separated by a question mark ("?"), that contains additional identification information that is not hierarchical in nature. The query string syntax is not generically defined, but it is commonly organized as a sequence of <key>=<value> pairs, with the pairs separated by a semicolon^[1][2][3] or an ampersand. For example:

Semicolon: key1=value1;key2=value2;key3=value3
Ampersand: key1=value1&key2=value2&key3=value3

The fragment is an optional part separated from the front parts by a hash ("#"). It holds additional identifying information that provides direction to a secondary resource, e.g., a section heading (in an article) identified by the remainder of the URI. When the primary resource is an HTML document, the fragment is often an id attribute of a specific element and web browsers will make sure this element is visible.

Examples[link]

The following figure displays two example URIs (foo://username:password@example.com:8042/over/there/index.dtb?type=animal&name=narwhal#nose and urn:example:animal:ferret:nose) and their component parts. (The examples are derived from RFC 3986 — STD 66, chapter 3).

  foo://username:password@example.com:8042/over/there/index.dtb?type=animal&name=narwhal#nose
  \_/   \_______________/ \_________/ \__/            \___/ \_/ \______________________/ \__/
   |           |               |       |                |    |            |                |
   |       userinfo         hostname  port              |    |          query          fragment
   |    \________________________________/\_____________|____|/ \__/         \__/ 
   |                    |                          |    |    |    |           |         
scheme              authority                    path   |    |    interpretable as keys
 name   \_______________________________________________|____|/       \____/     \_____/ 
   |                         |                          |    |          |           |
   |                 hierarchical part                  |    |    interpretable as values
   |                                                    |    |
   |            path               interpretable as filename |
   |   ___________|____________                              |
  / \ /                        \                             |
  urn:example:animal:ferret:nose               interpretable as extension

 scheme
  name  userinfo  hostname       query
  _|__   ___|__   ____|____   _____|_____
 /    \ /      \ /         \ /           \
 mailto:username@example.com?subject=Topic

Official IANA-registered schemes[link]

The official URI schemes registered with the IANA are as follows (note that "IETF Draft" in no way is a finalized specification and must not be treated so; refer to Section 2.2 of RFC 2026 for more details):

Unofficial but common URI schemes[link]

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