Name¶
lua-uri-file - File URI support for Lua URI library
Description¶
The class "uri.file" is used for URIs with the "file"
scheme. It inherits from the uri class.
A file URI without an authority doesn't have a well defined meaning. This
library considers such URIs to be invalid when they have a path which does not
start with '/' (for example "file:foo/bar"). It is likely that any
such URI should really be a relative URI reference. If the path does start
with a slash then this library will attempt to 'repair' the URI by adding an
empty authority part, so that "file:/foo/bar" will be changed
automatically to "
file:///foo/bar".
A host value of "localhost" is normalized to an empty host, so that
"
file://localhost/foo" will become "
file:///foo". An empty
path is normalized to '/'.
The path part is always considered to be case sensitive, so no case folding is
done even when converting to a filesystem path for Windows.
Query parts and fragments are left alone by this library, but are not used in
converting URIs to filesystem paths.
Converting between URIs and filesystem paths¶
A "uri.file" object can be converted into an absolute path suitable
for use on a particular operating system by calling the
"filesystem_path" method:
local uri = assert(URI:new("file:///foo/bar"))
print(uri:filesystem_path("unix")) -- /foo/bar
print(uri:filesystem_path("win32")) -- \foo\bar
This method will throw an exception if the path cannot be converted. For
example, a file URI containing a host name cannot be represented on a Unix
filesystem, but on a Win32 system it will be converted to a UNC path:
local uri = assert(URI:new("file://server/path"))
print(uri:filesystem_path("unix")) -- error
print(uri:filesystem_path("win32")) -- \\server\path
To convert a filesystem path into a URI, call the class method
"make_file_uri":
local FileURI = require "uri.file"
local uri = FileURI.make_file_uri("/foo/bar", "unix")
print(uri) -- file:///foo/bar
uri = FileURI.make_file_uri("C:\foo\bar", "win32")
print(uri) -- file:///C:/foo/bar
To convert a relative URI reference (a uri._relative object) into a filesystem
path you should first resolve it against an appropriate "file" URI,
and then call the "filesystem_path" method on that.
Methods¶
All the methods defined in
lua-uri(3) are supported. The
"userinfo", and "port" methods will always return nil, and
will throw an exception when passed anything other than nil. The
"host" method will normalize "localhost" to an empty host
name, and will throw an exception if given a new value of nil. The
"path" method will normalize an empty path or nil value to '/'.
In addition to the standard methods, file URIs support the
"filesystem_path" method, and the "uri.file" class
contains the "make_file_uri" function, both of which are described
above.
Operating systems supported¶
The conversion between a file URI and a path suitable for use on a particular
operating system are defined in additional classes, which are loaded
automatically based on the operating system name supplied to the two
conversion functions. For example, passing the string "win32" to the
functions will invoke the implementation in the class
"uri.file.win32". An exception will be thrown if no class exists to
support a given operating system. The following operating system classes are
provided:
- "uri.file.unix"
- A URI containing a host name will cause an exception to be thrown, as
there is no obvious way for these to be represented in Unix paths. If the
path contains an encoded null byte (%00) or encoded slash (%2F) then an
exception will be thrown.
Attempting to convert a relative path to a URI will cause an exception.
- "uri.file.win32"
- Forward slashes ('/') in URIs will be converted to backslashes ('\') in
paths, and vice versa.
URIs containing host names will be converted to UNC paths, starting with a
'\\' followed by the hostname and then the path part. If the path part of
a URI appears to begin with a drive letter, then the first slash will be
removed so that the resulting path starts with the letter. Encoded pipe
characters ('%7C') will be recognized as equivalent to colons for the
purpose of identifying drive letters, since they have been historically
used in that way, but I believe they are not allowed to occur in the path
unencoded in a URI nowadays.
The operating system names are case insensitive, and are folded to lowercase
before being converted into a Lua module name.
Currently there is no way for this library to recognise the operating system it
is running on, since Lua has no built-in way of providing that information.
References¶
The most up to date IETF standard for the "file" URI scheme is still
"RFC 1738 section 3.10", but this does not specify exactly how to
convert between URIs and filesystem paths on particular platforms. It does
however specify the equivalence between 'localhost' and an empty host.
The correct form of file URI to represent a Windows filesystem path is described
in a blog article:
<
http://blogs.msdn.com/ie/archive/2006/12/06/file-uris-in-windows.aspx>
There is a standard of sorts describing the conversion between Unix paths and
file URIs: <
http://equinox-project.org/spec/file-uri-spec.txt>