proposal for file: uri standard

[Alexander Larsson]

Are people ok with putting up this version on freedesktop.org?

On Mon, 2004-03-29 at 15:01, Alexander Larsson wrote:
> New proposal with a hostname section and the comments waldo had:
> 
> Standard for exchanging file: URIs
> ==================================
> 
> Rationale
> ---------
> 
> The use of URIs in the desktop is pervasive these days. All the major
> desktops have file handling system that use URIs instead of pathnames
> to be able to specify files not accessible in the normal UNIX file
> system. 
> 
> The URIs used in these systems are mostly based on the RFCs specifying
> the core URI mechanism and its various protocol versions. However
> there are sometimes extensions for new protocols that aren't
> standardized yet, and sometimes the standards aren't clear on some
> details. 
> 
> Passing of URIs between applications happens in various ways such as
> drag and drop, cut and paste and command line arguments. In order to be
> interoperable there needs to be some standardization of such URIs. Its
> the hope of many that eventually we'd have a common standard and
> perhaps even a common implementation. However, at the very least, we
> need a strict definition of how to specify URIs for absolute local
> filenames when exchanging them between applications. This document
> gives such a specification.
> 
> URI standards
> -------------
> 
> The specification for file: URIs, RFC2396[1] and RFC1738[2] says that
> file URIs are of the form:
>    file://<hostname>/<path>
> 
> Where the hostname and path parts can contain a limited subset of
> ASCII characters, representing their ASCII values, and any other bytes
> escaped by using a % followed by a two digit hex value. As a special
> case the hostname part can be "localhost" or empty meaning the machine
> the URI is being interpreted on.  
> 
> Given a URI like this we can unescape it into a hostname, and a string
> of octets (of undefined encoding), which maps 1:1 to a UNIX filename.
> 
> UNIX filenames
> --------------
> 
> An absolute filename in UNIX is a string containing filenames
> separated by and starting with a '/'. The filenames can contain any
> byte values except 0 and '/'.
> 
> There is no specified encoding for filenames, and although we hope
> that eventually all filenames will be encoded in UTF8 we can't rely on
> this, because then we would be unable to e.g. rename a file with a
> misencoded filename.
> 
> file: URIs on UNIX
> ------------------
> 
> Since each desktop has to have a way to generate displayable versions
> of filenames (this generally means somehow generating Unicode for it)
> we can rely on support for that in the platform. The internal form of
> the file reference (the URI) must always be convertible to the
> original UNIX byte-string so that we can operate of the file, so the
> display form of the filename should be generated at the last moment
> when displaying only.
> 
> This gives us the following definition for file: URI that are to be
> exchanged with other apps:
> 
> File URIs are of the form "file://<hostname>/<path>", where hostname
> can be empty, with all non-allowed bytes escaped, containing no
> escaped '/' or zero bytes. The unescaped byte string is not supposed to
> be interpreted in any way, and is not in a specified encoding. It
> corresponds exactly to the filename as used in UNIX system calls. If
> you need to display the unescaped filename, that should be handled the
> same way you display normal filenames. 
> 
> Hostnames
> ---------
> 
> When generating a file: uri the hostname part, if nonempty, should be
> whatever is returned from gethostname(). This means that the name is
> canonical for all users on the same machine, so that you can easily
> see if the referenced file is on the current machine. Note that
> "localhost" or an empty hostname needs to be handled specially, always
> meaning the host the uri is being interpreted on.
> 
> Backwards compatibility:
> ------------------------
> 
> Some current apps generate URIs of the form "file:/<path>". These
> are not correct according to RFC1738, so they should not be
> generated. However for backwards compatibility, it is recommended that
> such URIs are interpreted as file URIs with an empty hostname.
> 
> Some current apps generate file URIs by converting the filename from
> whatever locale the application runs in to UTF8. This behavior means
> that URIs are can't be converted to filenames without knowing the
> locale of the application that produced them, and that not all valid
> filenames can be converted to URIs. Such behavior is not allowed,
> and should be changed.
> 		      
> [1] http://www.ietf.org/rfc/rfc2396.txt
> [2] http://www.ietf.org/rfc/rfc1738.txt
> 
> 
> 
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>  Alexander Larsson                                            Red Hat, Inc 
>                    alexl at redhat.com    alla at lysator.liu.se 
> He's a leather-clad guerilla cat burglar on a mission from God. She's a foxy 
> paranoid soap star trying to make a difference in a man's world. They fight 
> crime! 
> 
> 
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=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 Alexander Larsson                                            Red Hat, Inc 
                   alexl at redhat.com    alla at lysator.liu.se 
He's a deeply religious voodoo househusband from a doomed world. She's a 
manipulative goth hooker who dreams of becoming Elvis. They fight crime!