Re: [Emacs-diffs] emacs-26 7a8f22b: * test/lisp/url/url-file-tests.el (url-file): Use file:///, not file://.

[Juanma Barranquero <lekktu@gmail.com>]

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On Thu, Jun 27, 2019 at 11:57 PM Ken Brown <kbrown@cornell.edu> wrote:

> This change causes the test to fail on Cygwin.  I think the original
"file://"
> is the correct prefix.  If concatenated with "/some/file", it yields the
URL
> "file:///some/file".  Your version with "file:///" as the prefix yields
> "file:////some/file", which would refer to a local file "//some/file".

It's a long-standing issue. The standard says that two slashes are to be
followed by a hostname, Three slashes, if there's no hostname.

So, in fact, Posix apps should strip the initial slash of an absolute
pathname before concatenating it to file:///

https://tools.ietf.org/html/rfc8089

Appendix B.  Example URIs
>    The syntax in Section 2 is intended to support file URIs that take
>    the following forms:
>    Local files:
>    o  A traditional file URI for a local file with an empty authority.
>       This is the most common format in use today.  For example:
>       *  "file:///path/to/file"



https://en.wikipedia.org/wiki/File_URI_scheme#How_many_slashes?


* A valid file URI must therefore begin with either file:/path,
> file:///path or file://hostname/path.
> * file://path (i.e. two slashes, without a hostname) is never correct, but
> is often used.


The test, as it is now, works for the native Windows port and fails for the
Cygwin port. So to work on both, some special-casing will have to be done.

Note that file:/// is already used in several places in the sources.

> Posix says that the meaning of a path name starting with exactly two
slashes is
> implementation-defined.  On Cygwin, it's interpreted as a UNC path name,
> referring to a file on a network.

This is not about Posix pathnames, but RFC8089 URI schemes.

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