Re: Absolute URL parsing bug

[Per Bothner <per at bothner dot com>]

Andrew Haley wrote:
> Per Bothner writes:
>  > Andrew Haley wrote:
>  > > [ An absolute file URL can look like:
>  > > 
>  > >    absoluteURI = "file" ":" abs_path
>  > >    abs_path = "/" path_segments
>  > > 
>  > > That is, there is no need for "//".
>  > 
>  > I don't see that in any of the specs.
>
> I got it from RFC 2396.  Which I might have read wrongly, of course.

I read more carefully.  In practice, it looks like "//" is optional. 
I.e. "file:///foo/bar" is the same as "file:/foo/bar".  There is a
subtle difference is the the former has an empty authority, while the 
latter has a missing (undefined) authority.  Thus resolving the relative 
URIs "/tmp/help" vs "//gcc.gnu.org/help" against the base URI 
"file://gnu.org/foo/" will yield "file://gnu.org/foo/help" vs 
"file://gcc.gnu.org/foo/help" respectively.  In practice, people seldom 
use non-empty authority components with file: URIs and I'm not sure it's 
well-defined.  Perhaps when using NFS?

>  > Technically, "file:/tmp/foo.html" is not a valid URI, as far as I
>  > can tell.  I notice that firefox rewrites it (in the navigation
>  > bar) to "file:///tmp/foo.html".
>  >
>  > Now in practice we may want to allow "file:/tmp/foo.html", but it should 
>  > be viewed as an unofficial short-hand for "file:///tmp/foo.html".
>  > 
>  > > And indeed, the URL spec in the
>  > > SDK docs says 'If the spec's path component begins with a slash
>  > > character "/" then the path is treated as absolute...' ]
>  > 
>  > The *path* is absolute, but the URI isn't.
>  > 
>  > This matters when resolving a relative URL against a base URI, such as 
>  > he URL of the containing document.
>  > 
>  > If we have a base URI "http://bar.com/baz/index.html"; and a reference 
>  > "/tmp/foo.html" then the resolved URI is "http://bar.com/tmp/foo.html";.
>  > 
>  > > But we parse the spec looking for "//" to determine if a URL is
>  > > absolute,
>  > 
>  > A URL is absolute *only* if it has a "scheme".
>
> I don't really understand what you're suggesting.

My comments are mostly applicative to the URI class rather than the URL 
class.  (I'm not sure why they're separate.  I believe all URLs are 
URIs, accdoring to the IEFT, but not the Java class hierarchy.)  The URI 
class has a bunch of methods like resolve and isAbsolute, which require 
more care about these fine points.

>  Would it be OK to
> special-case "file" URIs so that "file:/" is rewritten to ""file:///" ?

Maybe for the URL class, but I don't think so for the URI class.
The difference is the getAuthority method.  My reading is that it should 
return null for "file:/" and "" for "file:///".  But I haven't tested 
what JDK does - and it wouldn't surprise me if the URI and URL classes 
are different in this respect.
--
	--Per Bothner
per@bothner.com   http://per.bothner.com/