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Re: Registering the about: URI scheme

From: Lachlan Hunt <lachlan.hunt@lachy.id.au>
Date: Tue, 27 Jan 2009 14:26:18 +0100
Message-ID: <497F0B7A.3050204@lachy.id.au>
To: Joseph A Holsten <joseph@josephholsten.com>
Cc: HTML WG <public-html@w3.org>

Joseph A Holsten wrote:
> I've posted the merged version of Lachlan and my drafts here:
>     http://josephholsten.com/about-uri-scheme/draft-holsten-about-uri-scheme.txt 
> with inline comments and editing marks in html here:
>     http://josephholsten.com/about-uri-scheme/draft-holsten-about-uri-scheme.html 
> and source control here:
>     http://github.com/josephholsten/about-uri-scheme/
> My changes mostly amount to adding the required IANA and Security 
> Considerations sections.
> As to whether different browsers use the exact same representation of 
> the about:blank resource, I think that is content type specific 
> decision, and belongs in the HTML5 spec. I'd care more that the DOM is 
> identical than the actual document.

The DOM is generated based on the content type, and for interoperability 
reasons this needs to be defined as text/html;charset=UTF-8.  It should 
go into the RFC, rather than HTML5, because ideally, all uses of 
about:blank will be handled the same in all applications.

This statement is grammatically incorrect.

   "If the application may use a document of MIME type 'text/html' and
    character encoding 'UTF-8', about:blank SHOULD be represented with
    an empty document."

I suggest you use the phrasing from my draft and add a reference to HTML5.

> Lachlan, I don't know what you mean when you mention Origin in Security 
> Considerations. Care to explain?

I meant to say something about the security implications in terms of the 
origin as defined in HTML5 [1].

I also noticed you omitted the opera: URI examples that I included in my 
draft [2].  Was that intentional, or had you just used the old revision?

Finally, I concur with all of Julian's suggestions and was going to 
suggest roughly the same changes.

Julian Reschke wrote:
> - "abouturi = "about:" segment" - restricting to segment sounds good,
> but does this reflect reality?

Looking at the syntax from RFC 3986:

segment       = *pchar
pchar         = unreserved / pct-encoded / sub-delims / ":" / "@"
unreserved    = ALPHA / DIGIT / "-" / "." / "_" / "~"
pct-encoded   = "%" HEXDIG HEXDIG
sub-delims    = "!" / "$" / "&" / "'" / "(" / ")"
                  / "*" / "+" / "," / ";" / "="

That doesn't look right.  Mozilla uses a query string for some [3], 
which isn't permitted by that syntax.

I'm not sure about supporting percent encoding.  Testing with the URI 
about:confi%67, these are the results:

Opera: The address bar changes to "opera:config", but still returns
        an error.

Firefox: Says the URL is not valid.

IE8: Presents error page "Navigation to the webpage was cancelled".

Safari: Treats all about: URIs the same as about:blank, so unaffected.

Chrome: Treats all unknown about: URIs the same as about:blank, but
         testing with about:%63ache, the address bar is resolved to
         about:cache, but still returns a blank page.

So it appears that percent encoding isn't really supported among the 
browsers.  However, I'm not sure if we want to forbid them.  I'm 
inclined to make the syntax as lenient as possible so future 
implementations have few restrictions on what they can do.

[1] http://www.whatwg.org/specs/web-apps/current-work/#origin
[2] http://lachy.id.au/dev/specs/about-uri/draft-lachy-about-uri.txt

Lachlan Hunt - Opera Software
Received on Tuesday, 27 January 2009 13:26:58 UTC

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