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Re: Reminder: January 31 comment deadline for LCWD of Widgets 1.0: Packaging & Configuration spec

From: Marcos Caceres <marcosscaceres@gmail.com>
Date: Wed, 4 Feb 2009 17:35:18 +0000
Message-ID: <b21a10670902040935h5d9ed1b4i452fb632ae09324c@mail.gmail.com>
To: "Priestley, Mark, VF-Group" <Mark.Priestley@vodafone.com>
Cc: Arthur Barstow <art.barstow@nokia.com>, public-webapps <public-webapps@w3.org>

Hi Mark,
On Thu, Jan 29, 2009 at 6:29 PM, Priestley, Mark, VF-Group
<Mark.Priestley@vodafone.com> wrote:
>
> Hi Marcos, Art, All,
>
> Please find below Vodafone's comments on the Widgets 1.0: Packaging and
> Configuration specification. I have divided them into what I consider to
> be substantive comments and editorial comments.
>
> Thanks,
>
> Mark
>
>
> ------------------------------------------------------------------------
> ----------------------
> Substantive comments
> ------------------------------------------------------------------------
> ----------------------
> Step 5 Process the Digital Signatures
>
> We disagree with the stage 2, specifically "If the file entry is deemed
> by the [Widgets-DigSig] to be an invalid widget, then a widget user
> agent must treat this widget as an invalid widget.", on two grounds:
>
> (1) Because one signature is invalid it doesn't mean that all of the
> signatures are invalid;
> (2) Just because one signature or all signatures are invalid does not
> mean that the widget should not be installed, only that it should _not_
> be treated as a signed widget. The security policy of the device might
> be configured not to install an unsigned widget or a widget with an
> invalid signature but this should be dependent on the security policy
> implemented.

Sorry, I think you might have misunderstood what I was trying to say
here (probably I did not write it clearly enough). This assertion is
here to deal with instances where the digital signature deemed by the
Widgets Dig Sig spec to be somehow fully broken or completely
non-conforming in such a way that all processing must stop. I don't
yet know if Widgets Dig Sig will spit out such a result for any digsig
it is processing, but it seemed like a good idea to put this in here
at the time.

In other words, this is something that is controlled by the Widgets
Dig Sig spec. If it turns out that Widgets Dig Sig never results in an
invalid widget situation, then I will take this out. I've created a
red note in the spec that says "Issue: [Widgets-DigSig] may never
identify a widget package as invalid" as a reminder that we need to
sort this out.

FWIW, I think step 5  is buggy and needs a rewrite (I've added another
issue to the spec stating as such). I'll need to work with you to fix
it as we progress the Dig Sig spec.

> -----------------------------------------------
> Step 4 Locate Digital Signatures for the Widget
>
> I'm not sure whether the packaging and configuration specification is
> the correct place to do this but IMHO there needs to be a statement that
> a files with a file name corresponding to the naming convention for
> digital signatures are not accessible from the widget once the widget is
> installed / instantiated. Failure to impose this restriction will make
> it possible to include a signature and then reference it from the signed
> code, which presents a security hole.

Good point. This seems like something that needs to be in the yet to
be written a widget runtime security spec.  I've added an issue note
to the spec so we don't forget about this.

Just out of interest, can you present the nature of the security hole?
i.e., once an attacker has the signature, say, via an XSS attack, what
could they do with it?

> -----------------------------------------------
> 7.10 The access Element
>
> The access element defines a network attribute as "A boolean attribute
> that indicates that the widget might need to access network resources as
> specified in [Widgets-Security]. "
>
> Based on this description we would like to make the following
> observations and suggestion:
>
> The access element contains security permissions that will be used as
> hooks in the yet to be written [Widgets-Security] specification. The
> problem is that the permissions haven't yet been discussed in detail and
> so we may find that we want to represent additional context other than a
> black and white "is network access required?". For example, it may be
> the case that it is important from a security point of view to know
> which bearer or protocol will be used, or to nest a set of domains/URLs
> with which the widget wants to communicate. I do not have a strong view
> on what might be relevant here, and I am not suggesting that it needs to
> be considered as part of the last call of the Packaging and
> Configuration spec, only that it is likely that the permission will need
> to be more complex when we look at it from a security perspective.

I think we better start this soon, then. My feeling is that we will
need some kind of <domain> access declarations, and I would like to
see them in the configuration document.

__This has the potential to block progress of this specification.__

> There is also the case in which the network permission may be used to
> determine whether or not the user wants to install a widget,

This sounds reasonable.

> or by the
> widget user agent may want to indicate whether or not the widget can run
> when there is no available network connection. Some widgets may only
> operate when there is a network connection, whereas others may degrade
> gracefully.

This sounds like something authors need to deal with, not user agents.

> So to provide a degree of future-proofing we would like to suggest
> something like:
>
> <access>
>    <network use="true/false" required="true/false"/>
> </access>

We might not need this at all, actually: If we go down the declaring
domain route, then network is off unless a domain is declared.

> (I realise that the "use" attribute in the above example is a horrible
> name but I couldn't think of another word for access...There are
> probably also better ways of capturing the meaning - we open to
> suggested improvements)

This needs further discussion.

> Sorry for not raising this earlier but it has only become apparent when
> considering in more detail how the access element would be used.

No probs.

>
> ------------------------------------------------------------------------
> ----------------------
> Editorial comments
> ------------------------------------------------------------------------
> ----------------------
> 6 Widget Resources
>
> First 5 bullets should say "and/or" rather than "or" ?

"Zero and/or more" sounds weird to me (i.e., "Zero and more"). If you
feel strongly about this, I will change it; otherwise, I would prefer
to leave it as is.

> -----------------------------------------------
> 6.5 Content Localization
>
> "The container for localized content is a folder at the root of the
> widget whose the first five characters of the folder-name case
> insensitively match the string 'locales/'." Why the first five
> characters only?

That was a mistake, the sentence now reads:
"The container for localized content is a folder at the root of the
widget whose folder-name case insensitively match the string
'locales/'. A container for localized content may contain zero or more
localized folders."

> Also sentence has an extra "the" in the middle, i.e. "whose *the* first"

fixed.

> -----------------------------------------------
> 6.6 Start file and Default Start Files Sentence
>
> For consistency with other sections I suggest to add:
>
> "A default start file is a start file whose file-name case insensitively
> matches a file-name given in the first column of the default start files
> below and whose MIME type matches the MIME type given in the second
> column of the table."
>
> before the sentence starting: "A default start file is a start file that
> a widget user agent..."

Ok, I think there was a more significant problem: I've defined "custom
start files" and "default start files". As a result, I changed that
whole section.

> And then to combine the last two sentences before the default start
> files table to:
>
> "A widget user agent will attempt to locate a file entry whose file-name
> case insensitively matches one of the default start files based on the
> order they appear in the table below (from top to bottom). "

Can you please check that section again and let me know if the rewrite is ok?

> -----------------------------------------------
> 7.1 Namespace
>
> It seems a bit tough that an invalid configuration document results in a
> invalid widget as the configuration document is optional. Also, if the
> configuration document in the localised folder is invalid, it could be
> the case that there is a valid configuration document at the root of the
> widget.
>
> I don't have a strong opinion on this and have no objection to leaving
> the text as it is, I just wondered if there was a reason why this
> approach had been taken?

Although I agree that it's a bit cruel on developers, we made this
decision to make the behavior of configuration documents predictable.
I feel pretty strongly that we should leave it as is.

> -----------------------------------------------
> 7.2 Proprietary Extensions
>
> Should the "may" be a "should"? Otherwise, it could be interpreted as
> suggesting that vendors may equally use other approaches?

Right, fixed. This should, in fact, be a must (i.e., if you want to
extend, then you must use your own namespace).

> -----------------------------------------------
> 7.9 The icon Element
>
> (disclaimer - I may well be talking rubbish here as the following
> comments are based on a _very_ basic understanding of graphics formats)
>
> The text says that if the icon is vector format then the height and
> width attributes will be used, however, isn't one the point of using
> vector graphics that they could be re-sized to fit the available space.

Yes and no. Beyond certain sizes (e.g., too little, too big), the
rendering engine may have undesirable effects on a design (think, for
example, of a really tiny font having anti-alias applied to it:
because of sub-pixel interpolation, it becomes too blurry to read. The
same can happen with graphics, very thin lines can vanish or become
blurry, which can make a design look crappy). In such cases, it may be
desirable to use a bitmap.

> Therefore shouldn't there be a statement saying that the widget user
> agent MAY ignore these values?

No, the width and height attributes represent the _minimum_ size at
which an image may be used. Then, the vector graphic can behave in the
manner you describe (i.e., can be used to fill a rendering context
larger than the width and height).

>Equally should there be default sizes in case the attribute is not used?

Hmm... good point. I've added that as an issue in the relevant section.

> In terms of raster graphics the text currently says "If the file pointed
> to by the src is a supported raster graphic, this value may be ignored
> by the widget user agent." but shouldn't the "may" in this case be a
> "should"?

Correct, but that "should" should be a "must". Fixed.

> -----------------------------------------------
> 7.13 The feature Element
>
> In the sentence "The feature is used by an author to denote that, at
> runtime, a widget may require access to a feature." the use of "may
> require" is very slightly confusing given that the next attribute is
> "required". Suggest changing "require" to "try to" or "attempt to".

Changed "require" to "attempt to".

> Likewise in the definition of the name attribute in the sentence "A URI
> attribute that identifies a feature required by the widget at runtime
> (such as an API)." change "required by" to "that may be used".

Done.

> -----------------------------------------------
> 8 Steps for Processing a Widget Resource
>
> The sentence "The steps for processing a widget resource involves ten
> steps that a widget user agent must follow, in sequential order,
> responding accordingly if any of the steps result in an error." could be
> slightly misleading as some of the steps are skipped depending on the
> processing in a preceding step. I'm not sure if this is always in a
> response to an error?

Ok, I changed it to: "The steps for processing a widget resource
involves ten steps that a user agent must follow, in sequential order,
responding accordingly if any of the steps result in an error or if
the specification asks for the user agent to skip a step."

Is that any better?

> A minor comment on section 8 as a whole - some of the steps have an
> explicit link to go to the next step while others (like 9) don't. It
> would be nice if this was consistent.

Ok, I checked every step and made sure things are consistent. Once all
the comments are done, I'll do another editorial round to make sure
everything is more consistent.

> In addition, some of the algorithms, for example step 7, could be made
> clearer by explicitly stating when to go to the next step (i.e. in case
> of success in 7.1 and 7.2).

Ok, I did what you said for step 7 and Step 8. Can you let me know
which other ones need a rewrite?

> Finally, in Step 6 there is a sentence "Else, remove the last subtag of
> the range and repeat this step 2.d. (e.g., if the range ...". Just to be
> super clear perhaps "this step 2.d." could be change to "and go to 2.d
> of this algorithm"

Made the change you suggested.

Very much appreciate Vodafone taking the time to conduct this review.

Kind regards,
Marcos
-- 
Marcos Caceres
http://datadriven.com.au
Received on Wednesday, 4 February 2009 17:36:01 GMT

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