ISSUE-1: Mandatory algorithms (was Re: ISSUE-3: Algorithm discovery)

On Tue, Jul 10, 2012 at 10:22 AM, Seetharama Rao Durbha <
S.Durbha@cablelabs.com> wrote:

> On 7/9/12 7:26 PM, "Ryan Sleevi" <sleevi@google.com> wrote:
>
> >>Note that none of the above semantics would necessarily be altered by a
> MUST-IMPLEMENT registry (ISSUE-1), since there would still
> >>need to be some form of error handling for invalid constants/strings
> and for unsupported key+algorithm+operation tuples.
>
> The difference is whether the developer needs to 'explicitly' catch
> UnsupportedAlgorithmException and 'do something about it', or 'just not
> bother', as the algorithm they picked is guaranteed to be available.
>
> Errors caused by invalid constants/strings must be caught at development
> time.
>
>
>
I do not believe this is a reasonable approach, nor does it seem to be
encouraged by the recommendations for W3C standard web APIs. [1] [2] [3].

My comment was reflecting a the need to have the error handling state
machine fully defined in the spec. Failing to specify what happens when an
invalid constant/string is provided means the API is incomplete, and
developers have no way of knowing what will happen. Will the U-A just
crash? Will the API ever call the onerror callback? If not, what happens if
the user keeps calling processData() and supplying more data? Will it cause
a syntax error that causes all JavaScript to fail executing on the page?

When there (and there eventually will) exist two different sets of
MUST-IMPLEMENT, how will the web application behave then? When SHA-1 is
broken, or SHA-3 is the new MUST-IMPLEMENT, how will that be addressed?

If we update the specification, and say "SHA-1 is no longer MUST-IMPLEMENT
because it was broken", what does that mean for web applications that were
using SHA-1? What will their execution environments be like? Will it break
all script on that page?

For interop testing and for reference implementations, I do not believe we
will be able to escape the need to specify error handling. Which is why I
believe that these concerns remain wholly independent of the discussion of
MUST-IMPLEMENT question. Because we MUST have error handling, we implicitly
have discovery. The only question is whether we want to use error handling
as the /only/ form of discovery.

[1] http://lists.w3.org/Archives/Public/public-device-apis/2011Nov/0058.html
[2]
http://scriptlib-cg.github.com/api-design-cookbook/#don-t-use-numerical-constants
[3]
http://www.w3.org/2001/tag/doc/privacy-by-design-in-apis#privacy-enhancing-api-patterns