scheme-specific length limits (issue 48) (was: Re: other trac issues against 4395bis)

On 2011/03/30 18:26, Larry Masinter wrote:
> Opinions about open issues:
>
> tracker issue 48:     Can schemes set specific length limits? Should RFC4395bis say something about this?
> Ted: They can, in my opinion.  We should add text that says that they can and how to say that.

The only place where I can see this making sense is where the underlying 
protocol/format that the data in the scheme is referring to has some 
length limitations (the practical cases I can come up with are domain 
names (overall 255 octet limit) and DOS file names (8.3). In such cases, 
the length limit is intrinsic, it may not even have to be mentioned in 
the scheme definition. On the other hand, it would be completely foolish 
to define a scheme that imposes arbitrary limits that do not exist in 
the underlying protocol. As an example, it would be total nonsense to 
define something like the http: scheme to have a maximum length of 512 
(or any other number you prefer).

So given that there was no actual practical case where this was brought 
up (at least not that I can remember), my proposal would be to just 
leave this out.

> Larry: OK.   "IRI schemes can set specific length limits or other constraints, as long as the limits are implementable."

I'm not sure what is meant by "implementable". The software components 
that check scheme-specific constraints on URIs/IRIs are few and far 
between anyway. And I don't think we need to point out that it's a bad 
idea to specify a length restriction in terms of a function that is hard 
to implement.

>     Given issue #63, length limit must not depend on whether it is IRI vs. hex-encoded into URI.

What exactly does this mean? Does it mean that it's e.g. 512 octets, 
whether as an IRI or as an URI? Does it mean that it's e.g. 512 
characters, whether as an IRI or as an URI? Or does it mean that it's 
512 characters when written as an IRI with actual Unicode characters, 
but it can be longer for URIs that result from converting IRIs to 
percent-encoding?

I guess the later is desirable, but then we should actually say so. On 
the other hand, may be are situations where it's not as easy as that. An 
example would be the length limits on IDNs, which are given by using 
punycode and checking the length of the result. (Because punycode in a 
clever compression algorithm, the results are not exactly straightforward.)

So in summary: Close the issue without any changes (preferred) or be 
precise.

Regards,    Martin.

Received on Thursday, 31 March 2011 08:49:50 UTC