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bug#12827: [PATCH] Tweak web modules, support relative URIs

From: Mark H Weaver
Subject: bug#12827: [PATCH] Tweak web modules, support relative URIs
Date: Sun, 24 Feb 2013 14:55:54 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.2 (gnu/linux)

Daniel Hartwig <address@hidden> writes:

> On 24 February 2013 18:45, Mark H Weaver <address@hidden> wrote:
>> I would argue that Absolute-URIs are more often appropriate in typical
>> user code.  The reason is that outside of URI-handling libraries, most
>> code that deals with URIs simply use them as universal pointers,
>> i.e. they implicitly assume that each URI is sufficient by itself to
>> identify any resource in universe.
> Right.  RFC 3986 makes a convincing argument for the new terminology.
> These notes about usage also reflect the sentiment in that document.
> FWIW, I sat mostly on the fence, finally going away from URI-Reference
> due to these concerns I expressed in an earlier email:
>> The API seems less clean, and it is not immediately clear
>> that uri? is not the top of the URI-like type hierarchy.  The other
>> functions only indicate “uri” in their name.  I did not
>> wish to introduce parallel “build-uri-reference”, etc. for each of
>> these, and did consider adding #:reference? on some to select
>> weaker validation.
> and looking at some other Scheme URI modules.
> However, having read over your comments I think that we could
> reasonably get away with just introducing the procedures you mention
> below and not bother about renaming (or duplicating) the field getters
> to ‘uri-reference-path’ etc..

Hmm.  The cleanest solution would probably be to duplicate the field
getters, and make the 'uri-*' variants (e.g. 'uri-path') raise an error
when applied to a relative reference.  However, it's probably not that
important, so if you think it's better to simply extend 'uri-path' etc
to apply to all URI-References, I'm okay with that.

>> Here's what I suggest: instead of extending 'string->uri' and
>> 'build-uri' to produce relative URIs, rename those extended procedures
>> 'string->uri-reference' and 'build-uri-reference'.  These are long
>> names, but that's okay because users should think twice before using
>> them, and that's seldom needed.
> In your proposed solution, ‘uri?’ and ‘uri-reference?’ are the
> predicates and they respond according to the RFC rather than internal
> Guile details?

What do you mean by "rather than internal Guile details"?

Here's how I like to think about these types: URI-Reference is at the
top of the type hierarchy, and URI (a.k.a. Absolute-URI) and
Relative-Ref are subtypes.  Furthermore, every URI-Reference is either
an Absolute-URI or a Relative-Ref.

In other words, if you create a URI-Reference that happens to be
absolute, then you'll end up with a URI, in the same sense that if you
create a complex number whose imaginary part happens to be exact zero,
you'll end up with a real number.

> That is:
>   (uri? (string->uri-reference "http://example.net/";))
>   => #t
>   (uri-reference? (string->uri-reference "http://example.net/";))
>   => #t
>   (uri? (string->uri-reference "foo"))
>   => #f


>> Then, we extend 'string->uri' and 'build-uri' in a different way: we
>> extend them to handle relative references in their *inputs*, but
>> continue to provide absolute *outputs*, by adding an optional keyword
>> argument '#:base-uri'.  This would make it easy to implement the
>> simplest and safest strategy outlined above with a minimum of code
>> changes.
> This strategy does reflect the recommendation of RFC 3986 to resolve
> the references as they are read.  Also an elegant API, as it
> encourages immedately resolving uri-references and never creating (or
> considering to create) the context-sensitive relative-refs.
>> What do you think?
> I quite like it, particularly the last part about #:base-uri.
> Ludo, I think this is basically what you were suggesting in the first place? 
> :-)

Excellent!  BTW, to be clear, I suggest that 'string->uri' and
'build-uri' should be guaranteed to produce Absolute-URIs.  In other
words, they should raise an error if not given enough information to
produce an Absolute-URI.  Does that make sense?

Thanks again for your work on this :)


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