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Re: Including sjson (formerly (ice-9 json)) and fash.scm in guile proper

From: Christopher Allan Webber
Subject: Re: Including sjson (formerly (ice-9 json)) and fash.scm in guile proper?
Date: Mon, 15 May 2017 14:53:54 -0500
User-agent: mu4e 0.9.18; emacs 25.2.1

Mark H Weaver writes:

> I wrote:
>> Most of the modifications you've made are good, but I'm very
>> uncomfortable with the use of #nil in this API.  [...]
> Christopher Allan Webber <address@hidden> writes:
>> Oh!  No you got it backwards, the library *was* using #nil initially,
>> and I modified it to use 'null now instead. :)
> Ah, my mistake.  Excellent!
> Having now looked more closely, I'm mostly happy with the API, except
> for one issue: I don't like the way fash support was hacked in, with the
> 'use-fash' flag and the (if use-fash [fash-code] [alist-code]) sprinkled
> around.  If this truly needs to be done within the json library itself
> (which I wonder), then I'd prefer to generalize it to support any
> dictionary data structure, and thereby remove the dependency on fashes.

I agree that it's pretty hacky.  Allowing other dictionary structures is
fine by me.

> My main concern about fashes, besides the fact that Andy hasn't yet
> proposed adding them to Guile himself, is that the implementation is
> very complex, and I'd like to achieve some degree of confidence in its
> correctness before adding it.  I'd also tend to favor adding a simpler,
> truly immutable dictionary data structure based on Phil Bagwell's HAMTs
> (Hash Array Mapped Tries) to eliminate the need for thread
> synchronization, but I'm open to suggestions.

I don't really understand enough of the field to really know what the
right direction is.  I do know that I need something that's not O(n) for
json-ld processing, though I guess one option always would have been to
read in the sexp structure and transform it before doing all that
processing.   I've long wanted a better immutable dictionary
structure in Guile though, but am open to what it would be.

> Anyway, since writing my previous message in this thread, I've started
> carefully reviewing the code, making modifications as I go.  At this
> point, my proposed modifications have become quite extensive.  So far,
> I've reworked the code to greatly reduce heap allocations, support
> arbitrary dictionary types (removing the fash dependency, while still
> allowing its use), and fix various bugs (e.g. relying on unspecified
> evaluation order, failure to handle 12-character hex escapes properly,
> producing and accepting invalid JSON in some cases, etc).
> I'll followup with another message when I've completed my proposed
> revisions.  Feel free to ping me if it takes more than a week.

Wow, exciting!

>>> Otherwise, I'm generally in favor of incorporating this library into
>>> Guile, after we make sure that it is robust against malicious inputs.
>> Okay, cool!  The other thing is to add more specific error messages, as
>> discussed.
> Indeed, better error messages would be a good thing.
>> What examples of malicious inputs should we test against?
> I'm mostly trying to address that by careful code review.

Yay!  Thank you for doing it.

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