Re: JSON and the Unicode Standard
- --- In email@example.com, John Cowan <cowan@...> wrote:
>That's not quite right. JSON says nothing at all about number representations. All it knows is sequences of digits with the occasional decimal points. JSON says nothing about 2's complement vs signed magnitude integers, and it says nothing about word size or binary vs decimal.
> Mark Slater scripsit:
> > The RFC does state that parsers can limit the numbers they accept to
> > a specified range of their choice, just as they can impose a limit on
> > the size of strings, if they want. In practice, some libraries apply
> > unwritten limits to the range of numbers along the lines of "the range
> > (set?) of numbers that can be represented as a Java double."
> I think that limit is implied by the statement in the "Security
> where numbers are clearly constrained to IEEE 64-bit floats.
- --- In firstname.lastname@example.org, Dave Gamble <davegamble@...> wrote:
>There is another relevant section (ECMA-262, 8.4 The String Type, pg 28)
> To save people looking it up:
> ECMA-262, section 7.6:
> Two IdentifierName that are canonically equivalent according to the
> Unicode standard are not equal unless they are represented by the
> exact same sequence of code units (in other words, conforming
> ECMAScript implementations are only required to do bitwise comparison
> on IdentifierName values). The intent is that the incoming source text
> has been converted to normalised form C before it reaches the
> ECMAScript implementations may recognize identifier characters defined
> in later editions of the Unicode Standard. If portability is a
> concern, programmers should only employ identifier characters defined
> in Unicode 3.0.
When a String contains actual textual data, each element is considered to be a single UTF-16 code unit. Whether or not this is the actual storage format of a String, the characters within a String are numbered by their initial code unit element position as though they were represented using UTF-16. All operations on Strings (except as otherwise stated) treat them as sequences of undifferentiated 16-bit unsigned integers; they do not ensure the resulting String is in normalised form, nor do they ensure language-sensitive results.
NOTE The rationale behind this design was to keep the implementation of Strings as simple and high-performing as possible. The intent is that textual data coming into the execution environment from outside (e.g., user input, text read from a file or received over the network, etc.) be converted to Unicode Normalised Form C before the running program sees it. Usually this would occur at the same time incoming text is converted from its original character encoding to Unicode (and would impose no additional overhead). Since it is recommended that ECMAScript source code be in Normalised Form C, string literals are guaranteed to be normalised (if source text is guaranteed to be normalised), as long as they do not contain any Unicode escape sequences.
> I think it's fairly clear that a JSON parser has ABSOLUTELY NOI disagree with your first statement. The ECMA-262 standard, at least in my opinion, tries to side step a lot of these issues. It makes a fairly clear distinction between "what happens inside the ECMA-262 environment (which it obviously has near total control over)" and "what happens outside the ECMA-262 environment".
> BUSINESS poking around with actual data strings; Douglas has been very
> clear that you are to pass them bit-identical to the recipient. On the
> other hand, there's an argument for some kind of sanitation when it
> comes to object member names.
> I'm really tempted by the idea of a JSON-secure spec, which clamps
> down on these details.
IMHO, the ECMA-262 standard advocates that "stuff that happens outside the ECMA-262 environment should be treated as if it is NFC".
Since the sine qua non of JSON is the interchange of information between different environments and implementations, it must address any issues that can and will cause difficulties. Like it or not, the fact that it's Unicode means these things can and will happen, and it's simply not practical to expect or insist that every implementation treat JSON Strings as "just a simple array of Unicode Code Points".
> Arguing the Unicode details is decidedly NOT compatible with theI completely agree that these details are NOT compatible with the "spirit" of JSON.
> "spirit" of JSON, which Douglas has been very clear about; a
> lightweight, simple, modern data representation.
But.... so what? Unicode is not simple. I'm not the one who made it that way, but the way that RFC 4627 is written, you must deal with it. There are ways RFC 4627 could have been written such that the JSON to be parsed is considered a stream of 8 bit bytes, and therefore stripped of its Unicode semantics (if any). However, it very clearly and plainly says "JSON text SHALL be encoded in Unicode.", which pretty much kills the idea that you can just treat it as raw bytes.
There's a saying about formalized standards: The standard is right. Even it's mistakes.
As an aside, there is a RFC for "Unicode Format for Network Interchange", RFC 5198 (http://tools.ietf.org/html/rfc5198). It is 18 pages long. RFC 4627 is just 9 pages.
Actually, I would encourage people to read RFC 5198. I'm not sure I agree with all of it, but it goes over a lot of the issues I think are very relevant to this conversation. It's great background info if you're not familiar with the details.