Re: How do I evaluate a JSON response?

Garrett Smith wrote:

On 2010-06-19 02:33 PM, Thomas 'PointedEars' Lahn wrote:
Garrett Smith wrote:
On 6/16/2010 8:15 AM, Thomas 'PointedEars' Lahn wrote:
Garrett Smith wrote:
Thomas 'PointedEars' Lahn wrote:
Garrett Smith wrote:
Thomas 'PointedEars' Lahn wrote:
Garrett Smith wrote:
Thomas 'PointedEars' Lahn wrote:
Garrett Smith wrote:
Meeting those goals, the result should be valuable and
appreciated by many.
Which part of my suggestion did you not like?
Nothing, its fine but I did not see a regexp there that tests to
see if the string is valid JSON.
There cannot be such a regular expression in ECMAScript as it does
not support PCRE's recursive matches feature. An implementation of
a push-down automaton, a parser, is required.
A parser would be too much for the FAQ.
Probably, although I think it could be done in not too many lines for
the purpose of validation.
That would require more code to be downloaded and more processing to
run it. What about mobile devices?
You are confused. What good is shorter code that is not a solution?
I take it that, since you have not answered this, you have come to see
the flaw in your logic here.

If "not valid json" can be determined without writing a parser, and if
it that is more efficient, then the overhead of using a parser is
avoided. That's good.

In order to prove that, I'll need some tests.

You need a dosage of common sense instead. Or a course in theoretical
computer science.

It would make sense to allow the fallback to allow \t, as all
implementations are allowing that today.

No, it would make sense to implement what was specified, and work around the
borken implementations that way until they no longer needed that workaround,
and report the bug so that it is fixed.

I see you went from unicode escape sequences to hex escapes, but why
\x00 and not \x0?

Because \x0 would be a syntax error, see ES3/5 7.8.4.

"7.8.4 String Literals".
That is the wrong section. That section is describes character escape
sequences in Strings; look down to the section on Regular Expressions.

Look what the section on Regular Expressions refers to.

"7.8.5 Regular Expression Literals"
The specification there states:

| HexEscapeSequence ::
| x HexDigit HexDigit

And now go read in which terms that production is defined.

So you still manage to be correct, even though you've cited the wrong
section.

No, I did not. I thought I make it easier for you by referring you to the
referred definition, but I had not considered your reading problem. Sorry.

Or why not just use a decimal escape \0?

That is a possibility I was not aware of [15.10.2.11], indeed, but then I
had two different kinds of character escape sequences in one character
class, with one not being recognizable as easily. No advantage, only
disadvantages there; so no, thanks.

What are the disadvantages? I see one: "not recognizable easily".

I rest my case. You really can't read.

Is that so?

Yes, it is.

I could see how it could be mistaken for an octal escape
sequence, but octal 0 and decimal 0 are the same 0.

Rubbish.

What are the other disadvantages?

Learn to read.

The character range could be written more compactly;

Yes, one could write /[\dA-Fa-f]/. Or even /…[\dA-F]…/i if there would
be no other letters in the remaining expression.

instead of [0-9A-Fa-f], [0-9A-f], or even just [0-f], if that is not
considered too unreadable.

Neither expression is equivalent to begin with.


Right. [0-f] is not because it includes a bunch of other characters and
[0-9A-f] is not because it includes "G-Z".

You don't say!

I'm concerned with using /[\dA-F]/i

I am not, under the stated conditions. But these conditions may not apply
here.

So the following should be good:
/[\dA-Fa-f]/
[\dA-F]/i
/[0-9A-Fa-f]

You appear to have no idea what you are talking about.

That programmer was me. I did not want to have a string containing `\"',
I wanted a string containing `"'. Whatever you tried to prove, it did
not relate to what I wanted to have, and so not what I wanted to have
matched, too, by the regular expression.

I think we're both know what a JSONString can and cannot contain

No, "we're" don't.

JSONString can't contain the unescaped character ".

And nobody said it could.

JSON.parse(' "\"" ');

Must result in a SyntaxError.

Of course, but that is well beside the point.

"\""

e.g. in an HTTP response message body is with absolute certainty JSON text,
and so must pass validation. You are clinging to ECMAScript string literals
instead, where further escaping of JSON strings is necessary.

JSONStringCharacter may not contain backslash unless that is part of a
JSONEscapeSequence.

Correction: "must not".

I rest my case.

OK, so we agree on that.

Quite the contrary. Instead of proving me wrong, you have thus confirmed my
argument that /"[^\\"...]*"/ is insufficient to match a JSON string.


PointedEars
--
Prototype.js was written by people who don't know javascript for people
who don't know javascript. People who don't know javascript are not
the best source of advice on designing systems that use javascript.
-- Richard Cornford, cljs, <f806at$ail$1$8300dec7@xxxxxxxxxxxxxxxx>
.

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