Re: Proposal: Add JSON support

On Sun, Mar 28, 2010 at 7:36 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>> Here's another thought. Given that JSON is actually specified to consist
>> of a string of Unicode characters, what will we deliver to the client
>> where the client encoding is, say Latin1? Will it actually be a legal
>> JSON byte stream?
>
> No, it won't.  We will *not* be sending anything but latin1 in such a
> situation, and I really couldn't care less what the JSON spec says about
> it.  Delivering wrongly-encoded data to a client is a good recipe for
> all sorts of problems, since the client-side code is very unlikely to be
> expecting that.  A datatype doesn't get to make up its own mind whether
> to obey those rules.  Likewise, data on input had better match
> client_encoding, because it's otherwise going to fail the encoding
> checks long before a json datatype could have any say in the matter.
>
> While I've not read the spec, I wonder exactly what "consist of a string
> of Unicode characters" should actually be taken to mean.  Perhaps it
> only means that all the characters must be members of the Unicode set,
> not that the string can never be represented in any other encoding.
> There's more than one Unicode encoding anyway...

In practice, every parser/serializer I've used (including the one I
helped write) allows (and, often, forces) any non-ASCII character to
be encoded as \u followed by a string of four hex digits.

Whether it would be easy inside the backend, when generating JSON from
user data stored in tables that are not in a UTF-8 encoded cluster, to
convert to UTF-8, that's something else entirely. If it /is/ easy and
safe, then it's just a matter of scanning for multi-byte sequences and
replacing those with their \uXXXX equivalents. I have some simple and
fast code I could share, if it's needed, though I suspect it's not.
:)

UPDATE: Thanks, Robert, for pointing to the RFC.

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