Re: [PATCH] Generalized JSON output functions

On 05/20/2015 09:16 AM, Shulgin, Oleksandr wrote:
> Hi, Hackers!
>
> Attached is a patch against master to generalize the JSON-producing 
> functions in utils/adt/json.c and to provide a set of callbacks which 
> can be overridden the same way that is already provided for *parsing* 
> JSON.
>
> The motivation behind this to be able to produce specially-crafted 
> JSON in a logical replication output plugin, such that numeric (and 
> bigint) values are quoted.  This requirement, in turn, arises from the 
> fact that JavaScript specification, which is quite natural to expect 
> as a consumer for this JSON data, allows to silently drop significant 
> digits when converting from string to number object.
>
> I believe this is a well-known problem and I'm aware of a number of 
> tricks that might be used to avoid it, but none of them seems to be 
> optimal from my standpoint.
>
> I can also imagine this can be used to convert date/time to string 
> differently, or adding indentation depending on the depth in object 
> hierarchy, etc.


I'm not necessarily opposed to this, but it sure seems like a lot of 
changes, and moderately invasive ones, to support something that could 
be done, at the cost of reparsing, with a simple loadable extension that 
I could create in a few hours of programming. The parser API was created 
precisely to make this sort of transformation close to trivial. Other 
fairly obvious transformations include translating to XML or YAML, and a 
less obvious one could be something very specialized, like translating 
certain fields. Anyway, for this purpose I could imagine a function like:
    json_format (        j json (or text),        indent_spaces smallint default 0,        space_after_colon boolean
defaultfalse,        space_after_comma boolean default false,        quote_numerics boolean default false)    returns
json

cheers

andrew