Re: new json funcs - Mailing list pgsql-hackers

On 01/28/2014 01:22 PM, Alvaro Herrera wrote:
> Josh Berkus wrote:
>> On 01/27/2014 01:06 PM, Alvaro Herrera wrote:
>>> Andrew Dunstan escribió:
>>>
>>>> I'm not sure I understand the need. This is the difference between
>>>> the _text variants and their parents. Why would you call
>>>> json_object_field when you want the dequoted text?
>>> Because I first need to know its type.  Sometimes it's an array, or an
>>> object, or a boolean, and for those I won't call the _text version
>>> afterwards but just use the original.
>> It would make more sense to extract them as JSON, check the type, and
>> convert.
> That's what I'm already doing.  My question is how do I convert it?
> I have this, but would like to get rid of it:
>
> /*
>   * dequote_jsonval
>   *        Take a string value extracted from a JSON object, and return a copy of it
>   *        with the quoting removed.
>   *
>   * Another alternative to this would be to run the extraction routine again,
>   * using the "_text" variant which returns the value without quotes; but this
>   * complicates the logic a lot because not all values are extracted in
>   * the same way (some are extracted using json_object_field, others
>   * using json_array_element).  Dequoting the object already at hand is a
>   * lot easier.
>   */
> static char *
> dequote_jsonval(char *jsonval)
> {
>     char   *result;
>     int        inputlen = strlen(jsonval);
>     int        i;
>     int        j = 0;
>
>     result = palloc(strlen(jsonval) + 1);
>
>     /* skip the start and end quotes right away */
>     for (i = 1; i < inputlen - 1; i++)
>     {
>         /*
>          * XXX this skips the \ in a \" sequence but leaves other escaped
>          * sequences in place.  Are there other cases we need to handle
>          * specially?
>          */
>         if (jsonval[i] == '\\' &&
>             jsonval[i + 1] == '"')
>         {
>             i++;
>             continue;
>         }
>
>         result[j++] = jsonval[i];
>     }
>     result[j] = '\0';
>
>     return result;
> }
>



Well, TIMTOWTDI. Here's roughly what I would do, in json.c, making the
json lexer do the work for us:
   extern char *   dequote_scalar_json_string(char *jsonval)   {        text *json = cstring_to_text(jsonval);
JsonLexContext*lex = makeJsonLexContext(json, true);        JsonTokenType tok;        char *ret; 
        json_lex(lex);        tok = lex_peek(lex);        if (tok == JSON_TOKEN_STRING)
ret=pstrdup(lex->strval->data);       else            ret = jsonval;        pfree(lex->strval->data);
pfree(lex->strval);       pfree(lex);        pfree(json); 
        return ret;   }


I'm not sure if we should have a gadget like this at the SQL level also.


cheers

andrew