Function jsonPathFromCstring

src/backend/utils/adt/jsonpath.c:167–194

* Converts C-string to a jsonpath value. * * Uses jsonpath parser to turn string into an AST, then * flattenJsonPathParseItem() does second pass turning AST into binary * representation of jsonpath. */

 * representation of jsonpath.
 */
static Datum
jsonPathFromCstring(char *in, int len)
{
	JsonPathParseResult *jsonpath = parsejsonpath(in, len);
	JsonPath   *res;
	StringInfoData buf;

	initStringInfo(&buf);
	enlargeStringInfo(&buf, 4 * len /* estimation */ );

	appendStringInfoSpaces(&buf, JSONPATH_HDRSZ);

	if (!jsonpath)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
				 errmsg("invalid input syntax for type %s: \"%s\"", "jsonpath",
						in)));

	flattenJsonPathParseItem(&buf, jsonpath->expr, 0, false);

	res = (JsonPath *) buf.data;
	SET_VARSIZE(res, buf.len);
	res->header = JSONPATH_VERSION;
	if (jsonpath->lax)
		res->header |= JSONPATH_LAX;

	PG_RETURN_JSONPATH_P(res);
}

/*
 * Converts jsonpath value to a C-string.