Re: printing JsonbPair values of input JSONB on server side?

Thanks a lot for the suggestions. I changed the code below (with `pnstrdup`
and `DatumGetCString`).
But the code still crashes at the two problem lines (either one alone
crashes the server). The input is:

select print_kv_pair('{"a":1, "b": 2}');

Any further insight?

-- modified code --

PG_FUNCTION_INFO_V1(print_kv_pair);
Datum
print_kv_pair(PG_FUNCTION_ARGS)
{
Jsonb *jb1 = PG_GETARG_JSONB_P(0);
JsonbIterator *it1;
JsonbValue v1;
JsonbIteratorToken r1;
JsonbParseState *state = NULL;

if (jb1 == NULL)
PG_RETURN_JSONB_P(jb1);

if (!JB_ROOT_IS_OBJECT(jb1))
ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("Can only take objects")));

elog(NOTICE, "print_kv_pair(): ok0");

it1 = JsonbIteratorInit(&jb1->root);
r1 = JsonbIteratorNext(&it1, &v1, false);

if (r1 != WJB_BEGIN_OBJECT)
ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("Iterator was not an object")));

elog(NOTICE, "print_kv_pair(): ok1");
// pushJsonbValue(&state, r1, NULL); //?? do wee need this?
// r1 = JsonbIteratorNext(&it1, &v1, false); //this seems unnecessary

JsonbValue *object = &v1;

elog(NOTICE, "print_kv_pair(): ok2");
Assert(object->type == jbvObject);

elog(NOTICE, "print_kv_pair(): ok3, nPairs = %d",
object->val.object.nPairs);

//iterating through key-value pairs
JsonbPair *ptr;
for (ptr = object->val.object.pairs;
ptr - object->val.object.pairs < object->val.object.nPairs;
ptr++)
{
//problem lines!!! //either elog crashes pg server
char *buf = pnstrdup(ptr->key.val.string.val,
ptr->key.val.string.len);
elog(NOTICE, "print_kv_pair(): k = %s",
(ptr->key).val.string.val); //debug
elog(NOTICE, "print_kv_pair(): v = %s",
DatumGetCString(DirectFunctionCall1(numeric_out,
NumericGetDatum(ptr->value.val.numeric))) ); //debug
}

elog(NOTICE, "print_kv_pair(): ok4");

PG_RETURN_JSONB_P(JsonbValueToJsonb(object));
}

On Mon, Mar 18, 2019 at 3:20 PM Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>
wrote:

> >>>>> "T" == T L <tinlyx(at)gmail(dot)com> writes:
>
> T> //Problem line!!!
> T> // elog(NOTICE, "print_kv_pair(): k = %s, v = %s",
> T> ptr-> key.val.string.val, numeric_out(ptr->value.val.numeric));
>
> string.val isn't a C string (notice the "not null terminated" comment in
> the structure definition), and you can't call numeric_out like that.
> Either of those would crash it.
>
> You could use pnstrdup to get a valid C string, and use
> DatumGetCString(DirectFunctionCall1(
> numeric_out,
> NumericGetDatum(ptr->value.val.numeric)))
>
> to get the numeric value as a C string.
>
> --
> Andrew (irc:RhodiumToad)
>