Stackoverflows while decoding recursive pointers

[sugawarayuuta]

Speaking of correctness, I found an issue regarding recursive structure in various json libraries. consider this example:

type (
    recursivePointer *recursivePointer
    recursiveMap     map[string]recursiveMap
    recursiveSlice   []recursiveSlice
)

func main() {
    json.Unmarshal([]byte("123"), new(recursivePointer))
}

O = resulted in an error, X = stack-overflow, ? = hanging	library	enc-pointer	enc-slice	enc-map	dec-pointer	dec-slice	dec-map
jsonv1	O	O	O	?	O	O
jsonv2	O	O	O	X	O	O
sonicjson	O	O	O	?	O	O
gojson	X	X	X	X	X	X
jsoniter	O	O	O	X	O	O
sonnetjson	O	O	O	X	O	O
segjson	X	X	X	X	X	X

while this is a minor bug, it's better to not have stackoverflows than having it. What do you think about adding an extra error to these libraries to prevent this?

[dsnet]

IIRC, the v1 code has logic to handle this in the simple case of a pointer being a reference to itself, but fails for the more general case of a cyclic pointer somewhere in the tree.

We should fix this in v2, but should fix the general case, but not the one-off special case. However, since this arises very rarely in practice (and isn't a security flaw since a malicious JSON input can't produce a cyclic pointer situation), the fix should ideally be low cost in memory and CPU.