`FilteringParserDelegate` can go into an infinite loop if underlying parser is non-blocking

[simonbasle]

Jackson version (BOM): 2.15.2

While experimenting with JsonPointer in Spring Framework, I tried to build up on the existing FilteringParserDelegate and associated JsonPointerBasedTokenFilter. Unfortunately, this doesn't seem to work with a non-blocking JsonParser delegate, for several reasons:

• it doesn't delegate method canParseAsync() (ends up returning the default interface implem => false)
• it doesn't delegate method getNonBlockingInputFeeder() (same as above => null)
• it isn't aware of JsonToken.NOT_AVAILABLE

While the first two are easily circumvented by extending FilteringParserDelegate, the last one is the truly problematic one. It results in going down the code path of a "scalar value", and will continuously call delegate.nextToken() which continues to result in NOT_AVAILABLE.

This leads to an infinite loop when attempting to filter based on a JsonPointer on top of a non-blocking parser.

Is there anything fundamentally preventing FilteringParserDelegate from being compatible with non-blocking parsers that I might have overlooked? Otherwise I think it's pretty close, hopefully that can be fixed 😄