Is it possible?

Yes, but not in one shot.

Why?

By design, ArduinoJson stores the complete representation of the JSON object tree in memory.

If you use the zero-copy mode (mutable input), the whole JSON input must stay in memory.

If the input is read-only (like a Stream), the JsonBuffer needs to make copies of the input, so the result is almost the same (except for spaces and punctuation).

How to solve?

One cool feature of ArduinoJson is that, when it parses an object from a Stream, it stops reading when it encounters the closing }, and the same is true for arrays.

This feature allows to parse streams in chunks, you just need to call JsonBuffer::parseObject() in a loop. Of course, don’t forget to skip the commas (,) between the objects. As usual, don’t reuse the JsonBuffer, declare it inside the loop.

For example, if you want to parse the huge response of a 10-day forecast of Weather Underground, you can skip the beginning until you see "forecastday": [ in the stream (use Stream::find()), and then parse the objects for each day one after the other.

See also