(define json
  "{\"foo\":123}
   {\"bar\":999}")

(call-with-input-string json
  (lambda (in)
    (let loop ((in in) (result '()))
      (receive (object remainder)
        (read-json in consume-trailing-whitespace: #f chunk-size: (* 5 1024))
        (if object
            (loop remainder (cons object result))
            result)))))