public static double jsonNodeToDouble(JsonNode node, String about) {
        if (!node.isFloatingPointNumber()) {
            throw new NumberFormatException(about + ": expected a floating point " +
                "type, but got " + node.getNodeType());
        }
        return node.asDouble();
    }
Copy a byte buffer into an array.  This will not affect the buffer's
position or mark.
clients/src/main/java/org/apache/kafka/common/protocol/MessageUtil.java