memory corruption bug with ReadableByteChannel RLP streaming

[esaulpaugh]

In some situations it's possible that, when using an Iterator<RLPItem> created from a ReadableByteChannel, a buffer reuse problem can cause the data defining RLPItems from earlier in the stream to be overwritten with arbitrary data from later in the stream.

This can happen if a buffer used inside the iterator (default size: 8192 bytes) becomes full and gets rewound back to index 0 to accept additional input.

Fix: 5acdcb8

The fix is for the iterator implementation to never reuse any of the buffers, any of which can escape the iterator.

Recommended temporary workarounds:

Never iterate over a ReadableByteChannel which may serve more data than the initial buffer can hold.

or

Do not hold a reference to an RLPItem from the iterator past the next call to Iterator#hasNext or #next. The easiest way to ensure this is to replace all calls to next() on these iterators with next().duplicate(), which will create an independent copy of the item.