Expand description
Packet Decoder
BitStream is the key to making this problem tractable. It works like an iterator, allowing
us to consume an arbitrary number of bits from the input and convert this to a number.
It works by maintaining an internal u64 buffer. If the requested number of bits is larger than
the buffer’s current size then additional bits are added to the buffer 4 at a time from each
hexadecimal digit of the input data.
Additionally it keeps track of the total number of bits consumed so far. This is needed when parsing packets that use the total length in bits to determine sub-packets.
The decoded packet data is stored as a tree-like struct allowing recursive solutions to part 1 and part 2 to reuse the same decoded input.