Similar to the previous commit; make sure that the ValidationContext has
access to the new Tx format so new code can use it directly.
In practically all cases (outside of the unit tests) callers already had
a Tx instance. Making it just a matter of sending it with.
Notice that the Tx object is immutable and implicitly shared which makes
it cheaper to pass around.
We add a Token class to Tx, which adds an easy to use API when compared
to the plain iterator. The main point of the API chosen is to make sure
we don't do unneeded parsing or copying for tokens unless needed.
Additionally refactor the ValidationPrivate::UnspentOutput class to
inherit from the Tx::Output class in order to avoid lots of duplicated
logic on handling the data.
The new SIGHASH_UTXO has a possible attack vector where prepared huge
outputs are used and required to be hashed for the signing preimage.
At most you can force the full node to prepare 20GB of (utxo) data
_prior_ to creation of the preimage. Which is a big issue when it comes
to memory usage of the node.
What this change does is we ensure that the class used for this data is
a ConstBuf as given to us from the utxo. Which are just pointers and not
full data, the data is memory mapped.
So we ensure shallow copies to avoid actually requiring the data to be
in memory until the point where it is used. And it can get swapped out
immediately after.
This ensures we are immune to the SIGHASH_UTXO attack vector.
tomFlowee
John Galt