While here, remove the serializedTx field from Tx. This field was
originally intended to be used to cache the bytes of the serialized
transaction, but it was never used and can effectively leak memory if
the Tx was created with a call to NewTxFromBytes.
ok @davecgh
bytes.Reader is a little bit more efficient than a bytes.Buffer when
just reading, so in situations where only an io.Reader is needed (for
Block and Tx deserialization), switch to a bytes.Reader.
ok @davecgh
Currently, transaction hash caching is provided via Block directly, but a
transaction is not always part of a block and there are several cases
where only the transaction needs to be dealt with without wanting to pass
the entire block and transaction index around to be able to get at the
cached hash.
So, this commit adds a new type named Tx which is a wrapper that provides
easier and more efficient manipulation of raw wire protocol transactions.
It memoizes the hash for the transaction on its first access so subsequent
accesses don't have to repeat the relatively expensive hashing operations.
The idea is the callers can pass around pointers to these Tx types instead
of raw btcwire.MsgTx pointers.
For now, the Block API has not been changed, but the plan is to change it
to provide access to these wrapped transactions rather than having it do
the transaction hash caching directly.
This is only the first part of a series of changes working towards
optimizations noted in conformal/btcd#25.
