This commit changes all cases which generate default timestamps to
time.Now to limit the timestamp to one second precision. The code which
serializes and deserializes timestamps already does this, but it is useful
to make sure defaults don't exceed the precision of the protocol either.
With this change there is less chance that developers using defaults will
end up with structures that have a higher time precision than what will
ultimately be sent across the wire.
This commit introduces two new functions for Blockheader named Serialize
and Deserialize. The functions provide a stable mechanism for serializing
and deserializing block headers to and from disk. The main benefit here
is deserialization of the header since typically only full blocks are
serialized to disk. Then when a header is needed, only the header portion
of the block is read and deserialized.
This commit removes the TxnCount field from the BlockHeader type and
updates the tests accordingly. Note that this change does not affect the
actual wire protocol encoding in any way.
The reason the field has been removed is it really doesn't belong there
even though the wire protocol wiki entry on the official bitcoin wiki
implies it does. The implication is an artifact from the way the
reference implementation serializes headers (MsgHeaders) messages. It
includes the transaction count, which is naturally always 0 for headers,
along with every header. However, in reality, a block header does not
include the transaction count. This can be evidenced by looking at how a
block hash is calculated. It is only up to and including the Nonce field
(a total of 80 bytes).
From an API standpoint, having the field as part of the BlockHeader type
results in several odd cases.
For example, the transaction count for MsgBlocks (the only place that
actually has a real transaction count since MsgHeaders does not) is
available by taking the len of the Transactions slice. As such, having
the extra field in the BlockHeader is really a useless field that could
potentially get out of sync and cause the encode to fail.
Another example is related to deserializing a block header from the
database in order to serve it in response to a getheaders (MsgGetheaders)
request. If a block header is assumed to have the transaction count as a
part of it, then derserializing a block header not only consumes more than
the 80 bytes that actually comprise the header as stated above, but you
then need to change the transaction count to 0 before sending the headers
(MsgHeaders) message. So, not only are you reading and deserializing more
bytes than needed, but worse, you generally have to make a copy of it so
you can change the transaction count without busting cached headers.
This is part 1 of #13.
This commit modifies the writeElement function to have a "fast path" which uses type
assertions for all of the types which btcwire write so the more expensive
reflection-based binary.Write can be avoided.
Also, this changes all cases that were writing raw ShaHash (32-byte) arrays (which
requires a stack copy) instead simply passing the pointer.
The following benchmark results show the results for serializing a block header
after these changes:
Before: BenchmarkWriteBlockHeader 500000 5566 ns/op
After: BenchmarkWriteBlockHeader 1000000 991 ns/op
This is part of the ongoing effort to optimize serialization as noted in
conformal/btcd#27.
Both of these depend on the serialized bytes which are dependent on the
version field in the block/transaction. They must be independent of the
protocol version so there is no need to require it.
The functions for generating transaction and block hashes contained a few
error checks for conditions which could never fail without run-time
panics. This commit removes those superfluous checks and adds explanatory
comments.
