Re: [Bitcoin-development] New P2P commands for diagnostics, SPV clients

[Mike Hearn <mike@plan99.net>]

> Yes, the format is something that must be hashed out (no pun
> intended).  Need input from potential users about what information
> they might need.

Matts point that a branch-per-transaction may duplicate data is well
made, that said, I suspect a format that tries to fix this would be
much more complicated.

How about see this project as a three part change?

First step - add the mempool command and make nodes sync up their
mempools on startup.

Second step - if protocol version >= X, the "block" message consists
of a header + num transactions + vector<hash>  instead of the full
transactions themselves.

On receiving such a block, we go look to see which transactions we're
missing from the mempool and request them with getdata. Each time we
receive a tx message we check to see if it was one we were missing
from a block. Once all transactions in the block message are in
memory, we go ahead and assemble the block, then verify as per normal.
This should speed up block propagation. Miners have an incentive to
upgrade because it should reduce wasted work.

Third step - new message, getmerkletx takes a vector<hash> and returns
a merkletx message: "merkle branch missing the root + transaction data
itself" for each requested transaction. The filtering commands are
added, so the block message now only lists transaction hashes that
match the filter which can then be requested with getmerkletx.