`bitcoind` notifies transactions once they're accepted into the mempool
and once they're confirmed in a block. Previously, reading a message
from ZMQ would allocate a buffer with the size of the message. This can
cause nodes to perform a large number of allocations within a small
amount periodically (3000 300B allocations every 10 mins on average),
which can cause a lot of GC pressure on lower resourced nodes. To remedy
this, we introduce two static buffers, one for blocks and another for
transactions, that will be reused for every message read. Each is
constrained by its maximum expected size.
In this commit, we create a new module for `walletdb` in order to allow
external projects to use the project without also having to depend on
the entirety of `btcwallet`. With this commit, projects that depend on
`walletdb` will benefit from a slimmer set of additional dependencies.
Since it's now possible for gozmq.Conn to block when calling Receive,
BitcoindConn hangs upon being stopped because its goroutines are waiting
for a message to be delivered. To address this, we modify it to close
its ZMQ connections driving the goroutines once it's been stopped. This
allows the goroutines to unblock by detecting the EOF error and exiting.
This unifies the logic of receiving an error when broadcasting a
confirmed transaction through btcd's/bitcoind's RPC interface. The btcd
dependency update is required in order for it to match bitcoind's
behavior. For older nodes that have yet to update, the confirmed
transaction will still be caught by the "transaction already exists"
case. This is not needed for bitcoind however, because its been sending
the same RPC error code for several major releases now.
