In this commit, we modify all existing historical rescans for
ChainNotifier backends to scan backwards rather than forwards. If we
know that a transaction has been confirmed, or outpoint spent, the it's
likely that the event has recently transpired assuming we've been
offline for a short period of time. Therefore, if we scan backwards
rather than forwards, then we can save potentially hundreds or thousands
of block fetches if the event recently happened close to the tip of the
chain.
We bound this search at the genesis block, to ensure we don't underflow
the uint32 used throughout the package in the main loop.
In this commit, we alter the different ChainNotifier implementations to
dispatch confirmation and spend notifications after blocks. We do this
to ensure the external consistency of our registered clients.
In this commit, we modify the logic within RegisterSpendNtfn for the
BitcoindNotifier to account for the recent changes made to the
TxNotifier. Since it is now able to handle spend notification
registration and dispatch, we can bypass all the current logic within
the BitcoindNotifier and interact directly with the TxNotifier instead.
The most notable changes include the following:
1. We'll only attempt a historical rescan if the TxNotifier tells us
so.
2. We'll dispatch the historical rescan within the main goroutine to
prevent WaitGroup panics, due to the asynchronous nature of the
notifier.
In this commit, we address a bug where it's possible that we still
attempt to manually scan for a transaction to determine whether it's
been included in the chain even after successfully checking the txindex
and not finding it there. Now, we'll short-circuit this process by
exiting early if the txindex lookup was successful but the transaction
in question was not found. Otherwise, we'll fall back to the manual
scan.
In this commit, we extend the different ChainNotifier implementations to
cache height hints for our spend events. Each outpoint we've requested a
spend notification for will have its initial height hint cached. We then
increment this height hint at every new block for unspent outpoints.
This allows us to retrieve the *exact* height at which the outpoint has
been spent. By doing this, we optimize the different ChainNotifier
implementations since they will no longer have to rescan forward (and
possibly fetch blocks in the neutrino/pruned node case) from the initial
height hint.
In this commit, we alter the different chain notifiers to query their
height hint cache before registering a confimation notification. We do
this as it's possible that the cache has a higher height hint, which
can potentially reduce the amount of blocked fetched when attempting
historical dispatches.
TestChainNotifier wraps the ChainNotifier interface to allow adding additional testing methods with access to private fields in the notifiers. These testing methods are only compiled when the build tag "debug" is set. UnsafeStart allows starting a notifier with a specified best block.
UnsafeStart is useful for the purpose of testing cases where a notifier's best block is out of date when it receives a new block.
This resolves the situation where a notifier's chain backend skips a series of blocks, causing the notifier to need to dispatch historical block notifications to clients.
Additionally, if the current notifier's best block has been reorged out, this logic enables the notifier to rewind to the common ancestor between the current chain and the outdated best block and dispatches notifications from the ancestor.
This prevents the situation where we notify clients about a newly connected block, and then the block connection itself fails. We also want to set our best block in between connecting the block and notifying clients, in case a client makes queries about the new block they have received.
If the chain backend misses telling the notifier about a series of disconnected blocks, the notifier is now able to disconnect the tip to its new best block.
If a client passes in their best known block when registering for block notifications, check to see if it's behind our best block. If so, dispatch the missed block notifications to the client.
This is necessary because clients that persist their best known block can miss new blocks while registering for notifications.
Clients can optionally pass their best block known into RegisterBlockEpochNtfn. This enables the notifiers to catch up clients on blocks they may have missed.
In this commit, we introduce a nice optimization with regards to lnd's
interaction with a bitcoind backend. Within lnd, we currently have three
different subsystems responsible for watching the chain: chainntnfs,
lnwallet, and routing/chainview. Each of these subsystems has an active
RPC and ZMQ connection to the underlying bitcoind node. This would incur
a toll on the underlying bitcoind node and would cause us to miss ZMQ
events, which are crucial to lnd. We remedy this issue by sharing the
same connection to a bitcoind node between the different clients within
lnd.
This commit fix a bug within the bitcoind notifier logic, which would
ignore the passed mempool argument, and notify spentness whether the
spending transaction was confirmed or not. The logic used to fix this is
similar to what is already done for the btcd backend.
In this commit, we fix a recently introduced bug which can result in a
panic when bitcoind nodes without a txindex active are started. The
issue was that we would still defence the transaction's blockhash, which
would be nil if we detected that the backend didn't have the txindex
active.
Before this commit, we relied on the need of full nodes to enable the
transaction index. This allowed us to fetch historical details about
transactions in order to register and dispatch confirmation and spend
notifications.
This commit allows us to drop that requirement by providing a fallback
method to use when the transaction index is not enabled. This fallback
method relies on manually scanning blocks for the transactions
requested, starting from the earliest height the transactions could have
been included in, to the current height in the chain.
