After joining the two forked chains, it is necessary to ensure they both agree on the same best hash before proceeding to UnsafeStart the notifier.
This is because when the BitcoindClient starts, it retrieves its best known block then calls GetBlockHeaderVerbose on the hash of the retrieved block. This block could be a reorged block if JoinNodes has not completed sync. If it is the case that the best block retrieved has been reorged out of the chain, GetBlockHeaderVerbose errors because bitcoind sets the number of confirmations to -1 on reorged blocks, and the btcd rpc client panics when parsing a block whose number of confirmations is negative.
This parsing error is expected to be fixed, and as a more permanent solution chain backends should ensure that the `best block` they retrieve during startup has not been reorged out of the chain.
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 extract some of the helper test variables and
functions into their own file and guard them under a build flag. This is
needed as some unit tests will be introduced in a future commit where
most of the same functions within the interface tests are reused. In
order to prevent these variables and functions from being exportable, we
guard them by the "debug" build tag.
rescanning
In this commit, we modify the rescan options Neutrino uses when
performing a rescan for historical chain events to disable disconnected
block notifications. This is needed as the Neutrino backend will mutate
its internal state while rewinding, which causes disconnected block
notifications to be sent. Since the notifier acts upon these
notifications, they would cause it to also rewind unnecessarily.
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.
In this commit, we extend our TxConfNotifier to cache height hints for
our confirmation events. Each transaction we've requested a confirmation
notification for will have its initial height hint cached. We increment
this height hint at every new block for unconfirmed transactions. This
allows us to retrieve the *exact* height at which the transaction has
been included in a block. By doing this, we optimize the different
ChainNotifier implementations since they will no longer have to scan
forward (and possibly fetch blocks in the neutrino/pruned node case)
from the initial height hint looking for the confirmation.
In this commit, we introduce two new interfaces: SpendHintCache and
ConfirmHintCache for a height hint cache. The SpendHintCache is
responsible for maintaining the earliest height at which an outpoint
could have been spent within the chain, while the ConfirmHintCache is
responsible for maintaining the earliest height at which a transaction
confirms within the chain. We also add an implementation of these
interfaces with a single struct HeightHintCache, backed by a channeldb
instance, which will cary the duties of the interfaces above.
Tests for the case where a chain backend skips a series of blocks, such that the notifier's best block is out of date. Also tests the case where a notifier's best block has been reorged out of the chain.
This tests the case where a client registers for block notifications with an outdated best block, to ensure that the client is properly caught up on the blocks that it has missed.
Switches all ChainNotifier parameters to be TestChainNotifiers. This allows access to the extra testing methods provided by the TestChainNotifier interface.
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.
In this commit, we update the neutrino backend for the ChainNotifier to
use the new API which requires that callers pass the outpoint along with
the pkScript to be notified of any spends.
In this commit, we update the RegisterSpendNtfn method to also take the
prev output script of the item that we're attempting to watch for. This
change is required due to the recent modifications in the neutrino
protocol (BIP 158 + 157). With the new protocol, we'll match on the
script, but then dispatch notifications based on the precise outpoint
that matches.
