In the historical dispatch of btcdnotify, the dispatcher checks if a
transaction has been included in a block. If this check happens before
the notifier has processed the update, it's possible that the
currentHeight of the notifier and the currentHeight of the chain might
be out of sync which causes an off by one error when calculating a
target height for the transaction confirmation. This change uses the
height of the block the transaction was found in, rather than the
currentHeight that's known by the notifier to eliminate this.
This race condition can occur if a transaction is included in a block
right when a notification is being added to the notifier for it AND when
the confirmation requires > 1 confirmations. In this case, the
confirmation gets added to the confirmation heap twice.
This test adds a test for a consumer that registers for a transaction
confirmation but takes some time to check if that confirmation has
occured.
The test reveals a race condition that can cause btcdnotify to add a
confirmation entry to its internal heap twice. If the notification
consumer is not prompt in reading from the confirmation channel, this
can cause the notifier to block indefinitely.
Sam Lewis