We subscribe to transactions upon broadcast, where we use output index `0` for the subscription.
In order to ensure that this subscription is guaranteed to be for the locking script (and not a change output) we now ensure that the locking script output is always at index `0` of the outputs of the transaction.
We chose this solution because otherwise we would have to add more information to broadcasting a transaction.
This solution is less intrusive, because the order of transaction outputs should not have any side effects and ensuring index `0` makes the whole behaviour more deterministic.
The Electrum block-header subscription did not provide us with block headers, because upon the connection being closed by a node the subscription would end.
Re-newing the the subscription upon re-connect is not easily achievable, that's why we opted for a polling mode for now, where we start a block header subscription on every update iteration, that is only used once (when the subscription is made).
We need to check two things:
- balance to be higher than dust amount (546).
- balance to be higher than min-relay fee.
Additionally, the tx_builder might fail if not enough funds are in the wallet to pay for the overall transaction fees.
Fees are hard to compute and it is too easy to get wrong and lose a lot of money. Hence, a hardcoded maximum of 100,000 satoshi for a single transaction is in place.
Electrum has an estimate-fee feature which takes as input the block you want a tx to be included.
The result is a recommendation of BTC/vbyte.
Using this recommendation and the knowledge about the size of our transactions we compute an appropriate fee.
The size of the transactions were taken from real transactions as published on bitcoin testnet.
Note: in reality these sizes might fluctuate a bit but not for much.
Alice chooses the fee for TxPunish because she is the one that cares.
Bob chooses the fee for TxRefund because he is the one that cares.
Note must be taken here because if the fee is too low (e.g. < min tx fee) then she might not be able to publish TxRedeem at all.
Alice chooses the fee for TxRedeem because she is the one that cares. Note must be taken here because if the fee is too low (e.g. < min tx fee) then she might not be able to publish TxRedeem at all.
Edge cases of UTXOs where value < fee cause the BDK's `coin_select` calculation to panic.
This issue was fixed upstream thus we point the BDK dependency against the commit of the merged fix.
In order for the re-construction of TxLock to be meaningful, we limit
`Message2` to the PSBT instead of the full struct. This is a breaking
change in the network layer.
The PSBT is valid if:
- It has at most two outputs (we allow a change output)
- One of the outputs pays the agreed upon amount to a shared output script
Resolves#260.
This allows us to construct instances of bitcoin::Wallet for test
purposes that use a different blockchain and database implementation.
We also parameterize the electrum-client to make it possible to
construct a bitcoin::Wallet for tests that doesn't have one. This
is necessary because the client validates the connection as it is
constructed and we don't want to provide an Electrum backend for
unit tests.
Instead of watching for status changes directly on bitcoin::Wallet,
we return a Subscription object back to the caller. This subscription
object can be re-used multiple times.
Among other things, this now allows callers of `broadcast` to decide
on what to wait for given the returned Subscription object.
The new API is also more concise which allows us to remove some of
the functions on the actor states in favor of simple inline calls.
Co-authored-by: rishflab <rishflab@hotmail.com>
We define the sync interval as 1/10th of the blocktime. For the
special case of our tests, we however check at max once per second.
The tests have a super fast blocktime. As such we shouldn't hammer
the nodes with a request every 100ms.
We have a repeated pattern where we construct one of our
Tx{Cancel,Redeem,Punish,Refund,Lock} transactions and wait until
the status of this transaction changes. We can make this more
ergonomic by creating and implementing a `Watchable` trait that
gives access to the TxId and relevant script for this transaction.
This allows us to remove a parameter from the `watch_until_status`
function.
Additionally, there is a 2nd pattern: "Completing" one of these
transaction and waiting until they are confirmed with the configured
number of blocks for finality. We can make this more ergonomic by
returning a future from `broadcast` that callers can await in case
they want to wait for the broadcasted transaction to reach finality.
The execution params don't change throughout the lifetime of the
program. They can be set in the wallet at the very beginning.
This simplifies the interface of the wallet functions.
We achieve our optimizations in three ways:
1. Batching calls instead of making them individually.
To get access to the batch calls, we replace all our
calls to the HTTP interface with RPC calls.
2. Never directly make network calls based on function
calls on the wallet.
Instead, inquiring about the status of a script always
just returns information based on local data. With every
call, we check when we last refreshed the local data and
do so if the data is considered to be too old. This
interval is configurable.
3. Use electrum's notification feature to get updated
with the latest blockheight.
Co-authored-by: Thomas Eizinger <thomas@eizinger.io>
Co-authored-by: Rishab Sharma <rishflab@hotmail.com>
We reduce indirection by constructing TxPunish directly based off
`State3` and make the type itself more powerful by moving the logic
of completing it with a signature onto it.
This allows us to have access to RedeemTx from within the scope
of the state transition which we are going to need for more
efficient watching of what happens to this TX on the blockchain.
The CLI has sensible default values for all parameters,
thus a config file is not really an advantage but just
keeps getting in our way, so re remove it.
The bitcoin::Wallet::sync_wallet function doesn't do anything else
other than delegating. As such, we have just as much information
about what went wrong inside this function as we have outside.
By moving the .context call into the function, we can avoid repeating
us on every call-site.
This reduces the overall amount of LoC that imports take up in our
codebase by almost 100.
It also makes merge-conflicts less likely because there is less
grouping together of imports that may lead to layout changes which
in turn can cause merge conflicts.
