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 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>
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.
1. We can generalize the signing interface by passing a PSBT in
instead of the `TxLock` transaction.
2. Knowing the transaction ID of a transaction that we are about
to sign is not very useful. Instead, it is much more useful to know
what failed. Hence we add a `.context` to the call of `sign_and_finalize`.
3. In case the signing succeeds, we will immediately broadcast it
afterwards. The new broadcasting interface will tell us that we broadcasted
the "lock" transaction.
We eliminate unnecessary layers of indirection for broadcasting logic
and force our callers to provide us with the `kind` of transaction
that we are publishing.
Eventually, we can replace this string with some type-system magic
we can derive the name from the actual transaction. For now, we just
require the caller to duplicate this information because it is faster
and good enough TM.
This struct is a wallet. The only thing it can meaningfully broadcast
are transactions. The fact that they have to be signed for that is
implied. You cannot broadcast unsigned transactions.
Abstracting over the individual bits of functionality of the wallet
does have its place, especially if one wants to keep a separation
of an abstract protocol library that other people can use with their
own wallets.
However, at the moment, the traits only cause unnecessary friction.
We can always add such abstraction layers again once we need them.
Log messages are ideally as close to the functionality they are talking about, otherwise we might end up repeating ourselves on several callsites or the log messages gets outdated if the behaviour changes.
If the current balance is 0, we wait until the user deposits money
to the given address. After that, we simply swap the full balance.
Not only does this simplify the interface by removing a parameter,
but it also integrates the `deposit` command into the `buy-xmr`
command.
Syncing a wallet that is backed by electrum includes transactions
that are part of the mempool when computing the balance.
As such, waiting for a deposit is a very quick action because it
allows us to build our lock transaction on top of the yet to be
confirmed deposit transactions.
This patch introduces another function to the `bitcoin::Wallet` that
relies on the currently statically encoded fee rate. To make sure
future developers don't forget to adjust both, we extract a function
that "selects" a fee rate and return the constant from there.
Fixes#196.
These traits were only used once within the `TxLock` constructor.
Looking at the rest of the codebase, we don't really seem to follow
any abstractions here where the protocol shouldn't know about the
exact types that is being passed in.
As such, these types are just noise and might as well be removed in
favor of simplicity.
BDK already has a log line for the sync that we could enable if we
wanted such a log.
Additionally, _we_ are not actually syncing the wallet, bdk is so our
log line was lying. It should have said "calling bdk to sync wallet".
