[ldk-sample] / src / sweep.rs

use std::io::{Read, Seek, SeekFrom};
use std::path::PathBuf;
use std::sync::Arc;
use std::time::Duration;
use std::{fs, io};

use lightning::chain::chaininterface::{BroadcasterInterface, ConfirmationTarget, FeeEstimator};
use lightning::sign::{EntropySource, KeysManager, SpendableOutputDescriptor};
use lightning::util::logger::Logger;
use lightning::util::persist::KVStorePersister;
use lightning::util::ser::{Readable, WithoutLength};

use bitcoin::secp256k1::Secp256k1;
use bitcoin::{LockTime, PackedLockTime};
use rand::{thread_rng, Rng};

use crate::hex_utils;
use crate::BitcoindClient;
use crate::ChannelManager;
use crate::FilesystemLogger;
use crate::FilesystemPersister;

/// If we have any pending claimable outputs, we should slowly sweep them to our Bitcoin Core
/// wallet. We technically don't need to do this - they're ours to spend when we want and can just
/// use them to build new transactions instead, but we cannot feed them direclty into Bitcoin
/// Core's wallet so we have to sweep.
///
/// Note that this is unececssary for [`SpendableOutputDescriptor::StaticOutput`]s, which *do* have
/// an associated secret key we could simply import into Bitcoin Core's wallet, but for consistency
/// we don't do that here either.
pub(crate) async fn periodic_sweep(
        ldk_data_dir: String, keys_manager: Arc<KeysManager>, logger: Arc<FilesystemLogger>,
        persister: Arc<FilesystemPersister>, bitcoind_client: Arc<BitcoindClient>,
        channel_manager: Arc<ChannelManager>,
) {
        // Regularly claim outputs which are exclusively spendable by us and send them to Bitcoin Core.
        // Note that if you more tightly integrate your wallet with LDK you may not need to do this -
        // these outputs can just be treated as normal outputs during coin selection.
        let pending_spendables_dir =
                format!("{}/{}", ldk_data_dir, crate::PENDING_SPENDABLE_OUTPUT_DIR);
        let processing_spendables_dir = format!("{}/processing_spendable_outputs", ldk_data_dir);
        let spendables_dir = format!("{}/spendable_outputs", ldk_data_dir);

        // We batch together claims of all spendable outputs generated each day, however only after
        // batching any claims of spendable outputs which were generated prior to restart. On a mobile
        // device we likely won't ever be online for more than a minute, so we have to ensure we sweep
        // any pending claims on startup, but for an always-online node you may wish to sweep even less
        // frequently than this (or move the interval await to the top of the loop)!
        //
        // There is no particular rush here, we just have to ensure funds are availably by the time we
        // need to send funds.
        let mut interval = tokio::time::interval(Duration::from_secs(60 * 60 * 24));

        loop {
                interval.tick().await; // Note that the first tick completes immediately
                if let Ok(dir_iter) = fs::read_dir(&pending_spendables_dir) {
                        // Move any spendable descriptors from pending folder so that we don't have any
                        // races with new files being added.
                        for file_res in dir_iter {
                                let file = file_res.unwrap();
                                // Only move a file if its a 32-byte-hex'd filename, otherwise it might be a
                                // temporary file.
                                if file.file_name().len() == 64 {
                                        fs::create_dir_all(&processing_spendables_dir).unwrap();
                                        let mut holding_path = PathBuf::new();
                                        holding_path.push(&processing_spendables_dir);
                                        holding_path.push(&file.file_name());
                                        fs::rename(file.path(), holding_path).unwrap();
                                }
                        }
                        // Now concatenate all the pending files we moved into one file in the
                        // `spendable_outputs` directory and drop the processing directory.
                        let mut outputs = Vec::new();
                        if let Ok(processing_iter) = fs::read_dir(&processing_spendables_dir) {
                                for file_res in processing_iter {
                                        outputs.append(&mut fs::read(file_res.unwrap().path()).unwrap());
                                }
                        }
                        if !outputs.is_empty() {
                                let key = hex_utils::hex_str(&keys_manager.get_secure_random_bytes());
                                persister
                                        .persist(&format!("spendable_outputs/{}", key), &WithoutLength(&outputs))
                                        .unwrap();
                                fs::remove_dir_all(&processing_spendables_dir).unwrap();
                        }
                }
                // Iterate over all the sets of spendable outputs in `spendables_dir` and try to claim
                // them.
                // Note that here we try to claim each set of spendable outputs over and over again
                // forever, even long after its been claimed. While this isn't an issue per se, in practice
                // you may wish to track when the claiming transaction has confirmed and remove the
                // spendable outputs set. You may also wish to merge groups of unspent spendable outputs to
                // combine batches.
                if let Ok(dir_iter) = fs::read_dir(&spendables_dir) {
                        for file_res in dir_iter {
                                let mut outputs: Vec<SpendableOutputDescriptor> = Vec::new();
                                let mut file = fs::File::open(file_res.unwrap().path()).unwrap();
                                loop {
                                        // Check if there are any bytes left to read, and if so read a descriptor.
                                        match file.read_exact(&mut [0; 1]) {
                                                Ok(_) => {
                                                        file.seek(SeekFrom::Current(-1)).unwrap();
                                                }
                                                Err(e) if e.kind() == io::ErrorKind::UnexpectedEof => break,
                                                Err(e) => Err(e).unwrap(),
                                        }
                                        outputs.push(Readable::read(&mut file).unwrap());
                                }
                                let destination_address = bitcoind_client.get_new_address().await;
                                let output_descriptors = &outputs.iter().map(|a| a).collect::<Vec<_>>();
                                let tx_feerate =
                                        bitcoind_client.get_est_sat_per_1000_weight(ConfirmationTarget::Background);

                                // We set nLockTime to the current height to discourage fee sniping.
                                // Occasionally randomly pick a nLockTime even further back, so
                                // that transactions that are delayed after signing for whatever reason,
                                // e.g. high-latency mix networks and some CoinJoin implementations, have
                                // better privacy.
                                // Logic copied from core: https://github.com/bitcoin/bitcoin/blob/1d4846a8443be901b8a5deb0e357481af22838d0/src/wallet/spend.cpp#L936
                                let mut cur_height = channel_manager.current_best_block().height();

                                // 10% of the time
                                if thread_rng().gen_range(0, 10) == 0 {
                                        // subtract random number between 0 and 100
                                        cur_height = cur_height.saturating_sub(thread_rng().gen_range(0, 100));
                                }

                                let locktime: PackedLockTime =
                                        LockTime::from_height(cur_height).map_or(PackedLockTime::ZERO, |l| l.into());

                                if let Ok(spending_tx) = keys_manager.spend_spendable_outputs(
                                        output_descriptors,
                                        Vec::new(),
                                        destination_address.script_pubkey(),
                                        tx_feerate,
                                        Some(locktime),
                                        &Secp256k1::new(),
                                ) {
                                        // Note that, most likely, we've already sweeped this set of outputs
                                        // and they're already confirmed on-chain, so this broadcast will fail.
                                        bitcoind_client.broadcast_transactions(&[&spending_tx]);
                                } else {
                                        lightning::log_error!(
                                                logger,
                                                "Failed to sweep spendable outputs! This may indicate the outputs are dust. Will try again in a day.");
                                }
                        }
                }
        }
}