feat: add force_min_change_sats to PayoutQueueConfig (#414)

* chore: add force_min_change_sats to PayoutQueueConfig

* feat: add min change output when configured on queue

proto/api/bria.proto

@@ -291,6 +291,7 @@ message PayoutQueueConfig {
   }
   optional uint32 cpfp_payouts_after_mins = 6;
   optional uint32 cpfp_payouts_after_blocks = 7;
+  optional uint64 force_min_change_sats = 8;
 }
 
 enum TxPriority {

src/api/server/convert.rs

@@ -241,6 +241,7 @@ impl From<PayoutQueue> for proto::PayoutQueue {
             consolidate_deprecated_keychains: payout_queue.config.consolidate_deprecated_keychains,
             cpfp_payouts_after_mins: payout_queue.config.cpfp_payouts_after_mins,
             cpfp_payouts_after_blocks: payout_queue.config.cpfp_payouts_after_blocks,
+            force_min_change_sats: payout_queue.config.force_min_change_sats.map(u64::from),
         });
         proto::PayoutQueue {
             id,

src/cli/api_client.rs

@@ -306,6 +306,7 @@ impl ApiClient {
         manual_trigger: Option<bool>,
         cpfp_payouts_after_mins: Option<u32>,
         cpfp_payouts_after_blocks: Option<u32>,
+        force_min_change_sats: Option<u64>,
     ) -> anyhow::Result<()> {
         let tx_priority = match tx_priority {
             TxPriority::NextBlock => proto::TxPriority::NextBlock as i32,
@@ -331,6 +332,7 @@ impl ApiClient {
             trigger,
             cpfp_payouts_after_mins,
             cpfp_payouts_after_blocks,
+            force_min_change_sats,
         };
 
         let request = tonic::Request::new(proto::CreatePayoutQueueRequest {
@@ -525,6 +527,7 @@ impl ApiClient {
         interval_trigger: Option<u32>,
         cpfp_payouts_after_mins: Option<u32>,
         cpfp_payouts_after_blocks: Option<u32>,
+        force_min_change_sats: Option<u64>,
     ) -> anyhow::Result<()> {
         let tx_priority = tx_priority.map(|priority| match priority {
             TxPriority::NextBlock => proto::TxPriority::NextBlock as i32,
@@ -543,6 +546,7 @@ impl ApiClient {
                 trigger,
                 cpfp_payouts_after_mins,
                 cpfp_payouts_after_blocks,
+                force_min_change_sats,
             })
         } else {
             None

src/cli/mod.rs

@@ -345,6 +345,8 @@ enum Command {
         cpfp_payouts_after_mins: Option<u32>,
         #[clap(long = "cpfp-after-blocks")]
         cpfp_payouts_after_blocks: Option<u32>,
+        #[clap(long)]
+        min_change: Option<u64>,
     },
     /// Trigger Payout Queue
     TriggerPayoutQueue {
@@ -500,6 +502,8 @@ enum Command {
         cpfp_payouts_after_mins: Option<u32>,
         #[clap(long = "cpfp-after-blocks")]
         cpfp_payouts_after_blocks: Option<u32>,
+        #[clap(long)]
+        min_change: Option<u64>,
     },
     /// Get Batch details
     GetBatch {
@@ -851,6 +855,7 @@ pub async fn run() -> anyhow::Result<()> {
             manual_trigger,
             cpfp_payouts_after_mins,
             cpfp_payouts_after_blocks,
+            min_change,
         } => {
             let client = api_client(cli.bria_home, url, api_key);
             client
@@ -863,6 +868,7 @@ pub async fn run() -> anyhow::Result<()> {
                     manual_trigger,
                     cpfp_payouts_after_mins,
                     cpfp_payouts_after_blocks,
+                    min_change,
                 )
                 .await?;
         }
@@ -944,6 +950,7 @@ pub async fn run() -> anyhow::Result<()> {
             interval_trigger,
             cpfp_payouts_after_mins,
             cpfp_payouts_after_blocks,
+            min_change,
         } => {
             let client = api_client(cli.bria_home, url, api_key);
             client
@@ -955,6 +962,7 @@ pub async fn run() -> anyhow::Result<()> {
                     interval_trigger,
                     cpfp_payouts_after_mins,
                     cpfp_payouts_after_blocks,
+                    min_change,
                 )
                 .await?;
         }

src/job/process_payout_queue.rs

@@ -200,7 +200,8 @@ pub async fn construct_psbt(
     let mut cfg = PsbtBuilderConfig::builder()
         .consolidate_deprecated_keychains(queue_cfg.consolidate_deprecated_keychains)
         .fee_rate(fee_rate)
-        .reserved_utxos(reserved_utxos);
+        .reserved_utxos(reserved_utxos)
+        .force_min_change_output(queue_cfg.force_min_change_sats);
     if !for_estimation && queue_cfg.should_cpfp() {
         let keychain_ids = wallets.values().flat_map(|w| w.keychain_ids());
         let utxos = utxos

src/payout_queue/config.rs

@@ -1,7 +1,7 @@
 use serde::{Deserialize, Serialize};
 use std::time::Duration;
 
-use crate::primitives::TxPriority;
+use crate::primitives::{Satoshis, TxPriority};
 
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
 pub struct PayoutQueueConfig {
@@ -10,6 +10,7 @@ pub struct PayoutQueueConfig {
     pub cpfp_payouts_after_mins: Option<u32>,
     #[serde(default)]
     pub cpfp_payouts_after_blocks: Option<u32>,
+    pub force_min_change_sats: Option<Satoshis>,
     pub consolidate_deprecated_keychains: bool,
     pub trigger: PayoutQueueTrigger,
 }
@@ -55,6 +56,7 @@ impl Default for PayoutQueueConfig {
             },
             cpfp_payouts_after_mins: None,
             cpfp_payouts_after_blocks: None,
+            force_min_change_sats: None,
         }
     }
 }

src/wallet/psbt_builder.rs

@@ -70,9 +70,11 @@ pub struct PsbtBuilderConfig {
     #[builder(default)]
     reserved_utxos: HashMap<KeychainId, Vec<OutPoint>>,
     #[builder(default)]
-    pub cpfp_utxos: HashMap<KeychainId, Vec<CpfpUtxo>>,
+    cpfp_utxos: HashMap<KeychainId, Vec<CpfpUtxo>>,
     #[builder(default)]
     for_estimation: bool,
+    #[builder(default)]
+    force_min_change_output: Option<Satoshis>,
 }
 
 impl PsbtBuilderConfig {
@@ -550,6 +552,9 @@ impl PsbtBuilder<AcceptingCurrentKeychainState> {
         let mut builder = wallet.build_tx();
         builder.fee_rate(self.cfg.fee_rate);
         builder.drain_to(change_address.script_pubkey());
+        if let Some(sats) = self.cfg.force_min_change_output {
+            builder.add_recipient(change_address.script_pubkey(), u64::from(sats));
+        }
 
         for (_, destination, satoshis) in payouts.iter() {
             builder.add_recipient(destination.script_pubkey(), u64::from(*satoshis));
@@ -602,12 +607,12 @@ impl PsbtBuilder<AcceptingCurrentKeychainState> {
                     .iter()
                     .filter(|out| out.script_pubkey == script_pubkey)
                     .count();
-                let subtract_fee = if n_change_outputs > 1 {
-                    crate::fees::output_fee(&self.cfg.fee_rate, script_pubkey)
-                        + self.cfg.fee_rate.fee_vb(HEADER_VBYTES)
-                } else {
-                    self.cfg.fee_rate.fee_vb(HEADER_VBYTES)
-                };
+                // Here we are subtracting HEADER_VBYTES because we only need them 1 time
+                // and they will be added later if this is the first TX we are building
+                // also removing redundant change_output weight
+                let subtract_fee = self.cfg.fee_rate.fee_vb(HEADER_VBYTES)
+                    + (1.max(n_change_outputs) - 1) as u64
+                        * crate::fees::output_fee(&self.cfg.fee_rate, script_pubkey);
                 let inputs = psbt
                     .unsigned_tx
                     .input

tests/psbt_builder.rs

@@ -373,6 +373,64 @@ async fn build_psbt_with_cpfp() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+#[serial]
+async fn build_psbt_with_min_change_output() -> anyhow::Result<()> {
+    let pool = helpers::init_pool().await?;
+
+    let domain_current_keychain_id = Uuid::new_v4();
+    let xpub = XPub::try_from(("tpubDD4vFnWuTMEcZiaaZPgvzeGyMzWe6qHW8gALk5Md9kutDvtdDjYFwzauEFFRHgov8pAwup5jX88j5YFyiACsPf3pqn5hBjvuTLRAseaJ6b4", Some("m/84'/0'/0'"))).unwrap();
+    let keychain_cfg = KeychainConfig::wpkh(xpub);
+    let domain_current_keychain = KeychainWallet::new(
+        pool.clone(),
+        Network::Regtest,
+        domain_current_keychain_id.into(),
+        keychain_cfg,
+    );
+    let domain_addr = domain_current_keychain.new_external_address().await?;
+
+    let bitcoind = helpers::bitcoind_client().await?;
+    let wallet_funding = 100_000_000;
+    let wallet_funding_sats = Satoshis::from(wallet_funding);
+    helpers::fund_addr(&bitcoind, &domain_addr, wallet_funding)?;
+    let tx_id = helpers::fund_addr(&bitcoind, &domain_addr, wallet_funding)?;
+    helpers::gen_blocks(&bitcoind, 10)?;
+
+    let sats_per_vbyte: f64 = 100.0;
+    let fee = FeeRate::from_sat_per_vb(sats_per_vbyte as f32);
+    let min_change = Satoshis::from(100_000_000);
+    let cfg = PsbtBuilderConfig::builder()
+        .consolidate_deprecated_keychains(true)
+        .fee_rate(fee)
+        .force_min_change_output(Some(min_change))
+        .build()
+        .unwrap();
+    let builder = PsbtBuilder::new(cfg);
+
+    let domain_wallet_id = WalletId::new();
+    let domain_send_amount = wallet_funding_sats - Satoshis::from(50_000_000);
+    let destination = Address::parse_from_trusted_source("mgWUuj1J1N882jmqFxtDepEC73Rr22E9GU");
+    let payouts_one = vec![(Uuid::new_v4(), destination.clone(), domain_send_amount)];
+
+    let builder = builder
+        .wallet_payouts(domain_wallet_id, payouts_one)
+        .accept_current_keychain();
+    while !find_tx_id(&pool, domain_current_keychain_id, tx_id).await? {
+        let blockchain = helpers::electrum_blockchain().await?;
+        domain_current_keychain.sync(blockchain).await?;
+    }
+    let builder = domain_current_keychain
+        .dispatch_bdk_wallet(builder)
+        .await?
+        .next_wallet();
+    let FinishedPsbtBuild { wallet_totals, .. } = builder.finish();
+    assert_eq!(wallet_totals.len(), 1);
+    let domain_wallet_total = wallet_totals.get(&domain_wallet_id).unwrap();
+    assert!(domain_wallet_total.change_satoshis >= min_change);
+
+    Ok(())
+}
+
 async fn find_tx_id(
     pool: &sqlx::PgPool,
     keychain_id: Uuid,