Experimenting with two-party PSBT signing.

side-node/src/bitcoin/clients/esplora.rs

@@ -39,17 +39,45 @@ impl EsploraWallet {
         recipient: Address,
         amount: Amount,
     ) -> Result<bitcoin::Transaction, anyhow::Error> {
-        let mut tx_builder = self.wallet.build_tx();
+        let mut tx_builder = self.build_tx()?;
         tx_builder
             .add_recipient(recipient.script_pubkey(), amount)
             .enable_rbf();
         let mut psbt = tx_builder.finish()?;
-        let finalized = self.wallet.sign(&mut psbt, SignOptions::default())?;
-        assert!(finalized);
-        let tx = psbt.extract_tx()?;
+        let tx = self.sign(&mut psbt, true)?.extract_tx()?;
         Ok(tx)
     }
 
+    pub(crate) fn build_tx(
+        &mut self,
+    ) -> Result<
+        bdk_wallet::TxBuilder<bdk_wallet::wallet::coin_selection::BranchAndBoundCoinSelection>,
+        anyhow::Error,
+    > {
+        Ok(self.wallet.build_tx())
+    }
+
+    pub(crate) fn sign(
+        &self,
+        psbt: &mut bitcoin::Psbt,
+        finalize: bool,
+    ) -> Result<bitcoin::Psbt, anyhow::Error> {
+        tracing::info!("{} signing PSBT", self.name);
+
+        let options = SignOptions {
+            try_finalize: finalize,
+            ..Default::default()
+        };
+
+        let finalized = self.wallet.sign(psbt, options)?;
+
+        // make sure the PSBT is finalized if we asked for it
+        if finalize {
+            assert!(finalized)
+        }
+        Ok(psbt.to_owned())
+    }
+
     /// Syncs the wallet with the latest state of the Bitcoin blockchain
     pub(crate) async fn sync(&mut self) -> Result<(), anyhow::Error> {
         tracing::info!("{} full scan sync start", self.name);
@@ -105,6 +133,10 @@ impl EsploraWallet {
         );
         self.client.broadcast(tx).await
     }
+
+    pub(crate) fn wallet(&mut self) -> &Wallet {
+        &self.wallet
+    }
 }
 
 /// Creates a Bitcoin descriptor wallet with the mnemonic in the given user directory.

side-node/src/bitcoin/driver.rs

@@ -4,25 +4,13 @@ use tracing_subscriber::filter::EnvFilter;
 use tracing_subscriber::util::SubscriberInitExt;
 use tracing_subscriber::{fmt, layer::SubscriberExt};
 
+use super::clients::esplora::EsploraWallet;
+
 pub(crate) async fn simple_transfer() -> Result<(), anyhow::Error> {
-    tracing_setup();
-
-    let mut dave = clients::esplora::create_wallet("dave", Network::Signet)?;
-    let mut sammy = clients::esplora::create_wallet("sammy", Network::Signet)?;
-
-    let _next_address = dave.next_unused_address()?;
-
-    let _ = dave.balance();
-    dave.sync().await?;
-    let _ = dave.balance();
-
-    let _sammy = sammy.balance();
-    sammy.sync().await?;
-    let _ = sammy.balance();
-
+    let (mut dave, mut sammy) = setup().await?;
 
     let send_amount = Amount::from_sat(500);
-   ensure_enough_sats(dave, send_amount);
+    ensure_enough_sats(&dave, send_amount);
 
     let sammy_address = sammy.next_unused_address()?.address;
     let tx = dave.build_and_sign_send_tx(sammy_address, send_amount)?;
@@ -31,8 +19,21 @@ pub(crate) async fn simple_transfer() -> Result<(), anyhow::Error> {
     Ok(())
 }
 
+async fn setup() -> Result<(EsploraWallet, EsploraWallet), anyhow::Error> {
+    tracing_setup();
+    let mut dave = clients::esplora::create_wallet("dave", Network::Signet)?;
+    let mut sammy = clients::esplora::create_wallet("sammy", Network::Signet)?;
+    let _ = dave.balance();
+    dave.sync().await?;
+    let _ = dave.balance();
+    let _sammy = sammy.balance();
+    sammy.sync().await?;
+    let _ = sammy.balance();
+    Ok((dave, sammy))
+}
+
 /// Exit if the wallet does not have enough sats to send.
-fn ensure_enough_sats(wallet: EsploraWallet, send_amount: bitcoin::Amount) -> _ {
+fn ensure_enough_sats(wallet: &EsploraWallet, send_amount: bitcoin::Amount) {
     if wallet.balance().total() < send_amount {
         tracing::error!(
             "Please send at least {} sats to the receiving address. Exiting.",
@@ -43,12 +44,38 @@ fn ensure_enough_sats(wallet: EsploraWallet, send_amount: bitcoin::Amount) -> _
 }
 
 pub(crate) async fn htlc() -> anyhow::Result<()> {
-    // dave will be our sender
-    let mut dave = clients::esplora::create_wallet("dave", Network::Signet)?;
+    let (mut dave, mut sammy) = setup().await?;
 
-    // sammy will be our liquidity router
-    let mut sammy = clients::esplora::create_wallet("sammy", Network::Signet)?;
+    // format a new commitment transaction like in Lightning
+    let mut commitment_builder = dave.build_tx()?;
+    let amount = Amount::from_sat(500);
+    let recipient = sammy.next_unused_address()?.script_pubkey();
+    commitment_builder.add_recipient(recipient, amount);
+    commitment_builder.enable_rbf();
+    let psbt = commitment_builder
+        .finish()
+        .expect("unable to build commitment");
 
+    // sign the commitment transaction
+    let mut dave_psbt = dave.sign(&mut psbt.clone(), false)?;
+    let sammy_psbt = sammy.sign(&mut psbt.clone(), false)?;
+
+    dave_psbt
+        .combine(sammy_psbt)
+        .expect("problem combining bitcoin PSBTs"); // these guys love mutability
+
+    let finalized = dave
+        .wallet()
+        .finalize_psbt(&mut dave_psbt, bdk_wallet::SignOptions::default())
+        .expect("couldn't finalize");
+
+    assert!(finalized);
+    let tx = dave_psbt.extract_tx()?;
+
+    let _ = dave.broadcast(&tx).await.expect("couldn't broadcast");
+
+    let _ = sammy.sync();
+    sammy.balance();
     Ok(())
 }