Merge #563: gui: Add automated coin selection for spend

9e2407e gui: auto-select coins for spend (jp1ac4)

Pull request description:

  This adds automated coin selection from #560 to the GUI.

  The new "Auto-select" button uses automated coin selection to select coins for a spend, which the user can then modify as required.

  The button can only be clicked once the recipients and feerate have been validated, and it does not appear when creating a self-send.

  I haven't added any validation on the amount before making the button clickable, but it may be hard to anticipate all coin selection errors once fees are taken into consideration.

ACKs for top commit:
  darosior:
    light ACK 9e2407e

Tree-SHA512: 6ce3389d849470b3beb6ac8df75d2c3b7b6c04ee881dd0e9116c4d87f54376a8ed6666cbfd0ff0152a3eb839c8f7f17a175fe078ef030f03451430b84ab40cb6

gui/src/app/error.rs

@@ -46,6 +46,7 @@ impl std::fmt::Display for Error {
                 DaemonError::Rpc(code, e) => {
                     write!(f, "[{:?}] {}", code, e)
                 }
+                DaemonError::CoinSelectionError => write!(f, "{}", e),
             },
             Self::Unexpected(e) => write!(f, "Unexpected error: {}", e),
             Self::HardwareWallet(e) => write!(f, "{}", e),

gui/src/app/state/spend/step.rs

@@ -19,7 +19,7 @@ use crate::{
     app::{cache::Cache, error::Error, message::Message, state::psbt, view, wallet::Wallet},
     daemon::{
         model::{remaining_sequence, Coin, SpendTx},
-        Daemon,
+        Daemon, DaemonError,
     },
 };
 
@@ -67,6 +67,9 @@ pub trait Step {
 pub struct DefineSpend {
     balance_available: Amount,
     recipients: Vec<Recipient>,
+    /// Will be `true` if coins for spend were manually selected by user.
+    /// Otherwise, will be `false` (including for self-send).
+    is_user_coin_selection: bool,
     is_valid: bool,
     is_duplicate: bool,
 
@@ -113,6 +116,7 @@ impl DefineSpend {
             coins_labels: HashMap::new(),
             batch_label: form::Value::default(),
             recipients: vec![Recipient::default()],
+            is_user_coin_selection: false, // Start with auto-selection until user edits selection.
             is_valid: false,
             is_duplicate: false,
             feerate: form::Value::default(),
@@ -151,25 +155,68 @@ impl DefineSpend {
         self
     }
 
-    fn check_valid(&mut self) {
-        self.is_valid = self.feerate.valid
+    fn form_values_are_valid(&self) -> bool {
+        self.feerate.valid
             && !self.feerate.value.is_empty()
-            && (self.batch_label.valid || self.recipients.len() < 2);
+            && (self.batch_label.valid || self.recipients.len() < 2)
+            // Recipients will be empty for self-send.
+            && self.recipients.iter().all(|r| r.valid())
+    }
+
+    fn check_valid(&mut self) {
+        self.is_valid =
+            self.form_values_are_valid() && self.coins.iter().any(|(_, selected)| *selected);
         self.is_duplicate = false;
-        if !self.coins.iter().any(|(_, selected)| *selected) {
-            self.is_valid = false;
-        }
         for (i, recipient) in self.recipients.iter().enumerate() {
-            if !recipient.valid() {
-                self.is_valid = false;
-            }
             if !self.is_duplicate && !recipient.address.value.is_empty() {
                 self.is_duplicate = self.recipients[..i]
                     .iter()
                     .any(|r| r.address.value == recipient.address.value);
             }
         }
     }
+    fn auto_select_coins(&mut self, daemon: Arc<dyn Daemon + Sync + Send>) {
+        // Set non-input values in the same way as for user selection.
+        let mut outputs: HashMap<Address<address::NetworkUnchecked>, u64> = HashMap::new();
+        for recipient in &self.recipients {
+            outputs.insert(
+                Address::from_str(&recipient.address.value).expect("Checked before"),
+                recipient.amount().expect("Checked before"),
+            );
+        }
+        let feerate_vb = self.feerate.value.parse::<u64>().unwrap_or(0);
+        // Create a spend with empty inputs in order to use auto-selection.
+        match daemon.create_spend_tx(&[], &outputs, feerate_vb) {
+            Ok(spend) => {
+                self.warning = None;
+                let selected_coins: Vec<OutPoint> = spend
+                    .psbt
+                    .unsigned_tx
+                    .input
+                    .iter()
+                    .map(|c| c.previous_output)
+                    .collect();
+                // Mark coins as selected.
+                for (coin, selected) in &mut self.coins {
+                    *selected = selected_coins.contains(&coin.outpoint);
+                }
+                // As coin selection was successful, we can assume there is nothing left to select.
+                self.amount_left_to_select = Some(Amount::from_sat(0));
+            }
+            Err(e) => {
+                if let DaemonError::CoinSelectionError = e {
+                    // For coin selection error (insufficient funds), do not make any changes to
+                    // selected coins on screen and just show user how much is left to select.
+                    // User can then either:
+                    // - modify recipient amounts and/or feerate and let coin selection run again, or
+                    // - select coins manually.
+                    self.amount_left_to_select();
+                } else {
+                    self.warning = Some(e.into());
+                }
+            }
+        }
+    }
     fn amount_left_to_select(&mut self) {
         // We need the feerate in order to compute the required amount of BTC to
         // select. Return early if we don't to not do unnecessary computation.
@@ -319,11 +366,24 @@ impl Step for DefineSpend {
                     view::CreateSpendMessage::SelectCoin(i) => {
                         if let Some(coin) = self.coins.get_mut(i) {
                             coin.1 = !coin.1;
+                            // Once user edits selection, auto-selection can no longer be used.
+                            self.is_user_coin_selection = true;
                             self.amount_left_to_select();
                         }
                     }
                     _ => {}
                 }
+
+                // Attempt to select coins automatically if:
+                // - all form values have been added and validated
+                // - not a self-send
+                // - user has not yet selected coins manually
+                if self.form_values_are_valid()
+                    && !self.recipients.is_empty()
+                    && !self.is_user_coin_selection
+                {
+                    self.auto_select_coins(daemon);
+                }
                 self.check_valid();
             }
             Message::Psbt(res) => match res {

gui/src/app/view/warning.rs

@@ -34,6 +34,9 @@ impl From<&Error> for WarningMessage {
                     WarningMessage("Communication with Daemon failed".to_string())
                 }
                 DaemonError::DaemonStopped => WarningMessage("Daemon stopped".to_string()),
+                DaemonError::CoinSelectionError => {
+                    WarningMessage("Error when selecting coins for spend".to_string())
+                }
             },
             Error::Unexpected(_) => WarningMessage("Unknown error".to_string()),
             Error::HardwareWallet(_) => WarningMessage("Hardware wallet error".to_string()),

gui/src/daemon/embedded.rs

@@ -2,7 +2,7 @@ use std::collections::{HashMap, HashSet};
 
 use super::{model::*, Daemon, DaemonError};
 use liana::{
-    commands::LabelItem,
+    commands::{CommandError, LabelItem},
     config::Config,
     miniscript::bitcoin::{address, psbt::Psbt, Address, OutPoint, Txid},
     DaemonControl, DaemonHandle,
@@ -90,7 +90,10 @@ impl Daemon for EmbeddedDaemon {
     ) -> Result<CreateSpendResult, DaemonError> {
         self.control()?
             .create_spend(destinations, coins_outpoints, feerate_vb)
-            .map_err(|e| DaemonError::Unexpected(e.to_string()))
+            .map_err(|e| match e {
+                CommandError::CoinSelectionError(_) => DaemonError::CoinSelectionError,
+                e => DaemonError::Unexpected(e.to_string()),
+            })
     }
 
     fn update_spend_tx(&self, psbt: &Psbt) -> Result<(), DaemonError> {

gui/src/daemon/mod.rs

@@ -30,6 +30,8 @@ pub enum DaemonError {
     Start(StartupError),
     // Error if the client is not supported.
     ClientNotSupported,
+    /// Error when selecting coins for spend.
+    CoinSelectionError,
 }
 
 impl std::fmt::Display for DaemonError {
@@ -42,6 +44,7 @@ impl std::fmt::Display for DaemonError {
             Self::Unexpected(e) => write!(f, "Daemon unexpected error: {}", e),
             Self::Start(e) => write!(f, "Daemon did not start: {}", e),
             Self::ClientNotSupported => write!(f, "Daemon communication is not supported"),
+            Self::CoinSelectionError => write!(f, "Coin selection error"),
         }
     }
 }