gui: display (estimated) feerate

For transactions that have been broadcast, the feerate is calculated
using the transaction's actual size. For PSBTs, the feerate is
calculated using the max satisfaction size for all inputs, whether
they have been signed or not.

gui/src/app/state/recovery.rs

@@ -155,7 +155,7 @@ impl State for RecoveryPanel {
                                 .cloned()
                                 .collect();
                             let sigs = desc.partial_spend_info(&psbt).unwrap();
-                            Ok(SpendTx::new(None, psbt, coins, sigs))
+                            Ok(SpendTx::new(None, psbt, coins, sigs, desc.max_sat_vbytes()))
                         },
                         Message::Recovery,
                     );

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

@@ -432,7 +432,13 @@ impl Step for SaveSpend {
             .unwrap();
         self.spend = Some(psbt::PsbtState::new(
             self.wallet.clone(),
-            SpendTx::new(None, psbt, draft.inputs.clone(), sigs),
+            SpendTx::new(
+                None,
+                psbt,
+                draft.inputs.clone(),
+                sigs,
+                self.wallet.main_descriptor.max_sat_vbytes(),
+            ),
             false,
         ));
     }

gui/src/app/view/home.rs

@@ -210,6 +210,15 @@ pub fn payment_view<'a>(
                     .align_items(Alignment::Center)
                     .push(h3("Miner fee: ").style(color::GREY_3))
                     .push(amount_with_size(&fee_amount, H3_SIZE))
+                    .push(text(" ").size(H3_SIZE))
+                    .push(
+                        text(format!(
+                            "({} sats/vbyte)",
+                            fee_amount.to_sat() / tx.tx.vsize() as u64
+                        ))
+                        .size(H4_SIZE)
+                        .style(color::GREY_3),
+                    )
             }))
             .push(card::simple(
                 Column::new()

gui/src/app/view/psbt.rs

@@ -196,7 +196,13 @@ pub fn spend_header<'a>(tx: &SpendTx) -> Element<'a, Message> {
                     Row::new()
                         .align_items(Alignment::Center)
                         .push(h3("Miner fee: ").style(color::GREY_3))
-                        .push(amount_with_size(&tx.fee_amount, H3_SIZE)),
+                        .push(amount_with_size(&tx.fee_amount, H3_SIZE))
+                        .push(text(" ").size(H3_SIZE))
+                        .push(
+                            text(format!("(~{} sats/vbyte)", &tx.min_feerate_vb()))
+                                .size(H4_SIZE)
+                                .style(color::GREY_3),
+                        ),
                 ),
         )
         .into()

gui/src/app/view/transactions.rs

@@ -171,6 +171,15 @@ pub fn tx_view<'a>(
                                 .align_items(Alignment::Center)
                                 .push(h3("Miner fee: ").style(color::GREY_3))
                                 .push(amount_with_size(&fee_amount, H3_SIZE))
+                                .push(text(" ").size(H3_SIZE))
+                                .push(
+                                    text(format!(
+                                        "({} sats/vbyte)",
+                                        fee_amount.to_sat() / tx.tx.vsize() as u64
+                                    ))
+                                    .size(H4_SIZE)
+                                    .style(color::GREY_3),
+                                )
                         })),
                 ),
             )

gui/src/daemon/mod.rs

@@ -97,7 +97,13 @@ pub trait Daemon: Debug {
                 .main
                 .partial_spend_info(&tx.psbt)
                 .map_err(|e| DaemonError::Unexpected(e.to_string()))?;
-            spend_txs.push(model::SpendTx::new(tx.updated_at, tx.psbt, coins, sigs))
+            spend_txs.push(model::SpendTx::new(
+                tx.updated_at,
+                tx.psbt,
+                coins,
+                sigs,
+                info.descriptors.main.max_sat_vbytes(),
+            ))
         }
         spend_txs.sort_by(|a, b| {
             if a.status == b.status {

gui/src/daemon/model.rs

@@ -30,6 +30,9 @@ pub struct SpendTx {
     pub change_indexes: Vec<usize>,
     pub spend_amount: Amount,
     pub fee_amount: Amount,
+    /// The maximum size difference (in virtual bytes) of
+    /// an input in this transaction before and after satisfaction.
+    pub max_sat_vbytes: usize,
     pub status: SpendStatus,
     pub sigs: PartialSpendInfo,
     pub updated_at: Option<u32>,
@@ -49,6 +52,7 @@ impl SpendTx {
         psbt: Psbt,
         coins: Vec<Coin>,
         sigs: PartialSpendInfo,
+        max_sat_vbytes: usize,
     ) -> Self {
         let mut change_indexes = Vec::new();
         let (change_amount, spend_amount) = psbt.unsigned_tx.output.iter().enumerate().fold(
@@ -87,6 +91,7 @@ impl SpendTx {
             change_indexes,
             spend_amount,
             fee_amount: inputs_amount - spend_amount - change_amount,
+            max_sat_vbytes,
             status,
             sigs,
         }
@@ -122,6 +127,14 @@ impl SpendTx {
     pub fn is_self_send(&self) -> bool {
         !self.coins.is_empty() && self.spend_amount == Amount::from_sat(0)
     }
+
+    /// Feerate obtained if all transaction inputs have the maximum satisfaction size.
+    pub fn min_feerate_vb(&self) -> u64 {
+        // This assumes all inputs are internal (have same max satisfaction size).
+        let max_tx_vbytes =
+            self.psbt.unsigned_tx.vsize() + (self.max_sat_vbytes * self.psbt.inputs.len());
+        self.fee_amount.to_sat() / max_tx_vbytes as u64
+    }
 }
 
 #[derive(Debug, Clone)]