feat(esplora): include previous TxOuts for fee calculation

The previous `TxOut` for transactions received from an external
wallet are added as floating `TxOut`s to `TxGraph` to allow for
fee calculation.

crates/esplora/src/async_ext.rs

@@ -1,7 +1,7 @@
 use async_trait::async_trait;
 use bdk_chain::collections::btree_map;
 use bdk_chain::{
-    bitcoin::{BlockHash, OutPoint, ScriptBuf, Txid},
+    bitcoin::{BlockHash, OutPoint, ScriptBuf, TxOut, Txid},
     collections::BTreeMap,
     local_chain::{self, CheckPoint},
     BlockId, ConfirmationTimeHeightAnchor, TxGraph,
@@ -204,6 +204,24 @@ impl EsploraAsyncExt for esplora_client::AsyncClient {
                         if let Some(anchor) = anchor_from_status(&tx.status) {
                             let _ = graph.insert_anchor(tx.txid, anchor);
                         }
+
+                        let previous_outputs = tx.vin.iter().filter_map(|vin| {
+                            let prevout = vin.prevout.as_ref()?;
+                            Some((
+                                OutPoint {
+                                    txid: vin.txid,
+                                    vout: vin.vout,
+                                },
+                                TxOut {
+                                    script_pubkey: prevout.scriptpubkey.clone(),
+                                    value: prevout.value,
+                                },
+                            ))
+                        });
+
+                        for (outpoint, txout) in previous_outputs {
+                            let _ = graph.insert_txout(outpoint, txout);
+                        }
                     }
                 }
 

crates/esplora/src/blocking_ext.rs

@@ -3,7 +3,7 @@ use std::thread::JoinHandle;
 use bdk_chain::collections::btree_map;
 use bdk_chain::collections::BTreeMap;
 use bdk_chain::{
-    bitcoin::{BlockHash, OutPoint, ScriptBuf, Txid},
+    bitcoin::{BlockHash, OutPoint, ScriptBuf, TxOut, Txid},
     local_chain::{self, CheckPoint},
     BlockId, ConfirmationTimeHeightAnchor, TxGraph,
 };
@@ -194,6 +194,24 @@ impl EsploraExt for esplora_client::BlockingClient {
                         if let Some(anchor) = anchor_from_status(&tx.status) {
                             let _ = graph.insert_anchor(tx.txid, anchor);
                         }
+
+                        let previous_outputs = tx.vin.iter().filter_map(|vin| {
+                            let prevout = vin.prevout.as_ref()?;
+                            Some((
+                                OutPoint {
+                                    txid: vin.txid,
+                                    vout: vin.vout,
+                                },
+                                TxOut {
+                                    script_pubkey: prevout.scriptpubkey.clone(),
+                                    value: prevout.value,
+                                },
+                            ))
+                        });
+
+                        for (outpoint, txout) in previous_outputs {
+                            let _ = graph.insert_txout(outpoint, txout);
+                        }
                     }
                 }
 

crates/esplora/tests/async_ext.rs

@@ -109,6 +109,19 @@ pub async fn test_update_tx_graph_without_keychain() -> anyhow::Result<()> {
         )
         .await?;
 
+    // Check to see if we have the floating txouts available from our two created transactions'
+    // previous outputs in order to calculate transaction fees.
+    let fee_calculations = graph_update
+        .full_txs()
+        .map(|tx| graph_update.calculate_fee(tx.tx).is_ok())
+        .collect::<Vec<_>>();
+
+    // Ensure there are exactly two fee calculations.
+    assert_eq!(fee_calculations.len(), 2);
+
+    // Ensure that both fee calculations are successful.
+    assert!(fee_calculations.iter().all(|&is_ok| is_ok));
+
     let mut graph_update_txids: Vec<Txid> = graph_update.full_txs().map(|tx| tx.txid).collect();
     graph_update_txids.sort();
     let mut expected_txids = vec![txid1, txid2];

crates/esplora/tests/blocking_ext.rs

@@ -136,6 +136,19 @@ pub fn test_update_tx_graph_without_keychain() -> anyhow::Result<()> {
         1,
     )?;
 
+    // Check to see if we have the floating txouts available from our two created transactions'
+    // previous outputs in order to calculate transaction fees.
+    let fee_calculations = graph_update
+        .full_txs()
+        .map(|tx| graph_update.calculate_fee(tx.tx).is_ok())
+        .collect::<Vec<_>>();
+
+    // Ensure there are exactly two fee calculations.
+    assert_eq!(fee_calculations.len(), 2);
+
+    // Ensure that both fee calculations are successful.
+    assert!(fee_calculations.iter().all(|&is_ok| is_ok));
+
     let mut graph_update_txids: Vec<Txid> = graph_update.full_txs().map(|tx| tx.txid).collect();
     graph_update_txids.sort();
     let mut expected_txids = vec![txid1, txid2];