Expose InputPair outpoint over FFI

payjoin-ffi/csharp/UnitTests.cs

@@ -305,6 +305,30 @@ public void InputPairRejectsInvalidOutpoint()
         });
     }
 
+    [Fact]
+    public void InputPairExposesOutpoint()
+    {
+        const string txid = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
+        const uint vout = 7;
+        var txin = new TxIn(
+            new OutPoint(txid, vout),
+            new byte[] {},
+            uint.MaxValue,
+            new byte[][] {}
+        );
+        var psbtIn = new PsbtInput(
+            new TxOut(12345, Convert.FromHexString("00140000000000000000000000000000000000000000")),
+            null,
+            null
+        );
+        using var inputPair = new InputPair(txin, psbtIn, null);
+
+        var outpoint = inputPair.Outpoint();
+
+        Assert.Equal(txid, outpoint.txid);
+        Assert.Equal(vout, outpoint.vout);
+    }
+
     [Fact]
     public void SenderBuilderRejectsBadPsbt()
     {

payjoin-ffi/src/receive/mod.rs

@@ -1114,6 +1114,9 @@ impl InputPair {
             .map(Self)
             .map_err(|err| InputPairError::InvalidPsbtInput(Arc::new(err.into())))
     }
+
+    /// Returns the outpoint spent by this input pair.
+    pub fn outpoint(&self) -> OutPoint { self.0.outpoint().into() }
 }
 
 impl From<InputPair> for payjoin::receive::InputPair {

payjoin/src/core/receive/mod.rs

@@ -216,6 +216,9 @@ impl InputPair {
         Self::new_segwit_input_pair(txout, outpoint, Some(expected_weight))
     }
 
+    /// Returns the outpoint spent by this input pair.
+    pub fn outpoint(&self) -> OutPoint { self.txin.previous_output }
+
     pub(crate) fn previous_txout(&self) -> TxOut {
         InternalInputPair::from(self)
             .previous_txout()
@@ -541,6 +544,18 @@ pub(crate) mod tests {
         assert_eq!(input_pair.expected_weight, expected_satifiability_weight);
     }
 
+    #[test]
+    fn input_pair_outpoint_returns_previous_output() {
+        let txout = TxOut {
+            value: Amount::from_sat(123),
+            script_pubkey: ScriptBuf::new_p2wpkh(&WPubkeyHash::from_byte_array(DUMMY20)),
+        };
+        let outpoint = OutPoint { txid: Txid::from_byte_array(DUMMY32), vout: 31 };
+        let input_pair = InputPair::new_p2wpkh(txout, outpoint).unwrap();
+
+        assert_eq!(input_pair.outpoint(), outpoint);
+    }
+
     #[test]
     fn create_p2pkh_input_pair() {
         let p2sh_txout = TxOut {