Replace PSBT::GetInputUTXO with PSBTInput::GetUTXO

Now that PSBTInput's track their own prevouts, there's no need for a
PSBT global function to fetch input specific data.

src/node/psbt.cpp

@@ -35,7 +35,7 @@ PSBTAnalysis AnalyzePSBT(PartiallySignedTransaction psbtx)
 
         // Check for a UTXO
         CTxOut utxo;
-        if (psbtx.GetInputUTXO(utxo, i)) {
+        if (input.GetUTXO(utxo)) {
             if (!MoneyRange(utxo.nValue) || !MoneyRange(in_amt + utxo.nValue)) {
                 result.SetInvalid(strprintf("PSBT is not valid. Input %u has invalid value", i));
                 return result;
@@ -123,7 +123,7 @@ PSBTAnalysis AnalyzePSBT(PartiallySignedTransaction psbtx)
             PSBTInput& input = psbtx.inputs[i];
             Coin newcoin;
 
-            if (SignPSBTInput(DUMMY_SIGNING_PROVIDER, psbtx, i, nullptr, /*options=*/{}) != PSBTError::OK || !psbtx.GetInputUTXO(newcoin.out, i)) {
+            if (SignPSBTInput(DUMMY_SIGNING_PROVIDER, psbtx, i, nullptr, /*options=*/{}) != PSBTError::OK || !input.GetUTXO(newcoin.out)) {
                 success = false;
                 break;
             } else {

src/psbt.cpp

@@ -100,20 +100,18 @@ bool PartiallySignedTransaction::AddOutput(const PSBTOutput& psbtout)
     return false;
 }
 
-bool PartiallySignedTransaction::GetInputUTXO(CTxOut& utxo, int input_index) const
+bool PSBTInput::GetUTXO(CTxOut& utxo) const
 {
-    const PSBTInput& input = inputs[input_index];
-    uint32_t prevout_index = tx->vin[input_index].prevout.n;
-    if (input.non_witness_utxo) {
-        if (prevout_index >= input.non_witness_utxo->vout.size()) {
+    if (non_witness_utxo) {
+        if (prev_out >= non_witness_utxo->vout.size()) {
             return false;
         }
-        if (input.non_witness_utxo->GetHash() != tx->vin[input_index].prevout.hash) {
+        if (non_witness_utxo->GetHash() != prev_txid) {
             return false;
         }
-        utxo = input.non_witness_utxo->vout[prevout_index];
-    } else if (!input.witness_utxo.IsNull()) {
-        utxo = input.witness_utxo;
+        utxo = non_witness_utxo->vout[prev_out];
+    } else if (!witness_utxo.IsNull()) {
+        utxo = witness_utxo;
     } else {
         return false;
     }
@@ -435,9 +433,9 @@ PrecomputedTransactionData PrecomputePSBTData(const PartiallySignedTransaction&
 {
     const CMutableTransaction& tx = *psbt.tx;
     bool have_all_spent_outputs = true;
-    std::vector<CTxOut> utxos(tx.vin.size());
-    for (size_t idx = 0; idx < tx.vin.size(); ++idx) {
-        if (!psbt.GetInputUTXO(utxos[idx], idx)) have_all_spent_outputs = false;
+    std::vector<CTxOut> utxos;
+    for (const PSBTInput& input : psbt.inputs) {
+        if (!input.GetUTXO(utxos.emplace_back())) have_all_spent_outputs = false;
     }
     PrecomputedTransactionData txdata;
     if (have_all_spent_outputs) {

src/psbt.h

@@ -310,6 +310,13 @@ public:
     void Merge(const PSBTInput& input);
     uint32_t GetVersion() const { return m_psbt_version; }
     COutPoint GetOutPoint() const;
+    /**
+     * Retrieves the UTXO for this input
+     *
+     * @param[out] utxo The UTXO of this input
+     * @return Whether the UTXO could be retrieved
+     */
+    bool GetUTXO(CTxOut& utxo) const;
 
     explicit PSBTInput(uint32_t psbt_version, const Txid& prev_txid, uint32_t prev_out, std::optional<uint32_t> sequence = std::nullopt)
         : m_psbt_version(psbt_version),
@@ -1087,14 +1094,6 @@ public:
     bool AddInput(const PSBTInput& psbtin);
     bool AddOutput(const PSBTOutput& psbtout);
     explicit PartiallySignedTransaction(const CMutableTransaction& tx);
-    /**
-     * Finds the UTXO for a given input index
-     *
-     * @param[out] utxo The UTXO of the input if found
-     * @param[in] input_index Index of the input to retrieve the UTXO of
-     * @return Whether the UTXO for the specified input was found
-     */
-    bool GetInputUTXO(CTxOut& utxo, int input_index) const;
 
     template <typename Stream>
     inline void Serialize(Stream& s) const {

src/test/fuzz/psbt.cpp

@@ -68,9 +68,9 @@ FUZZ_TARGET(psbt)
         (void)output.IsNull();
     }
 
-    for (size_t i = 0; i < psbt.inputs.size(); ++i) {
+    for (const PSBTInput& input : psbt.inputs) {
         CTxOut tx_out;
-        if (psbt.GetInputUTXO(tx_out, i)) {
+        if (input.GetUTXO(tx_out)) {
             (void)tx_out.IsNull();
             (void)tx_out.ToString();
         }