rpc, tests: in utxoupdatepsbt also look for the transaction in the txindex

Previously only the segwit utxos being spent by the psbt were looked for and
added to the psbt. Now, the full transaction corresponding to each of these
utxos (legacy and segwit) is looked for in the txindex and mempool and added
to the psbt. If txindex is disabled and the transaction is not in the mempool,
then we fall back to getting just the utxo (if segwit) from the utxo set.

src/rpc/rawtransaction.cpp

@@ -169,7 +169,7 @@ static std::vector<RPCArg> CreateTxDoc()
     };
 }
 
-// Update PSBT with information from the mempool, the UTXO set, and the provided descriptors
+// Update PSBT with information from the mempool, the UTXO set, the txindex, and the provided descriptors
 PartiallySignedTransaction ProcessPSBT(const std::string& psbt_string, const std::any& context, const HidingSigningProvider& provider)
 {
     // Unserialize the transactions
@@ -179,50 +179,78 @@ PartiallySignedTransaction ProcessPSBT(const std::string& psbt_string, const std
         throw JSONRPCError(RPC_DESERIALIZATION_ERROR, strprintf("TX decode failed %s", error));
     }
 
-    // Fetch previous transactions (inputs):
-    CCoinsView viewDummy;
-    CCoinsViewCache view(&viewDummy);
-    {
-        NodeContext& node = EnsureAnyNodeContext(context);
-        const CTxMemPool& mempool = EnsureMemPool(node);
-        ChainstateManager& chainman = EnsureChainman(node);
-        LOCK2(cs_main, mempool.cs);
-        CCoinsViewCache &viewChain = chainman.ActiveChainstate().CoinsTip();
-        CCoinsViewMemPool viewMempool(&viewChain, mempool);
-        view.SetBackend(viewMempool); // temporarily switch cache backend to db+mempool view
+    if (g_txindex) g_txindex->BlockUntilSyncedToCurrentChain();
+    const NodeContext& node = EnsureAnyNodeContext(context);
 
-        for (const CTxIn& txin : psbtx.tx->vin) {
-            view.AccessCoin(txin.prevout); // Load entries from viewChain into view; can fail.
+    // If we can't find the corresponding full transaction for all of our inputs,
+    // this will be used to find just the utxos for the segwit inputs for which
+    // the full transaction isn't found
+    std::map<COutPoint, Coin> coins;
+
+    // Fetch previous transactions:
+    // First, look in the txindex and the mempool
+    for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
+        PSBTInput& psbt_input = psbtx.inputs.at(i);
+        const CTxIn& tx_in = psbtx.tx->vin.at(i);
+
+        // The `non_witness_utxo` is the whole previous transaction
+        if (psbt_input.non_witness_utxo) continue;
+
+        CTransactionRef tx;
+
+        // Look in the txindex
+        if (g_txindex) {
+            uint256 block_hash;
+            g_txindex->FindTx(tx_in.prevout.hash, block_hash, tx);
+        }
+        // If we still don't have it look in the mempool
+        if (!tx) {
+            tx = node.mempool->get(tx_in.prevout.hash);
+        }
+        if (tx) {
+            psbt_input.non_witness_utxo = tx;
+        } else {
+            coins[tx_in.prevout]; // Create empty map entry keyed by prevout
         }
-
-        view.SetBackend(viewDummy); // switch back to avoid locking mempool for too long
     }
 
-    // Fill the inputs
-    const PrecomputedTransactionData txdata = PrecomputePSBTData(psbtx);
-    for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
-        PSBTInput& input = psbtx.inputs.at(i);
+    // If we still haven't found all of the inputs, look for the missing ones in the utxo set
+    if (!coins.empty()) {
+        FindCoins(node, coins);
+        for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
+            PSBTInput& input = psbtx.inputs.at(i);
 
-        if (input.non_witness_utxo || !input.witness_utxo.IsNull()) {
-            continue;
+            // If there are still missing utxos, add them if they were found in the utxo set
+            if (!input.non_witness_utxo) {
+                const CTxIn& tx_in = psbtx.tx->vin.at(i);
+                const Coin& coin = coins.at(tx_in.prevout);
+                if (!coin.out.IsNull() && IsSegWitOutput(provider, coin.out.scriptPubKey)) {
+                    input.witness_utxo = coin.out;
+                }
+            }
         }
+    }
 
-        const Coin& coin = view.AccessCoin(psbtx.tx->vin[i].prevout);
+    const PrecomputedTransactionData& txdata = PrecomputePSBTData(psbtx);
 
-        if (IsSegWitOutput(provider, coin.out.scriptPubKey)) {
-            input.witness_utxo = coin.out;
+    for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
+        if (PSBTInputSigned(psbtx.inputs.at(i))) {
+            continue;
         }
 
         // Update script/keypath information using descriptor data.
         // Note that SignPSBTInput does a lot more than just constructing ECDSA signatures
         // we don't actually care about those here, in fact.
-        SignPSBTInput(provider, psbtx, i, &txdata, /*sighash=*/1);
+        SignPSBTInput(provider, psbtx, /*index=*/i, &txdata, /*sighash=*/1);
     }
 
     // Update script/keypath information using descriptor data.
     for (unsigned int i = 0; i < psbtx.tx->vout.size(); ++i) {
         UpdatePSBTOutput(provider, psbtx, i);
     }
+
+    RemoveUnnecessaryTransactions(psbtx, /*sighash_type=*/1);
+
     return psbtx;
 }
 
@@ -1632,7 +1660,7 @@ static RPCHelpMan converttopsbt()
 static RPCHelpMan utxoupdatepsbt()
 {
     return RPCHelpMan{"utxoupdatepsbt",
-            "\nUpdates all segwit inputs and outputs in a PSBT with data from output descriptors, the UTXO set or the mempool.\n",
+            "\nUpdates all segwit inputs and outputs in a PSBT with data from output descriptors, the UTXO set, txindex, or the mempool.\n",
             {
                 {"psbt", RPCArg::Type::STR, RPCArg::Optional::NO, "A base64 string of a PSBT"},
                 {"descriptors", RPCArg::Type::ARR, RPCArg::Optional::OMITTED_NAMED_ARG, "An array of either strings or objects", {