rpc: extract psbt updating logic into ProcessPSBT

This function is called from utxoupdatepsbt and will be modified
in a following commit to allow for updating inputs with the
`non_witness_utxo` as well.

Author: ishaanam

src/rpc/rawtransaction.cpp

@@ -169,6 +169,63 @@ static std::vector<RPCArg> CreateTxDoc()
     };
 }
 
+// Update PSBT with information from the mempool, the UTXO set, and the provided descriptors
+PartiallySignedTransaction ProcessPSBT(const std::string& psbt_string, const std::any& context, const HidingSigningProvider& provider)
+{
+    // Unserialize the transactions
+    PartiallySignedTransaction psbtx;
+    std::string error;
+    if (!DecodeBase64PSBT(psbtx, psbt_string, error)) {
+        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
+
+        for (const CTxIn& txin : psbtx.tx->vin) {
+            view.AccessCoin(txin.prevout); // Load entries from viewChain into view; can fail.
+        }
+
+        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 (input.non_witness_utxo || !input.witness_utxo.IsNull()) {
+            continue;
+        }
+
+        const Coin& coin = view.AccessCoin(psbtx.tx->vin[i].prevout);
+
+        if (IsSegWitOutput(provider, coin.out.scriptPubKey)) {
+            input.witness_utxo = coin.out;
+        }
+
+        // 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);
+    }
+
+    // Update script/keypath information using descriptor data.
+    for (unsigned int i = 0; i < psbtx.tx->vout.size(); ++i) {
+        UpdatePSBTOutput(provider, psbtx, i);
+    }
+    return psbtx;
+}
+
 static RPCHelpMan getrawtransaction()
 {
     return RPCHelpMan{
@@ -1594,13 +1651,6 @@ static RPCHelpMan utxoupdatepsbt()
             },
         [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
 {
-    // Unserialize the transactions
-    PartiallySignedTransaction psbtx;
-    std::string error;
-    if (!DecodeBase64PSBT(psbtx, request.params[0].get_str(), error)) {
-        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, strprintf("TX decode failed %s", error));
-    }
-
     // Parse descriptors, if any.
     FlatSigningProvider provider;
     if (!request.params[1].isNull()) {
@@ -1609,53 +1659,12 @@ static RPCHelpMan utxoupdatepsbt()
             EvalDescriptorStringOrObject(descs[i], provider);
         }
     }
-    // We don't actually need private keys further on; hide them as a precaution.
-    HidingSigningProvider public_provider(&provider, /*hide_secret=*/true, /*hide_origin=*/false);
-
-    // Fetch previous transactions (inputs):
-    CCoinsView viewDummy;
-    CCoinsViewCache view(&viewDummy);
-    {
-        NodeContext& node = EnsureAnyNodeContext(request.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
-
-        for (const CTxIn& txin : psbtx.tx->vin) {
-            view.AccessCoin(txin.prevout); // Load entries from viewChain into view; can fail.
-        }
-
-        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 (input.non_witness_utxo || !input.witness_utxo.IsNull()) {
-            continue;
-        }
-
-        const Coin& coin = view.AccessCoin(psbtx.tx->vin[i].prevout);
-
-        if (IsSegWitOutput(provider, coin.out.scriptPubKey)) {
-            input.witness_utxo = coin.out;
-        }
-
-        // 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(public_provider, psbtx, i, &txdata, /*sighash=*/1);
-    }
 
-    // Update script/keypath information using descriptor data.
-    for (unsigned int i = 0; i < psbtx.tx->vout.size(); ++i) {
-        UpdatePSBTOutput(public_provider, psbtx, i);
-    }
+    // We don't actually need private keys further on; hide them as a precaution.
+    const PartiallySignedTransaction& psbtx = ProcessPSBT(
+        request.params[0].get_str(),
+        request.context,
+        HidingSigningProvider(&provider, /*hide_secret=*/true, /*hide_origin=*/false));
 
     CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
     ssTx << psbtx;