Add support for descriptors to utxoupdatepsbt

This adds a descriptors argument to the utxoupdatepsbt RPC. This means:
* Input and output scripts and keys will be filled in when known
* P2SH-witness outputs will be filled in from the UTXO set when a descriptor
  is provided to show they're segwit outputs.

Author: sipa

src/rpc/rawtransaction.cpp

@@ -1490,12 +1490,19 @@ UniValue converttopsbt(const JSONRPCRequest& request)
 
 UniValue utxoupdatepsbt(const JSONRPCRequest& request)
 {
-    if (request.fHelp || request.params.size() != 1) {
+    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2) {
         throw std::runtime_error(
             RPCHelpMan{"utxoupdatepsbt",
-            "\nUpdates a PSBT with witness UTXOs retrieved from the UTXO set or the mempool.\n",
+            "\nUpdates all segwit inputs and outputs in a PSBT with data from output descriptors, the UTXO set or the mempool.\n",
             {
-                {"psbt", RPCArg::Type::STR, RPCArg::Optional::NO, "A base64 string of a PSBT"}
+                {"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", {
+                    {"", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "An output descriptor"},
+                    {"", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED, "An object with an output descriptor and extra information", {
+                         {"desc", RPCArg::Type::STR, RPCArg::Optional::NO, "An output descriptor"},
+                         {"range", RPCArg::Type::RANGE, "1000", "Up to what index HD chains should be explored (either end or [begin,end])"},
+                    }},
+                }},
             },
             RPCResult {
                 "  \"psbt\"          (string) The base64-encoded partially signed transaction with inputs updated\n"
@@ -1505,7 +1512,7 @@ UniValue utxoupdatepsbt(const JSONRPCRequest& request)
             }}.ToString());
     }
 
-    RPCTypeCheck(request.params, {UniValue::VSTR}, true);
+    RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VARR}, true);
 
     // Unserialize the transactions
     PartiallySignedTransaction psbtx;
@@ -1514,6 +1521,17 @@ UniValue utxoupdatepsbt(const JSONRPCRequest& request)
         throw JSONRPCError(RPC_DESERIALIZATION_ERROR, strprintf("TX decode failed %s", error));
     }
 
+    // Parse descriptors, if any.
+    FlatSigningProvider provider;
+    if (!request.params[1].isNull()) {
+        auto descs = request.params[1].get_array();
+        for (size_t i = 0; i < descs.size(); ++i) {
+            EvalDescriptorStringOrObject(descs[i], provider);
+        }
+    }
+    // We don't actually need private keys further on; hide them as a precaution.
+    HidingSigningProvider public_provider(&provider, /* nosign */ true, /* nobip32derivs */ false);
+
     // Fetch previous transactions (inputs):
     CCoinsView viewDummy;
     CCoinsViewCache view(&viewDummy);
@@ -1540,9 +1558,19 @@ UniValue utxoupdatepsbt(const JSONRPCRequest& request)
 
         const Coin& coin = view.AccessCoin(psbtx.tx->vin[i].prevout);
 
-        if (IsSegWitOutput(DUMMY_SIGNING_PROVIDER, coin.out.scriptPubKey)) {
+        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, /* sighash_type */ 1);
+    }
+
+    // Update script/keypath information using descriptor data.
+    for (unsigned int i = 0; i < psbtx.tx->vout.size(); ++i) {
+        UpdatePSBTOutput(public_provider, psbtx, i);
     }
 
     CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);

test/functional/rpc_psbt.py

@@ -314,18 +314,32 @@ def run_test(self):
         vout3 = find_output(self.nodes[0], txid3, 11)
         self.sync_all()
 
-        # Update a PSBT with UTXOs from the node
-        # Bech32 inputs should be filled with witness UTXO. Other inputs should not be filled because they are non-witness
+        def test_psbt_input_keys(psbt_input, keys):
+            """Check that the psbt input has only the expected keys."""
+            assert_equal(set(keys), set(psbt_input.keys()))
+
+        # Create a PSBT. None of the inputs are filled initially
         psbt = self.nodes[1].createpsbt([{"txid":txid1, "vout":vout1},{"txid":txid2, "vout":vout2},{"txid":txid3, "vout":vout3}], {self.nodes[0].getnewaddress():32.999})
         decoded = self.nodes[1].decodepsbt(psbt)
-        assert "witness_utxo" not in decoded['inputs'][0] and "non_witness_utxo" not in decoded['inputs'][0]
-        assert "witness_utxo" not in decoded['inputs'][1] and "non_witness_utxo" not in decoded['inputs'][1]
-        assert "witness_utxo" not in decoded['inputs'][2] and "non_witness_utxo" not in decoded['inputs'][2]
+        test_psbt_input_keys(decoded['inputs'][0], [])
+        test_psbt_input_keys(decoded['inputs'][1], [])
+        test_psbt_input_keys(decoded['inputs'][2], [])
+
+        # Update a PSBT with UTXOs from the node
+        # Bech32 inputs should be filled with witness UTXO. Other inputs should not be filled because they are non-witness
         updated = self.nodes[1].utxoupdatepsbt(psbt)
         decoded = self.nodes[1].decodepsbt(updated)
-        assert "witness_utxo" in decoded['inputs'][0] and "non_witness_utxo" not in decoded['inputs'][0]
-        assert "witness_utxo" not in decoded['inputs'][1] and "non_witness_utxo" not in decoded['inputs'][1]
-        assert "witness_utxo" not in decoded['inputs'][2] and "non_witness_utxo" not in decoded['inputs'][2]
+        test_psbt_input_keys(decoded['inputs'][0], ['witness_utxo'])
+        test_psbt_input_keys(decoded['inputs'][1], [])
+        test_psbt_input_keys(decoded['inputs'][2], [])
+
+        # Try again, now while providing descriptors, making P2SH-segwit work, and causing bip32_derivs and redeem_script to be filled in
+        descs = [self.nodes[1].getaddressinfo(addr)['desc'] for addr in [addr1,addr2,addr3]]
+        updated = self.nodes[1].utxoupdatepsbt(psbt, descs)
+        decoded = self.nodes[1].decodepsbt(updated)
+        test_psbt_input_keys(decoded['inputs'][0], ['witness_utxo', 'bip32_derivs'])
+        test_psbt_input_keys(decoded['inputs'][1], [])
+        test_psbt_input_keys(decoded['inputs'][2], ['witness_utxo', 'bip32_derivs', 'redeem_script'])
 
         # Two PSBTs with a common input should not be joinable
         psbt1 = self.nodes[1].createpsbt([{"txid":txid1, "vout":vout1}], {self.nodes[0].getnewaddress():Decimal('10.999')})