From 26fe9b990995f9cb5eee21d40b4daaad19f7181f Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Sat, 16 Feb 2019 14:59:16 -0800
Subject: 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.
---
 src/rpc/rawtransaction.cpp | 38 +++++++++++++++++++++++++++++++++-----
 1 file changed, 33 insertions(+), 5 deletions(-)

(limited to 'src/rpc/rawtransaction.cpp')

diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index 7675ad0109..eabf89bdba 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/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);
-- 
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