Merge #15427: Add support for descriptors to utxoupdatepsbt

26fe9b990995f9cb5eee21d40b4daaad19f7181f Add support for descriptors to utxoupdatepsbt (Pieter Wuille)
3135c1a2d2e2fb31bc362c848bd2456d576e408b Abstract out UpdatePSBTOutput from FillPSBT (Pieter Wuille)
fb90ec3c33e824f5abb6a68452c683d6ce8b3e4a Abstract out EvalDescriptorStringOrObject from scantxoutset (Pieter Wuille)
eaf4f887348a08c620732125ad4430e1a133d434 Abstract out IsSegWitOutput from utxoupdatepsbt (Pieter Wuille)

Pull request description:

  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 inputs will be filled in from the UTXO set when a descriptor is provided that shows they're spending segwit outputs.

  This also moves some (newly) shared code to separate functions: `UpdatePSBTOutput` (an analogue to `SignPSBTInput`), `IsSegWitOutput`, and `EvalDescriptorStringOrObject` (implementing the string or object notation parsing used in `scantxoutset`).

ACKs for top commit:
  jnewbery:
    utACK 26fe9b990995f9cb5eee21d40b4daaad19f7181f
  laanwj:
    utACK 26fe9b990995f9cb5eee21d40b4daaad19f7181f (will hold merging until response to promag's comments)
  promag:
    ACK 26fe9b9, checked refactors and tests look comprehensive. Still missing a release note but can be added later.

Tree-SHA512: 1d833b7351b59d6c5ded6da399ff371a8a2a6ad04c0a8f90e6e46105dc737fa6f2740b1e5340280d59e01f42896c40b720c042f44417e38dfbee6477b894b245

4 files changed, 81 insertions, 41 deletions

diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 50c4589d9f..9f3748cb65 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -2247,41 +2247,12 @@ UniValue scantxoutset(const JSONRPCRequest& request)
 
         // loop through the scan objects
         for (const UniValue& scanobject : request.params[1].get_array().getValues()) {
-            std::string desc_str;
-            std::pair<int64_t, int64_t> range = {0, 1000};
-            if (scanobject.isStr()) {
-                desc_str = scanobject.get_str();
-            } else if (scanobject.isObject()) {
-                UniValue desc_uni = find_value(scanobject, "desc");
-                if (desc_uni.isNull()) throw JSONRPCError(RPC_INVALID_PARAMETER, "Descriptor needs to be provided in scan object");
-                desc_str = desc_uni.get_str();
-                UniValue range_uni = find_value(scanobject, "range");
-                if (!range_uni.isNull()) {
-                    range = ParseDescriptorRange(range_uni);
-                }
-            } else {
-                throw JSONRPCError(RPC_INVALID_PARAMETER, "Scan object needs to be either a string or an object");
-            }
-
             FlatSigningProvider provider;
-            auto desc = Parse(desc_str, provider);
-            if (!desc) {
-                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Invalid descriptor '%s'", desc_str));
-            }
-            if (!desc->IsRange()) {
-                range.first = 0;
-                range.second = 0;
-            }
-            for (int i = range.first; i <= range.second; ++i) {
-                std::vector<CScript> scripts;
-                if (!desc->Expand(i, provider, scripts, provider)) {
-                    throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Cannot derive script without private keys: '%s'", desc_str));
-                }
-                for (const auto& script : scripts) {
-                    std::string inferred = InferDescriptor(script, provider)->ToString();
-                    needles.emplace(script);
-                    descriptors.emplace(std::move(script), std::move(inferred));
-                }
+            auto scripts = EvalDescriptorStringOrObject(scanobject, provider);
+            for (const auto& script : scripts) {
+                std::string inferred = InferDescriptor(script, provider)->ToString();
+                needles.emplace(script);
+                descriptors.emplace(std::move(script), std::move(inferred));
             }
         }
 
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index 9da24afe79..966ff3fedc 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -1495,12 +1495,19 @@ 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"
@@ -1510,7 +1517,7 @@ 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;
@@ -1519,6 +1526,17 @@ 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);
@@ -1545,11 +1563,19 @@ UniValue utxoupdatepsbt(const JSONRPCRequest& request)
 
         const Coin& coin = view.AccessCoin(psbtx.tx->vin[i].prevout);
 
-        std::vector<std::vector<unsigned char>> solutions_data;
-        txnouttype which_type = Solver(coin.out.scriptPubKey, solutions_data);
-        if (which_type == TX_WITNESS_V0_SCRIPTHASH || which_type == TX_WITNESS_V0_KEYHASH || which_type == TX_WITNESS_UNKNOWN) {
+        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);
diff --git a/src/rpc/util.cpp b/src/rpc/util.cpp
index 4642cf16b1..67ccb225b5 100644
--- a/src/rpc/util.cpp
+++ b/src/rpc/util.cpp
@@ -6,6 +6,7 @@
 #include <keystore.h>
 #include <outputtype.h>
 #include <rpc/util.h>
+#include <script/descriptor.h>
 #include <tinyformat.h>
 #include <util/strencodings.h>
 
@@ -697,3 +698,40 @@ std::pair<int64_t, int64_t> ParseDescriptorRange(const UniValue& value)
     }
     return {low, high};
 }
+
+std::vector<CScript> EvalDescriptorStringOrObject(const UniValue& scanobject, FlatSigningProvider& provider)
+{
+    std::string desc_str;
+    std::pair<int64_t, int64_t> range = {0, 1000};
+    if (scanobject.isStr()) {
+        desc_str = scanobject.get_str();
+    } else if (scanobject.isObject()) {
+        UniValue desc_uni = find_value(scanobject, "desc");
+        if (desc_uni.isNull()) throw JSONRPCError(RPC_INVALID_PARAMETER, "Descriptor needs to be provided in scan object");
+        desc_str = desc_uni.get_str();
+        UniValue range_uni = find_value(scanobject, "range");
+        if (!range_uni.isNull()) {
+            range = ParseDescriptorRange(range_uni);
+        }
+    } else {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, "Scan object needs to be either a string or an object");
+    }
+
+    auto desc = Parse(desc_str, provider);
+    if (!desc) {
+        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Invalid descriptor '%s'", desc_str));
+    }
+    if (!desc->IsRange()) {
+        range.first = 0;
+        range.second = 0;
+    }
+    std::vector<CScript> ret;
+    for (int i = range.first; i <= range.second; ++i) {
+        std::vector<CScript> scripts;
+        if (!desc->Expand(i, provider, scripts, provider)) {
+            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Cannot derive script without private keys: '%s'", desc_str));
+        }
+        std::move(scripts.begin(), scripts.end(), std::back_inserter(ret));
+    }
+    return ret;
+}
diff --git a/src/rpc/util.h b/src/rpc/util.h
index 0eb2fef5c3..8762281d73 100644
--- a/src/rpc/util.h
+++ b/src/rpc/util.h
@@ -9,6 +9,8 @@
 #include <outputtype.h>
 #include <pubkey.h>
 #include <rpc/protocol.h>
+#include <script/script.h>
+#include <script/sign.h>
 #include <script/standard.h>
 #include <univalue.h>
 
@@ -84,6 +86,9 @@ UniValue JSONRPCTransactionError(TransactionError terr, const std::string& err_s
 //! Parse a JSON range specified as int64, or [int64, int64]
 std::pair<int64_t, int64_t> ParseDescriptorRange(const UniValue& value);
 
+/** Evaluate a descriptor given as a string, or as a {"desc":...,"range":...} object, with default range of 1000. */
+std::vector<CScript> EvalDescriptorStringOrObject(const UniValue& scanobject, FlatSigningProvider& provider);
+
 struct RPCArg {
     enum class Type {
         OBJ,