Merge bitcoin/bitcoin#22513: rpc: Allow walletprocesspsbt to sign without finalizing

a99ed8986554fa1ecc854e43ea373d957e598db8 psbt: sign without finalizing (Andrew Chow)

Pull request description:

  It can be useful to sign an input with `walletprocesspsbt` but not finalize that input if it is complete. This PR adds another option to `walletprocesspsbt` to be able to do that. We will still finalize by default.

  This does not materially change the PSBT workflow since `finalizepsbt` needs to be called in order to extract the tx for broadcast.

ACKs for top commit:
  meshcollider:
    utACK a99ed8986554fa1ecc854e43ea373d957e598db8
  Sjors:
    utACK a99ed89

Tree-SHA512: c88e5d3222109c5f4e763b1b9d97ce4655f68f2985a4509caab2d4e7f5bac5047328fd69696e82a330f5c5a333e0312568ae293515689b77a4747ca2f17caca6

11 files changed, 32 insertions, 20 deletions

diff --git a/src/psbt.cpp b/src/psbt.cpp
index b3d8e052bc..6585766807 100644
--- a/src/psbt.cpp
+++ b/src/psbt.cpp
@@ -247,7 +247,7 @@ PrecomputedTransactionData PrecomputePSBTData(const PartiallySignedTransaction&
     return txdata;
 }
 
-bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index, const PrecomputedTransactionData* txdata, int sighash, SignatureData* out_sigdata)
+bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index, const PrecomputedTransactionData* txdata, int sighash,  SignatureData* out_sigdata, bool finalize)
 {
     PSBTInput& input = psbt.inputs.at(index);
     const CMutableTransaction& tx = *psbt.tx;
@@ -295,6 +295,10 @@ bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction&
     }
     // Verify that a witness signature was produced in case one was required.
     if (require_witness_sig && !sigdata.witness) return false;
+
+    // If we are not finalizing, set sigdata.complete to false to not set the scriptWitness
+    if (!finalize && sigdata.complete) sigdata.complete = false;
+
     input.FromSignatureData(sigdata);
 
     // If we have a witness signature, put a witness UTXO.
@@ -324,7 +328,7 @@ bool FinalizePSBT(PartiallySignedTransaction& psbtx)
     bool complete = true;
     const PrecomputedTransactionData txdata = PrecomputePSBTData(psbtx);
     for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
-        complete &= SignPSBTInput(DUMMY_SIGNING_PROVIDER, psbtx, i, &txdata, SIGHASH_ALL);
+        complete &= SignPSBTInput(DUMMY_SIGNING_PROVIDER, psbtx, i, &txdata, SIGHASH_ALL, nullptr, true);
     }
 
     return complete;
diff --git a/src/psbt.h b/src/psbt.h
index f6b82b43de..7808a247c0 100644
--- a/src/psbt.h
+++ b/src/psbt.h
@@ -578,7 +578,7 @@ bool PSBTInputSigned(const PSBTInput& input);
  * txdata should be the output of PrecomputePSBTData (which can be shared across
  * multiple SignPSBTInput calls). If it is nullptr, a dummy signature will be created.
  **/
-bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index, const PrecomputedTransactionData* txdata, int sighash = SIGHASH_ALL, SignatureData* out_sigdata = nullptr);
+bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index, const PrecomputedTransactionData* txdata, int sighash = SIGHASH_ALL, SignatureData* out_sigdata = nullptr, bool finalize = true);
 
 /** Counts the unsigned inputs of a PSBT. */
 size_t CountPSBTUnsignedInputs(const PartiallySignedTransaction& psbt);
diff --git a/src/rpc/client.cpp b/src/rpc/client.cpp
index 93e49cb9a8..90fbd823a4 100644
--- a/src/rpc/client.cpp
+++ b/src/rpc/client.cpp
@@ -115,6 +115,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "walletcreatefundedpsbt", 4, "bip32derivs" },
     { "walletprocesspsbt", 1, "sign" },
     { "walletprocesspsbt", 3, "bip32derivs" },
+    { "walletprocesspsbt", 4, "finalize" },
     { "createpsbt", 0, "inputs" },
     { "createpsbt", 1, "outputs" },
     { "createpsbt", 2, "locktime" },
diff --git a/src/wallet/external_signer_scriptpubkeyman.cpp b/src/wallet/external_signer_scriptpubkeyman.cpp
index efef1ec754..6a73efb472 100644
--- a/src/wallet/external_signer_scriptpubkeyman.cpp
+++ b/src/wallet/external_signer_scriptpubkeyman.cpp
@@ -60,10 +60,10 @@ bool ExternalSignerScriptPubKeyMan::DisplayAddress(const CScript scriptPubKey, c
 }
 
 // If sign is true, transaction must previously have been filled
-TransactionError ExternalSignerScriptPubKeyMan::FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type, bool sign, bool bip32derivs, int* n_signed) const
+TransactionError ExternalSignerScriptPubKeyMan::FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type, bool sign, bool bip32derivs, int* n_signed, bool finalize) const
 {
     if (!sign) {
-        return DescriptorScriptPubKeyMan::FillPSBT(psbt, txdata, sighash_type, false, bip32derivs, n_signed);
+        return DescriptorScriptPubKeyMan::FillPSBT(psbt, txdata, sighash_type, false, bip32derivs, n_signed, finalize);
     }
 
     // Already complete if every input is now signed
@@ -79,6 +79,6 @@ TransactionError ExternalSignerScriptPubKeyMan::FillPSBT(PartiallySignedTransact
         tfm::format(std::cerr, "Failed to sign: %s\n", strFailReason);
         return TransactionError::EXTERNAL_SIGNER_FAILED;
     }
-    FinalizePSBT(psbt); // This won't work in a multisig setup
+    if (finalize) FinalizePSBT(psbt); // This won't work in a multisig setup
     return TransactionError::OK;
 }
diff --git a/src/wallet/external_signer_scriptpubkeyman.h b/src/wallet/external_signer_scriptpubkeyman.h
index 61df3d0015..53d65d9e46 100644
--- a/src/wallet/external_signer_scriptpubkeyman.h
+++ b/src/wallet/external_signer_scriptpubkeyman.h
@@ -28,6 +28,6 @@ class ExternalSignerScriptPubKeyMan : public DescriptorScriptPubKeyMan
 
   bool DisplayAddress(const CScript scriptPubKey, const ExternalSigner &signer) const;
 
-  TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = 1 /* SIGHASH_ALL */, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr) const override;
+  TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = 1 /* SIGHASH_ALL */, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr, bool finalize = true) const override;
 };
 #endif // BITCOIN_WALLET_EXTERNAL_SIGNER_SCRIPTPUBKEYMAN_H
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index c895d5af8c..bb5b388791 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -4551,6 +4551,7 @@ static RPCHelpMan walletprocesspsbt()
             "       \"NONE|ANYONECANPAY\"\n"
             "       \"SINGLE|ANYONECANPAY\""},
                     {"bip32derivs", RPCArg::Type::BOOL, RPCArg::Default{true}, "Include BIP 32 derivation paths for public keys if we know them"},
+                    {"finalize", RPCArg::Type::BOOL, RPCArg::Default{true}, "Also finalize inputs if possible"},
                 },
                 RPCResult{
                     RPCResult::Type::OBJ, "", "",
@@ -4572,7 +4573,7 @@ static RPCHelpMan walletprocesspsbt()
     // the user could have gotten from another RPC command prior to now
     wallet.BlockUntilSyncedToCurrentChain();
 
-    RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VBOOL, UniValue::VSTR});
+    RPCTypeCheck(request.params, {UniValue::VSTR});
 
     // Unserialize the transaction
     PartiallySignedTransaction psbtx;
@@ -4587,11 +4588,12 @@ static RPCHelpMan walletprocesspsbt()
     // Fill transaction with our data and also sign
     bool sign = request.params[1].isNull() ? true : request.params[1].get_bool();
     bool bip32derivs = request.params[3].isNull() ? true : request.params[3].get_bool();
+    bool finalize = request.params[4].isNull() ? true : request.params[4].get_bool();
     bool complete = true;
 
     if (sign) EnsureWalletIsUnlocked(*pwallet);
 
-    const TransactionError err{wallet.FillPSBT(psbtx, complete, nHashType, sign, bip32derivs)};
+    const TransactionError err{wallet.FillPSBT(psbtx, complete, nHashType, sign, bip32derivs, nullptr, finalize)};
     if (err != TransactionError::OK) {
         throw JSONRPCTransactionError(err);
     }
diff --git a/src/wallet/scriptpubkeyman.cpp b/src/wallet/scriptpubkeyman.cpp
index 0b4632bd99..a82eaa4879 100644
--- a/src/wallet/scriptpubkeyman.cpp
+++ b/src/wallet/scriptpubkeyman.cpp
@@ -610,7 +610,7 @@ SigningResult LegacyScriptPubKeyMan::SignMessage(const std::string& message, con
     return SigningResult::SIGNING_FAILED;
 }
 
-TransactionError LegacyScriptPubKeyMan::FillPSBT(PartiallySignedTransaction& psbtx, const PrecomputedTransactionData& txdata, int sighash_type, bool sign, bool bip32derivs, int* n_signed) const
+TransactionError LegacyScriptPubKeyMan::FillPSBT(PartiallySignedTransaction& psbtx, const PrecomputedTransactionData& txdata, int sighash_type, bool sign, bool bip32derivs, int* n_signed, bool finalize) const
 {
     if (n_signed) {
         *n_signed = 0;
@@ -639,7 +639,7 @@ TransactionError LegacyScriptPubKeyMan::FillPSBT(PartiallySignedTransaction& psb
         }
         SignatureData sigdata;
         input.FillSignatureData(sigdata);
-        SignPSBTInput(HidingSigningProvider(this, !sign, !bip32derivs), psbtx, i, &txdata, sighash_type);
+        SignPSBTInput(HidingSigningProvider(this, !sign, !bip32derivs), psbtx, i, &txdata, sighash_type, nullptr, finalize);
 
         bool signed_one = PSBTInputSigned(input);
         if (n_signed && (signed_one || !sign)) {
@@ -2074,7 +2074,7 @@ SigningResult DescriptorScriptPubKeyMan::SignMessage(const std::string& message,
     return SigningResult::OK;
 }
 
-TransactionError DescriptorScriptPubKeyMan::FillPSBT(PartiallySignedTransaction& psbtx, const PrecomputedTransactionData& txdata, int sighash_type, bool sign, bool bip32derivs, int* n_signed) const
+TransactionError DescriptorScriptPubKeyMan::FillPSBT(PartiallySignedTransaction& psbtx, const PrecomputedTransactionData& txdata, int sighash_type, bool sign, bool bip32derivs, int* n_signed, bool finalize) const
 {
     if (n_signed) {
         *n_signed = 0;
@@ -2124,7 +2124,7 @@ TransactionError DescriptorScriptPubKeyMan::FillPSBT(PartiallySignedTransaction&
             }
         }
 
-        SignPSBTInput(HidingSigningProvider(keys.get(), !sign, !bip32derivs), psbtx, i, &txdata, sighash_type);
+        SignPSBTInput(HidingSigningProvider(keys.get(), !sign, !bip32derivs), psbtx, i, &txdata, sighash_type, nullptr, finalize);
 
         bool signed_one = PSBTInputSigned(input);
         if (n_signed && (signed_one || !sign)) {
diff --git a/src/wallet/scriptpubkeyman.h b/src/wallet/scriptpubkeyman.h
index 2d447f1d67..9d2304a542 100644
--- a/src/wallet/scriptpubkeyman.h
+++ b/src/wallet/scriptpubkeyman.h
@@ -224,7 +224,7 @@ public:
     /** Sign a message with the given script */
     virtual SigningResult SignMessage(const std::string& message, const PKHash& pkhash, std::string& str_sig) const { return SigningResult::SIGNING_FAILED; };
     /** Adds script and derivation path information to a PSBT, and optionally signs it. */
-    virtual TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = 1 /* SIGHASH_ALL */, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr) const { return TransactionError::INVALID_PSBT; }
+    virtual TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = 1 /* SIGHASH_ALL */, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr, bool finalize = true) const { return TransactionError::INVALID_PSBT; }
 
     virtual uint256 GetID() const { return uint256(); }
 
@@ -388,7 +388,7 @@ public:
 
     bool SignTransaction(CMutableTransaction& tx, const std::map<COutPoint, Coin>& coins, int sighash, std::map<int, bilingual_str>& input_errors) const override;
     SigningResult SignMessage(const std::string& message, const PKHash& pkhash, std::string& str_sig) const override;
-    TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = 1 /* SIGHASH_ALL */, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr) const override;
+    TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = 1 /* SIGHASH_ALL */, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr, bool finalize = true) const override;
 
     uint256 GetID() const override;
 
@@ -593,7 +593,7 @@ public:
 
     bool SignTransaction(CMutableTransaction& tx, const std::map<COutPoint, Coin>& coins, int sighash, std::map<int, bilingual_str>& input_errors) const override;
     SigningResult SignMessage(const std::string& message, const PKHash& pkhash, std::string& str_sig) const override;
-    TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = 1 /* SIGHASH_ALL */, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr) const override;
+    TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = 1 /* SIGHASH_ALL */, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr, bool finalize = true) const override;
 
     uint256 GetID() const override;
 
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 2382ac268d..e4c3822305 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -1849,7 +1849,7 @@ bool CWallet::SignTransaction(CMutableTransaction& tx, const std::map<COutPoint,
     return false;
 }
 
-TransactionError CWallet::FillPSBT(PartiallySignedTransaction& psbtx, bool& complete, int sighash_type, bool sign, bool bip32derivs, size_t * n_signed) const
+TransactionError CWallet::FillPSBT(PartiallySignedTransaction& psbtx, bool& complete, int sighash_type, bool sign, bool bip32derivs, size_t * n_signed, bool finalize) const
 {
     if (n_signed) {
         *n_signed = 0;
@@ -1881,7 +1881,7 @@ TransactionError CWallet::FillPSBT(PartiallySignedTransaction& psbtx, bool& comp
     // Fill in information from ScriptPubKeyMans
     for (ScriptPubKeyMan* spk_man : GetAllScriptPubKeyMans()) {
         int n_signed_this_spkm = 0;
-        TransactionError res = spk_man->FillPSBT(psbtx, txdata, sighash_type, sign, bip32derivs, &n_signed_this_spkm);
+        TransactionError res = spk_man->FillPSBT(psbtx, txdata, sighash_type, sign, bip32derivs, &n_signed_this_spkm, finalize);
         if (res != TransactionError::OK) {
             return res;
         }
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 3390d632e7..e294358609 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -555,6 +555,8 @@ public:
      * @param[in]  sighash_type the sighash type to use when signing (if PSBT does not specify)
      * @param[in]  sign whether to sign or not
      * @param[in]  bip32derivs whether to fill in bip32 derivation information if available
+     * @param[out] n_signed the number of inputs signed by this wallet
+     * @param[in] finalize whether to create the final scriptSig or scriptWitness if possible
      * return error
      */
     TransactionError FillPSBT(PartiallySignedTransaction& psbtx,
@@ -562,7 +564,8 @@ public:
                   int sighash_type = 1 /* SIGHASH_ALL */,
                   bool sign = true,
                   bool bip32derivs = true,
-                  size_t* n_signed = nullptr) const;
+                  size_t* n_signed = nullptr,
+                  bool finalize = true) const;
 
     /**
      * Submit the transaction to the node's mempool and then relay to peers.
diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index 4ac4f27d8a..a8034849cc 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -120,7 +120,9 @@ class PSBTTest(BitcoinTestFramework):
         self.nodes[0].walletpassphrase(passphrase="password", timeout=1000000)
 
         # Sign the transaction and send
-        signed_tx = self.nodes[0].walletprocesspsbt(psbtx)['psbt']
+        signed_tx = self.nodes[0].walletprocesspsbt(psbt=psbtx, finalize=False)['psbt']
+        finalized_tx = self.nodes[0].walletprocesspsbt(psbt=psbtx, finalize=True)['psbt']
+        assert signed_tx != finalized_tx
         final_tx = self.nodes[0].finalizepsbt(signed_tx)['hex']
         self.nodes[0].sendrawtransaction(final_tx)