Merge bitcoin/bitcoin#22514: psbt: Actually use SIGHASH_DEFAULT for PSBT signing

c0405ee27fa23a9868f04c052bdc94d7accc57e2 rpc: Document that DEFAULT is for Taproot, ALL for everything else (Andrew Chow)
d3992669df826899a3de78a77a366dab46028026 psbt: Actually use SIGHASH_DEFAULT (Andrew Chow)
eb9a1a2c595a03475fd4275b104676b7e2200f07 psbt: Make sighash_type std::optional<int> (Andrew Chow)

Pull request description:

  Make the behavior align with the help text by actually using SIGHASH_DEFAULT as the default sighash for signing PSBTs.

ACKs for top commit:
  Sjors:
    re-utACK c0405ee27fa23a9868f04c052bdc94d7accc57e2

Tree-SHA512: 5199fb41de416b2f10ac451f824e7c94b428ba11fdb9e50f0027c692e959ce5813a340c34a4e52d7aa128e12008303d80939a693eff36a869720e45442119828

8 files changed, 19 insertions, 17 deletions

diff --git a/src/core_read.cpp b/src/core_read.cpp
index 2149b428d2..484f41f262 100644
--- a/src/core_read.cpp
+++ b/src/core_read.cpp
@@ -248,7 +248,7 @@ std::vector<unsigned char> ParseHexUV(const UniValue& v, const std::string& strN
 
 int ParseSighashString(const UniValue& sighash)
 {
-    int hash_type = SIGHASH_ALL;
+    int hash_type = SIGHASH_DEFAULT;
     if (!sighash.isNull()) {
         static std::map<std::string, int> map_sighash_values = {
             {std::string("DEFAULT"), int(SIGHASH_DEFAULT)},
diff --git a/src/psbt.h b/src/psbt.h
index 1171ecf1dd..21daa050ea 100644
--- a/src/psbt.h
+++ b/src/psbt.h
@@ -57,7 +57,7 @@ struct PSBTInput
     std::map<CPubKey, KeyOriginInfo> hd_keypaths;
     std::map<CKeyID, SigPair> partial_sigs;
     std::map<std::vector<unsigned char>, std::vector<unsigned char>> unknown;
-    int sighash_type = 0;
+    std::optional<int> sighash_type;
 
     bool IsNull() const;
     void FillSignatureData(SignatureData& sigdata) const;
@@ -86,9 +86,9 @@ struct PSBTInput
             }
 
             // Write the sighash type
-            if (sighash_type > 0) {
+            if (sighash_type != std::nullopt) {
                 SerializeToVector(s, PSBT_IN_SIGHASH);
-                SerializeToVector(s, sighash_type);
+                SerializeToVector(s, *sighash_type);
             }
 
             // Write the redeem script
@@ -201,7 +201,9 @@ struct PSBTInput
                     } else if (key.size() != 1) {
                         throw std::ios_base::failure("Sighash type key is more than one byte type");
                     }
-                    UnserializeFromVector(s, sighash_type);
+                    int sighash;
+                    UnserializeFromVector(s, sighash);
+                    sighash_type = sighash;
                     break;
                 case PSBT_IN_REDEEMSCRIPT:
                 {
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index e10bf34273..78c1596219 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -785,7 +785,7 @@ static RPCHelpMan signrawtransactionwithkey()
                                 },
                         },
                         },
-                    {"sighashtype", RPCArg::Type::STR, RPCArg::Default{"DEFAULT"}, "The signature hash type. Must be one of:\n"
+                    {"sighashtype", RPCArg::Type::STR, RPCArg::Default{"DEFAULT for Taproot, ALL otherwise"}, "The signature hash type. Must be one of:\n"
             "       \"DEFAULT\"\n"
             "       \"ALL\"\n"
             "       \"NONE\"\n"
@@ -1255,8 +1255,8 @@ static RPCHelpMan decodepsbt()
         }
 
         // Sighash
-        if (input.sighash_type > 0) {
-            in.pushKV("sighash", SighashToStr((unsigned char)input.sighash_type));
+        if (input.sighash_type != std::nullopt) {
+            in.pushKV("sighash", SighashToStr((unsigned char)*input.sighash_type));
         }
 
         // Redeem script and witness script
diff --git a/src/wallet/rpc/spend.cpp b/src/wallet/rpc/spend.cpp
index a92ecd37db..978174b340 100644
--- a/src/wallet/rpc/spend.cpp
+++ b/src/wallet/rpc/spend.cpp
@@ -709,7 +709,7 @@ RPCHelpMan signrawtransactionwithwallet()
                             },
                         },
                     },
-                    {"sighashtype", RPCArg::Type::STR, RPCArg::Default{"DEFAULT"}, "The signature hash type. Must be one of\n"
+                    {"sighashtype", RPCArg::Type::STR, RPCArg::Default{"DEFAULT for Taproot, ALL otherwise"}, "The signature hash type. Must be one of\n"
             "       \"DEFAULT\"\n"
             "       \"ALL\"\n"
             "       \"NONE\"\n"
@@ -1167,7 +1167,7 @@ RPCHelpMan walletprocesspsbt()
                 {
                     {"psbt", RPCArg::Type::STR, RPCArg::Optional::NO, "The transaction base64 string"},
                     {"sign", RPCArg::Type::BOOL, RPCArg::Default{true}, "Also sign the transaction when updating (requires wallet to be unlocked)"},
-                    {"sighashtype", RPCArg::Type::STR, RPCArg::Default{"DEFAULT"}, "The signature hash type to sign with if not specified by the PSBT. Must be one of\n"
+                    {"sighashtype", RPCArg::Type::STR, RPCArg::Default{"DEFAULT for Taproot, ALL otherwise"}, "The signature hash type to sign with if not specified by the PSBT. Must be one of\n"
             "       \"DEFAULT\"\n"
             "       \"ALL\"\n"
             "       \"NONE\"\n"
diff --git a/src/wallet/scriptpubkeyman.cpp b/src/wallet/scriptpubkeyman.cpp
index 1769429efe..a9e2624188 100644
--- a/src/wallet/scriptpubkeyman.cpp
+++ b/src/wallet/scriptpubkeyman.cpp
@@ -633,7 +633,7 @@ TransactionError LegacyScriptPubKeyMan::FillPSBT(PartiallySignedTransaction& psb
         }
 
         // Get the Sighash type
-        if (sign && input.sighash_type > 0 && input.sighash_type != sighash_type) {
+        if (sign && input.sighash_type != std::nullopt && *input.sighash_type != sighash_type) {
             return TransactionError::SIGHASH_MISMATCH;
         }
 
@@ -2114,7 +2114,7 @@ TransactionError DescriptorScriptPubKeyMan::FillPSBT(PartiallySignedTransaction&
         }
 
         // Get the Sighash type
-        if (sign && input.sighash_type > 0 && input.sighash_type != sighash_type) {
+        if (sign && input.sighash_type != std::nullopt && *input.sighash_type != sighash_type) {
             return TransactionError::SIGHASH_MISMATCH;
         }
 
diff --git a/src/wallet/scriptpubkeyman.h b/src/wallet/scriptpubkeyman.h
index ebe064fa0a..dda31d2c0b 100644
--- a/src/wallet/scriptpubkeyman.h
+++ b/src/wallet/scriptpubkeyman.h
@@ -236,7 +236,7 @@ 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, bool finalize = true) const { return TransactionError::INVALID_PSBT; }
+    virtual TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = SIGHASH_DEFAULT, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr, bool finalize = true) const { return TransactionError::INVALID_PSBT; }
 
     virtual uint256 GetID() const { return uint256(); }
 
@@ -400,7 +400,7 @@ 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, bool finalize = true) const override;
+    TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = SIGHASH_DEFAULT, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr, bool finalize = true) const override;
 
     uint256 GetID() const override;
 
@@ -609,7 +609,7 @@ 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, bool finalize = true) const override;
+    TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = SIGHASH_DEFAULT, 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.h b/src/wallet/wallet.h
index dbf0f6375d..93150cc583 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -561,7 +561,7 @@ public:
      */
     TransactionError FillPSBT(PartiallySignedTransaction& psbtx,
                   bool& complete,
-                  int sighash_type = 1 /* SIGHASH_ALL */,
+                  int sighash_type = SIGHASH_DEFAULT,
                   bool sign = true,
                   bool bip32derivs = true,
                   size_t* n_signed = nullptr,
diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index a8034849cc..153a201e95 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -457,7 +457,7 @@ class PSBTTest(BitcoinTestFramework):
             wrpc = self.nodes[2].get_wallet_rpc("wallet{}".format(i))
             for key in signer['privkeys']:
                 wrpc.importprivkey(key)
-            signed_tx = wrpc.walletprocesspsbt(signer['psbt'])['psbt']
+            signed_tx = wrpc.walletprocesspsbt(signer['psbt'], True, "ALL")['psbt']
             assert_equal(signed_tx, signer['result'])
 
         # Combiner test