Merge #19215: psbt: Include and allow both non_witness_utxo and witness_utxo for segwit inputs

84d295e51341a126a6c3cbeea7a8caa04c7b5bc3 tests: Check that segwit inputs in psbt have both UTXO types (Andrew Chow)
46004790588c24174a0bec49b540d158ce163ffd psbt: always put a non_witness_utxo and don't remove it (Andrew Chow)
5279d8bc07d601fe6a67ad665fbc7591fe73c7de psbt: Allow both non_witness_utxo and witness_utxo (Andrew Chow)
72f6bec1da198764d4648a10a61c485e7ab65e9e rpc: show both UTXOs in decodepsbt (Andrew Chow)

Pull request description:

  Due to recent changes to hardware wallets, the full previous transaction will need to be provided for segwit inputs. Since some software may be checking for the existence of a `witness_utxo` to determine whether to produce a segwit signature, we keep that field to ease the transition.

  Because all of the sanity checks implemented by the `IsSane` functions were related to having mixed segwit and non-segwit data in a PSBT, those functions are removed as those checks are no longer proper.

  Some tests are updated/removed to accommodate this and a simple test added to check that both UTXOs are being added to segwit inputs.

  As discussed in the wallet IRC meeting, our own signer will not require `non_witness_utxo` for segwit inputs.

ACKs for top commit:
  Sjors:
    utACK 84d295e51341a126a6c3cbeea7a8caa04c7b5bc3 (didn't retest compared to 836d6fc, but fortunately HWI's CI tracks our master branch, with a bunch of hardware wallet simulators)
  ryanofsky:
    Code review re-ACK 84d295e51341a126a6c3cbeea7a8caa04c7b5bc3. No changes since last review, but now I understand the context better. I think it would good to improve the comments as suggested https://github.com/bitcoin/bitcoin/pull/19215#discussion_r447889473 and maybe refer to
  meshcollider:
    utACK 84d295e51341a126a6c3cbeea7a8caa04c7b5bc3

Tree-SHA512: ccc1fd3c16ac3859f5aca4fa489bd40f68be0b81bbdc4dd51188bbf28827a8642dc8b605a37318e5f16cf40f1c4910052dace2f27eca21bb58435f02a443e940

7 files changed, 15 insertions, 62 deletions

diff --git a/src/psbt.cpp b/src/psbt.cpp
index 10260740f0..3fb743e5db 100644
--- a/src/psbt.cpp
+++ b/src/psbt.cpp
@@ -35,14 +35,6 @@ bool PartiallySignedTransaction::Merge(const PartiallySignedTransaction& psbt)
     return true;
 }
 
-bool PartiallySignedTransaction::IsSane() const
-{
-    for (PSBTInput input : inputs) {
-        if (!input.IsSane()) return false;
-    }
-    return true;
-}
-
 bool PartiallySignedTransaction::AddInput(const CTxIn& txin, PSBTInput& psbtin)
 {
     if (std::find(tx->vin.begin(), tx->vin.end(), txin) != tx->vin.end()) {
@@ -144,8 +136,8 @@ void PSBTInput::Merge(const PSBTInput& input)
 {
     if (!non_witness_utxo && input.non_witness_utxo) non_witness_utxo = input.non_witness_utxo;
     if (witness_utxo.IsNull() && !input.witness_utxo.IsNull()) {
+        // TODO: For segwit v1, we will want to clear out the non-witness utxo when setting a witness one. For v0 and non-segwit, this is not safe
         witness_utxo = input.witness_utxo;
-        non_witness_utxo = nullptr; // Clear out any non-witness utxo when we set a witness one.
     }
 
     partial_sigs.insert(input.partial_sigs.begin(), input.partial_sigs.end());
@@ -158,18 +150,6 @@ void PSBTInput::Merge(const PSBTInput& input)
     if (final_script_witness.IsNull() && !input.final_script_witness.IsNull()) final_script_witness = input.final_script_witness;
 }
 
-bool PSBTInput::IsSane() const
-{
-    // Cannot have both witness and non-witness utxos
-    if (!witness_utxo.IsNull() && non_witness_utxo) return false;
-
-    // If we have a witness_script or a scriptWitness, we must also have a witness utxo
-    if (!witness_script.empty() && witness_utxo.IsNull()) return false;
-    if (!final_script_witness.IsNull() && witness_utxo.IsNull()) return false;
-
-    return true;
-}
-
 void PSBTOutput::FillSignatureData(SignatureData& sigdata) const
 {
     if (!redeem_script.empty()) {
@@ -261,11 +241,6 @@ bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction&
     bool require_witness_sig = false;
     CTxOut utxo;
 
-    // Verify input sanity, which checks that at most one of witness or non-witness utxos is provided.
-    if (!input.IsSane()) {
-        return false;
-    }
-
     if (input.non_witness_utxo) {
         // If we're taking our information from a non-witness UTXO, verify that it matches the prevout.
         COutPoint prevout = tx.vin[index].prevout;
@@ -299,10 +274,11 @@ bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction&
     if (require_witness_sig && !sigdata.witness) return false;
     input.FromSignatureData(sigdata);
 
-    // If we have a witness signature, use the smaller witness UTXO.
+    // If we have a witness signature, put a witness UTXO.
+    // TODO: For segwit v1, we should remove the non_witness_utxo
     if (sigdata.witness) {
         input.witness_utxo = utxo;
-        input.non_witness_utxo = nullptr;
+        // input.non_witness_utxo = nullptr;
     }
 
     // Fill in the missing info
@@ -356,10 +332,6 @@ TransactionError CombinePSBTs(PartiallySignedTransaction& out, const std::vector
             return TransactionError::PSBT_MISMATCH;
         }
     }
-    if (!out.IsSane()) {
-        return TransactionError::INVALID_PSBT;
-    }
-
     return TransactionError::OK;
 }
 
diff --git a/src/psbt.h b/src/psbt.h
index 0a8ea2ea0b..0951b76f83 100644
--- a/src/psbt.h
+++ b/src/psbt.h
@@ -62,18 +62,17 @@ struct PSBTInput
     void FillSignatureData(SignatureData& sigdata) const;
     void FromSignatureData(const SignatureData& sigdata);
     void Merge(const PSBTInput& input);
-    bool IsSane() const;
     PSBTInput() {}
 
     template <typename Stream>
     inline void Serialize(Stream& s) const {
         // Write the utxo
-        // If there is a non-witness utxo, then don't add the witness one.
         if (non_witness_utxo) {
             SerializeToVector(s, PSBT_IN_NON_WITNESS_UTXO);
             OverrideStream<Stream> os(&s, s.GetType(), s.GetVersion() | SERIALIZE_TRANSACTION_NO_WITNESS);
             SerializeToVector(os, non_witness_utxo);
-        } else if (!witness_utxo.IsNull()) {
+        }
+        if (!witness_utxo.IsNull()) {
             SerializeToVector(s, PSBT_IN_WITNESS_UTXO);
             SerializeToVector(s, witness_utxo);
         }
@@ -284,7 +283,6 @@ struct PSBTOutput
     void FillSignatureData(SignatureData& sigdata) const;
     void FromSignatureData(const SignatureData& sigdata);
     void Merge(const PSBTOutput& output);
-    bool IsSane() const;
     PSBTOutput() {}
 
     template <typename Stream>
@@ -401,7 +399,6 @@ struct PartiallySignedTransaction
     /** Merge psbt into this. The two psbts must have the same underlying CTransaction (i.e. the
       * same actual Bitcoin transaction.) Returns true if the merge succeeded, false otherwise. */
     NODISCARD bool Merge(const PartiallySignedTransaction& psbt);
-    bool IsSane() const;
     bool AddInput(const CTxIn& txin, PSBTInput& psbtin);
     bool AddOutput(const CTxOut& txout, const PSBTOutput& psbtout);
     PartiallySignedTransaction() {}
@@ -551,10 +548,6 @@ struct PartiallySignedTransaction
         if (outputs.size() != tx->vout.size()) {
             throw std::ios_base::failure("Outputs provided does not match the number of outputs in transaction.");
         }
-        // Sanity check
-        if (!IsSane()) {
-            throw std::ios_base::failure("PSBT is not sane.");
-        }
     }
 
     template <typename Stream>
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index faec359d1c..5f8c02df65 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -1104,6 +1104,7 @@ UniValue decodepsbt(const JSONRPCRequest& request)
         const PSBTInput& input = psbtx.inputs[i];
         UniValue in(UniValue::VOBJ);
         // UTXOs
+        bool have_a_utxo = false;
         if (!input.witness_utxo.IsNull()) {
             const CTxOut& txout = input.witness_utxo;
 
@@ -1121,7 +1122,9 @@ UniValue decodepsbt(const JSONRPCRequest& request)
             ScriptToUniv(txout.scriptPubKey, o, true);
             out.pushKV("scriptPubKey", o);
             in.pushKV("witness_utxo", out);
-        } else if (input.non_witness_utxo) {
+            have_a_utxo = true;
+        }
+        if (input.non_witness_utxo) {
             UniValue non_wit(UniValue::VOBJ);
             TxToUniv(*input.non_witness_utxo, uint256(), non_wit, false);
             in.pushKV("non_witness_utxo", non_wit);
@@ -1132,7 +1135,9 @@ UniValue decodepsbt(const JSONRPCRequest& request)
                 // Hack to just not show fee later
                 have_all_utxos = false;
             }
-        } else {
+            have_a_utxo = true;
+        }
+        if (!have_a_utxo) {
             have_all_utxos = false;
         }
 
diff --git a/src/test/fuzz/psbt.cpp b/src/test/fuzz/psbt.cpp
index 64328fb66e..908e2b16f2 100644
--- a/src/test/fuzz/psbt.cpp
+++ b/src/test/fuzz/psbt.cpp
@@ -39,7 +39,6 @@ void test_one_input(const std::vector<uint8_t>& buffer)
     }
 
     (void)psbt.IsNull();
-    (void)psbt.IsSane();
 
     Optional<CMutableTransaction> tx = psbt.tx;
     if (tx) {
@@ -50,7 +49,6 @@ void test_one_input(const std::vector<uint8_t>& buffer)
     for (const PSBTInput& input : psbt.inputs) {
         (void)PSBTInputSigned(input);
         (void)input.IsNull();
-        (void)input.IsSane();
     }
 
     for (const PSBTOutput& output : psbt.outputs) {
diff --git a/src/wallet/scriptpubkeyman.cpp b/src/wallet/scriptpubkeyman.cpp
index 3cc2611524..38d94335a3 100644
--- a/src/wallet/scriptpubkeyman.cpp
+++ b/src/wallet/scriptpubkeyman.cpp
@@ -597,11 +597,6 @@ TransactionError LegacyScriptPubKeyMan::FillPSBT(PartiallySignedTransaction& psb
             continue;
         }
 
-        // Verify input looks sane. This will check that we have at most one uxto, witness or non-witness.
-        if (!input.IsSane()) {
-            return TransactionError::INVALID_PSBT;
-        }
-
         // Get the Sighash type
         if (sign && input.sighash_type > 0 && input.sighash_type != sighash_type) {
             return TransactionError::SIGHASH_MISMATCH;
@@ -2086,11 +2081,6 @@ TransactionError DescriptorScriptPubKeyMan::FillPSBT(PartiallySignedTransaction&
             continue;
         }
 
-        // Verify input looks sane. This will check that we have at most one uxto, witness or non-witness.
-        if (!input.IsSane()) {
-            return TransactionError::INVALID_PSBT;
-        }
-
         // Get the Sighash type
         if (sign && input.sighash_type > 0 && input.sighash_type != sighash_type) {
             return TransactionError::SIGHASH_MISMATCH;
diff --git a/src/wallet/test/psbt_wallet_tests.cpp b/src/wallet/test/psbt_wallet_tests.cpp
index 3f85a48ff3..ce7e661b67 100644
--- a/src/wallet/test/psbt_wallet_tests.cpp
+++ b/src/wallet/test/psbt_wallet_tests.cpp
@@ -64,7 +64,7 @@ BOOST_AUTO_TEST_CASE(psbt_updater_test)
     CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
     ssTx << psbtx;
     std::string final_hex = HexStr(ssTx);
-    BOOST_CHECK_EQUAL(final_hex, "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");
+    BOOST_CHECK_EQUAL(final_hex, "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");
 
     // Mutate the transaction so that one of the inputs is invalid
     psbtx.tx->vin[0].prevout.n = 2;
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 19acfa3322..235b269805 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -2507,13 +2507,8 @@ TransactionError CWallet::FillPSBT(PartiallySignedTransaction& psbtx, bool& comp
             continue;
         }
 
-        // Verify input looks sane. This will check that we have at most one uxto, witness or non-witness.
-        if (!input.IsSane()) {
-            return TransactionError::INVALID_PSBT;
-        }
-
         // If we have no utxo, grab it from the wallet.
-        if (!input.non_witness_utxo && input.witness_utxo.IsNull()) {
+        if (!input.non_witness_utxo) {
             const uint256& txhash = txin.prevout.hash;
             const auto it = mapWallet.find(txhash);
             if (it != mapWallet.end()) {