Merge bitcoin/bitcoin#28107: util: Type-safe transaction identifiers

940a49978c Use type-safe txid types in orphanage (dergoegge)
ed70e65016 Introduce types for txids & wtxids (dergoegge)
cdb14d79e8 [net processing] Use HasWitness over comparing (w)txids (dergoegge)

Pull request description:

  We currently have two different identifiers for transactions: `txid` (refering to the hash of a transaction without witness data) and `wtxid` (referring to the hash of a transaction including witness data). Both are typed as `uint256` which could lead to type-safety bugs in which one transaction identifier type is passed where the other would be expected.

  This PR introduces explicit `Txid` and `Wtxid` types that (if used) would cause compilation errors for such type confusion bugs.

  (Only the orphanage is converted to use these types in this PR)

ACKs for top commit:
  achow101:
    ACK 940a49978c
  stickies-v:
    ACK 940a49978c
  hebasto:
    ACK 940a49978c, I have reviewed the code and it looks OK.
  instagibbs:
    re-ACK 940a49978c
  BrandonOdiwuor:
    re-ACK 940a49978c
  glozow:
    reACK 940a49978c

Tree-SHA512: 55298d1c2bb82b7a6995e96e554571c22eaf4a89fb2a4d7a236d70e0f625e8cca62ff2490e1c179c47bd93153fe6527b56870198f026f5ee7753d64d7a424c92

src/Makefile.am

@@ -328,6 +328,7 @@ BITCOIN_CORE_H = \
   util/time.h \
   util/tokenpipe.h \
   util/trace.h \
+  util/transaction_identifier.h \
   util/translation.h \
   util/types.h \
   util/ui_change_type.h \

src/net_processing.cpp

@@ -1947,9 +1947,9 @@ void PeerManagerImpl::BlockConnected(
     {
         LOCK(m_recent_confirmed_transactions_mutex);
         for (const auto& ptx : pblock->vtx) {
-            m_recent_confirmed_transactions.insert(ptx->GetHash());
+            m_recent_confirmed_transactions.insert(ptx->GetHash().ToUint256());
-            if (ptx->GetHash() != ptx->GetWitnessHash()) {
+            if (ptx->HasWitness()) {
-                m_recent_confirmed_transactions.insert(ptx->GetWitnessHash());
+                m_recent_confirmed_transactions.insert(ptx->GetWitnessHash().ToUint256());
             }
         }
     }
@@ -3003,8 +3003,8 @@ bool PeerManagerImpl::ProcessOrphanTx(Peer& peer)
     while (CTransactionRef porphanTx = m_orphanage.GetTxToReconsider(peer.m_id)) {
         const MempoolAcceptResult result = m_chainman.ProcessTransaction(porphanTx);
         const TxValidationState& state = result.m_state;
-        const uint256& orphanHash = porphanTx->GetHash();
+        const Txid& orphanHash = porphanTx->GetHash();
-        const uint256& orphan_wtxid = porphanTx->GetWitnessHash();
+        const Wtxid& orphan_wtxid = porphanTx->GetWitnessHash();
 
         if (result.m_result_type == MempoolAcceptResult::ResultType::VALID) {
             LogPrint(BCLog::TXPACKAGES, "   accepted orphan tx %s (wtxid=%s)\n", orphanHash.ToString(), orphan_wtxid.ToString());
@@ -3052,7 +3052,7 @@ bool PeerManagerImpl::ProcessOrphanTx(Peer& peer)
                 // See also comments in https://github.com/bitcoin/bitcoin/pull/18044#discussion_r443419034
                 // for concerns around weakening security of unupgraded nodes
                 // if we start doing this too early.
-                m_recent_rejects.insert(porphanTx->GetWitnessHash());
+                m_recent_rejects.insert(porphanTx->GetWitnessHash().ToUint256());
                 // If the transaction failed for TX_INPUTS_NOT_STANDARD,
                 // then we know that the witness was irrelevant to the policy
                 // failure, since this check depends only on the txid
@@ -3061,10 +3061,10 @@ bool PeerManagerImpl::ProcessOrphanTx(Peer& peer)
                 // processing of this transaction in the event that child
                 // transactions are later received (resulting in
                 // parent-fetching by txid via the orphan-handling logic).
-                if (state.GetResult() == TxValidationResult::TX_INPUTS_NOT_STANDARD && porphanTx->GetWitnessHash() != porphanTx->GetHash()) {
+                if (state.GetResult() == TxValidationResult::TX_INPUTS_NOT_STANDARD && porphanTx->HasWitness()) {
                     // We only add the txid if it differs from the wtxid, to
                     // avoid wasting entries in the rolling bloom filter.
-                    m_recent_rejects.insert(porphanTx->GetHash());
+                    m_recent_rejects.insert(porphanTx->GetHash().ToUint256());
                 }
             }
             m_orphanage.EraseTx(orphanHash);
@@ -4319,8 +4319,8 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
                 // regardless of what witness is provided, we will not accept
                 // this, so we don't need to allow for redownload of this txid
                 // from any of our non-wtxidrelay peers.
-                m_recent_rejects.insert(tx.GetHash());
+                m_recent_rejects.insert(tx.GetHash().ToUint256());
-                m_recent_rejects.insert(tx.GetWitnessHash());
+                m_recent_rejects.insert(tx.GetWitnessHash().ToUint256());
                 m_txrequest.ForgetTxHash(tx.GetHash());
                 m_txrequest.ForgetTxHash(tx.GetWitnessHash());
             }
@@ -4339,7 +4339,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
                 // See also comments in https://github.com/bitcoin/bitcoin/pull/18044#discussion_r443419034
                 // for concerns around weakening security of unupgraded nodes
                 // if we start doing this too early.
-                m_recent_rejects.insert(tx.GetWitnessHash());
+                m_recent_rejects.insert(tx.GetWitnessHash().ToUint256());
                 m_txrequest.ForgetTxHash(tx.GetWitnessHash());
                 // If the transaction failed for TX_INPUTS_NOT_STANDARD,
                 // then we know that the witness was irrelevant to the policy
@@ -4349,8 +4349,8 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
                 // processing of this transaction in the event that child
                 // transactions are later received (resulting in
                 // parent-fetching by txid via the orphan-handling logic).
-                if (state.GetResult() == TxValidationResult::TX_INPUTS_NOT_STANDARD && tx.GetWitnessHash() != tx.GetHash()) {
+                if (state.GetResult() == TxValidationResult::TX_INPUTS_NOT_STANDARD && tx.HasWitness()) {
-                    m_recent_rejects.insert(tx.GetHash());
+                    m_recent_rejects.insert(tx.GetHash().ToUint256());
                     m_txrequest.ForgetTxHash(tx.GetHash());
                 }
                 if (RecursiveDynamicUsage(*ptx) < 100000) {
@@ -5780,9 +5780,14 @@ bool PeerManagerImpl::SendMessages(CNode* pto)
                     LOCK(tx_relay->m_bloom_filter_mutex);
 
                     for (const auto& txinfo : vtxinfo) {
-                        const uint256& hash = peer->m_wtxid_relay ? txinfo.tx->GetWitnessHash() : txinfo.tx->GetHash();
+                        CInv inv{
-                        CInv inv(peer->m_wtxid_relay ? MSG_WTX : MSG_TX, hash);
+                            peer->m_wtxid_relay ? MSG_WTX : MSG_TX,
-                        tx_relay->m_tx_inventory_to_send.erase(hash);
+                            peer->m_wtxid_relay ?
+                                txinfo.tx->GetWitnessHash().ToUint256() :
+                                txinfo.tx->GetHash().ToUint256(),
+                        };
+                        tx_relay->m_tx_inventory_to_send.erase(inv.hash);
+
                         // Don't send transactions that peers will not put into their mempool
                         if (txinfo.fee < filterrate.GetFee(txinfo.vsize)) {
                             continue;
@@ -5790,7 +5795,7 @@ bool PeerManagerImpl::SendMessages(CNode* pto)
                         if (tx_relay->m_bloom_filter) {
                             if (!tx_relay->m_bloom_filter->IsRelevantAndUpdate(*txinfo.tx)) continue;
                         }
-                        tx_relay->m_tx_inventory_known_filter.insert(hash);
+                        tx_relay->m_tx_inventory_known_filter.insert(inv.hash);
                         vInv.push_back(inv);
                         if (vInv.size() == MAX_INV_SZ) {
                             m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::INV, vInv));

src/primitives/transaction.cpp

@@ -12,6 +12,7 @@
 #include <tinyformat.h>
 #include <uint256.h>
 #include <util/strencodings.h>
+#include <util/transaction_identifier.h>
 #include <version.h>
 
 #include <cassert>
@@ -65,22 +66,23 @@ std::string CTxOut::ToString() const
 CMutableTransaction::CMutableTransaction() : nVersion(CTransaction::CURRENT_VERSION), nLockTime(0) {}
 CMutableTransaction::CMutableTransaction(const CTransaction& tx) : vin(tx.vin), vout(tx.vout), nVersion(tx.nVersion), nLockTime(tx.nLockTime) {}
 
-uint256 CMutableTransaction::GetHash() const
+Txid CMutableTransaction::GetHash() const
 {
-    return (CHashWriter{SERIALIZE_TRANSACTION_NO_WITNESS} << *this).GetHash();
+    return Txid::FromUint256((CHashWriter{SERIALIZE_TRANSACTION_NO_WITNESS} << *this).GetHash());
 }
 
-uint256 CTransaction::ComputeHash() const
+Txid CTransaction::ComputeHash() const
 {
-    return (CHashWriter{SERIALIZE_TRANSACTION_NO_WITNESS} << *this).GetHash();
+    return Txid::FromUint256((CHashWriter{SERIALIZE_TRANSACTION_NO_WITNESS} << *this).GetHash());
 }
 
-uint256 CTransaction::ComputeWitnessHash() const
+Wtxid CTransaction::ComputeWitnessHash() const
 {
     if (!HasWitness()) {
-        return hash;
+        return Wtxid::FromUint256(hash.ToUint256());
     }
-    return (CHashWriter{0} << *this).GetHash();
+
+    return Wtxid::FromUint256((CHashWriter{0} << *this).GetHash());
 }
 
 CTransaction::CTransaction(const CMutableTransaction& tx) : vin(tx.vin), vout(tx.vout), nVersion(tx.nVersion), nLockTime(tx.nLockTime), hash{ComputeHash()}, m_witness_hash{ComputeWitnessHash()} {}

src/primitives/transaction.h

@@ -11,6 +11,7 @@
 #include <script/script.h>
 #include <serialize.h>
 #include <uint256.h>
+#include <util/transaction_identifier.h> // IWYU pragma: export
 
 #include <cstddef>
 #include <cstdint>
@@ -309,11 +310,11 @@ public:
 
 private:
     /** Memory only. */
-    const uint256 hash;
+    const Txid hash;
-    const uint256 m_witness_hash;
+    const Wtxid m_witness_hash;
 
-    uint256 ComputeHash() const;
+    Txid ComputeHash() const;
-    uint256 ComputeWitnessHash() const;
+    Wtxid ComputeWitnessHash() const;
 
 public:
     /** Convert a CMutableTransaction into a CTransaction. */
@@ -334,8 +335,8 @@ public:
         return vin.empty() && vout.empty();
     }
 
-    const uint256& GetHash() const { return hash; }
+    const Txid& GetHash() const { return hash; }
-    const uint256& GetWitnessHash() const { return m_witness_hash; };
+    const Wtxid& GetWitnessHash() const { return m_witness_hash; };
 
     // Return sum of txouts.
     CAmount GetValueOut() const;
@@ -405,7 +406,7 @@ struct CMutableTransaction
     /** Compute the hash of this CMutableTransaction. This is computed on the
      * fly, as opposed to GetHash() in CTransaction, which uses a cached result.
      */
-    uint256 GetHash() const;
+    Txid GetHash() const;
 
     bool HasWitness() const
     {

src/test/fuzz/package_eval.cpp

@@ -238,7 +238,7 @@ FUZZ_TARGET(tx_package_eval, .init = initialize_tx_pool)
         }
         if (fuzzed_data_provider.ConsumeBool()) {
             const auto& txid = fuzzed_data_provider.ConsumeBool() ?
-                                   txs.back()->GetHash() :
+                                   txs.back()->GetHash().ToUint256() :
                                    PickValue(fuzzed_data_provider, mempool_outpoints).hash;
             const auto delta = fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(-50 * COIN, +50 * COIN);
             tx_pool.PrioritiseTransaction(txid, delta);

src/test/fuzz/tx_pool.cpp

@@ -227,7 +227,7 @@ FUZZ_TARGET(tx_pool_standard, .init = initialize_tx_pool)
         }
         if (fuzzed_data_provider.ConsumeBool()) {
             const auto& txid = fuzzed_data_provider.ConsumeBool() ?
-                                   tx->GetHash() :
+                                   tx->GetHash().ToUint256() :
                                    PickValue(fuzzed_data_provider, outpoints_rbf).hash;
             const auto delta = fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(-50 * COIN, +50 * COIN);
             tx_pool.PrioritiseTransaction(txid, delta);
@@ -344,7 +344,7 @@ FUZZ_TARGET(tx_pool, .init = initialize_tx_pool)
         }
         if (fuzzed_data_provider.ConsumeBool()) {
             const auto& txid = fuzzed_data_provider.ConsumeBool() ?
-                                   mut_tx.GetHash() :
+                                   mut_tx.GetHash().ToUint256() :
                                    PickValue(fuzzed_data_provider, txids);
             const auto delta = fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(-50 * COIN, +50 * COIN);
             tx_pool.PrioritiseTransaction(txid, delta);

src/test/orphanage_tests.cpp

@@ -3,6 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <arith_uint256.h>
+#include <primitives/transaction.h>
 #include <pubkey.h>
 #include <script/sign.h>
 #include <script/signingprovider.h>
@@ -29,8 +30,8 @@ public:
     CTransactionRef RandomOrphan() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
     {
         LOCK(m_mutex);
-        std::map<uint256, OrphanTx>::iterator it;
+        std::map<Txid, OrphanTx>::iterator it;
-        it = m_orphans.lower_bound(InsecureRand256());
+        it = m_orphans.lower_bound(Txid::FromUint256(InsecureRand256()));
         if (it == m_orphans.end())
             it = m_orphans.begin();
         return it->second.tx;

src/txorphanage.cpp

@@ -7,6 +7,7 @@
 #include <consensus/validation.h>
 #include <logging.h>
 #include <policy/policy.h>
+#include <primitives/transaction.h>
 
 #include <cassert>
 
@@ -20,8 +21,8 @@ bool TxOrphanage::AddTx(const CTransactionRef& tx, NodeId peer)
 {
     LOCK(m_mutex);
 
-    const uint256& hash = tx->GetHash();
+    const Txid& hash = tx->GetHash();
-    const uint256& wtxid = tx->GetWitnessHash();
+    const Wtxid& wtxid = tx->GetWitnessHash();
     if (m_orphans.count(hash))
         return false;
 
@@ -53,16 +54,16 @@ bool TxOrphanage::AddTx(const CTransactionRef& tx, NodeId peer)
     return true;
 }
 
-int TxOrphanage::EraseTx(const uint256& txid)
+int TxOrphanage::EraseTx(const Txid& txid)
 {
     LOCK(m_mutex);
     return EraseTxNoLock(txid);
 }
 
-int TxOrphanage::EraseTxNoLock(const uint256& txid)
+int TxOrphanage::EraseTxNoLock(const Txid& txid)
 {
     AssertLockHeld(m_mutex);
-    std::map<uint256, OrphanTx>::iterator it = m_orphans.find(txid);
+    std::map<Txid, OrphanTx>::iterator it = m_orphans.find(txid);
     if (it == m_orphans.end())
         return 0;
     for (const CTxIn& txin : it->second.tx->vin)
@@ -100,10 +101,10 @@ void TxOrphanage::EraseForPeer(NodeId peer)
     m_peer_work_set.erase(peer);
 
     int nErased = 0;
-    std::map<uint256, OrphanTx>::iterator iter = m_orphans.begin();
+    std::map<Txid, OrphanTx>::iterator iter = m_orphans.begin();
     while (iter != m_orphans.end())
     {
-        std::map<uint256, OrphanTx>::iterator maybeErase = iter++; // increment to avoid iterator becoming invalid
+        std::map<Txid, OrphanTx>::iterator maybeErase = iter++; // increment to avoid iterator becoming invalid
         if (maybeErase->second.fromPeer == peer)
         {
             nErased += EraseTxNoLock(maybeErase->second.tx->GetHash());
@@ -123,10 +124,10 @@ void TxOrphanage::LimitOrphans(unsigned int max_orphans)
         // Sweep out expired orphan pool entries:
         int nErased = 0;
         int64_t nMinExpTime = nNow + ORPHAN_TX_EXPIRE_TIME - ORPHAN_TX_EXPIRE_INTERVAL;
-        std::map<uint256, OrphanTx>::iterator iter = m_orphans.begin();
+        std::map<Txid, OrphanTx>::iterator iter = m_orphans.begin();
         while (iter != m_orphans.end())
         {
-            std::map<uint256, OrphanTx>::iterator maybeErase = iter++;
+            std::map<Txid, OrphanTx>::iterator maybeErase = iter++;
             if (maybeErase->second.nTimeExpire <= nNow) {
                 nErased += EraseTxNoLock(maybeErase->second.tx->GetHash());
             } else {
@@ -159,7 +160,7 @@ void TxOrphanage::AddChildrenToWorkSet(const CTransaction& tx)
             for (const auto& elem : it_by_prev->second) {
                 // Get this source peer's work set, emplacing an empty set if it didn't exist
                 // (note: if this peer wasn't still connected, we would have removed the orphan tx already)
-                std::set<uint256>& orphan_work_set = m_peer_work_set.try_emplace(elem->second.fromPeer).first->second;
+                std::set<Txid>& orphan_work_set = m_peer_work_set.try_emplace(elem->second.fromPeer).first->second;
                 // Add this tx to the work set
                 orphan_work_set.insert(elem->first);
                 LogPrint(BCLog::TXPACKAGES, "added %s (wtxid=%s) to peer %d workset\n",
@@ -173,9 +174,9 @@ bool TxOrphanage::HaveTx(const GenTxid& gtxid) const
 {
     LOCK(m_mutex);
     if (gtxid.IsWtxid()) {
-        return m_wtxid_to_orphan_it.count(gtxid.GetHash());
+        return m_wtxid_to_orphan_it.count(Wtxid::FromUint256(gtxid.GetHash()));
     } else {
-        return m_orphans.count(gtxid.GetHash());
+        return m_orphans.count(Txid::FromUint256(gtxid.GetHash()));
     }
 }
 
@@ -187,7 +188,7 @@ CTransactionRef TxOrphanage::GetTxToReconsider(NodeId peer)
     if (work_set_it != m_peer_work_set.end()) {
         auto& work_set = work_set_it->second;
         while (!work_set.empty()) {
-            uint256 txid = *work_set.begin();
+            Txid txid = *work_set.begin();
             work_set.erase(work_set.begin());
 
             const auto orphan_it = m_orphans.find(txid);
@@ -215,7 +216,7 @@ void TxOrphanage::EraseForBlock(const CBlock& block)
 {
     LOCK(m_mutex);
 
-    std::vector<uint256> vOrphanErase;
+    std::vector<Txid> vOrphanErase;
 
     for (const CTransactionRef& ptx : block.vtx) {
         const CTransaction& tx = *ptx;
@@ -226,7 +227,7 @@ void TxOrphanage::EraseForBlock(const CBlock& block)
             if (itByPrev == m_outpoint_to_orphan_it.end()) continue;
             for (auto mi = itByPrev->second.begin(); mi != itByPrev->second.end(); ++mi) {
                 const CTransaction& orphanTx = *(*mi)->second.tx;
-                const uint256& orphanHash = orphanTx.GetHash();
+                const auto& orphanHash = orphanTx.GetHash();
                 vOrphanErase.push_back(orphanHash);
             }
         }
@@ -235,7 +236,7 @@ void TxOrphanage::EraseForBlock(const CBlock& block)
     // Erase orphan transactions included or precluded by this block
     if (vOrphanErase.size()) {
         int nErased = 0;
-        for (const uint256& orphanHash : vOrphanErase) {
+        for (const auto& orphanHash : vOrphanErase) {
             nErased += EraseTxNoLock(orphanHash);
         }
         LogPrint(BCLog::TXPACKAGES, "Erased %d orphan tx included or conflicted by block\n", nErased);

src/txorphanage.h

@@ -34,7 +34,7 @@ public:
     CTransactionRef GetTxToReconsider(NodeId peer) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
 
     /** Erase an orphan by txid */
-    int EraseTx(const uint256& txid) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
+    int EraseTx(const Txid& txid) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
 
     /** Erase all orphans announced by a peer (eg, after that peer disconnects) */
     void EraseForPeer(NodeId peer) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
@@ -71,10 +71,10 @@ protected:
 
     /** Map from txid to orphan transaction record. Limited by
      *  -maxorphantx/DEFAULT_MAX_ORPHAN_TRANSACTIONS */
-    std::map<uint256, OrphanTx> m_orphans GUARDED_BY(m_mutex);
+    std::map<Txid, OrphanTx> m_orphans GUARDED_BY(m_mutex);
 
     /** Which peer provided the orphans that need to be reconsidered */
-    std::map<NodeId, std::set<uint256>> m_peer_work_set GUARDED_BY(m_mutex);
+    std::map<NodeId, std::set<Txid>> m_peer_work_set GUARDED_BY(m_mutex);
 
     using OrphanMap = decltype(m_orphans);
 
@@ -96,10 +96,10 @@ protected:
 
     /** Index from wtxid into the m_orphans to lookup orphan
      *  transactions using their witness ids. */
-    std::map<uint256, OrphanMap::iterator> m_wtxid_to_orphan_it GUARDED_BY(m_mutex);
+    std::map<Wtxid, OrphanMap::iterator> m_wtxid_to_orphan_it GUARDED_BY(m_mutex);
 
     /** Erase an orphan by txid */
-    int EraseTxNoLock(const uint256& txid) EXCLUSIVE_LOCKS_REQUIRED(m_mutex);
+    int EraseTxNoLock(const Txid& txid) EXCLUSIVE_LOCKS_REQUIRED(m_mutex);
 };
 
 #endif // BITCOIN_TXORPHANAGE_H

src/util/transaction_identifier.h

@@ -0,0 +1,67 @@
+#ifndef BITCOIN_UTIL_TRANSACTION_IDENTIFIER_H
+#define BITCOIN_UTIL_TRANSACTION_IDENTIFIER_H
+
+#include <uint256.h>
+#include <util/types.h>
+
+/** transaction_identifier represents the two canonical transaction identifier
+ * types (txid, wtxid).*/
+template <bool has_witness>
+class transaction_identifier
+{
+    uint256 m_wrapped;
+
+    // Note: Use FromUint256 externally instead.
+    transaction_identifier(const uint256& wrapped) : m_wrapped{wrapped} {}
+
+    // TODO: Comparisons with uint256 should be disallowed once we have
+    // converted most of the code to using the new txid types.
+    constexpr int Compare(const uint256& other) const { return m_wrapped.Compare(other); }
+    constexpr int Compare(const transaction_identifier<has_witness>& other) const { return m_wrapped.Compare(other.m_wrapped); }
+    template <typename Other>
+    constexpr int Compare(const Other& other) const
+    {
+        static_assert(ALWAYS_FALSE<Other>, "Forbidden comparison type");
+        return 0;
+    }
+
+public:
+    transaction_identifier() : m_wrapped{} {}
+
+    template <typename Other>
+    bool operator==(const Other& other) const { return Compare(other) == 0; }
+    template <typename Other>
+    bool operator!=(const Other& other) const { return Compare(other) != 0; }
+    template <typename Other>
+    bool operator<(const Other& other) const { return Compare(other) < 0; }
+
+    uint256 ToUint256() const { return m_wrapped; }
+    static transaction_identifier FromUint256(const uint256& id) { return {id}; }
+
+    /** Wrapped `uint256` methods. */
+    constexpr bool IsNull() const { return m_wrapped.IsNull(); }
+    constexpr void SetNull() { m_wrapped.SetNull(); }
+    std::string GetHex() const { return m_wrapped.GetHex(); }
+    std::string ToString() const { return m_wrapped.ToString(); }
+    constexpr const std::byte* data() const { return reinterpret_cast<const std::byte*>(m_wrapped.data()); }
+    constexpr const std::byte* begin() const { return reinterpret_cast<const std::byte*>(m_wrapped.begin()); }
+    constexpr const std::byte* end() const { return reinterpret_cast<const std::byte*>(m_wrapped.end()); }
+    template <typename Stream> void Serialize(Stream& s) const { m_wrapped.Serialize(s); }
+    template <typename Stream> void Unserialize(Stream& s) { m_wrapped.Unserialize(s); }
+
+    /** Conversion function to `uint256`.
+     *
+     * Note: new code should use `ToUint256`.
+     *
+     * TODO: This should be removed once the majority of the code has switched
+     * to using the Txid and Wtxid types. Until then it makes for a smoother
+     * transition to allow this conversion. */
+    operator uint256() const { return m_wrapped; }
+};
+
+/** Txid commits to all transaction fields except the witness. */
+using Txid = transaction_identifier<false>;
+/** Wtxid commits to all transaction fields including the witness. */
+using Wtxid = transaction_identifier<true>;
+
+#endif // BITCOIN_UTIL_TRANSACTION_IDENTIFIER_H

src/validation.cpp

@@ -618,7 +618,7 @@ private:
 
         const CTransactionRef& m_ptx;
         /** Txid. */
-        const uint256& m_hash;
+        const Txid& m_hash;
         TxValidationState m_state;
         /** A temporary cache containing serialized transaction data for signature verification.
          * Reused across PolicyScriptChecks and ConsensusScriptChecks. */
@@ -1870,7 +1870,7 @@ bool CheckInputScripts(const CTransaction& tx, TxValidationState& state,
     // transaction).
     uint256 hashCacheEntry;
     CSHA256 hasher = g_scriptExecutionCacheHasher;
-    hasher.Write(tx.GetWitnessHash().begin(), 32).Write((unsigned char*)&flags, sizeof(flags)).Finalize(hashCacheEntry.begin());
+    hasher.Write(UCharCast(tx.GetWitnessHash().begin()), 32).Write((unsigned char*)&flags, sizeof(flags)).Finalize(hashCacheEntry.begin());
     AssertLockHeld(cs_main); //TODO: Remove this requirement by making CuckooCache not require external locks
     if (g_scriptExecutionCache.contains(hashCacheEntry, !cacheFullScriptStore)) {
         return true;

src/wallet/transaction.h

@@ -330,8 +330,8 @@ public:
     bool isInactive() const { return state<TxStateInactive>(); }
     bool isUnconfirmed() const { return !isAbandoned() && !isConflicted() && !isConfirmed(); }
     bool isConfirmed() const { return state<TxStateConfirmed>(); }
-    const uint256& GetHash() const { return tx->GetHash(); }
+    const Txid& GetHash() const { return tx->GetHash(); }
-    const uint256& GetWitnessHash() const { return tx->GetWitnessHash(); }
+    const Wtxid& GetWitnessHash() const { return tx->GetWitnessHash(); }
     bool IsCoinBase() const { return tx->IsCoinBase(); }
 
 private: