Merge bitcoin/bitcoin#21584: Fix assumeutxo crash due to invalid base_blockhash

fa340b87944764ea4e8e04038fe7471fd452bc23 refactor: Avoid magic value of all-zeros in assumeutxo base_blockhash (MarcoFalke)
fae33f98e6a8d5934edbdce2eb8688112eac41a8 Fix assumeutxo crash due to invalid base_blockhash (MarcoFalke)
fa5668bfb34e2778936af30e9fb6bd3c6bcf41fd refactor: Use type-safe assumeutxo hash (MarcoFalke)
00000077098a23e0ac9781f5f799c90fd2fd97de refactor: Remove unused code (MarcoFalke)
faa921f78788be0f236c6b10ed3f92dcf148d1cb move-only: Add util/hash_type (MarcoFalke)

Pull request description:

  Starting with commit d6af06d68aa, a block hash of all-zeros is invalid and will lead to a crash of the node. Can be tested by cherry-picking the test changes without the other changes.

  Stack trace (copied from https://github.com/bitcoin/bitcoin/pull/21584#discussion_r612673879):

  ```
  #0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
  #1  0x00007ffff583c8b1 in __GI_abort () at abort.c:79
  #2  0x00007ffff582c42a in __assert_fail_base (fmt=0x7ffff59b3a38 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n",
      assertion=assertion@entry=0x555556c8b450 "!hashBlock.IsNull()", file=file@entry=0x555556c8b464 "txdb.cpp", line=line@entry=89,
      function=function@entry=0x555556c8b46d "virtual bool CCoinsViewDB::BatchWrite(CCoinsMap &, const uint256 &)") at assert.c:92
  #3  0x00007ffff582c4a2 in __GI___assert_fail (assertion=0x555556c8b450 "!hashBlock.IsNull()", file=0x555556c8b464 "txdb.cpp", line=89,
      function=0x555556c8b46d "virtual bool CCoinsViewDB::BatchWrite(CCoinsMap &, const uint256 &)") at assert.c:101
  #4  0x000055555636738b in CCoinsViewDB::BatchWrite (this=0x5555577975c0, mapCoins=std::unordered_map with 110 elements = {...}, hashBlock=...) at txdb.cpp:89
  #5  0x00005555564a2e80 in CCoinsViewBacked::BatchWrite (this=0x5555577975f8, mapCoins=std::unordered_map with 110 elements = {...}, hashBlock=...) at coins.cpp:30
  #6  0x00005555564a43de in CCoinsViewCache::Flush (this=0x55555778eaf0) at coins.cpp:223
  #7  0x00005555563fc11d in ChainstateManager::PopulateAndValidateSnapshot (this=0x55555740b038 <g_chainman>, snapshot_chainstate=..., coins_file=..., metadata=...)
      at validation.cpp:5422
  #8  0x00005555563fab3d in ChainstateManager::ActivateSnapshot (this=0x55555740b038 <g_chainman>, coins_file=..., metadata=..., in_memory=true) at validation.cpp:5299
  #9  0x0000555555e8c893 in validation_chainstatemanager_tests::CreateAndActivateUTXOSnapshot<validation_chainstatemanager_tests::chainstatemanager_activate_snapshot::test_method()::$_12>(NodeContext&, boost::filesystem::path, validation_chainstatemanager_tests::chainstatemanager_activate_snapshot::test_method()::$_12) (node=...,
      root=..., malleation=...) at test/validation_chainstatemanager_tests.cpp:199
  #10 0x0000555555e8877a in validation_chainstatemanager_tests::chainstatemanager_activate_snapshot::test_method (this=0x7fffffffc8d0)
      at test/validation_chainstatemanager_tests.cpp:262

ACKs for top commit:
  laanwj:
    Code review re-ACK fa340b87944764ea4e8e04038fe7471fd452bc23
  jamesob:
    ACK fa340b87944764ea4e8e04038fe7471fd452bc23 ([`jamesob/ackr/21584.1.MarcoFalke.fix_assumeutxo_crash_due`](https://github.com/jamesob/bitcoin/tree/ackr/21584.1.MarcoFalke.fix_assumeutxo_crash_due))

Tree-SHA512: c2c4e66c1abfd400ef18a04f22fec1f302f1ff4d27a18050f492f688319deb4ccdd165ff792eee0a1f816e7b69fb64080662b79517ab669e3d26b9eb77802851

10 files changed, 130 insertions, 123 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 41fab024c6..770bb76226 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -246,6 +246,7 @@ BITCOIN_CORE_H = \
   util/fees.h \
   util/getuniquepath.h \
   util/golombrice.h \
+  util/hash_type.h \
   util/hasher.h \
   util/macros.h \
   util/message.h \
diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index 45d93ca014..fc5a9d84cc 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -451,11 +451,11 @@ public:
         m_assumeutxo_data = MapAssumeutxo{
             {
                 110,
-                {uint256S("0x1ebbf5850204c0bdb15bf030f47c7fe91d45c44c712697e4509ba67adb01c618"), 110},
+                {AssumeutxoHash{uint256S("0x1ebbf5850204c0bdb15bf030f47c7fe91d45c44c712697e4509ba67adb01c618")}, 110},
             },
             {
                 210,
-                {uint256S("0x9c5ed99ef98544b34f8920b6d1802f72ac28ae6e2bd2bd4c316ff10c230df3f2"), 210},
+                {AssumeutxoHash{uint256S("0x9c5ed99ef98544b34f8920b6d1802f72ac28ae6e2bd2bd4c316ff10c230df3f2")}, 210},
             },
         };
 
@@ -559,9 +559,3 @@ void SelectParams(const std::string& network)
     SelectBaseParams(network);
     globalChainParams = CreateChainParams(gArgs, network);
 }
-
-std::ostream& operator<<(std::ostream& o, const AssumeutxoData& aud)
-{
-    o << strprintf("AssumeutxoData(%s, %s)", aud.hash_serialized.ToString(), aud.nChainTx);
-    return o;
-}
diff --git a/src/chainparams.h b/src/chainparams.h
index 6f23199986..5c2351eea6 100644
--- a/src/chainparams.h
+++ b/src/chainparams.h
@@ -10,6 +10,7 @@
 #include <consensus/params.h>
 #include <primitives/block.h>
 #include <protocol.h>
+#include <util/hash_type.h>
 
 #include <memory>
 #include <vector>
@@ -25,6 +26,10 @@ struct CCheckpointData {
     }
 };
 
+struct AssumeutxoHash : public BaseHash<uint256> {
+    explicit AssumeutxoHash(const uint256& hash) : BaseHash(hash) {}
+};
+
 /**
  * Holds configuration for use during UTXO snapshot load and validation. The contents
  * here are security critical, since they dictate which UTXO snapshots are recognized
@@ -32,7 +37,7 @@ struct CCheckpointData {
  */
 struct AssumeutxoData {
     //! The expected hash of the deserialized UTXO set.
-    const uint256 hash_serialized;
+    const AssumeutxoHash hash_serialized;
 
     //! Used to populate the nChainTx value, which is used during BlockManager::LoadBlockIndex().
     //!
@@ -41,8 +46,6 @@ struct AssumeutxoData {
     const unsigned int nChainTx;
 };
 
-std::ostream& operator<<(std::ostream& o, const AssumeutxoData& aud);
-
 using MapAssumeutxo = std::map<int, const AssumeutxoData>;
 
 /**
diff --git a/src/coins.h b/src/coins.h
index 5a6f73652b..816b4864a3 100644
--- a/src/coins.h
+++ b/src/coins.h
@@ -20,8 +20,6 @@
 #include <functional>
 #include <unordered_map>
 
-class ChainstateManager;
-
 /**
  * A UTXO entry.
  *
diff --git a/src/script/standard.h b/src/script/standard.h
index f2bf4a8af3..12ab9979a8 100644
--- a/src/script/standard.h
+++ b/src/script/standard.h
@@ -8,6 +8,7 @@
 
 #include <script/interpreter.h>
 #include <uint256.h>
+#include <util/hash_type.h>
 
 #include <string>
 #include <variant>
@@ -18,70 +19,6 @@ class CKeyID;
 class CScript;
 struct ScriptHash;
 
-template<typename HashType>
-class BaseHash
-{
-protected:
-    HashType m_hash;
-
-public:
-    BaseHash() : m_hash() {}
-    explicit BaseHash(const HashType& in) : m_hash(in) {}
-
-    unsigned char* begin()
-    {
-        return m_hash.begin();
-    }
-
-    const unsigned char* begin() const
-    {
-        return m_hash.begin();
-    }
-
-    unsigned char* end()
-    {
-        return m_hash.end();
-    }
-
-    const unsigned char* end() const
-    {
-        return m_hash.end();
-    }
-
-    operator std::vector<unsigned char>() const
-    {
-        return std::vector<unsigned char>{m_hash.begin(), m_hash.end()};
-    }
-
-    std::string ToString() const
-    {
-        return m_hash.ToString();
-    }
-
-    bool operator==(const BaseHash<HashType>& other) const noexcept
-    {
-        return m_hash == other.m_hash;
-    }
-
-    bool operator!=(const BaseHash<HashType>& other) const noexcept
-    {
-        return !(m_hash == other.m_hash);
-    }
-
-    bool operator<(const BaseHash<HashType>& other) const noexcept
-    {
-        return m_hash < other.m_hash;
-    }
-
-    size_t size() const
-    {
-        return m_hash.size();
-    }
-
-    unsigned char* data() { return m_hash.data(); }
-    const unsigned char* data() const { return m_hash.data(); }
-};
-
 /** A reference to a CScript: the Hash160 of its serialization (see script.h) */
 class CScriptID : public BaseHash<uint160>
 {
diff --git a/src/test/validation_chainstatemanager_tests.cpp b/src/test/validation_chainstatemanager_tests.cpp
index 82e70b5cdc..0b912acb08 100644
--- a/src/test/validation_chainstatemanager_tests.cpp
+++ b/src/test/validation_chainstatemanager_tests.cpp
@@ -226,10 +226,8 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, TestChain100Setup)
 
     // Snapshot should refuse to load at this height.
     BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(m_node, m_path_root));
-    BOOST_CHECK(chainman.ActiveChainstate().m_from_snapshot_blockhash.IsNull());
-    BOOST_CHECK_EQUAL(
-        chainman.ActiveChainstate().m_from_snapshot_blockhash,
-        chainman.SnapshotBlockhash().value_or(uint256()));
+    BOOST_CHECK(!chainman.ActiveChainstate().m_from_snapshot_blockhash);
+    BOOST_CHECK(!chainman.SnapshotBlockhash());
 
     // Mine 10 more blocks, putting at us height 110 where a valid assumeutxo value can
     // be found.
@@ -263,15 +261,20 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, TestChain100Setup)
     BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(
         m_node, m_path_root, [](CAutoFile& auto_infile, SnapshotMetadata& metadata) {
             // Wrong hash
+            metadata.m_base_blockhash = uint256::ZERO;
+    }));
+    BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(
+        m_node, m_path_root, [](CAutoFile& auto_infile, SnapshotMetadata& metadata) {
+            // Wrong hash
             metadata.m_base_blockhash = uint256::ONE;
     }));
 
     BOOST_REQUIRE(CreateAndActivateUTXOSnapshot(m_node, m_path_root));
 
     // Ensure our active chain is the snapshot chainstate.
-    BOOST_CHECK(!chainman.ActiveChainstate().m_from_snapshot_blockhash.IsNull());
+    BOOST_CHECK(!chainman.ActiveChainstate().m_from_snapshot_blockhash->IsNull());
     BOOST_CHECK_EQUAL(
-        chainman.ActiveChainstate().m_from_snapshot_blockhash,
+        *chainman.ActiveChainstate().m_from_snapshot_blockhash,
         *chainman.SnapshotBlockhash());
 
     const AssumeutxoData& au_data = *ExpectedAssumeutxo(snapshot_height, ::Params());
@@ -347,7 +350,7 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, TestChain100Setup)
 
     // Snapshot blockhash should be unchanged.
     BOOST_CHECK_EQUAL(
-        chainman.ActiveChainstate().m_from_snapshot_blockhash,
+        *chainman.ActiveChainstate().m_from_snapshot_blockhash,
         loaded_snapshot_blockhash);
 }
 
diff --git a/src/test/validation_tests.cpp b/src/test/validation_tests.cpp
index d0317aca0a..1e5baec01a 100644
--- a/src/test/validation_tests.cpp
+++ b/src/test/validation_tests.cpp
@@ -135,11 +135,11 @@ BOOST_AUTO_TEST_CASE(test_assumeutxo)
     }
 
     const auto out110 = *ExpectedAssumeutxo(110, *params);
-    BOOST_CHECK_EQUAL(out110.hash_serialized, uint256S("1ebbf5850204c0bdb15bf030f47c7fe91d45c44c712697e4509ba67adb01c618"));
+    BOOST_CHECK_EQUAL(out110.hash_serialized.ToString(), "1ebbf5850204c0bdb15bf030f47c7fe91d45c44c712697e4509ba67adb01c618");
     BOOST_CHECK_EQUAL(out110.nChainTx, (unsigned int)110);
 
     const auto out210 = *ExpectedAssumeutxo(210, *params);
-    BOOST_CHECK_EQUAL(out210.hash_serialized, uint256S("9c5ed99ef98544b34f8920b6d1802f72ac28ae6e2bd2bd4c316ff10c230df3f2"));
+    BOOST_CHECK_EQUAL(out210.hash_serialized.ToString(), "9c5ed99ef98544b34f8920b6d1802f72ac28ae6e2bd2bd4c316ff10c230df3f2");
     BOOST_CHECK_EQUAL(out210.nChainTx, (unsigned int)210);
 }
 
diff --git a/src/util/hash_type.h b/src/util/hash_type.h
new file mode 100644
index 0000000000..13b831cf19
--- /dev/null
+++ b/src/util/hash_type.h
@@ -0,0 +1,72 @@
+// Copyright (c) 2020-2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_HASH_TYPE_H
+#define BITCOIN_UTIL_HASH_TYPE_H
+
+template <typename HashType>
+class BaseHash
+{
+protected:
+    HashType m_hash;
+
+public:
+    BaseHash() : m_hash() {}
+    explicit BaseHash(const HashType& in) : m_hash(in) {}
+
+    unsigned char* begin()
+    {
+        return m_hash.begin();
+    }
+
+    const unsigned char* begin() const
+    {
+        return m_hash.begin();
+    }
+
+    unsigned char* end()
+    {
+        return m_hash.end();
+    }
+
+    const unsigned char* end() const
+    {
+        return m_hash.end();
+    }
+
+    operator std::vector<unsigned char>() const
+    {
+        return std::vector<unsigned char>{m_hash.begin(), m_hash.end()};
+    }
+
+    std::string ToString() const
+    {
+        return m_hash.ToString();
+    }
+
+    bool operator==(const BaseHash<HashType>& other) const noexcept
+    {
+        return m_hash == other.m_hash;
+    }
+
+    bool operator!=(const BaseHash<HashType>& other) const noexcept
+    {
+        return !(m_hash == other.m_hash);
+    }
+
+    bool operator<(const BaseHash<HashType>& other) const noexcept
+    {
+        return m_hash < other.m_hash;
+    }
+
+    size_t size() const
+    {
+        return m_hash.size();
+    }
+
+    unsigned char* data() { return m_hash.data(); }
+    const unsigned char* data() const { return m_hash.data(); }
+};
+
+#endif // BITCOIN_UTIL_HASH_TYPE_H
diff --git a/src/validation.cpp b/src/validation.cpp
index 639c1f6879..4f9b8687b7 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1158,7 +1158,7 @@ void CoinsViews::InitCache()
     m_cacheview = std::make_unique<CCoinsViewCache>(&m_catcherview);
 }
 
-CChainState::CChainState(CTxMemPool& mempool, BlockManager& blockman, uint256 from_snapshot_blockhash)
+CChainState::CChainState(CTxMemPool& mempool, BlockManager& blockman, std::optional<uint256> from_snapshot_blockhash)
     : m_mempool(mempool),
       m_blockman(blockman),
       m_from_snapshot_blockhash(from_snapshot_blockhash) {}
@@ -1169,8 +1169,8 @@ void CChainState::InitCoinsDB(
     bool should_wipe,
     std::string leveldb_name)
 {
-    if (!m_from_snapshot_blockhash.IsNull()) {
-        leveldb_name += "_" + m_from_snapshot_blockhash.ToString();
+    if (m_from_snapshot_blockhash) {
+        leveldb_name += "_" + m_from_snapshot_blockhash->ToString();
     }
 
     m_coins_views = std::make_unique<CoinsViews>(
@@ -3877,7 +3877,7 @@ bool CVerifyDB::VerifyDB(
     int reportDone = 0;
     LogPrintf("[0%%]..."); /* Continued */
 
-    bool is_snapshot_cs = !chainstate.m_from_snapshot_blockhash.IsNull();
+    const bool is_snapshot_cs{!chainstate.m_from_snapshot_blockhash};
 
     for (pindex = chainstate.m_chain.Tip(); pindex && pindex->pprev; pindex = pindex->pprev) {
         const int percentageDone = std::max(1, std::min(99, (int)(((double)(chainstate.m_chain.Height() - pindex->nHeight)) / (double)nCheckDepth * (nCheckLevel >= 4 ? 50 : 100))));
@@ -4458,8 +4458,8 @@ std::string CChainState::ToString()
 {
     CBlockIndex* tip = m_chain.Tip();
     return strprintf("Chainstate [%s] @ height %d (%s)",
-        m_from_snapshot_blockhash.IsNull() ? "ibd" : "snapshot",
-        tip ? tip->nHeight : -1, tip ? tip->GetBlockHash().ToString() : "null");
+                     m_from_snapshot_blockhash ? "snapshot" : "ibd",
+                     tip ? tip->nHeight : -1, tip ? tip->GetBlockHash().ToString() : "null");
 }
 
 bool CChainState::ResizeCoinsCaches(size_t coinstip_size, size_t coinsdb_size)
@@ -4662,10 +4662,10 @@ double GuessVerificationProgress(const ChainTxData& data, const CBlockIndex *pin
     return std::min<double>(pindex->nChainTx / fTxTotal, 1.0);
 }
 
-std::optional<uint256> ChainstateManager::SnapshotBlockhash() const {
+std::optional<uint256> ChainstateManager::SnapshotBlockhash() const
+{
     LOCK(::cs_main);
-    if (m_active_chainstate != nullptr &&
-            !m_active_chainstate->m_from_snapshot_blockhash.IsNull()) {
+    if (m_active_chainstate && m_active_chainstate->m_from_snapshot_blockhash) {
         // If a snapshot chainstate exists, it will always be our active.
         return m_active_chainstate->m_from_snapshot_blockhash;
     }
@@ -4688,9 +4688,9 @@ std::vector<CChainState*> ChainstateManager::GetAll()
     return out;
 }
 
-CChainState& ChainstateManager::InitializeChainstate(CTxMemPool& mempool, const uint256& snapshot_blockhash)
+CChainState& ChainstateManager::InitializeChainstate(CTxMemPool& mempool, const std::optional<uint256>& snapshot_blockhash)
 {
-    bool is_snapshot = !snapshot_blockhash.IsNull();
+    bool is_snapshot = snapshot_blockhash.has_value();
     std::unique_ptr<CChainState>& to_modify =
         is_snapshot ? m_snapshot_chainstate : m_ibd_chainstate;
 
@@ -4815,6 +4815,26 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
 
     uint256 base_blockhash = metadata.m_base_blockhash;
 
+    CBlockIndex* snapshot_start_block = WITH_LOCK(::cs_main, return m_blockman.LookupBlockIndex(base_blockhash));
+
+    if (!snapshot_start_block) {
+        // Needed for GetUTXOStats and ExpectedAssumeutxo to determine the height and to avoid a crash when base_blockhash.IsNull()
+        LogPrintf("[snapshot] Did not find snapshot start blockheader %s\n",
+                  base_blockhash.ToString());
+        return false;
+    }
+
+    int base_height = snapshot_start_block->nHeight;
+    auto maybe_au_data = ExpectedAssumeutxo(base_height, ::Params());
+
+    if (!maybe_au_data) {
+        LogPrintf("[snapshot] assumeutxo height in snapshot metadata not recognized " /* Continued */
+                  "(%d) - refusing to load snapshot\n", base_height);
+        return false;
+    }
+
+    const AssumeutxoData& au_data = *maybe_au_data;
+
     COutPoint outpoint;
     Coin coin;
     const uint64_t coins_count = metadata.m_coins_count;
@@ -4905,15 +4925,6 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
 
     assert(coins_cache.GetBestBlock() == base_blockhash);
 
-    CBlockIndex* snapshot_start_block = WITH_LOCK(::cs_main, return m_blockman.LookupBlockIndex(base_blockhash));
-
-    if (!snapshot_start_block) {
-        // Needed for GetUTXOStats to determine the height
-        LogPrintf("[snapshot] Did not find snapshot start blockheader %s\n",
-                  base_blockhash.ToString());
-        return false;
-    }
-
     CCoinsStats stats{CoinStatsHashType::HASH_SERIALIZED};
     auto breakpoint_fnc = [] { /* TODO insert breakpoint here? */ };
 
@@ -4927,19 +4938,7 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
     }
 
     // Assert that the deserialized chainstate contents match the expected assumeutxo value.
-
-    int base_height = snapshot_start_block->nHeight;
-    auto maybe_au_data = ExpectedAssumeutxo(base_height, ::Params());
-
-    if (!maybe_au_data) {
-        LogPrintf("[snapshot] assumeutxo height in snapshot metadata not recognized " /* Continued */
-            "(%d) - refusing to load snapshot\n", base_height);
-        return false;
-    }
-
-    const AssumeutxoData& au_data = *maybe_au_data;
-
-    if (stats.hashSerialized != au_data.hash_serialized) {
+    if (AssumeutxoHash{stats.hashSerialized} != au_data.hash_serialized) {
         LogPrintf("[snapshot] bad snapshot content hash: expected %s, got %s\n",
             au_data.hash_serialized.ToString(), stats.hashSerialized.ToString());
         return false;
diff --git a/src/validation.h b/src/validation.h
index 8fa45c3f77..1b50644185 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -553,7 +553,7 @@ public:
     //! CChainState instances.
     BlockManager& m_blockman;
 
-    explicit CChainState(CTxMemPool& mempool, BlockManager& blockman, uint256 from_snapshot_blockhash = uint256());
+    explicit CChainState(CTxMemPool& mempool, BlockManager& blockman, std::optional<uint256> from_snapshot_blockhash = std::nullopt);
 
     /**
      * Initialize the CoinsViews UTXO set database management data structures. The in-memory
@@ -584,9 +584,9 @@ public:
     /**
      * The blockhash which is the base of the snapshot this chainstate was created from.
      *
-     * IsNull() if this chainstate was not created from a snapshot.
+     * std::nullopt if this chainstate was not created from a snapshot.
      */
-    const uint256 m_from_snapshot_blockhash{};
+    const std::optional<uint256> m_from_snapshot_blockhash;
 
     /**
      * The set of all CBlockIndex entries with BLOCK_VALID_TRANSACTIONS (for itself and all ancestors) and
@@ -866,7 +866,7 @@ public:
     //                                  constructor
     //! @param[in] snapshot_blockhash   If given, signify that this chainstate
     //!                                 is based on a snapshot.
-    CChainState& InitializeChainstate(CTxMemPool& mempool, const uint256& snapshot_blockhash = uint256())
+    CChainState& InitializeChainstate(CTxMemPool& mempool, const std::optional<uint256>& snapshot_blockhash = std::nullopt)
         EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
     //! Get all chainstates currently being used.