chainparams: add allowed assumeutxo values

Values for mainnet and testnet will be specified in a follow-up PR that can be
scrutinized accordingly. This structure is required for use in snapshot activation
logic.

src/chainparams.cpp

@@ -8,7 +8,6 @@
 #include <chainparamsseeds.h>
 #include <consensus/merkle.h>
 #include <hash.h> // for signet block challenge hash
-#include <tinyformat.h>
 #include <util/system.h>
 #include <util/strencodings.h>
 #include <versionbitsinfo.h>
@@ -161,6 +160,10 @@ public:
             }
         };
 
+        m_assumeutxo_data = MapAssumeutxo{
+         // TODO to be specified in a future patch.
+        };
+
         chainTxData = ChainTxData{
             // Data from RPC: getchaintxstats 4096 0000000000000000000b9d2ec5a352ecba0592946514a92f14319dc2b367fc72
             /* nTime    */ 1603995752,
@@ -250,6 +253,10 @@ public:
             }
         };
 
+        m_assumeutxo_data = MapAssumeutxo{
+            // TODO to be specified in a future patch.
+        };
+
         chainTxData = ChainTxData{
             // Data from RPC: getchaintxstats 4096 000000000000006433d1efec504c53ca332b64963c425395515b01977bd7b3b0
             /* nTime    */ 1603359686,
@@ -431,6 +438,17 @@ public:
             }
         };
 
+        m_assumeutxo_data = MapAssumeutxo{
+            {
+                110,
+                {uint256S("0x76fd7334ac7c1baf57ddc0c626f073a655a35d98a4258cd1382c8cc2b8392e10"), 110},
+            },
+            {
+                210,
+                {uint256S("0x9c5ed99ef98544b34f8920b6d1802f72ac28ae6e2bd2bd4c316ff10c230df3f2"), 210},
+            },
+        };
+
         chainTxData = ChainTxData{
             0,
             0,
@@ -526,3 +544,9 @@ 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;
+}

src/chainparams.h

@@ -30,6 +30,26 @@ struct CCheckpointData {
     }
 };
 
+/**
+ * Holds configuration for use during UTXO snapshot load and validation. The contents
+ * here are security critical, since they dictate which UTXO snapshots are recognized
+ * as valid.
+ */
+struct AssumeutxoData {
+    //! The expected hash of the deserialized UTXO set.
+    const uint256 hash_serialized;
+
+    //! Used to populate the nChainTx value, which is used during BlockManager::LoadBlockIndex().
+    //!
+    //! We need to hardcode the value here because this is computed cumulatively using block data,
+    //! which we do not necessarily have at the time of snapshot load.
+    const unsigned int nChainTx;
+};
+
+std::ostream& operator<<(std::ostream& o, const AssumeutxoData& aud);
+
+using MapAssumeutxo = std::map<int, const AssumeutxoData>;
+
 /**
  * Holds various statistics on transactions within a chain. Used to estimate
  * verification progress during chain sync.
@@ -90,6 +110,11 @@ public:
     const std::string& Bech32HRP() const { return bech32_hrp; }
     const std::vector<SeedSpec6>& FixedSeeds() const { return vFixedSeeds; }
     const CCheckpointData& Checkpoints() const { return checkpointData; }
+
+    //! Get allowed assumeutxo configuration.
+    //! @see ChainstateManager
+    const MapAssumeutxo& Assumeutxo() const { return m_assumeutxo_data; }
+
     const ChainTxData& TxData() const { return chainTxData; }
 protected:
     CChainParams() {}
@@ -111,6 +136,7 @@ protected:
     bool m_is_test_chain;
     bool m_is_mockable_chain;
     CCheckpointData checkpointData;
+    MapAssumeutxo m_assumeutxo_data;
     ChainTxData chainTxData;
 };
 

src/node/coinstats.cpp

@@ -55,6 +55,18 @@ static void ApplyHash(CCoinsStats& stats, MuHash3072& muhash, const uint256& has
     muhash.Insert(MakeUCharSpan(ss));
 }
 
+//! Warning: be very careful when changing this! assumeutxo and UTXO snapshot
+//! validation commitments are reliant on the hash constructed by this
+//! function.
+//!
+//! If the construction of this hash is changed, it will invalidate
+//! existing UTXO snapshots. This will not result in any kind of consensus
+//! failure, but it will force clients that were expecting to make use of
+//! assumeutxo to do traditional IBD instead.
+//!
+//! It is also possible, though very unlikely, that a change in this
+//! construction could cause a previously invalid (and potentially malicious)
+//! UTXO snapshot to be considered valid.
 template <typename T>
 static void ApplyStats(CCoinsStats& stats, T& hash_obj, const uint256& hash, const std::map<uint32_t, Coin>& outputs)
 {

src/test/validation_tests.cpp

@@ -5,6 +5,7 @@
 #include <chainparams.h>
 #include <net.h>
 #include <signet.h>
+#include <uint256.h>
 #include <validation.h>
 
 #include <test/util/setup_common.h>
@@ -119,4 +120,27 @@ BOOST_AUTO_TEST_CASE(signet_parse_tests)
     BOOST_CHECK(!CheckSignetBlockSolution(block, signet_params->GetConsensus()));
 }
 
+//! Test retrieval of valid assumeutxo values.
+BOOST_AUTO_TEST_CASE(test_assumeutxo)
+{
+    const auto params = CreateChainParams(*m_node.args, CBaseChainParams::REGTEST);
+
+    // These heights don't have assumeutxo configurations associated, per the contents
+    // of chainparams.cpp.
+    std::vector<int> bad_heights{0, 100, 111, 115, 209, 211};
+
+    for (auto empty : bad_heights) {
+        const auto out = ExpectedAssumeutxo(empty, *params);
+        BOOST_CHECK(!out);
+    }
+
+    const auto out110 = *ExpectedAssumeutxo(110, *params);
+    BOOST_CHECK_EQUAL(out110.hash_serialized, uint256S("76fd7334ac7c1baf57ddc0c626f073a655a35d98a4258cd1382c8cc2b8392e10"));
+    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.nChainTx, (unsigned int)210);
+}
+
 BOOST_AUTO_TEST_SUITE_END()

src/validation.cpp

@@ -22,6 +22,7 @@
 #include <logging/timer.h>
 #include <node/ui_interface.h>
 #include <optional.h>
+#include <node/coinstats.h>
 #include <policy/policy.h>
 #include <policy/settings.h>
 #include <pow.h>
@@ -5192,6 +5193,18 @@ CChainState& ChainstateManager::InitializeChainstate(CTxMemPool& mempool, const
     return *to_modify;
 }
 
+const AssumeutxoData* ExpectedAssumeutxo(
+    const int height, const CChainParams& chainparams)
+{
+    const MapAssumeutxo& valid_assumeutxos_map = chainparams.Assumeutxo();
+    const auto assumeutxo_found = valid_assumeutxos_map.find(height);
+
+    if (assumeutxo_found != valid_assumeutxos_map.end()) {
+        return &assumeutxo_found->second;
+    }
+    return nullptr;
+}
+
 CChainState& ChainstateManager::ActiveChainstate() const
 {
     LOCK(::cs_main);

src/validation.h

@@ -53,6 +53,7 @@ struct ChainTxData;
 struct DisconnectedBlockTransactions;
 struct PrecomputedTransactionData;
 struct LockPoints;
+struct AssumeutxoData;
 
 /** Default for -minrelaytxfee, minimum relay fee for transactions */
 static const unsigned int DEFAULT_MIN_RELAY_TX_FEE = 1000;
@@ -1013,4 +1014,13 @@ inline bool IsBlockPruned(const CBlockIndex* pblockindex)
     return (fHavePruned && !(pblockindex->nStatus & BLOCK_HAVE_DATA) && pblockindex->nTx > 0);
 }
 
+/**
+ * Return the expected assumeutxo value for a given height, if one exists.
+ *
+ * @param height[in] Get the assumeutxo value for this height.
+ *
+ * @returns empty if no assumeutxo configuration exists for the given height.
+ */
+const AssumeutxoData* ExpectedAssumeutxo(const int height, const CChainParams& params);
+
 #endif // BITCOIN_VALIDATION_H