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.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;
 };