Add funds preservation rule

Sources/Stratis.Bitcoin.Features.Consensus/ConsensusErrors.cs

@@ -74,5 +74,7 @@ namespace Stratis.Bitcoin.Features.Consensus
         public static readonly ConsensusError ProofOfWorkTooHigh = new ConsensusError("proof-of-work-too-heigh", "proof of work too heigh");
 
         public static readonly ConsensusError CheckpointViolation = new ConsensusError("checkpoint-violation", "block header hash does not match the checkpointed value");
+        
+        public static readonly ConsensusError BadBlockTotalFundsChanged = new ConsensusError("bad-block-total-funds-changed", "total amount of funds in blockchain changed");
     }
 }

Sources/Stratis.Bitcoin.Features.Consensus/DeStreamFullNodeBuilderConsensusExtension.cs

@@ -133,6 +133,7 @@ namespace Stratis.Bitcoin.Features.Consensus
 
                     // rules that require the store to be loaded (coinview)
                     new DeStreamLoadCoinviewRule(),
+                    new DeStreamFundsPreservationRule(),
                     new TransactionDuplicationActivationRule(), // implements BIP30
                     new PowCoinviewRule(), // implements BIP68, MaxSigOps and BlockReward calculation
                     new DeStreamBlockFeeRule()
@@ -178,6 +179,7 @@ namespace Stratis.Bitcoin.Features.Consensus
 
                     // rules that require the store to be loaded (coinview)
                     new DeStreamLoadCoinviewRule(),
+                    new DeStreamFundsPreservationRule(),
                     new TransactionDuplicationActivationRule(), // implements BIP30
                     new PosCoinviewRule(), // implements BIP68, MaxSigOps and BlockReward calculation
                     new DeStreamBlockFeeRule()

Sources/Stratis.Bitcoin.Features.Consensus/Rules/CommonRules/DeStreamFundsPreservationRule.cs

+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using NBitcoin;
+using Stratis.Bitcoin.Consensus.Rules;
+
+namespace Stratis.Bitcoin.Features.Consensus.Rules.CommonRules
+{
+    /// <summary>
+    ///     A rule verifies that total amount of coins in blockchain is not changed
+    /// </summary>
+    [ExecutionRule]
+    public class DeStreamFundsPreservationRule : UtxoStoreConsensusRule
+    {
+        public override Task RunAsync(RuleContext context)
+        {
+            UnspentOutputSet inputs =
+                (context as UtxoRuleContext ??
+                 throw new NotSupportedException($"Rule context must be {nameof(UtxoRuleContext)}")).UnspentOutputSet;
+            long totalIn = context.ValidationContext.Block.Transactions.SelectMany(p =>
+                    p.Inputs.RemoveChangePointer().Where(q => q.PrevOut != null)
+                        .Select(q => inputs.AccessCoins(q.PrevOut.Hash)?.TryGetOutput(q.PrevOut.N)?.Value ?? 0))
+                .Sum(p => p ?? 0);
+
+            long totalOut = context.ValidationContext.Block.Transactions.SelectMany(p => p.Outputs.Select(q => q.Value))
+                .Sum(p => p);
+
+            if (totalIn != totalOut)
+                ConsensusErrors.BadBlockTotalFundsChanged.Throw();
+
+            return Task.CompletedTask;
+        }
+    }
+}
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