Re-add difficulty check for PoS, re-activate removed test

packages/blockchain/src/consensus/casper.ts

@@ -1,6 +1,8 @@
 import { ConsensusAlgorithm } from '@ethereumjs/common'
+import { BIGINT_0 } from '@ethereumjs/util'
 
 import type { Consensus } from '../types.js'
+import type { BlockHeader } from '@ethereumjs/block'
 
 /**
  * This class encapsulates Casper-related consensus functionality when used with the Blockchain class.
@@ -18,6 +20,14 @@ export class CasperConsensus implements Consensus {
 
   public async validateConsensus(): Promise<void> {}
 
-  public async validateDifficulty(): Promise<void> {}
+  public async validateDifficulty(header: BlockHeader): Promise<void> {
+    // TODO: This is not really part of consensus validation and it should be analyzed
+    // if it is possible to replace by a more generic hardfork check between block and
+    // blockchain along adding new blocks or headers
+    if (header.difficulty !== BIGINT_0) {
+      const msg = 'invalid difficulty.  PoS blocks must have difficulty 0'
+      throw new Error(`${msg} ${header.errorStr()}`)
+    }
+  }
   public async newBlock(): Promise<void> {}
 }

packages/blockchain/test/pos.spec.ts

@@ -1,5 +1,5 @@
 import { createBlockFromBlockData } from '@ethereumjs/block'
-import { Common, Hardfork } from '@ethereumjs/common'
+import { Chain, Common, Hardfork } from '@ethereumjs/common'
 import { bytesToHex } from '@ethereumjs/util'
 import { assert, describe, it } from 'vitest'
 
@@ -88,6 +88,29 @@ describe('Proof of Stake - inserting blocks into blockchain', () => {
         BigInt(1313601),
         'should have calculated the correct post-Merge total difficulty'
       )
+
+      const common = new Common({ chain: Chain.Mainnet, hardfork: Hardfork.London })
+      const powBlock = createBlockFromBlockData(
+        {
+          header: {
+            number: 16,
+            difficulty: BigInt(1),
+            parentHash: latestHeader.hash(),
+            timestamp: latestHeader.timestamp + BigInt(1),
+            gasLimit: BigInt(10000),
+          },
+        },
+        { common }
+      )
+      try {
+        await blockchain.putBlock(powBlock)
+        assert.fail('should throw when inserting PoW block')
+      } catch (err: any) {
+        assert.ok(
+          err.message.includes('invalid difficulty'),
+          'should throw with invalid difficulty message'
+        )
+      }
     })
   }
 })