Prevent Duplicate Transactions in Block

15Dkatz · Sep 29, 2022 · 4d98221 · 4d98221
1 parent 6c5fc2c
commit 4d98221
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Showing 2 changed files with 13 additions and 0 deletions.
diff --git a/blockchain/index.js b/blockchain/index.js
@@ -37,6 +37,7 @@ class Blockchain {
   validTransactionData({ chain }) {
     for (let i=1; i<chain.length; i++) {
       const block = chain[i];
+      const transactionSet = new Set();
       let rewardTransactionCount = 0;
 
       for (let transaction of block.data) {
@@ -67,6 +68,13 @@ class Blockchain {
             console.error('Invalid input amount');
             return false;
           }
+
+          if (transactionSet.has(transaction)) {
+            console.error('An identical transaction appears more than once in the block');
+            return false;
+          } else {
+            transactionSet.add(transaction);
+          }
         }
       }
     }

diff --git a/blockchain/index.test.js b/blockchain/index.test.js
@@ -236,7 +236,12 @@ describe('Blockchain', () => {
 
     describe('and a block contains multiple identical transactions', () => {
       it('returns false and logs an error', () => {
+        newChain.addBlock({
+          data: [transaction, transaction, transaction, rewardTransaction]
+        });
 
+        expect(blockchain.validTransactionData({ chain: newChain.chain })).toBe(false);
+        expect(errorMock).toHaveBeenCalled();
       });
     });
   });