Merge branch 'issue-54'

Author: Savjee

src/blockchain.js

@@ -192,10 +192,30 @@ class Blockchain {
  }
 
  // Making sure that the amount sent is not greater than existing balance
- if (this.getBalanceOfAddress(transaction.fromAddress) < transaction.amount) {
+ const walletBalance = this.getBalanceOfAddress(transaction.fromAddress);
+ if (walletBalance < transaction.amount) {
  throw new Error('Not enough balance');
  }
 
+ // Get all other pending transactions for the "from" wallet
+ const pendingTxForWallet = this.pendingTransactions
+ .filter(tx => tx.fromAddress === transaction.fromAddress);
+
+ // If the wallet has more pending transactions, calculate the total amount
+ // of spend coins so far. If this exceeds the balance, we refuse to add this
+ // transaction.
+ if (pendingTxForWallet.length > 0) {
+ const totalPendingAmount = pendingTxForWallet
+ .map(tx => tx.amount)
+ .reduce((prev, curr) => prev + curr);
+
+ const totalAmount = totalPendingAmount + transaction.amount;
+ if (totalAmount > walletBalance) {
+ throw new Error('Pending transactions for this wallet is higher than its balance.');
+ }
+ }
+ 
+
  this.pendingTransactions.push(transaction);
  debug('transaction added: %s', transaction);
  }

tests/blockchain.test.js

@@ -82,6 +82,36 @@ describe('Blockchain class', function() {
  });
  });
 
+ describe('minePendingTransactions', function() {
+ // It should not be possible for a user to create multiple pending
+ // transactions for a total amount higher than his balance.
+ // In this test we start with this situation:
+ // - Wallet "walletAddr" -> 80 coins (100 mining reward - 2 test tx)
+ // - Wallet "wallet2" -> 0 coins
+ it('should not allow pending transactions to go below zero', function() {
+ const blockchain = createBlockchainWithTx();
+ const walletAddr = signingKey.getPublic('hex');
+
+ // Verify that the wallets have the correct balance
+ assert.strict.equal(blockchain.getBalanceOfAddress('wallet2'), 0);
+ assert.strict.equal(blockchain.getBalanceOfAddress(walletAddr), 80);
+
+ // Create a transaction for 80 coins (from walletAddr -> "wallet2")
+ blockchain.addTransaction(createSignedTx(80));
+
+ // Try tro create another transaction for which we don't have the balance.
+ // Blockchain should refuse this!
+ assert.throws(() => { blockchain.addTransaction(createSignedTx(80)); }, Error);
+
+ // Mine transactions, send rewards to another address
+ blockchain.minePendingTransactions(1);
+
+ // Verify that the first transaction did go through.
+ assert.strict.equal(blockchain.getBalanceOfAddress(walletAddr), 0);
+ assert.strict.equal(blockchain.getBalanceOfAddress('wallet2'), 80);
+ });
+ });
+
  describe('helper functions', function() {
  it('should correctly set first block to genesis block', function() {
  assert.strict.deepEqual(blockchain.chain[0], blockchain.createGenesisBlock());