Adding the getHash() public method to the Transaction class

graphenej/src/main/java/cy/agorise/graphenej/Transaction.java

@@ -20,6 +20,7 @@ import java.lang.reflect.Type;
 import java.text.ParsePosition;
 import java.text.SimpleDateFormat;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Date;
 import java.util.List;
 import java.util.TimeZone;
@@ -97,6 +98,7 @@ public class Transaction implements ByteSerializable, JsonSerializable {
     public Transaction(BlockData blockData, List<BaseOperation> operationList){
         this.blockData = blockData;
         this.operations = operationList;
+        this.extensions = new Extensions();
     }
 
     /**
@@ -267,7 +269,19 @@ public class Transaction implements ByteSerializable, JsonSerializable {
         obj.addProperty(KEY_REF_BLOCK_PREFIX, blockData.getRefBlockPrefix());
 
         return obj;
+    }
 
+    /**
+     * Method that will return a hash of this transaction's data. The hash covers only the transaction
+     * attributes and not the signature or the chain id.
+     *
+     * @return  A hash of the serialized transaction.
+     */
+    public byte[] getHash(){
+        byte[] txBytes = toBytes();
+        byte[] toHash = Arrays.copyOfRange(txBytes, 32, txBytes.length); //Tx data only, without chain id
+        Sha256Hash hash = Sha256Hash.wrap(Sha256Hash.hash(toHash));
+        return Arrays.copyOfRange(hash.getBytes(), 0, 20); // The hash is only the first 20 bytes
     }
 
     /**

graphenej/src/test/java/cy/agorise/graphenej/TransactionTest.java

@@ -345,4 +345,21 @@ public class TransactionTest {
         // Broadcasting transaction
         broadcastTransaction(sourcePrivateKey, operationList, listener, null);
     }
+
+    @Test
+    public void testTransactionHash(){
+        ArrayList<BaseOperation> operations = new ArrayList<>();
+        TransferOperation transferOperation = new TransferOperationBuilder()
+                .setTransferAmount(new AssetAmount(UnsignedLong.valueOf("363"), new Asset("1.3.0")))
+                .setFee(new AssetAmount(UnsignedLong.valueOf("10420"), new Asset("1.3.0")))
+                .setSource(new UserAccount("1.2.1029856"))
+                .setDestination(new UserAccount("1.2.390320"))
+                .build();
+        BlockData blockData = new BlockData(50885, 2948192884L, 1543548351);
+        operations.add(transferOperation);
+        Transaction transaction = new Transaction(blockData, operations);
+        byte[] testHash = transaction.getHash();
+        // Making sure the generated hash matches the one we expect from the block explorer
+        Assert.assertArrayEquals(Util.hexToBytes("4fec588ccdd04daaf80666a3646a48b5189df041"), testHash);
+    }
 }