add support for block parsing

src/main/java/com/sparrowwallet/drongo/protocol/Block.java

@@ -0,0 +1,45 @@
+package com.sparrowwallet.drongo.protocol;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class Block extends Message {
+    private BlockHeader blockHeader;
+    private Sha256Hash hash;
+    private List<Transaction> transactions;
+
+    public Block(byte[] payload) {
+        super(payload, 0);
+    }
+
+    public void parse() {
+        blockHeader = new BlockHeader(payload, cursor);
+        cursor += blockHeader.getMessageSize();
+
+        hash = Sha256Hash.wrapReversed(Sha256Hash.hashTwice(payload, offset, cursor - offset));
+        if(cursor != payload.length) {
+            int numTransactions = (int)readVarInt();
+            transactions = new ArrayList<>(numTransactions);
+            for(int i = 0; i < numTransactions; i++) {
+                Transaction tx = new Transaction(payload, cursor);
+                transactions.add(tx);
+                cursor += tx.getMessageSize();
+            }
+        } else {
+            transactions = Collections.emptyList();
+        }
+    }
+
+    public BlockHeader getBlockHeader() {
+        return blockHeader;
+    }
+
+    public Sha256Hash getHash() {
+        return hash;
+    }
+
+    public List<Transaction> getTransactions() {
+        return transactions;
+    }
+}

src/main/java/com/sparrowwallet/drongo/protocol/BlockHeader.java

@@ -19,6 +19,10 @@ public class BlockHeader extends Message {
         super(rawheader, 0);
     }
 
+    public BlockHeader(byte[] blockdata, int offset) {
+        super(blockdata, offset);
+    }
+
     public BlockHeader(long version, Sha256Hash prevBlockHash, Sha256Hash merkleRoot, Sha256Hash witnessRoot, long time, long difficultyTarget, long nonce) {
         this.version = version;
         this.prevBlockHash = prevBlockHash;

src/main/java/com/sparrowwallet/drongo/protocol/Transaction.java

@@ -53,6 +53,10 @@ public class Transaction extends ChildMessage {
         super(rawtx, 0);
     }
 
+    public Transaction(byte[] blockdata, int offset) {
+        super(blockdata, offset);
+    }
+
     public long getVersion() {
         return version;
     }