Fixed issue preventing blocks from being served from the archive.

Now prefixing the byte buffer with the block height to mimic a cached block message.

src/main/java/org/qortal/api/resource/BlocksResource.java

@@ -140,7 +140,7 @@ public class BlocksResource {
             }
 
             // Not found, so try the block archive
-            byte[] bytes = BlockArchiveReader.getInstance().fetchSerializedBlockBytesForSignature(signature, repository);
+            byte[] bytes = BlockArchiveReader.getInstance().fetchSerializedBlockBytesForSignature(signature, false, repository);
             if (bytes != null) {
                 return Base58.encode(bytes);
             }

src/main/java/org/qortal/controller/Controller.java

@@ -1393,7 +1393,7 @@ public class Controller extends Thread {
 			// If we have no block data, we should check the archive in case it's there
 			if (blockData == null) {
 				if (Settings.getInstance().isArchiveEnabled()) {
-					byte[] bytes = BlockArchiveReader.getInstance().fetchSerializedBlockBytesForSignature(signature, repository);
+					byte[] bytes = BlockArchiveReader.getInstance().fetchSerializedBlockBytesForSignature(signature, true, repository);
 					if (bytes != null) {
 						CachedBlockMessage blockMessage = new CachedBlockMessage(bytes);
 						blockMessage.setId(message.getId());

src/main/java/org/qortal/repository/BlockArchiveReader.java

@@ -1,5 +1,6 @@
 package org.qortal.repository;
 
+import com.google.common.primitives.Ints;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.qortal.data.at.ATStateData;
@@ -13,10 +14,7 @@ import org.qortal.utils.Triple;
 
 import static org.qortal.transform.Transformer.INT_LENGTH;
 
-import java.io.File;
-import java.io.FileNotFoundException;
-import java.io.IOException;
-import java.io.RandomAccessFile;
+import java.io.*;
 import java.nio.ByteBuffer;
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -167,7 +165,7 @@ public class BlockArchiveReader {
         return null;
     }
 
-    public byte[] fetchSerializedBlockBytesForSignature(byte[] signature, Repository repository) {
+    public byte[] fetchSerializedBlockBytesForSignature(byte[] signature, boolean includeHeightPrefix, Repository repository) {
 
         if (this.fileListCache.isEmpty()) {
             this.fetchFileList();
@@ -175,7 +173,22 @@ public class BlockArchiveReader {
 
         Integer height = this.fetchHeightForSignature(signature, repository);
         if (height != null) {
-            return this.fetchSerializedBlockBytesForHeight(height);
+            byte[] blockBytes = this.fetchSerializedBlockBytesForHeight(height);
+
+            // When responding to a peer with a BLOCK message, we must prefix the byte array with the block height
+            // This mimics the toData() method in BlockMessage and CachedBlockMessage
+            if (includeHeightPrefix) {
+                ByteArrayOutputStream bytes = new ByteArrayOutputStream(blockBytes.length + INT_LENGTH);
+                try {
+                    bytes.write(Ints.toByteArray(height));
+                    bytes.write(blockBytes);
+                    return bytes.toByteArray();
+
+                } catch (IOException e) {
+                    return null;
+                }
+            }
+            return blockBytes;
         }
         return null;
     }