/**

* Copyright 2013 Ronald W Hoffman

*

* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

*

* http://www.apache.org/licenses/LICENSE-2.0

*

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

*/

package JavaBitcoin;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.nio.ByteBuffer;

import java.util.List;

/**

* <p>The 'headers' message is returned in response to a 'getheaders' message.

* Note that the returned header includes the block header (80 bytes) plus

* the transaction count (although the count is set to zero)</p>

*

* <p>Headers Message</p>

* <pre>

* Size Field Description

* ==== ===== ===========

* VarInt Count Number of headers

* Variable Entries Header entries

* </pre>

*/

public class HeadersMessage {

/**

* Build the 'headers' message

*

* @param peer Destination peer

* @param chainList List of chain block headers

* @return Headers message

* @throws IOException Unable to write to the output stream

*/

public static Message buildHeadersMessage(Peer peer, List<byte[]> chainList) throws IOException {

//

// Write the header count

//

int hdrCount = chainList.size();

byte[] varCount = VarInt.encode(hdrCount);

ByteArrayOutputStream outStream = new ByteArrayOutputStream(hdrCount*81+2);

outStream.write(varCount);

//

// Write the headers (set the transaction count to 0)

//

for (byte[] hdrData : chainList) {

outStream.write(hdrData, 0, Block.HEADER_SIZE);

outStream.write(0);

}

//

// Build the message

//

byte[] msgData = outStream.toByteArray();

ByteBuffer buffer = MessageHeader.buildMessage("headers", msgData);

return new Message(buffer, peer, MessageHeader.HEADERS_CMD);

}

}