/**

* 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.ByteArrayInputStream;

import java.io.EOFException;

import java.io.IOException;

import java.nio.ByteBuffer;

import java.util.Map;

import java.util.HashMap;

/**

* <p>Each message on the network consists of the message header followed by an optional payload.</p>

*

* <p>Message Header:</p>

* <pre>

* Size Field Description

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

* 4 bytes Magic Magic number

* 12 bytes Command Null-terminated ASCII command

* 4 bytes Length Payload length

* 4 bytes Checksum First 4 bytes of the SHA-256 double digest of the payload

* </pre>

*/

public class MessageHeader {

/** Message header length */

public static final int HEADER_LENGTH = 24;

/** Checksum for zero-length payload */

public static final byte[] ZERO_LENGTH_CHECKSUM = new byte[] {

(byte)0x5d, (byte)0xf6, (byte)0xe0, (byte)0xe2

};

/** Message commands */

public static final int ADDR_CMD = 1;

public static final int ALERT_CMD = 2;

public static final int BLOCK_CMD = 3;

public static final int FILTERADD_CMD = 4;

public static final int FILTERCLEAR_CMD = 5;

public static final int FILTERLOAD_CMD = 6;

public static final int GETADDR_CMD = 7;

public static final int GETBLOCKS_CMD = 8;

public static final int GETDATA_CMD = 9;

public static final int GETHEADERS_CMD = 10;

public static final int HEADERS_CMD = 11;

public static final int INV_CMD = 12;

public static final int INVBLOCK_CMD = 13;

public static final int INVTX_CMD = 14;

public static final int MEMPOOL_CMD = 15;

public static final int MERKLEBLOCK_CMD = 16;

public static final int NOTFOUND_CMD = 17;

public static final int PING_CMD = 18;

public static final int PONG_CMD = 19;

public static final int REJECT_CMD = 20;

public static final int TX_CMD = 21;

public static final int VERACK_CMD = 22;

public static final int VERSION_CMD = 23;

/** Message command map */

public static final Map<String, Integer> cmdMap = new HashMap<>(20);

static {

cmdMap.put("addr", Integer.valueOf(ADDR_CMD));

cmdMap.put("alert", Integer.valueOf(ALERT_CMD));

cmdMap.put("block", Integer.valueOf(BLOCK_CMD));

cmdMap.put("filteradd", Integer.valueOf(FILTERADD_CMD));

cmdMap.put("filterclear", Integer.valueOf(FILTERCLEAR_CMD));

cmdMap.put("filterload", Integer.valueOf(FILTERLOAD_CMD));

cmdMap.put("getaddr", Integer.valueOf(GETADDR_CMD));

cmdMap.put("getblocks", Integer.valueOf(GETBLOCKS_CMD));

cmdMap.put("getdata", Integer.valueOf(GETDATA_CMD));

cmdMap.put("getheaders", Integer.valueOf(GETHEADERS_CMD));

cmdMap.put("headers", Integer.valueOf(HEADERS_CMD));

cmdMap.put("inv", Integer.valueOf(INV_CMD));

cmdMap.put("mempool", Integer.valueOf(MEMPOOL_CMD));

cmdMap.put("merkleblock", Integer.valueOf(MERKLEBLOCK_CMD));

cmdMap.put("notfound", Integer.valueOf(NOTFOUND_CMD));

cmdMap.put("ping", Integer.valueOf(PING_CMD));

cmdMap.put("pong", Integer.valueOf(PONG_CMD));

cmdMap.put("reject", Integer.valueOf(REJECT_CMD));

cmdMap.put("tx", Integer.valueOf(TX_CMD));

cmdMap.put("verack", Integer.valueOf(VERACK_CMD));

cmdMap.put("version", Integer.valueOf(VERSION_CMD));

}

/**

* Builds the message header and then constructs a buffer containing the message header

* and the message data

*

* @param cmd Message command

* @param msgData Message data

* @return Message buffer

*/

public static ByteBuffer buildMessage(String cmd, byte[] msgData) {

byte[] bytes = new byte[HEADER_LENGTH+msgData.length];

//

// Set the magic number

//

Utils.uint32ToByteArrayLE(Parameters.MAGIC_NUMBER, bytes, 0);

//

// Set the command name

//

for (int i=0; i<cmd.length(); i++)

bytes[4+i] = (byte)cmd.codePointAt(i);

//

// Set the payload length

//

Utils.uint32ToByteArrayLE(msgData.length, bytes, 16);

//

// Compute the payload checksum

//

// The message header contains a fixed checksum value when there is no payload

//

if (msgData.length == 0) {

System.arraycopy(ZERO_LENGTH_CHECKSUM, 0, bytes, 20, 4);

} else {

byte[] digest = Utils.doubleDigest(msgData);

System.arraycopy(digest, 0, bytes, 20, 4);

System.arraycopy(msgData, 0, bytes, 24, msgData.length);

}

return ByteBuffer.wrap(bytes);

}

/**

* Processes the message header and returns the message command. A VerificationException

* is thrown if the message header is incomplete, has an incorrect magic value, or the

* checksum is not correct.

*

* @param inStream Message data stream

* @param msgBytes Message bytes

* @return Message command

* @throws EOFException

* @throws IOException

* @throws VerificationException

*/

public static String processMessage(ByteArrayInputStream inStream, byte[] msgBytes)

throws EOFException, IOException, VerificationException {

if (inStream.available() < HEADER_LENGTH)

throw new EOFException("End-of-data while processing message header");

inStream.skip(HEADER_LENGTH);

//

// Verify the magic number

//

long magic = Utils.readUint32LE(msgBytes, 0);

if (magic != Parameters.MAGIC_NUMBER)

throw new VerificationException(String.format("Message header magic number %d is invalid", magic));

//

// Verify the payload checksum

//

if (msgBytes.length > HEADER_LENGTH) {

byte[] digest = Utils.doubleDigest(msgBytes, HEADER_LENGTH, msgBytes.length-HEADER_LENGTH);

if (digest[0] != msgBytes[20] || digest[1] != msgBytes[21] ||

digest[2] != msgBytes[22] || digest[3] != msgBytes[23])

throw new VerificationException("Message checksum incorrect");

}

//

// Build the command name

//

StringBuilder cmdString = new StringBuilder(16);

for (int i=4; i<16; i++) {

if (msgBytes[i] == 0)

break;

cmdString.appendCodePoint(((int)msgBytes[i])&0xff);

}

return cmdString.toString();

}

}