/*
 * Copyright (c) 2006-2011 Christian Plattner. All rights reserved.
 * Please refer to the LICENSE.txt for licensing details.
 */
package ch.ethz.ssh2.transport;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.SecureRandom;

import ch.ethz.ssh2.PacketFormatException;
import ch.ethz.ssh2.compression.Compressor;
import ch.ethz.ssh2.crypto.cipher.BlockCipher;
import ch.ethz.ssh2.crypto.cipher.CipherInputStream;
import ch.ethz.ssh2.crypto.cipher.CipherOutputStream;
import ch.ethz.ssh2.crypto.cipher.NullCipher;
import ch.ethz.ssh2.crypto.digest.MAC;
import ch.ethz.ssh2.log.Logger;
import ch.ethz.ssh2.packets.Packets;

/**
 * TransportConnection.
 *
 * @author Christian Plattner
 * @version $Id: TransportConnection.java 144 2014-04-25 12:48:25Z dkocher@sudo.ch $
 */
public class TransportConnection {
    private static final Logger log = Logger.getLogger(TransportConnection.class);

    int send_seq_number = 0;

    int recv_seq_number = 0;

    CipherInputStream cis;

    CipherOutputStream cos;

    boolean useRandomPadding;

    /* Depends on current MAC and CIPHER */

    MAC send_mac;

    byte[] send_mac_buffer;

    int send_padd_blocksize = 8;

    MAC recv_mac;

    byte[] recv_mac_buffer;

    byte[] recv_mac_buffer_cmp;

    int recv_padd_blocksize = 8;

    Compressor recv_comp;

    Compressor send_comp;

    boolean can_compress;

    byte[] recv_comp_buffer;

    byte[] send_comp_buffer;

    /* won't change */

    final byte[] send_padding_buffer = new byte[256];

    final byte[] send_packet_header_buffer = new byte[5];

    final byte[] recv_padding_buffer = new byte[256];

    final byte[] recv_packet_header_buffer = new byte[5];

    boolean recv_packet_header_present = false;

    ClientServerHello csh;

    final SecureRandom rnd;

    public TransportConnection(InputStream is, OutputStream os, SecureRandom rnd) {
        this.cis = new CipherInputStream(new NullCipher(), is);
        this.cos = new CipherOutputStream(new NullCipher(), os);
        this.rnd = rnd;
    }

    public void changeRecvCipher(BlockCipher bc, MAC mac) {
        cis.changeCipher(bc);
        recv_mac = mac;
        recv_mac_buffer = (mac != null) ? new byte[mac.size()] : null;
        recv_mac_buffer_cmp = (mac != null) ? new byte[mac.size()] : null;
        recv_padd_blocksize = bc.getBlockSize();

        if (recv_padd_blocksize < 8) {
            recv_padd_blocksize = 8;
        }
    }

    public void changeSendCipher(BlockCipher bc, MAC mac) {
        if ((bc instanceof NullCipher) == false) {
            /* Only use zero byte padding for the first few packets */
            useRandomPadding = true;
            /* Once we start encrypting, there is no way back */
        }

        cos.changeCipher(bc);
        send_mac = mac;
        send_mac_buffer = (mac != null) ? new byte[mac.size()] : null;
        send_padd_blocksize = bc.getBlockSize();

        if (send_padd_blocksize < 8) {
            send_padd_blocksize = 8;
        }
    }

    public void changeRecvCompression(Compressor comp) {
        recv_comp = comp;

        if (comp != null) {
            recv_comp_buffer = new byte[comp.getBufferSize()];
        }
    }

    public void changeSendCompression(Compressor comp) {
        send_comp = comp;

        if (comp != null) {
            send_comp_buffer = new byte[comp.getBufferSize()];
        }
    }

    public void sendMessage(byte[] message) throws IOException {
        sendMessage(message, 0, message.length, 0);
    }

    public void sendMessage(byte[] message, int off, int len) throws IOException {
        sendMessage(message, off, len, 0);
    }

    public int getPacketOverheadEstimate() {
        // return an estimate for the paket overhead (for send operations)
        return 5 + 4 + (send_padd_blocksize - 1) + send_mac_buffer.length;
    }

    public void sendMessage(byte[] message, int off, int len, int padd) throws IOException {
        if (padd < 4) {
            padd = 4;
        }
        else if (padd > 64) {
            padd = 64;
        }

        if (send_comp != null && can_compress) {
            len = send_comp.compress(message, off, len, send_comp_buffer);
            message = send_comp_buffer;
        }

        int packet_len = 5 + len + padd; /* Minimum allowed padding is 4 */
        int slack = packet_len % send_padd_blocksize;

        if (slack != 0) {
            packet_len += (send_padd_blocksize - slack);
        }

        if (packet_len < 16) {
            packet_len = 16;
        }

        int padd_len = packet_len - (5 + len);

        if (useRandomPadding) {
            for (int i = 0; i < padd_len; i = i + 4) {
                /*
                 * don't waste calls to rnd.nextInt() (by using only 8bit of the
                 * output). just believe me: even though we may write here up to 3
                 * bytes which won't be used, there is no "buffer overflow" (i.e.,
                 * arrayindexoutofbounds). the padding buffer is big enough =) (256
                 * bytes, and that is bigger than any current cipher block size + 64).
                 */
                int r = rnd.nextInt();
                send_padding_buffer[i] = (byte) r;
                send_padding_buffer[i + 1] = (byte)(r >> 8);
                send_padding_buffer[i + 2] = (byte)(r >> 16);
                send_padding_buffer[i + 3] = (byte)(r >> 24);
            }
        }
        else {
            /* use zero padding for unencrypted traffic */
            for (int i = 0; i < padd_len; i++) {
                send_padding_buffer[i] = 0;
            }

            /* Actually this code is paranoid: we never filled any
             * bytes into the padding buffer so far, therefore it should
             * consist of zeros only.
             */
        }

        send_packet_header_buffer[0] = (byte)((packet_len - 4) >> 24);
        send_packet_header_buffer[1] = (byte)((packet_len - 4) >> 16);
        send_packet_header_buffer[2] = (byte)((packet_len - 4) >> 8);
        send_packet_header_buffer[3] = (byte)((packet_len - 4));
        send_packet_header_buffer[4] = (byte) padd_len;
        cos.write(send_packet_header_buffer, 0, 5);
        cos.write(message, off, len);
        cos.write(send_padding_buffer, 0, padd_len);

        if (send_mac != null) {
            send_mac.initMac(send_seq_number);
            send_mac.update(send_packet_header_buffer, 0, 5);
            send_mac.update(message, off, len);
            send_mac.update(send_padding_buffer, 0, padd_len);
            send_mac.getMac(send_mac_buffer, 0);
            cos.writePlain(send_mac_buffer, 0, send_mac_buffer.length);
        }

        cos.flush();

        if (log.isDebugEnabled()) {
            log.debug("Sent " + Packets.getMessageName(message[off] & 0xff) + " " + len + " bytes payload");
        }

        send_seq_number++;
    }

    public int peekNextMessageLength() throws IOException {
        if (recv_packet_header_present == false) {
            cis.read(recv_packet_header_buffer, 0, 5);
            recv_packet_header_present = true;
        }

        int packet_length = ((recv_packet_header_buffer[0] & 0xff) << 24) |
                            ((recv_packet_header_buffer[1] & 0xff) << 16) |
                            ((recv_packet_header_buffer[2] & 0xff) << 8)  |
                            ((recv_packet_header_buffer[3] & 0xff));
        int padding_length = recv_packet_header_buffer[4] & 0xff;

        if (packet_length > TransportManager.MAX_PACKET_SIZE || packet_length < 12) {
            throw new PacketFormatException(String.format("Illegal packet size (%d)", packet_length));
        }

        int payload_length = packet_length - padding_length - 1;

        if (payload_length < 0) {
            throw new PacketFormatException(String.format("Illegal padding_length in packet from remote (%d)", padding_length));
        }

        return payload_length;
    }

    public int receiveMessage(byte buffer[], int off, int len) throws IOException {
        if (recv_packet_header_present == false) {
            cis.read(recv_packet_header_buffer, 0, 5);
        }
        else {
            recv_packet_header_present = false;
        }

        int packet_length = ((recv_packet_header_buffer[0] & 0xff) << 24) |
                            ((recv_packet_header_buffer[1] & 0xff) << 16) |
                            ((recv_packet_header_buffer[2] & 0xff) << 8)  |
                            ((recv_packet_header_buffer[3] & 0xff));
        int padding_length = recv_packet_header_buffer[4] & 0xff;

        if (packet_length > TransportManager.MAX_PACKET_SIZE || packet_length < 12) {
            throw new PacketFormatException(String.format("Illegal packet size (%d)", packet_length));
        }

        int payload_length = packet_length - padding_length - 1;

        if (payload_length < 0) {
            throw new PacketFormatException(String.format("Illegal padding_length in packet from remote (%d)", padding_length));
        }

        if (payload_length >= len) {
            throw new IOException("Receive buffer too small (" + len + ", need " + payload_length + ")");
        }

        cis.read(buffer, off, payload_length);
        cis.read(recv_padding_buffer, 0, padding_length);

        if (recv_mac != null) {
            cis.readPlain(recv_mac_buffer, 0, recv_mac_buffer.length);
            recv_mac.initMac(recv_seq_number);
            recv_mac.update(recv_packet_header_buffer, 0, 5);
            recv_mac.update(buffer, off, payload_length);
            recv_mac.update(recv_padding_buffer, 0, padding_length);
            recv_mac.getMac(recv_mac_buffer_cmp, 0);

            for (int i = 0; i < recv_mac_buffer.length; i++) {
                if (recv_mac_buffer[i] != recv_mac_buffer_cmp[i]) {
                    throw new IOException("Remote sent corrupt MAC.");
                }
            }
        }

        recv_seq_number++;

        if (log.isDebugEnabled()) {
            log.debug("Received " + Packets.getMessageName(buffer[off] & 0xff) + " " + payload_length
                      + " bytes payload");
        }

        if (recv_comp != null && can_compress) {
            int[] uncomp_len = new int[] {payload_length};
            buffer = recv_comp.uncompress(buffer, off, uncomp_len);
            return uncomp_len[0];
        }
        else {
            return payload_length;
        }
    }

    public void startCompression() {
        can_compress = true;
    }
}