/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you 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 io.netty.handler.codec.socksx.v5;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.DecoderException;
import io.netty.handler.codec.DecoderResult;
import io.netty.handler.codec.ReplayingDecoder;
import io.netty.handler.codec.socksx.SocksVersion;
import io.netty.handler.codec.socksx.v5.Socks5CommandRequestDecoder.State;

import java.util.List;

Decodes a single Socks5CommandRequest from the inbound ByteBufs. On successful decode, this decoder will forward the received data to the next handler, so that other handler can remove or replace this decoder later. On failed decode, this decoder will discard the received data, so that other handler closes the connection later. /**
 * Decodes a single {@link Socks5CommandRequest} from the inbound {@link ByteBuf}s.
 * On successful decode, this decoder will forward the received data to the next handler, so that
 * other handler can remove or replace this decoder later.  On failed decode, this decoder will
 * discard the received data, so that other handler closes the connection later.
 */
public class Socks5CommandRequestDecoder extends ReplayingDecoder<State> {

    enum State {
        INIT,
        SUCCESS,
        FAILURE
    }

    private final Socks5AddressDecoder addressDecoder;

    public Socks5CommandRequestDecoder() {
        this(Socks5AddressDecoder.DEFAULT);
    }

    public Socks5CommandRequestDecoder(Socks5AddressDecoder addressDecoder) {
        super(State.INIT);
        if (addressDecoder == null) {
            throw new NullPointerException("addressDecoder");
        }

        this.addressDecoder = addressDecoder;
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        try {
            switch (state()) {
            case INIT: {
                final byte version = in.readByte();
                if (version != SocksVersion.SOCKS5.byteValue()) {
                    throw new DecoderException(
                            "unsupported version: " + version + " (expected: " + SocksVersion.SOCKS5.byteValue() + ')');
                }

                final Socks5CommandType type = Socks5CommandType.valueOf(in.readByte());
                in.skipBytes(1); // RSV
                final Socks5AddressType dstAddrType = Socks5AddressType.valueOf(in.readByte());
                final String dstAddr = addressDecoder.decodeAddress(dstAddrType, in);
                final int dstPort = in.readUnsignedShort();

                out.add(new DefaultSocks5CommandRequest(type, dstAddrType, dstAddr, dstPort));
                checkpoint(State.SUCCESS);
            }
            case SUCCESS: {
                int readableBytes = actualReadableBytes();
                if (readableBytes > 0) {
                    out.add(in.readRetainedSlice(readableBytes));
                }
                break;
            }
            case FAILURE: {
                in.skipBytes(actualReadableBytes());
                break;
            }
            }
        } catch (Exception e) {
            fail(out, e);
        }
    }

    private void fail(List<Object> out, Exception cause) {
        if (!(cause instanceof DecoderException)) {
            cause = new DecoderException(cause);
        }

        checkpoint(State.FAILURE);

        Socks5Message m = new DefaultSocks5CommandRequest(
                Socks5CommandType.CONNECT, Socks5AddressType.IPv4, "0.0.0.0", 1);
        m.setDecoderResult(DecoderResult.failure(cause));
        out.add(m);
    }
}