/*
 * Copyright 2012 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.v4;

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.v4.Socks4ServerDecoder.State;
import io.netty.util.CharsetUtil;
import io.netty.util.NetUtil;

import java.util.List;

Decodes a single Socks4CommandRequest from the inbound ByteBufs. On successful decode, this decoder will forward the received data to the next handler, so that other handler can remove 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 Socks4CommandRequest} 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 this decoder later.  On failed decode, this decoder will discard the
 * received data, so that other handler closes the connection later.
 */
public class Socks4ServerDecoder extends ReplayingDecoder<State> {

    private static final int MAX_FIELD_LENGTH = 255;

    enum State {
        START,
        READ_USERID,
        READ_DOMAIN,
        SUCCESS,
        FAILURE
    }

    private Socks4CommandType type;
    private String dstAddr;
    private int dstPort;
    private String userId;

    public Socks4ServerDecoder() {
        super(State.START);
        setSingleDecode(true);
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        try {
            switch (state()) {
            case START: {
                final int version = in.readUnsignedByte();
                if (version != SocksVersion.SOCKS4a.byteValue()) {
                    throw new DecoderException("unsupported protocol version: " + version);
                }

                type = Socks4CommandType.valueOf(in.readByte());
                dstPort = in.readUnsignedShort();
                dstAddr = NetUtil.intToIpAddress(in.readInt());
                checkpoint(State.READ_USERID);
            }
            case READ_USERID: {
                userId = readString("userid", in);
                checkpoint(State.READ_DOMAIN);
            }
            case READ_DOMAIN: {
                // Check for Socks4a protocol marker 0.0.0.x
                if (!"0.0.0.0".equals(dstAddr) && dstAddr.startsWith("0.0.0.")) {
                    dstAddr = readString("dstAddr", in);
                }
                out.add(new DefaultSocks4CommandRequest(type, dstAddr, dstPort, userId));
                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);
        }

        Socks4CommandRequest m = new DefaultSocks4CommandRequest(
                type != null? type : Socks4CommandType.CONNECT,
                dstAddr != null? dstAddr : "",
                dstPort != 0? dstPort : 65535,
                userId != null? userId : "");

        m.setDecoderResult(DecoderResult.failure(cause));
        out.add(m);

        checkpoint(State.FAILURE);
    }

    
Reads a variable-length NUL-terminated string as defined in SOCKS4.
/**
     * Reads a variable-length NUL-terminated string as defined in SOCKS4.
     */
    private static String readString(String fieldName, ByteBuf in) {
        int length = in.bytesBefore(MAX_FIELD_LENGTH + 1, (byte) 0);
        if (length < 0) {
            throw new DecoderException("field '" + fieldName + "' longer than " + MAX_FIELD_LENGTH + " chars");
        }

        String value = in.readSlice(length).toString(CharsetUtil.US_ASCII);
        in.skipBytes(1); // Skip the NUL.

        return value;
    }
}