http://netty.io/netty-all/: Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers and clients. (The Netty Project) 
/*
 * 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.haproxy;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.LineBasedFrameDecoder;
import io.netty.handler.codec.ProtocolDetectionResult;
import io.netty.util.CharsetUtil;

import java.util.List;


Decodes an HAProxy proxy protocol header

See Also:
/**
 * Decodes an HAProxy proxy protocol header
 *
 * @see <a href="http://haproxy.1wt.eu/download/1.5/doc/proxy-protocol.txt">Proxy Protocol Specification</a>
 */
public class HAProxyMessageDecoder extends ByteToMessageDecoder {
    
Maximum possible length of a v1 proxy protocol header per spec

/**
     * Maximum possible length of a v1 proxy protocol header per spec
     */
    private static final int V1_MAX_LENGTH = 108;

    
Maximum possible length of a v2 proxy protocol header (fixed 16 bytes + max unsigned short)

/**
     * Maximum possible length of a v2 proxy protocol header (fixed 16 bytes + max unsigned short)
     */
    private static final int V2_MAX_LENGTH = 16 + 65535;

    
Minimum possible length of a fully functioning v2 proxy protocol header (fixed 16 bytes + v2 address info space)

/**
     * Minimum possible length of a fully functioning v2 proxy protocol header (fixed 16 bytes + v2 address info space)
     */
    private static final int V2_MIN_LENGTH = 16 + 216;

    
Maximum possible length for v2 additional TLV data (max unsigned short - max v2 address info space)

/**
     * Maximum possible length for v2 additional TLV data (max unsigned short - max v2 address info space)
     */
    private static final int V2_MAX_TLV = 65535 - 216;

    
Version 1 header delimiter is always '\r\n' per spec

/**
     * Version 1 header delimiter is always '\r\n' per spec
     */
    private static final int DELIMITER_LENGTH = 2;

    
Binary header prefix

/**
     * Binary header prefix
     */
    private static final byte[] BINARY_PREFIX = {
            (byte) 0x0D,
            (byte) 0x0A,
            (byte) 0x0D,
            (byte) 0x0A,
            (byte) 0x00,
            (byte) 0x0D,
            (byte) 0x0A,
            (byte) 0x51,
            (byte) 0x55,
            (byte) 0x49,
            (byte) 0x54,
            (byte) 0x0A
    };

    private static final byte[] TEXT_PREFIX = {
            (byte) 'P',
            (byte) 'R',
            (byte) 'O',
            (byte) 'X',
            (byte) 'Y',
    };

    
Binary header prefix length

/**
     * Binary header prefix length
     */
    private static final int BINARY_PREFIX_LENGTH = BINARY_PREFIX.length;

    /**
     * {@link ProtocolDetectionResult} for {@link HAProxyProtocolVersion#V1}.
     */
    private static final ProtocolDetectionResult<HAProxyProtocolVersion> DETECTION_RESULT_V1 =
            ProtocolDetectionResult.detected(HAProxyProtocolVersion.V1);

    /**
     * {@link ProtocolDetectionResult} for {@link HAProxyProtocolVersion#V2}.
     */
    private static final ProtocolDetectionResult<HAProxyProtocolVersion> DETECTION_RESULT_V2 =
            ProtocolDetectionResult.detected(HAProxyProtocolVersion.V2);

    
true if we're discarding input because we're already over maxLength 
/**
     * {@code true} if we're discarding input because we're already over maxLength
     */
    private boolean discarding;

    
Number of discarded bytes

/**
     * Number of discarded bytes
     */
    private int discardedBytes;

    
true if we're finished decoding the proxy protocol header 
/**
     * {@code true} if we're finished decoding the proxy protocol header
     */
    private boolean finished;

    
Protocol specification version

/**
     * Protocol specification version
     */
    private int version = -1;

    
The latest v2 spec (2014/05/18) allows for additional data to be sent in the proxy protocol header beyond the
address information block so now we need a configurable max header size

/**
     * The latest v2 spec (2014/05/18) allows for additional data to be sent in the proxy protocol header beyond the
     * address information block so now we need a configurable max header size
     */
    private final int v2MaxHeaderSize;

    
Creates a new decoder with no additional data (TLV) restrictions

/**
     * Creates a new decoder with no additional data (TLV) restrictions
     */
    public HAProxyMessageDecoder() {
        v2MaxHeaderSize = V2_MAX_LENGTH;
    }

    
Creates a new decoder with restricted additional data (TLV) size


Note: limiting TLV size only affects processing of v2, binary headers. Also, as allowed by the 1.5 spec
TLV data is currently ignored. For maximum performance it would be best to configure your upstream proxy host to
NOT send TLV data and instantiate with a max TLV size of 0. 


Params:
  • maxTlvSize – maximum number of bytes allowed for additional data (Type-Length-Value vectors) in a v2 header
/**
     * Creates a new decoder with restricted additional data (TLV) size
     * <p>
     * <b>Note:</b> limiting TLV size only affects processing of v2, binary headers. Also, as allowed by the 1.5 spec
     * TLV data is currently ignored. For maximum performance it would be best to configure your upstream proxy host to
     * <b>NOT</b> send TLV data and instantiate with a max TLV size of {@code 0}.
     * </p>
     *
     * @param maxTlvSize maximum number of bytes allowed for additional data (Type-Length-Value vectors) in a v2 header
     */
    public HAProxyMessageDecoder(int maxTlvSize) {
        if (maxTlvSize < 1) {
            v2MaxHeaderSize = V2_MIN_LENGTH;
        } else if (maxTlvSize > V2_MAX_TLV) {
            v2MaxHeaderSize = V2_MAX_LENGTH;
        } else {
            int calcMax = maxTlvSize + V2_MIN_LENGTH;
            if (calcMax > V2_MAX_LENGTH) {
                v2MaxHeaderSize = V2_MAX_LENGTH;
            } else {
                v2MaxHeaderSize = calcMax;
            }
        }
    }

    
Returns the proxy protocol specification version in the buffer if the version is found.
Returns -1 if no version was found in the buffer.

/**
     * Returns the proxy protocol specification version in the buffer if the version is found.
     * Returns -1 if no version was found in the buffer.
     */
    private static int findVersion(final ByteBuf buffer) {
        final int n = buffer.readableBytes();
        // per spec, the version number is found in the 13th byte
        if (n < 13) {
            return -1;
        }

        int idx = buffer.readerIndex();
        return match(BINARY_PREFIX, buffer, idx) ? buffer.getByte(idx + BINARY_PREFIX_LENGTH) : 1;
    }

    
Returns the index in the buffer of the end of header if found.
Returns -1 if no end of header was found in the buffer.

/**
     * Returns the index in the buffer of the end of header if found.
     * Returns -1 if no end of header was found in the buffer.
     */
    private static int findEndOfHeader(final ByteBuf buffer) {
        final int n = buffer.readableBytes();

        // per spec, the 15th and 16th bytes contain the address length in bytes
        if (n < 16) {
            return -1;
        }

        int offset = buffer.readerIndex() + 14;

        // the total header length will be a fixed 16 byte sequence + the dynamic address information block
        int totalHeaderBytes = 16 + buffer.getUnsignedShort(offset);

        // ensure we actually have the full header available
        if (n >= totalHeaderBytes) {
            return totalHeaderBytes;
        } else {
            return -1;
        }
    }

    
Returns the index in the buffer of the end of line found.
Returns -1 if no end of line was found in the buffer.

/**
     * Returns the index in the buffer of the end of line found.
     * Returns -1 if no end of line was found in the buffer.
     */
    private static int findEndOfLine(final ByteBuf buffer) {
        final int n = buffer.writerIndex();
        for (int i = buffer.readerIndex(); i < n; i++) {
            final byte b = buffer.getByte(i);
            if (b == '\r' && i < n - 1 && buffer.getByte(i + 1) == '\n') {
                return i;  // \r\n
            }
        }
        return -1;  // Not found.
    }

    @Override
    public boolean isSingleDecode() {
        // ByteToMessageDecoder uses this method to optionally break out of the decoding loop after each unit of work.
        // Since we only ever want to decode a single header we always return true to save a bit of work here.
        return true;
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        super.channelRead(ctx, msg);
        if (finished) {
            ctx.pipeline().remove(this);
        }
    }

    @Override
    protected final void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        // determine the specification version
        if (version == -1) {
            if ((version = findVersion(in)) == -1) {
                return;
            }
        }

        ByteBuf decoded;

        if (version == 1) {
            decoded = decodeLine(ctx, in);
        } else {
            decoded = decodeStruct(ctx, in);
        }

        if (decoded != null) {
            finished = true;
            try {
                if (version == 1) {
                    out.add(HAProxyMessage.decodeHeader(decoded.toString(CharsetUtil.US_ASCII)));
                } else {
                    out.add(HAProxyMessage.decodeHeader(decoded));
                }
            } catch (HAProxyProtocolException e) {
                fail(ctx, null, e);
            }
        }
    }

    
Create a frame out of the ByteBuf and return it. Based on code from LineBasedFrameDecoder.decode(ChannelHandlerContext, ByteBuf). 
Params:
Returns:frame the ByteBuf which represent the frame or null if no frame could be created
/**
     * Create a frame out of the {@link ByteBuf} and return it.
     * Based on code from {@link LineBasedFrameDecoder#decode(ChannelHandlerContext, ByteBuf)}.
     *
     * @param ctx     the {@link ChannelHandlerContext} which this {@link HAProxyMessageDecoder} belongs to
     * @param buffer  the {@link ByteBuf} from which to read data
     * @return frame  the {@link ByteBuf} which represent the frame or {@code null} if no frame could
     *                be created
     */
    private ByteBuf decodeStruct(ChannelHandlerContext ctx, ByteBuf buffer) throws Exception {
        final int eoh = findEndOfHeader(buffer);
        if (!discarding) {
            if (eoh >= 0) {
                final int length = eoh - buffer.readerIndex();
                if (length > v2MaxHeaderSize) {
                    buffer.readerIndex(eoh);
                    failOverLimit(ctx, length);
                    return null;
                }
                return buffer.readSlice(length);
            } else {
                final int length = buffer.readableBytes();
                if (length > v2MaxHeaderSize) {
                    discardedBytes = length;
                    buffer.skipBytes(length);
                    discarding = true;
                    failOverLimit(ctx, "over " + discardedBytes);
                }
                return null;
            }
        } else {
            if (eoh >= 0) {
                buffer.readerIndex(eoh);
                discardedBytes = 0;
                discarding = false;
            } else {
                discardedBytes = buffer.readableBytes();
                buffer.skipBytes(discardedBytes);
            }
            return null;
        }
    }

    
Create a frame out of the ByteBuf and return it. Based on code from LineBasedFrameDecoder.decode(ChannelHandlerContext, ByteBuf). 
Params:
Returns:frame the ByteBuf which represent the frame or null if no frame could be created
/**
     * Create a frame out of the {@link ByteBuf} and return it.
     * Based on code from {@link LineBasedFrameDecoder#decode(ChannelHandlerContext, ByteBuf)}.
     *
     * @param ctx     the {@link ChannelHandlerContext} which this {@link HAProxyMessageDecoder} belongs to
     * @param buffer  the {@link ByteBuf} from which to read data
     * @return frame  the {@link ByteBuf} which represent the frame or {@code null} if no frame could
     *                be created
     */
    private ByteBuf decodeLine(ChannelHandlerContext ctx, ByteBuf buffer) throws Exception {
        final int eol = findEndOfLine(buffer);
        if (!discarding) {
            if (eol >= 0) {
                final int length = eol - buffer.readerIndex();
                if (length > V1_MAX_LENGTH) {
                    buffer.readerIndex(eol + DELIMITER_LENGTH);
                    failOverLimit(ctx, length);
                    return null;
                }
                ByteBuf frame = buffer.readSlice(length);
                buffer.skipBytes(DELIMITER_LENGTH);
                return frame;
            } else {
                final int length = buffer.readableBytes();
                if (length > V1_MAX_LENGTH) {
                    discardedBytes = length;
                    buffer.skipBytes(length);
                    discarding = true;
                    failOverLimit(ctx, "over " + discardedBytes);
                }
                return null;
            }
        } else {
            if (eol >= 0) {
                final int delimLength = buffer.getByte(eol) == '\r' ? 2 : 1;
                buffer.readerIndex(eol + delimLength);
                discardedBytes = 0;
                discarding = false;
            } else {
                discardedBytes = buffer.readableBytes();
                buffer.skipBytes(discardedBytes);
            }
            return null;
        }
    }

    private void failOverLimit(final ChannelHandlerContext ctx, int length) {
        failOverLimit(ctx, String.valueOf(length));
    }

    private void failOverLimit(final ChannelHandlerContext ctx, String length) {
        int maxLength = version == 1 ? V1_MAX_LENGTH : v2MaxHeaderSize;
        fail(ctx, "header length (" + length + ") exceeds the allowed maximum (" + maxLength + ')', null);
    }

    private void fail(final ChannelHandlerContext ctx, String errMsg, Exception e) {
        finished = true;
        ctx.close(); // drop connection immediately per spec
        HAProxyProtocolException ppex;
        if (errMsg != null && e != null) {
            ppex = new HAProxyProtocolException(errMsg, e);
        } else if (errMsg != null) {
            ppex = new HAProxyProtocolException(errMsg);
        } else if (e != null) {
            ppex = new HAProxyProtocolException(e);
        } else {
            ppex = new HAProxyProtocolException();
        }
        throw ppex;
    }

    
Returns the ProtocolDetectionResult for the given ByteBuf. 
/**
     * Returns the {@link ProtocolDetectionResult} for the given {@link ByteBuf}.
     */
    public static ProtocolDetectionResult<HAProxyProtocolVersion> detectProtocol(ByteBuf buffer) {
        if (buffer.readableBytes() < 12) {
            return ProtocolDetectionResult.needsMoreData();
        }

        int idx = buffer.readerIndex();

        if (match(BINARY_PREFIX, buffer, idx)) {
            return DETECTION_RESULT_V2;
        }
        if (match(TEXT_PREFIX, buffer, idx)) {
            return DETECTION_RESULT_V1;
        }
        return ProtocolDetectionResult.invalid();
    }

    private static boolean match(byte[] prefix, ByteBuf buffer, int idx) {
        for (int i = 0; i < prefix.length; i++) {
            final byte b = buffer.getByte(idx + i);
            if (b != prefix[i]) {
                return false;
            }
        }
        return true;
    }
}