com.alexkasko.netty.ftp.CrlfStringDecoder Maven / Gradle / Ivy

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Netty handler, partial implementation of RFC 959 "File Transfer Protocol (FTP)" for receiving FTP files. Both active and passive modes are supported.

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package com.alexkasko.netty.ftp;

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.frame.FrameDecoder;

import java.nio.charset.Charset;

/**
 * {@link FrameDecoder} implementation, that accumulates input strings until {@code \r\n}
 * and sends accumulated string upstream.
 *
 * @author alexkasko
 * Date: 12/28/12
 */
public class CrlfStringDecoder extends FrameDecoder {
    private static final byte CR = 13;
    private static final byte LF = 10;

    private final int maxRequestLengthBytes;
    private final Charset encoding;

    /**
     * Constructor, uses {@code 256} max string length and {@code UTF-8} encoding
     */
    public CrlfStringDecoder() {
        this(1<< 8, "UTF-8");
    }

    /**
     * Constructor
     *
     * @param maxRequestLengthBytes max length of accumulated string in bytes
     * @param encoding string encoding to use before sending it upstream
     */
    public CrlfStringDecoder(int maxRequestLengthBytes, String encoding) {
        if(maxRequestLengthBytes <= 0) throw new IllegalArgumentException(
                "Provided maxRequestLengthBytes: [" + maxRequestLengthBytes +"] must be positive");
        this.maxRequestLengthBytes = maxRequestLengthBytes;
        this.encoding = Charset.forName(encoding);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected Object decode(ChannelHandlerContext ctx, Channel channel, ChannelBuffer cb) throws Exception {
        byte[] data = new byte[maxRequestLengthBytes];
        int lineLength = 0;
        while (true) {
            if (!cb.readable()) {
                cb.resetReaderIndex();
                return null;
            }
            byte nextByte = cb.readByte();
            if (nextByte == CR) {
                nextByte = cb.readByte();
                if (nextByte == LF) {
                    return new String(data, encoding);
                }
            } else if (nextByte == LF) {
                return new String(data, encoding);
            } else {
                if (lineLength >= maxRequestLengthBytes) throw new IllegalArgumentException(
                        "Request size threshold exceeded: [" + maxRequestLengthBytes + "]");
                data[lineLength] = nextByte;
                lineLength += 1;
            }
        }
    }
}