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The Netty project is an effort to provide an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.
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/*
 * 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 org.jboss.netty.handler.codec.http;

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.http.HttpHeaders.Names;
import org.jboss.netty.handler.codec.http.HttpHeaders.Values;
import org.jboss.netty.handler.codec.oneone.OneToOneEncoder;
import org.jboss.netty.util.CharsetUtil;

import java.io.UnsupportedEncodingException;
import java.util.Map;

import static org.jboss.netty.buffer.ChannelBuffers.*;
import static org.jboss.netty.handler.codec.http.HttpConstants.*;

/**
 * Encodes an {@link HttpMessage} or an {@link HttpChunk} into
 * a {@link ChannelBuffer}.
 *
 * Extensibility
 *
 * Please note that this encoder is designed to be extended to implement
 * a protocol derived from HTTP, such as
 * RTSP and
 * ICAP.
 * To implement the encoder of such a derived protocol, extend this class and
 * implement all abstract methods properly.
 * @apiviz.landmark
 */
public abstract class HttpMessageEncoder extends OneToOneEncoder {

    private static final byte[] CRLF = { CR, LF };
    private static final ChannelBuffer LAST_CHUNK =
        copiedBuffer("0\r\n\r\n", CharsetUtil.US_ASCII);

    private volatile boolean transferEncodingChunked;

    /**
     * Creates a new instance.
     */
    protected HttpMessageEncoder() {
    }

    @Override
    protected Object encode(ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
        if (msg instanceof HttpMessage) {
            HttpMessage m = (HttpMessage) msg;
            boolean contentMustBeEmpty;
            if (m.isChunked()) {
                // if Content-Length is set then the message can't be HTTP chunked
                if (HttpCodecUtil.isContentLengthSet(m)) {
                    contentMustBeEmpty = false;
                    transferEncodingChunked = false;
                    HttpCodecUtil.removeTransferEncodingChunked(m);
                } else {
                    // check if the Transfer-Encoding is set to chunked already.
                    // if not add the header to the message
                    if (!HttpCodecUtil.isTransferEncodingChunked(m)) {
                        m.headers().add(Names.TRANSFER_ENCODING, Values.CHUNKED);
                    }
                    contentMustBeEmpty = true;
                    transferEncodingChunked = true;
                }
            } else {
                transferEncodingChunked = contentMustBeEmpty = HttpCodecUtil.isTransferEncodingChunked(m);
            }

            ChannelBuffer header = dynamicBuffer(
                    channel.getConfig().getBufferFactory());
            encodeInitialLine(header, m);
            encodeHeaders(header, m);
            header.writeByte(CR);
            header.writeByte(LF);

            ChannelBuffer content = m.getContent();
            if (!content.readable()) {
                return header; // no content
            } else if (contentMustBeEmpty) {
                throw new IllegalArgumentException(
                        "HttpMessage.content must be empty " +
                        "if Transfer-Encoding is chunked.");
            } else {
                return wrappedBuffer(header, content);
            }
        }

        if (msg instanceof HttpChunk) {
            HttpChunk chunk = (HttpChunk) msg;
            if (transferEncodingChunked) {
                if (chunk.isLast()) {
                    transferEncodingChunked = false;
                    if (chunk instanceof HttpChunkTrailer) {
                        ChannelBuffer trailer = dynamicBuffer(
                                channel.getConfig().getBufferFactory());
                        trailer.writeByte((byte) '0');
                        trailer.writeByte(CR);
                        trailer.writeByte(LF);
                        encodeTrailingHeaders(trailer, (HttpChunkTrailer) chunk);
                        trailer.writeByte(CR);
                        trailer.writeByte(LF);
                        return trailer;
                    } else {
                        return LAST_CHUNK.duplicate();
                    }
                } else {
                    ChannelBuffer content = chunk.getContent();
                    int contentLength = content.readableBytes();

                    return wrappedBuffer(
                            copiedBuffer(
                                    Integer.toHexString(contentLength),
                                    CharsetUtil.US_ASCII),
                            wrappedBuffer(CRLF),
                            content.slice(content.readerIndex(), contentLength),
                            wrappedBuffer(CRLF));
                }
            } else {
                return chunk.getContent();
            }
        }

        // Unknown message type.
        return msg;
    }

    private static void encodeHeaders(ChannelBuffer buf, HttpMessage message) {
        try {
            for (Map.Entry h: message.headers()) {
                encodeHeader(buf, h.getKey(), h.getValue());
            }
        } catch (UnsupportedEncodingException e) {
            throw (Error) new Error().initCause(e);
        }
    }

    private static void encodeTrailingHeaders(ChannelBuffer buf, HttpChunkTrailer trailer) {
        try {
            for (Map.Entry h: trailer.trailingHeaders()) {
                encodeHeader(buf, h.getKey(), h.getValue());
            }
        } catch (UnsupportedEncodingException e) {
            throw (Error) new Error().initCause(e);
        }
    }

    private static void encodeHeader(ChannelBuffer buf, String header, String value)
            throws UnsupportedEncodingException {
        encodeAscii(header, buf);
        buf.writeByte(COLON);
        buf.writeByte(SP);
        encodeAscii(value, buf);
        buf.writeByte(CR);
        buf.writeByte(LF);
    }

    protected static void encodeAscii(String s, ChannelBuffer buf) {
        for (int i = 0; i < s.length(); i++) {
            buf.writeByte(c2b(s.charAt(i)));
        }
    }

    private static byte c2b(char c) {
        if (c > 255) {
            return '?';
        }
        return (byte) c;
    }

    protected abstract void encodeInitialLine(ChannelBuffer buf, HttpMessage message) throws Exception;
}