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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 2010 Red Hat, Inc.
 *
 * Red Hat 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 java.util.Queue;

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelDownstreamHandler;
import org.jboss.netty.channel.ChannelEvent;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.ChannelUpstreamHandler;
import org.jboss.netty.util.internal.LinkedTransferQueue;

/**
 * A combination of {@link HttpRequestEncoder} and {@link HttpResponseDecoder}
 * which enables easier client side HTTP implementation. {@link HttpClientCodec}
 * provides additional state management for HEAD and CONNECT
 * requests, which {@link HttpResponseDecoder} lacks.  Please refer to
 * {@link HttpResponseDecoder} to learn what additional state management needs
 * to be done for HEAD and CONNECT and why
 * {@link HttpResponseDecoder} can not handle it by itself.
 *
 * @author The Netty Project
 * @author Trustin Lee
 * @version $Rev: 2368 $, $Date: 2010-10-18 17:19:03 +0900 (Mon, 18 Oct 2010) $
 *
 * @see HttpServerCodec
 *
 * @apiviz.has org.jboss.netty.handler.codec.http.HttpResponseDecoder
 * @apiviz.has org.jboss.netty.handler.codec.http.HttpRequestEncoder
 */
public class HttpClientCodec implements ChannelUpstreamHandler,
        ChannelDownstreamHandler {

    /** A queue that is used for correlating a request and a response. */
    final Queue queue = new LinkedTransferQueue();

    /** If true, decoding stops (i.e. pass-through) */
    volatile boolean done;

    private final HttpRequestEncoder encoder = new Encoder();
    private final HttpResponseDecoder decoder;

    /**
     * Creates a new instance with the default decoder options
     * ({@code maxInitialLineLength (4096}}, {@code maxHeaderSize (8192)}, and
     * {@code maxChunkSize (8192)}).
     */
    public HttpClientCodec() {
        this(4096, 8192, 8192);
    }

    /**
     * Creates a new instance with the specified decoder options.
     */
    public HttpClientCodec(
            int maxInitialLineLength, int maxHeaderSize, int maxChunkSize) {
        decoder = new Decoder(maxInitialLineLength, maxHeaderSize, maxChunkSize);
    }

    public void handleUpstream(ChannelHandlerContext ctx, ChannelEvent e)
            throws Exception {
        decoder.handleUpstream(ctx, e);
    }

    public void handleDownstream(ChannelHandlerContext ctx, ChannelEvent e)
            throws Exception {
        encoder.handleDownstream(ctx, e);
    }

    private final class Encoder extends HttpRequestEncoder {

        Encoder() {
            super();
        }

        @Override
        protected Object encode(ChannelHandlerContext ctx, Channel channel,
                Object msg) throws Exception {
            if (msg instanceof HttpRequest && !done) {
                queue.offer(((HttpRequest) msg).getMethod());
            }
            return super.encode(ctx, channel, msg);
        }
    }

    private final class Decoder extends HttpResponseDecoder {

        Decoder(int maxInitialLineLength, int maxHeaderSize, int maxChunkSize) {
            super(maxInitialLineLength, maxHeaderSize, maxChunkSize);
        }

        @Override
        protected Object decode(ChannelHandlerContext ctx, Channel channel,
                ChannelBuffer buffer, State state) throws Exception {
            if (done) {
                return buffer.readBytes(actualReadableBytes());
            } else {
                return super.decode(ctx, channel, buffer, state);
            }
        }

        @Override
        protected boolean isContentAlwaysEmpty(HttpMessage msg) {
            final int statusCode = ((HttpResponse) msg).getStatus().getCode();
            if (statusCode == 100) {
                // 100-continue response should be excluded from paired comparison.
                return true;
            }

            // Get the method of the HTTP request that corresponds to the
            // current response.
            HttpMethod method = queue.poll();

            char firstChar = method.getName().charAt(0);
            switch (firstChar) {
            case 'H':
                // According to 4.3, RFC2616:
                // All responses to the HEAD request method MUST NOT include a
                // message-body, even though the presence of entity-header fields
                // might lead one to believe they do.
                if (HttpMethod.HEAD.equals(method)) {
                    // Interesting edge case:
                    // Zero-byte chunk will appear if Transfer-Encoding of the
                    // response is 'chunked'.  This is probably because of the
                    // trailing headers.
                    return !msg.isChunked();
                }
                break;
            case 'C':
                // Successful CONNECT request results in a response with empty body.
                if (statusCode == 200) {
                    if (HttpMethod.CONNECT.equals(method)) {
                        // Proxy connection established - Not HTTP anymore.
                        done = true;
                        queue.clear();
                        return true;
                    }
                }
                break;
            }

            return super.isContentAlwaysEmpty(msg);
        }
    }
}