/*
 * 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.http;

import io.netty.buffer.ByteBuf;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.CombinedChannelDuplexHandler;
import io.netty.handler.codec.PrematureChannelClosureException;
import io.netty.util.ReferenceCountUtil;

import java.util.ArrayDeque;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.atomic.AtomicLong;

A combination of HttpRequestEncoder and HttpResponseDecoder which enables easier client side HTTP implementation. HttpClientCodec provides additional state management for HEAD and CONNECT requests, which HttpResponseDecoder lacks. Please refer to HttpResponseDecoder to learn what additional state management needs to be done for HEAD and CONNECT and why HttpResponseDecoder can not handle it by itself. If the Channel is closed and there are missing responses, a PrematureChannelClosureException is thrown. 
See Also:
HttpServerCodec/**
 * A combination of {@link HttpRequestEncoder} and {@link HttpResponseDecoder}
 * which enables easier client side HTTP implementation. {@link HttpClientCodec}
 * provides additional state management for <tt>HEAD</tt> and <tt>CONNECT</tt>
 * requests, which {@link HttpResponseDecoder} lacks.  Please refer to
 * {@link HttpResponseDecoder} to learn what additional state management needs
 * to be done for <tt>HEAD</tt> and <tt>CONNECT</tt> and why
 * {@link HttpResponseDecoder} can not handle it by itself.
 *
 * If the {@link Channel} is closed and there are missing responses,
 * a {@link PrematureChannelClosureException} is thrown.
 *
 * @see HttpServerCodec
 */
public final class HttpClientCodec extends CombinedChannelDuplexHandler<HttpResponseDecoder, HttpRequestEncoder>
        implements HttpClientUpgradeHandler.SourceCodec {

    
A queue that is used for correlating a request and a response. /** A queue that is used for correlating a request and a response. */
    private final Queue<HttpMethod> queue = new ArrayDeque<HttpMethod>();
    private final boolean parseHttpAfterConnectRequest;

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

    private final AtomicLong requestResponseCounter = new AtomicLong();
    private final boolean failOnMissingResponse;

    
Creates a new instance with the default decoder options (maxInitialLineLength (4096}, maxHeaderSize (8192), and maxChunkSize (8192)). /**
     * 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, false);
    }

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

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

    
Creates a new instance with the specified decoder options.
/**
     * Creates a new instance with the specified decoder options.
     */
    public HttpClientCodec(
            int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean failOnMissingResponse,
            boolean validateHeaders) {
        this(maxInitialLineLength, maxHeaderSize, maxChunkSize, failOnMissingResponse, validateHeaders, false);
    }

    
Creates a new instance with the specified decoder options.
/**
     * Creates a new instance with the specified decoder options.
     */
    public HttpClientCodec(
            int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean failOnMissingResponse,
            boolean validateHeaders, boolean parseHttpAfterConnectRequest) {
        init(new Decoder(maxInitialLineLength, maxHeaderSize, maxChunkSize, validateHeaders), new Encoder());
        this.failOnMissingResponse = failOnMissingResponse;
        this.parseHttpAfterConnectRequest = parseHttpAfterConnectRequest;
    }

    
Creates a new instance with the specified decoder options.
/**
     * Creates a new instance with the specified decoder options.
     */
    public HttpClientCodec(
            int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean failOnMissingResponse,
            boolean validateHeaders, int initialBufferSize) {
        this(maxInitialLineLength, maxHeaderSize, maxChunkSize, failOnMissingResponse, validateHeaders,
                initialBufferSize, false);
    }

    
Creates a new instance with the specified decoder options.
/**
     * Creates a new instance with the specified decoder options.
     */
    public HttpClientCodec(
            int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean failOnMissingResponse,
            boolean validateHeaders, int initialBufferSize, boolean parseHttpAfterConnectRequest) {
        init(new Decoder(maxInitialLineLength, maxHeaderSize, maxChunkSize, validateHeaders, initialBufferSize),
             new Encoder());
        this.parseHttpAfterConnectRequest = parseHttpAfterConnectRequest;
        this.failOnMissingResponse = failOnMissingResponse;
    }

    
Prepares to upgrade to another protocol from HTTP. Disables the Encoder. /**
     * Prepares to upgrade to another protocol from HTTP. Disables the {@link Encoder}.
     */
    @Override
    public void prepareUpgradeFrom(ChannelHandlerContext ctx) {
        ((Encoder) outboundHandler()).upgraded = true;
    }

    
Upgrades to another protocol from HTTP. Removes the Decoder and Encoder from the pipeline. /**
     * Upgrades to another protocol from HTTP. Removes the {@link Decoder} and {@link Encoder} from
     * the pipeline.
     */
    @Override
    public void upgradeFrom(ChannelHandlerContext ctx) {
        final ChannelPipeline p = ctx.pipeline();
        p.remove(this);
    }

    public void setSingleDecode(boolean singleDecode) {
        inboundHandler().setSingleDecode(singleDecode);
    }

    public boolean isSingleDecode() {
        return inboundHandler().isSingleDecode();
    }

    private final class Encoder extends HttpRequestEncoder {

        boolean upgraded;

        @Override
        protected void encode(
                ChannelHandlerContext ctx, Object msg, List<Object> out) throws Exception {

            if (upgraded) {
                out.add(ReferenceCountUtil.retain(msg));
                return;
            }

            if (msg instanceof HttpRequest && !done) {
                queue.offer(((HttpRequest) msg).method());
            }

            super.encode(ctx, msg, out);

            if (failOnMissingResponse && !done) {
                // check if the request is chunked if so do not increment
                if (msg instanceof LastHttpContent) {
                    // increment as its the last chunk
                    requestResponseCounter.incrementAndGet();
                }
            }
        }
    }

    private final class Decoder extends HttpResponseDecoder {
        Decoder(int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean validateHeaders) {
            super(maxInitialLineLength, maxHeaderSize, maxChunkSize, validateHeaders);
        }

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

        @Override
        protected void decode(
                ChannelHandlerContext ctx, ByteBuf buffer, List<Object> out) throws Exception {
            if (done) {
                int readable = actualReadableBytes();
                if (readable == 0) {
                    // if non is readable just return null
                    // https://github.com/netty/netty/issues/1159
                    return;
                }
                out.add(buffer.readBytes(readable));
            } else {
                int oldSize = out.size();
                super.decode(ctx, buffer, out);
                if (failOnMissingResponse) {
                    int size = out.size();
                    for (int i = oldSize; i < size; i++) {
                        decrement(out.get(i));
                    }
                }
            }
        }

        private void decrement(Object msg) {
            if (msg == null) {
                return;
            }

            // check if it's an Header and its transfer encoding is not chunked.
            if (msg instanceof LastHttpContent) {
                requestResponseCounter.decrementAndGet();
            }
        }

        @Override
        protected boolean isContentAlwaysEmpty(HttpMessage msg) {
            final int statusCode = ((HttpResponse) msg).status().code();
            if (statusCode == 100 || statusCode == 101) {
                // 100-continue and 101 switching protocols response should be excluded from paired comparison.
                // Just delegate to super method which has all the needed handling.
                return super.isContentAlwaysEmpty(msg);
            }

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

            char firstChar = method.name().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)) {
                    return true;

                    // The following code was inserted to work around the servers
                    // that behave incorrectly.  It has been commented out
                    // because it does not work with well behaving servers.
                    // Please note, even if the 'Transfer-Encoding: chunked'
                    // header exists in the HEAD response, the response should
                    // have absolutely no content.
                    //
                    //// Interesting edge case:
                    //// Some poorly implemented servers will send a zero-byte
                    //// chunk if Transfer-Encoding of the response is 'chunked'.
                    ////
                    //// 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 - Parse HTTP only if configured by parseHttpAfterConnectRequest,
                        // else pass through.
                        if (!parseHttpAfterConnectRequest) {
                            done = true;
                            queue.clear();
                        }
                        return true;
                    }
                }
                break;
            }

            return super.isContentAlwaysEmpty(msg);
        }

        @Override
        public void channelInactive(ChannelHandlerContext ctx)
                throws Exception {
            super.channelInactive(ctx);

            if (failOnMissingResponse) {
                long missingResponses = requestResponseCounter.get();
                if (missingResponses > 0) {
                    ctx.fireExceptionCaught(new PrematureChannelClosureException(
                            "channel gone inactive with " + missingResponses +
                            " missing response(s)"));
                }
            }
        }
    }
}