/*
 * Copyright 2017 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.Unpooled;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.ReferenceCountUtil;

import static io.netty.handler.codec.http.HttpHeaderNames.CONTENT_LENGTH;
import static io.netty.handler.codec.http.HttpResponseStatus.CONTINUE;
import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;

Sends a 100 CONTINUE HttpResponse to HttpRequests which contain a 'expect: 100-continue' header. It should only be used for applications which do not install the HttpObjectAggregator. 

By default it accepts all expectations.
 Since HttpServerExpectContinueHandler expects HttpRequests it should be added after HttpServerCodec but before any other handlers that might send a HttpResponse. 

ChannelPipeline p = ...; ... p.addLast("serverCodec", new HttpServerCodec()); p.addLast("respondExpectContinue", new HttpServerExpectContinueHandler());
 ...
 p.addLast("handler", new HttpRequestHandler());
 

/**
 * Sends a <a href="https://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html#sec8.2.3">100 CONTINUE</a>
 * {@link HttpResponse} to {@link HttpRequest}s which contain a 'expect: 100-continue' header. It
 * should only be used for applications which do <b>not</b> install the {@link HttpObjectAggregator}.
 * <p>
 * By default it accepts all expectations.
 * <p>
 * Since {@link HttpServerExpectContinueHandler} expects {@link HttpRequest}s it should be added after {@link
 * HttpServerCodec} but before any other handlers that might send a {@link HttpResponse}. <blockquote>
 * <pre>
 *  {@link io.netty.channel.ChannelPipeline} p = ...;
 *  ...
 *  p.addLast("serverCodec", new {@link HttpServerCodec}());
 *  p.addLast("respondExpectContinue", <b>new {@link HttpServerExpectContinueHandler}()</b>);
 *  ...
 *  p.addLast("handler", new HttpRequestHandler());
 *  </pre>
 * </blockquote>
 */
public class HttpServerExpectContinueHandler extends ChannelInboundHandlerAdapter {

    private static final FullHttpResponse EXPECTATION_FAILED = new DefaultFullHttpResponse(
            HTTP_1_1, HttpResponseStatus.EXPECTATION_FAILED, Unpooled.EMPTY_BUFFER);

    private static final FullHttpResponse ACCEPT = new DefaultFullHttpResponse(
            HTTP_1_1, CONTINUE, Unpooled.EMPTY_BUFFER);

    static {
        EXPECTATION_FAILED.headers().set(CONTENT_LENGTH, 0);
        ACCEPT.headers().set(CONTENT_LENGTH, 0);
    }

    
Produces a HttpResponse for HttpRequests which define an expectation. Returns null if the request should be rejected. See rejectResponse(HttpRequest). /**
     * Produces a {@link HttpResponse} for {@link HttpRequest}s which define an expectation. Returns {@code null} if the
     * request should be rejected. See {@link #rejectResponse(HttpRequest)}.
     */
    protected HttpResponse acceptMessage(@SuppressWarnings("unused") HttpRequest request) {
        return ACCEPT.retainedDuplicate();
    }

    
Returns the appropriate 4XX HttpResponse for the given HttpRequest. /**
     * Returns the appropriate 4XX {@link HttpResponse} for the given {@link HttpRequest}.
     */
    protected HttpResponse rejectResponse(@SuppressWarnings("unused") HttpRequest request) {
        return EXPECTATION_FAILED.retainedDuplicate();
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        if (msg instanceof HttpRequest) {
            HttpRequest req = (HttpRequest) msg;

            if (HttpUtil.is100ContinueExpected(req)) {
                HttpResponse accept = acceptMessage(req);

                if (accept == null) {
                    // the expectation failed so we refuse the request.
                    HttpResponse rejection = rejectResponse(req);
                    ReferenceCountUtil.release(msg);
                    ctx.writeAndFlush(rejection).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
                    return;
                }

                ctx.writeAndFlush(accept).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
                req.headers().remove(HttpHeaderNames.EXPECT);
            }
        }
        super.channelRead(ctx, msg);
    }
}