/*
 * Copyright 2016 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.http2;

import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPipeline;
import io.netty.util.internal.StringUtil;
import io.netty.util.internal.UnstableApi;

A ChannelDuplexHandler providing additional functionality for HTTP/2. Specifically it allows to: 

    
Create new outbound streams using newStream().
    
Iterate over all active streams using forEachActiveStream(Http2FrameStreamVisitor).

The Http2FrameCodec is required to be part of the ChannelPipeline before this handler is added, or else an IllegalStateException will be thrown. /**
 * A {@link ChannelDuplexHandler} providing additional functionality for HTTP/2. Specifically it allows to:
 * <ul>
 *     <li>Create new outbound streams using {@link #newStream()}.</li>
 *     <li>Iterate over all active streams using {@link #forEachActiveStream(Http2FrameStreamVisitor)}.</li>
 * </ul>
 *
 * <p>The {@link Http2FrameCodec} is required to be part of the {@link ChannelPipeline} before this handler is added,
 * or else an {@link IllegalStateException} will be thrown.
 */
@UnstableApi
public abstract class Http2ChannelDuplexHandler extends ChannelDuplexHandler {

    private volatile Http2FrameCodec frameCodec;

    @Override
    public final void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        frameCodec = requireHttp2FrameCodec(ctx);
        handlerAdded0(ctx);
    }

    protected void handlerAdded0(@SuppressWarnings("unused") ChannelHandlerContext ctx) throws Exception {
        // NOOP
    }

    @Override
    public final void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        try {
            handlerRemoved0(ctx);
        } finally {
            frameCodec = null;
        }
    }

    protected void handlerRemoved0(@SuppressWarnings("unused") ChannelHandlerContext ctx) throws Exception {
        // NOOP
    }

    
Creates a new Http2FrameStream object. 
This method is thread-safe.
/**
     * Creates a new {@link Http2FrameStream} object.
     *
     * <p>This method is <em>thread-safe</em>.
     */
    public final Http2FrameStream newStream() {
        Http2FrameCodec codec = frameCodec;
        if (codec == null) {
            throw new IllegalStateException(StringUtil.simpleClassName(Http2FrameCodec.class) + " not found." +
                    " Has the handler been added to a pipeline?");
        }
        return codec.newStream();
    }

    
Allows to iterate over all currently active streams.
This method may only be called from the eventloop thread.
/**
     * Allows to iterate over all currently active streams.
     *
     * <p>This method may only be called from the eventloop thread.
     */
    protected final void forEachActiveStream(Http2FrameStreamVisitor streamVisitor) throws Http2Exception {
        frameCodec.forEachActiveStream(streamVisitor);
    }

    private static Http2FrameCodec requireHttp2FrameCodec(ChannelHandlerContext ctx) {
        ChannelHandlerContext frameCodecCtx = ctx.pipeline().context(Http2FrameCodec.class);
        if (frameCodecCtx == null) {
            throw new IllegalArgumentException(Http2FrameCodec.class.getSimpleName()
                                               + " was not found in the channel pipeline.");
        }
        return (Http2FrameCodec) frameCodecCtx.handler();
    }
}