Netty源碼分析-WebSocketServerProtocolHandler

WebSocketServerProtocolHandler源碼分析

 

package io.netty.handler.codec.http.websocketx;

import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandler;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelPipeline;
import io.netty.handler.codec.http.DefaultFullHttpResponse;
import io.netty.handler.codec.http.FullHttpRequest;
import io.netty.handler.codec.http.FullHttpResponse;
import io.netty.handler.codec.http.HttpHeaders;
import io.netty.handler.codec.http.HttpResponseStatus;
import io.netty.util.AttributeKey;

import java.util.List;

import static io.netty.handler.codec.http.HttpVersion.*;


public class WebSocketServerProtocolHandler extends WebSocketProtocolHandler {


    public enum ServerHandshakeStateEvent {
        @Deprecated
        HANDSHAKE_COMPLETE
    }

    public static final class HandshakeComplete {
        private final String requestUri;
        private final HttpHeaders requestHeaders;
        private final String selectedSubprotocol;

        HandshakeComplete(String requestUri, HttpHeaders requestHeaders, String selectedSubprotocol) {
            this.requestUri = requestUri;
            this.requestHeaders = requestHeaders;
            this.selectedSubprotocol = selectedSubprotocol;
        }

        public String requestUri() {
            return requestUri;
        }

        public HttpHeaders requestHeaders() {
            return requestHeaders;
        }

        public String selectedSubprotocol() {
            return selectedSubprotocol;
        }
    }

    private static final AttributeKey<WebSocketServerHandshaker> HANDSHAKER_ATTR_KEY =
            AttributeKey.valueOf(WebSocketServerHandshaker.class, "HANDSHAKER");

    //websocket的path
    private final String websocketPath;
    //子協議
    private final String subprotocols;
    //是否允許擴展 默認false
    private final boolean allowExtensions;
    //數據荷載最大長度默認65536
    private final int maxFramePayloadLength;
    //是否允許確實掩碼 默認false
    private final boolean allowMaskMismatch;
    //
    private final boolean checkStartsWith;

    public WebSocketServerProtocolHandler(String websocketPath, String subprotocols,
                                          boolean allowExtensions, int maxFrameSize, boolean allowMaskMismatch,
                                          boolean checkStartsWith, boolean dropPongFrames) {
        super(dropPongFrames);
        this.websocketPath = websocketPath;
        this.subprotocols = subprotocols;
        this.allowExtensions = allowExtensions;
        maxFramePayloadLength = maxFrameSize;
        this.allowMaskMismatch = allowMaskMismatch;
        this.checkStartsWith = checkStartsWith;
    }

    //在channel連接成功後會回調次方法，插入websocket握手用處理器
    @Override
    public void handlerAdded(ChannelHandlerContext ctx) {
        ChannelPipeline cp = ctx.pipeline();
        //如果沒有握手處理器
        if (cp.get(WebSocketServerProtocolHandshakeHandler.class) == null) {
            // Add the WebSocketHandshakeHandler before this one.
            //插入握手處理器到當前處理器的前面
           //pipeline.addLast("http-codec", new HttpServerCodec());
            //pipeline.addLast("aggregator", new HttpObjectAggregator(655360));
            //pipeline.addLast("http-chunked", new ChunkedWriteHandler());
            //插入位置，順序非常重要，必須插在http編解碼器的後面，必須插在當前處理器的前面
           // pipeline.addLast("webSocketHandler", new WebSocketServerProtocolHandler("/websocket"));
            ctx.pipeline().addBefore(ctx.name(), WebSocketServerProtocolHandshakeHandler.class.getName(),
                    new WebSocketServerProtocolHandshakeHandler(websocketPath, subprotocols,
                            allowExtensions, maxFramePayloadLength, allowMaskMismatch, checkStartsWith));
        }
        if (cp.get(Utf8FrameValidator.class) == null) {
            // Add the UFT8 checking before this one.
            //插入在當前處理器的前面
            ctx.pipeline().addBefore(ctx.name(), Utf8FrameValidator.class.getName(),
                    new Utf8FrameValidator());
        }
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, WebSocketFrame frame, List<Object> out) throws Exception {
        //如果是close幀
        if (frame instanceof CloseWebSocketFrame) {
            //獲取channel中關聯的握手器去關閉當前channel
            WebSocketServerHandshaker handshaker = getHandshaker(ctx.channel());
            if (handshaker != null) {
                //因爲計數器需要+1，因爲傳入到close方法中會調用channel.write方法進行輸出，底層會再次釋放
                frame.retain();
                handshaker.close(ctx.channel(), (CloseWebSocketFrame) frame);
            } else {
                //沒有握手器輸出空字節後關閉底層socket
                ctx.writeAndFlush(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
            }
            return;
        }

        //調用父類，父類處理了ping-pong 二幀。
        super.decode(ctx, frame, out);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        //如果是websocket相關異常則返回http響應後關閉底層流
        if (cause instanceof WebSocketHandshakeException) {
            FullHttpResponse response = new DefaultFullHttpResponse(
                    HTTP_1_1, HttpResponseStatus.BAD_REQUEST, Unpooled.wrappedBuffer(cause.getMessage().getBytes()));
            ctx.channel().writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
        } else {
            ctx.fireExceptionCaught(cause);
            ctx.close();
        }
    }

    //從channel獲取關聯的握手器
    static WebSocketServerHandshaker getHandshaker(Channel channel) {
        return channel.attr(HANDSHAKER_ATTR_KEY).get();
    }

    //握手器綁定到channel
    static void setHandshaker(Channel channel, WebSocketServerHandshaker handshaker) {
        channel.attr(HANDSHAKER_ATTR_KEY).set(handshaker);
    }

    //
    static ChannelHandler forbiddenHttpRequestResponder() {
        return new ChannelInboundHandlerAdapter() {
            @Override
            public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
                //返回拒絕的http響應
                if (msg instanceof FullHttpRequest) {
                    ((FullHttpRequest) msg).release();
                    FullHttpResponse response =
                            new DefaultFullHttpResponse(HTTP_1_1, HttpResponseStatus.FORBIDDEN);
                    ctx.channel().writeAndFlush(response);
                } else {
                    //向下傳播
                    ctx.fireChannelRead(msg);
                }
            }
        };
    }
}