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   /*
    * Copyright 2020 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:
    *
    *   https://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.example.stomp.websocket;
  
  import io.netty.channel.ChannelFutureListener;
  import io.netty.channel.ChannelHandler.Sharable;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.DefaultFileRegion;
  import io.netty.channel.SimpleChannelInboundHandler;
  import io.netty.handler.codec.http.DefaultFullHttpResponse;
  import io.netty.handler.codec.http.DefaultHttpResponse;
  import io.netty.handler.codec.http.FullHttpRequest;
  import io.netty.handler.codec.http.FullHttpResponse;
  import io.netty.handler.codec.http.HttpHeaderNames;
  import io.netty.handler.codec.http.HttpHeaderValues;
  import io.netty.handler.codec.http.HttpResponse;
  import io.netty.handler.codec.http.HttpUtil;
  import io.netty.handler.codec.http.LastHttpContent;
  import io.netty.util.CharsetUtil;
  
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.io.RandomAccessFile;
  import java.net.URL;
  
  import static io.netty.handler.codec.http.HttpHeaderNames.*;
  import static io.netty.handler.codec.http.HttpHeaderValues.KEEP_ALIVE;
  import static io.netty.handler.codec.http.HttpHeaderValues.*;
  import static io.netty.handler.codec.http.HttpResponseStatus.*;
  import static io.netty.handler.codec.http.HttpVersion.*;
  
  @Sharable
  public final class StompWebSocketClientPageHandler extends SimpleChannelInboundHandler<FullHttpRequest> {
  
      static final StompWebSocketClientPageHandler INSTANCE = new StompWebSocketClientPageHandler();
  
      private StompWebSocketClientPageHandler() {
      }
  
      @Override
      protected void channelRead0(ChannelHandlerContext ctx, FullHttpRequest request) {
          if (request.headers().contains(HttpHeaderNames.UPGRADE, HttpHeaderValues.WEBSOCKET, true)) {
              ctx.fireChannelRead(request.retain());
              return;
          }
  
          if (request.decoderResult().isFailure()) {
              FullHttpResponse badRequest = new DefaultFullHttpResponse(request.protocolVersion(), BAD_REQUEST);
              sendResponse(badRequest, ctx, true);
              return;
          }
  
          if (!sendResource(request, ctx)) {
              FullHttpResponse notFound = new DefaultFullHttpResponse(request.protocolVersion(), NOT_FOUND);
              notFound.headers().set(CONTENT_TYPE, TEXT_PLAIN);
              String payload = "Requested resource " + request.uri() + " not found";
              notFound.content().writeCharSequence(payload, CharsetUtil.UTF_8);
              HttpUtil.setContentLength(notFound, notFound.content().readableBytes());
              sendResponse(notFound, ctx, true);
          }
      }
  
      private static boolean sendResource(FullHttpRequest request, ChannelHandlerContext ctx) {
          if (request.uri().isEmpty() || !request.uri().startsWith("/")) {
              return false;
          }
  
          String requestResource = request.uri().substring(1);
          if (requestResource.isEmpty()) {
              requestResource = "index.html";
          }
  
          URL resourceUrl = INSTANCE.getClass().getResource(requestResource);
          if (resourceUrl == null) {
              return false;
          }
  
          RandomAccessFile raf = null;
          long fileLength = -1L;
          try {
              raf = new RandomAccessFile(resourceUrl.getFile(), "r");
              fileLength = raf.length();
          } catch (FileNotFoundException fne) {
              System.out.println("File not found " + fne.getMessage());
              return false;
          } catch (IOException io) {
             System.out.println("Cannot read file length " + io.getMessage());
             return false;
         } finally {
             if (fileLength < 0 && raf != null) {
                 try {
                     raf.close();
                 } catch (IOException io) {
                     // Nothing to do
                 }
             }
         }
 
         HttpResponse response = new DefaultHttpResponse(request.protocolVersion(), OK);
         HttpUtil.setContentLength(response, fileLength);
 
         String contentType = "application/octet-stream";
         if (requestResource.endsWith("html")) {
             contentType = "text/html; charset=UTF-8";
         } else if (requestResource.endsWith("css")) {
             contentType = "text/css; charset=UTF-8";
         } else if (requestResource.endsWith("js")) {
             contentType = "application/javascript";
         }
 
         response.headers().set(CONTENT_TYPE, contentType);
         sendResponse(response, ctx, false);
         ctx.write(new DefaultFileRegion(raf.getChannel(), 0, fileLength));
         ctx.writeAndFlush(LastHttpContent.EMPTY_LAST_CONTENT);
         return true;
     }
 
     private static void sendResponse(HttpResponse response, ChannelHandlerContext ctx, boolean autoFlush) {
         if (HttpUtil.isKeepAlive(response)) {
             if (response.protocolVersion().equals(HTTP_1_0)) {
                 response.headers().set(CONNECTION, KEEP_ALIVE);
             }
             ctx.write(response);
         } else {
             response.headers().set(CONNECTION, CLOSE);
             ctx.write(response).addListener(ChannelFutureListener.CLOSE);
         }
 
         if (autoFlush) {
             ctx.flush();
         }
     }
 }