Netty HTTP 服务端入门开发

一. HTTP 简介

　　HTTP(超文本传输协议) 协议是建立在 TCP 传输协议之上的应用层协议,它的发展是万维网协会和 Internet 工作小组和 IETF 合作的结果. HTTP 是一个属于应用层的面向对象的协议,由于其便捷,快速的方式,适用于分布式超媒体信息系统.

　　HTTP 协议的主要特点如下:

1. 支持 Client/Server 模式.
2. 简单---- 客户端向服务器请求服务时,只需指定服务的 URL, 携带必要的请求参数或者消息体;
3. 灵活---- HTTP 允许传输任意类型的数据对象,传输内容类型有 HTTP 消息头中得 Content-Type 指定.
4. 无状态---- HTTP 协议是无状态协议,无状态是指协议对于会话状态没有记忆功能,缺少状态意味着如果后续处理需要之前的信息,则它必须重传.这样导致每次连接传送的数据量加大另外一方面,在服务器不需要之前的信息时,它的应答就较快,负载较轻.

　　netty 的 Http 协议栈是基于 Netty 的 Nio 通信框架开发的.因此, Netty 的 Http 协议也是异步非阻塞的.

代码如下:

HttpFileServer

package netty.protocol.http;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpRequestDecoder;
import io.netty.handler.codec.http.HttpResponseEncoder;
import io.netty.handler.stream.ChunkedWriteHandler;

/**
 * TODO
 *
 * @description
 * @author ez
 * @time 2015年6月3日 上午10:47:37
 */
public class HttpFileServer {
    private static final String DEFAULT_URL = "/src/main/java/netty/protocol/http/";

    public void run(final int port, final String url) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch)
                                throws Exception {
                            ch.pipeline().addLast("http-decoder",
                                    new HttpRequestDecoder()); // http 请求消息解码器,
                            /*
                             * httpObject 解码器,
                             * 它的作用是将多个消息转换为单一的FullHttpRequest或FullHttpResponse
                             * 对象,原因是HTTP 解码器在每个HTTP消息中会生成多个消息对象 (
                             * HttpRequest/HttpResponse
                             * ,HttpContent,LastHttpContent)
                             */
                            ch.pipeline().addLast("http-aggregator",
                                    new HttpObjectAggregator(65536));
                            /*
                             * HTTP 响应消息编码器
                             */
                            ch.pipeline().addLast("http-encoder",
                                    new HttpResponseEncoder());
                            /*
                             * ChunkedWriteHandler
                             * 的主要作用是支持异步发送大的码流(例如大文件传输),但不占用过多的内存,防止JAVA内存溢出
                             */
                            ch.pipeline().addLast("http-chunked",
                                    new ChunkedWriteHandler());
                            /*
                             * 业务处理类
                             */
                            ch.pipeline().addLast("fileServerHandler",
                                    new HttpFileServerHandler(url));
                        }
                    });
            ChannelFuture future = b.bind("localhost", port).sync();
            System.out.println("HTTP文件目录服务器启动，网址是 : " + "http://localhost:"
                    + port + url);
            future.channel().closeFuture().sync();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8080;
        if (args.length > 0) {
            try {
                port = Integer.parseInt(args[0]);
            } catch (NumberFormatException e) {
                e.printStackTrace();
            }
        }
        String url = DEFAULT_URL;
        if (args.length > 1)
            url = args[1];
        new HttpFileServer().run(port, url);
    }
}

ServerHandler

package netty.protocol.http;

import static io.netty.handler.codec.http.HttpHeaders.isKeepAlive;
import static io.netty.handler.codec.http.HttpHeaders.setContentLength;
import static io.netty.handler.codec.http.HttpHeaders.Names.CONNECTION;
import static io.netty.handler.codec.http.HttpHeaders.Names.CONTENT_TYPE;
import static io.netty.handler.codec.http.HttpHeaders.Names.LOCATION;
import static io.netty.handler.codec.http.HttpMethod.GET;
import static io.netty.handler.codec.http.HttpResponseStatus.BAD_REQUEST;
import static io.netty.handler.codec.http.HttpResponseStatus.FORBIDDEN;
import static io.netty.handler.codec.http.HttpResponseStatus.FOUND;
import static io.netty.handler.codec.http.HttpResponseStatus.INTERNAL_SERVER_ERROR;
import static io.netty.handler.codec.http.HttpResponseStatus.METHOD_NOT_ALLOWED;
import static io.netty.handler.codec.http.HttpResponseStatus.NOT_FOUND;
import static io.netty.handler.codec.http.HttpResponseStatus.OK;
import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelProgressiveFuture;
import io.netty.channel.ChannelProgressiveFutureListener;
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.HttpHeaders;
import io.netty.handler.codec.http.HttpResponse;
import io.netty.handler.codec.http.HttpResponseStatus;
import io.netty.handler.codec.http.LastHttpContent;
import io.netty.handler.stream.ChunkedFile;
import io.netty.util.CharsetUtil;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.RandomAccessFile;
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.util.regex.Pattern;

import javax.activation.MimetypesFileTypeMap;

public class HttpFileServerHandler extends
        SimpleChannelInboundHandler<FullHttpRequest> {
    private final String url;

    public HttpFileServerHandler(String url) {
        this.url = url;
    }

    @Override
    public void messageReceived(ChannelHandlerContext ctx,
            FullHttpRequest request) throws Exception {
        /*
         * 首先对HTTP请求消息的解码结构进行判断,如果解码失败,直接构造HTTP404 错误返回,
         */
        if (!request.getDecoderResult().isSuccess()) {
            sendError(ctx, BAD_REQUEST);
            return;
        }
        /*
         * 如果不是get请求, 则构造 HTTP405 返回
         */
        if (request.getMethod() != GET) {
            sendError(ctx, METHOD_NOT_ALLOWED);
            return;
        }
        final String uri = request.getUri();
        /*
         * 对URL进行解码, 使用 UTF-8字符集,解码之后对URI进行合法性判断,
         */
        final String path = sanitizeUri(uri);
        if (path == null) {
            sendError(ctx, FORBIDDEN);
            return;
        }
        File file = new File(path);
        if (file.isHidden() || !file.exists()) {
            sendError(ctx, NOT_FOUND);
            return;
        }
        if (file.isDirectory()) {
            if (uri.endsWith("/")) {
                sendListing(ctx, file);
            } else {
                sendRedirect(ctx, uri + '/');
            }
            return;
        }
        if (!file.isFile()) {
            sendError(ctx, FORBIDDEN);
            return;
        }
        RandomAccessFile randomAccessFile = null;
        try {
            randomAccessFile = new RandomAccessFile(file, "r");// 以只读的方式打开文件
        } catch (FileNotFoundException fnfe) {
            sendError(ctx, NOT_FOUND);
            return;
        }
        long fileLength = randomAccessFile.length();
        HttpResponse response = new DefaultHttpResponse(HTTP_1_1, OK);
        setContentLength(response, fileLength);
        setContentTypeHeader(response, file);
        if (isKeepAlive(request)) {
            response.headers().set(CONNECTION, HttpHeaders.Values.KEEP_ALIVE);
        }
        ctx.write(response);
        ChannelFuture sendFileFuture;
        sendFileFuture = ctx.write(new ChunkedFile(randomAccessFile, 0,
                fileLength, 8192), ctx.newProgressivePromise());
        sendFileFuture.addListener(new ChannelProgressiveFutureListener() {
            public void operationProgressed(ChannelProgressiveFuture future,
                    long progress, long total) {
                if (total < 0) { // total unknown
                    System.err.println("Transfer progress: " + progress);
                } else {
                    System.err.println("Transfer progress: " + progress + " / "
                            + total);
                }
            }

            public void operationComplete(ChannelProgressiveFuture future)
                    throws Exception {
                System.out.println("Transfer complete.");
            }
        });
        /*
         * 如果是chunked 编码, 最后需要发送一个编码结束的空消息体,将LastHttpContent的EMPTY_LAST_CONTENT
         * 发送到缓存区中,标识所有的消息体已经发送完成,同时调用flush方法将之前在发送缓冲区的消息刷新到SocketChannel中发送给对方
         */
        ChannelFuture lastContentFuture = ctx
                .writeAndFlush(LastHttpContent.EMPTY_LAST_CONTENT);
        /*
         * 如果是非 Keep-Alive 的,最后一包消息发送完之后,服务端要主动关闭连接.
         */
        if (!isKeepAlive(request)) {
            lastContentFuture.addListener(ChannelFutureListener.CLOSE);
        }
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
            throws Exception {
        cause.printStackTrace();
        if (ctx.channel().isActive()) {
            sendError(ctx, INTERNAL_SERVER_ERROR);
        }
    }

    private static final Pattern INSECURE_URI = Pattern.compile(".*[<>&\"].*");

    private String sanitizeUri(String uri) {
        try {
            uri = URLDecoder.decode(uri, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            try {
                uri = URLDecoder.decode(uri, "ISO-8859-1");
            } catch (UnsupportedEncodingException e1) {
                throw new Error();
            }
        }
        if (!uri.startsWith(url)) {
            return null;
        }
        if (!uri.startsWith("/")) {
            return null;
        }
        uri = uri.replace('/', File.separatorChar);
        if (uri.contains(File.separator + '.')
                || uri.contains('.' + File.separator) || uri.startsWith(".")
                || uri.endsWith(".") || INSECURE_URI.matcher(uri).matches()) {
            return null;
        }
        return System.getProperty("user.dir") + File.separator + uri;
    }

    private static final Pattern ALLOWED_FILE_NAME = Pattern
            .compile("[A-Za-z0-9][-_A-Za-z0-9\\.]*");

    private static void sendListing(ChannelHandlerContext ctx, File dir) {
        FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, OK);
        response.headers().set(CONTENT_TYPE, "text/html; charset=UTF-8");
        StringBuilder buf = new StringBuilder();
        String dirPath = dir.getPath();
        buf.append("<!DOCTYPE html>\r\n");
        buf.append("<html><head><title>");
        buf.append(dirPath);
        buf.append(" 目录：");
        buf.append("</title></head><body>\r\n");
        buf.append("<h3>");
        buf.append(dirPath).append(" 目录：");
        buf.append("</h3>\r\n");
        buf.append("<ul>");
        buf.append("<li>链接：<a href=\"../\">..</a></li>\r\n");
        for (File f : dir.listFiles()) {
            if (f.isHidden() || !f.canRead()) {
                continue;
            }
            String name = f.getName();
            if (!ALLOWED_FILE_NAME.matcher(name).matches()) {
                continue;
            }
            buf.append("<li>链接：<a href=\"");
            buf.append(name);
            buf.append("\">");
            buf.append(name);
            buf.append("</a></li>\r\n");
        }
        buf.append("</ul></body></html>\r\n");
        ByteBuf buffer = Unpooled.copiedBuffer(buf, CharsetUtil.UTF_8);
        response.content().writeBytes(buffer);
        buffer.release();
        ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
    }

    private static void sendRedirect(ChannelHandlerContext ctx, String newUri) {
        FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, FOUND);
        response.headers().set(LOCATION, newUri);
        ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
    }

    private static void sendError(ChannelHandlerContext ctx,
            HttpResponseStatus status) {
        FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1,
                status, Unpooled.copiedBuffer("Failure: " + status.toString()
                        + "\r\n", CharsetUtil.UTF_8));
        response.headers().set(CONTENT_TYPE, "text/plain; charset=UTF-8");
        ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
    }

    private static void setContentTypeHeader(HttpResponse response, File file) {
        MimetypesFileTypeMap mimeTypesMap = new MimetypesFileTypeMap();
        response.headers().set(CONTENT_TYPE,
                mimeTypesMap.getContentType(file.getPath()));
    }
}

以上内容出自 <netty 权威指南>