Socket流转发异常：转发HTTP请求后未收到Web服务器响应

我做了一个HTTP请求监听程序，需求是：从客户端Socket（Socket1）的InputStream提取数据后，转发到连接Web服务器的Socket（Socket2）的OutputStream；再把Web服务器返回的Socket2的InputStream回传给Socket1的OutputStream。目前Web服务器能成功收到请求，但我这边收不到响应。查资料说要关闭Socket输出流后再读输入流，我试了调用socket.shutdownOutput()，但问题还是没解决。相关代码如下：

原监听方法代码 #

private static void runHttpListener(Boolean simulate){
    try {
        ServerSocket server = new ServerSocket(PORT_HTTP_REQUEST);
        System.out.println("HTTP listener active on Port "+PORT_HTTP_REQUEST);
        boolean keepAlive = true;
        while (keepAlive) {               
            //Empfangen und auslesen
            Socket socketReceivingProxy = server.accept();  
            System.out.println("HTTP-Listener: Accepted client connection");              
            InputStream proxyInputStream = socketReceivingProxy.getInputStream();
            OutputStream proxyOutputStream = socketReceivingProxy.getOutputStream();
            //TODO: extract information from stream
            
            //forward
            InputStream result = sendHttpRequestToDestination(proxyInputStream, simulate);
            result.transferTo(proxyOutputStream);
            

            result.close();
            proxyOutputStream.close();
            socketReceivingProxy.close();
        }
        server.close();  
        System.out.println("HTTP listener closed");    
    } catch (Exception e) {
        e.printStackTrace();
    }
}

原转发方法代码 #

private static InputStream sendHttpRequestToDestination(InputStream incomingRequest, Boolean simulate){
    try{
        
        Socket socketForwardingWebapp = new Socket(simulate?URL_WEB_SERVER_SIMULATION:URL_WEB_SERVER, 
            simulate?PORT_WEB_SERVER_SIMULATION:PORT_WEB_SERVER);
        System.out.println("HTTP-Forwarding: Created socket "+socketForwardingWebapp.getInetAddress()+":"+socketForwardingWebapp.getPort());  
        InputStream webappInputStream = socketForwardingWebapp.getInputStream();
        OutputStream outputStream = socketForwardingWebapp.getOutputStream();
        if(incomingRequest.available()>0){
            System.out.println("Incoming Request can be forwarded");
            long bytesTransfered = incomingRequest.transferTo(outputStream);
            System.out.print("stream copied");
            socketForwardingWebapp.shutdownOutput();
            System.out.println("Bytes forwareded: "+bytesTransfered);
        }
        return webappInputStream;
    }catch(Exception exc){
        exc.printStackTrace();
    }
    return null;
}

问题分析 #

你的代码存在几个关键问题导致收不到响应：

• 错误依赖available()判断请求数据：incomingRequest.available()>0仅返回当前缓冲区可读取的字节数，并非请求总长度，若请求数据未完全到达，会跳过转发（你这里服务器已收到请求，说明此场景未触发，但逻辑本身存在隐患）。
• 未确保请求数据完全发送：调用transferTo后未手动flush输出流，部分数据可能滞留在缓冲区，导致服务器未收到完整请求。
• HTTP Keep-Alive阻塞：HTTP/1.1默认启用Keep-Alive，服务器发送响应后不会立即关闭Socket，transferTo会一直阻塞直到输入流遇到EOF，导致客户端永远收不到响应。
• 资源管理不完整：转发方法中创建的socketForwardingWebapp未被正确关闭，仅关闭返回的InputStream无法保证Socket被释放，影响服务器响应传输。

修复后的代码 #

封装资源类（用于传递Socket和InputStream） #

private static class SocketInputStreamPair {
    private final Socket socket;
    private final InputStream inputStream;

    public SocketInputStreamPair(Socket socket, InputStream inputStream) {
        this.socket = socket;
        this.inputStream = inputStream;
    }

    public Socket getSocket() {
        return socket;
    }

    public InputStream getInputStream() {
        return inputStream;
    }
}

修改后的转发方法 #

private static SocketInputStreamPair sendHttpRequestToDestination(InputStream incomingRequest, Boolean simulate){
    try{
        Socket socketForwardingWebapp = new Socket(
            simulate ? URL_WEB_SERVER_SIMULATION : URL_WEB_SERVER, 
            simulate ? PORT_WEB_SERVER_SIMULATION : PORT_WEB_SERVER
        );
        System.out.println("HTTP-Forwarding: Created socket "+socketForwardingWebapp.getInetAddress()+":"+socketForwardingWebapp.getPort());  
        InputStream webappInputStream = socketForwardingWebapp.getInputStream();
        OutputStream outputStream = socketForwardingWebapp.getOutputStream();

        // 直接转发所有请求数据，直到输入流结束，不再依赖available()
        long bytesTransfered = incomingRequest.transferTo(outputStream);
        // 手动flush确保所有数据发送到服务器
        outputStream.flush();
        socketForwardingWebapp.shutdownOutput();
        System.out.println("Bytes forwarded: "+bytesTransfered);

        return new SocketInputStreamPair(socketForwardingWebapp, webappInputStream);
    }catch(Exception exc){
        exc.printStackTrace();
    }
    return null;
}

修改后的监听方法 #

private static void runHttpListener(Boolean simulate){
    try (ServerSocket server = new ServerSocket(PORT_HTTP_REQUEST)) {
        System.out.println("HTTP listener active on Port "+PORT_HTTP_REQUEST);
        boolean keepAlive = true;
        while (keepAlive) {               
            try (Socket socketReceivingProxy = server.accept()) {  
                System.out.println("HTTP-Listener: Accepted client connection");              
                InputStream proxyInputStream = socketReceivingProxy.getInputStream();
                OutputStream proxyOutputStream = socketReceivingProxy.getOutputStream();

                // 转发请求并获取服务器响应流和对应的Socket
                SocketInputStreamPair pair = sendHttpRequestToDestination(proxyInputStream, simulate);
                if (pair == null) {
                    continue;
                }

                try (Socket serverSocket = pair.getSocket();
                     InputStream serverInputStream = pair.getInputStream()) {
                    // 转发服务器响应到客户端
                    serverInputStream.transferTo(proxyOutputStream);
                    // flush确保响应发送到客户端
                    proxyOutputStream.flush();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        System.out.println("HTTP listener closed");    
    } catch (Exception e) {
        e.printStackTrace();
    }
}

额外说明 #

如果需要支持HTTP/1.1的Keep-Alive，需解析请求和响应的Connection头：

• 若头值为keep-alive，则保留Socket等待下一次请求
• 若为close，则关闭Socket
  另外，对于chunked编码的响应，需正确解析分块数据，不能仅依赖InputStream的EOF。

内容的提问来源于stack exchange，提问作者Jones