Question

从我的Android应用程序中，我想将数据发布到服务器并获取响应，处理它然后发回并获得另一个请求。由于在不再对流程做出响应之前是持续沟通，因此我更倾向于使用 HttpURLConnection http.keepAlive = true 。

我尝试重用套接字是成功的，但我遇到的问题是：

我试图从客户端（Android应用程序）发起关闭，因为如果终止从服务器开始，然后服务器进入 TIME_WAIT 州。我不希望我的服务器进入该状态，所以我更喜欢我的客户端启动终止。但不幸的是我找不到使用 HttpURLConnection
经过几个小时的搜索，我放弃了做上述尝试从基于服务器的启动关闭开始 keepalivetimeout ，但是当服务器发送 FIN 时，客户端只响应 ACK ，因此连接被搁置服务器中的 FIN_WAIT_2 和代理中的 CLOSE_WAIT 。

Packets log snippet

源代码：

private HttpStatus communicateWithMDMServer(String httpUrl, String dataToSend, boolean keepAlive) {
    HttpStatus status = new HttpStatus(HTTP_STATUS_FAILURE);

    try {

        initializeConnection(httpUrl,keepAlive);
        postDataToConnection(connection, dataToSend);
        status = readDataFromConnection(connection);

    } catch (MalformedURLException e) {
        MDMLogger.error("Failed to send data to server as the URL provided is not valid "+ e.getMessage()+"\n");
        e.printStackTrace();
    } catch (IOException e) {
        MDMLogger.error("Failed to send the status to the server : IOException "+ e.getMessage()+"\n"+e.getStackTrace());
        e.printStackTrace();
        readErrorStreamAndPrint(connection);
    }
    connection.disconnect();
    return status;
}

/**
 * API to close connection, calling this will not force the connection to shutdown
 * this will work based on the Connection header set.
 * @param connection
 */
public void closeConnection(){
    if(connection != null){
        connection.disconnect();
    }
}


/**
 * Used to initialize the HttpURLConnection for the given url
 * All properties required for connection are preset here 
 * Connection Time Out : 20 Seconds
 * Connection Type     : keep alive
 * Content Type        : application/json;charset=UTF-8
 * And also All certificates will be evaluated as Valid.[ TODO will be removed soon]
 * @param httpUrl
 * @return
 * @throws MalformedURLException
 * @throws IOException
 */
private void initializeConnection(String httpUrl, boolean keepAlive) throws MalformedURLException, IOException{

    URL url = new URL(httpUrl);
    connection = (HttpsURLConnection) url.openConnection();

    connection.setConnectTimeout(20000);
    connection.setReadTimeout(20000);
    connection.setDoInput(true);
    connection.setDoOutput(true);
    connection.setRequestMethod("POST");                                                                        //NO I18N
    connection.setRequestProperty("Content-Type", "application/json;charset=UTF-8");                            //NO I18N
    connection.setRequestProperty("Connection", "Keep-Alive");      //NO I18N
}


/**
 * API to post data to given connection 
 * call to this API will close the @OutputStream
 * @param connection
 * @param data
 * @throws IOException
 */
private void postDataToConnection(URLConnection connection , String data) throws IOException{

    OutputStream outStream = connection.getOutputStream();
    BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(outStream));
    writer.write(data);
    writer.flush();
    writer.close();
    outStream.close();
}

/**
 * API to read error stream and log
 * @param connection
 */
private void readErrorStreamAndPrint(URLConnection connection){
    try{
        InputStream inStream = ((HttpURLConnection) connection).getErrorStream();
        String responseData = "";
        String line;
        BufferedReader br=new BufferedReader(new InputStreamReader(inStream));
        while ((line=br.readLine()) != null) {
            responseData+=line;
        }
        MDMLogger.error("ErrorStream Says "+responseData);
    } catch (IOException ioe) {
        MDMLogger.debug("Exception on reading ErrorStream");
    }
}


/**
 * API to read data from given connection and return {@code com.manageengine.mdm.framework.communication.HttpStatus}
 * call to this API will close the @InputStream
 * @param connection
 * @return
 * @throws IOException
 */
private HttpStatus readDataFromConnection(URLConnection connection) throws IOException{

    HttpStatus status = new HttpStatus(HTTP_STATUS_FAILURE);
    int responseCode=((HttpURLConnection) connection).getResponseCode();
    MDMLogger.info("Response Code: "+responseCode);
    InputStream inStream = connection.getInputStream();
    MDMLogger.info("Response Header: "+connection.getHeaderFields());
    String responseData = "";
    if (responseCode == HttpURLConnection.HTTP_OK) {
        responseData = readStreamAsString(inStream);
        status.setStatus(HTTP_STATUS_SUCCESS);
        status.setUrlDataBuffer(responseData);
        MDMLogger.info("communicateWithMDMServer : Response is \n"  + status.getUrlDataBuffer());
        MDMLogger.info("Successfully send the data to server and received success response ");
    }
    else {
        status.setStatus(HTTP_STATUS_FAILURE);
        MDMLogger.error("Data sent successfully but failed to get the response and the response code is : " + responseCode);
    }
    inStream.close();
    return status;
}

/**
 * Read the InputStream to String until EOF
 * Call to this API will not close @InputStream
 * @param inStream
 * @return
 * @throws IOException
 */
private String readStreamAsString(InputStream inStream) throws IOException{
    StringBuilder responseData = new StringBuilder();
    String line;
    BufferedReader br=new BufferedReader(new InputStreamReader(inStream));
    while ((line=br.readLine()) != null) {
        responseData.append(line);
    }
    return responseData.toString();
}

有人可以帮忙吗？

Answer 1

当您使用http.keepAlive = true连接时，开始在连接池中回收并保持打开状态。即使服务器关闭了它仍在监听的连接，客户端仍然认为它可以发送数据。毕竟，服务器FIN仅表示服务器不会发送更多数据。

由于连接池的内部逻辑无法访问，因此您几乎无法控制。然而，当您使用https时，您可以打开较低层的窗口，并可以通过Socket访问所创建的HttpsURLConnection.setSSLSocketFactory(SSLSocketFactory)。

您可以为默认工厂（SSLSocketFactory.getDefault()）创建一个允许关闭Socket的包装器。类似于简化的事情：

public class MySSLSocketFactory extends SSLSocketFactory {

    private SSLSocketFactory factory = (SSLSocketFactory) SSLSocketFactory.getDefault();
    private Socket last;

    public void closeLastSocket() {
        if (last != null) {
            last.close();
        }
    }

    public Socket createSocket() throws IOException {
        return this.last = factory.createSocket();
    }

    ...

}

当您关闭底层套接字时，该连接不应符合回收条件，并将被丢弃。因此，如果您执行closeLastSocket和disconnect，则连接甚至不应该进入池中，如果您执行相反的操作，则只有在创建新连接时才会丢弃该连接。

Answer 2

我发现了一些有趣的想法there

以下是关于FIN的一些消息：

这里了解调用很重要 connection.disconnent()不保证触发FIN。来自 HttpURLConnection 的文档：

阅读完回复正文后，应通过致电HttpURLConnection关闭disconnect()。断开连接释放连接所拥有的资源，以便它们可以被关闭或重用。

这里强调的是：正如你从前面所看到的那样截图，是服务器决定终止连接因为第一个FIN是，在某些时候，而不是我们的断开连接的号召由目的地而非来源发送。

为什么android HttpURLConnection没有发回FIN？

2 个答案: