为什么我的 android 客户端无法接收来自 winsock c++ 服务器的字符串消息？

Question

我正在尝试构建一个 android 应用程序，该应用程序使用 TCP 套接字与在 Windows 上运行的 c++ 服务器进行通信。我成功地从应用程序向服务器发送了一个字符串，但我无法反其道而行之。请帮助我，因为我一直在尝试解决这个问题。

Android 客户端：

String mystr="Hello World...";
char[] buffin=new char[128];
String input =null;
Integer count = 0;
class TextRcv extends AsyncTask<Void, Void, Integer>
{

    @Override
    protected Integer doInBackground(Void... params) {

        //Sending a string (WORKING)
        Socket clientSocket = null;
        try {
            clientSocket= new Socket("192.168.1.5",8889);
            DataOutputStream oos= new DataOutputStream(clientSocket.getOutputStream());
            oos.writeBytes(mystr);
            //oos.writeBytes(String.valueOf(mystr.length()));//write the length of the string first
            //byte[] bufferout=mystr.getBytes();
            //oos.write(bufferout, 0, bufferout.length);
            oos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

        //Recieving a String (Not working)
        try {
            BufferedReader in = null;
            if (clientSocket != null)
            {
                in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            }
            else
            {
                Log.e("samer ","CLIENTSOCKET NULL");
            }

            if (in != null)
            {
                count=in.read(buffin);
            }
            else
            {
                Log.e("samer ","BUFFERREADER NULL");
            }

            if(count>0)
            {
                input=new String(buffin,0,count);
            }
            if (clientSocket != null) {
                clientSocket.close();
            }

        } catch (IOException e) {
            Log.i("samer count: ",String.valueOf(count));//RETURNS 0 !!
            Log.i("buff samer: ", String.valueOf(buffin));//Returns garbage
            e.printStackTrace();
        }
        return count;
    }

    @Override
    protected void onPostExecute(Integer count) {
        super.onPostExecute(count);

        Toast toast=Toast.makeText(getApplicationContext(),String.valueOf(count),Toast.LENGTH_LONG);
        toast.show();
    }
}

尽管在 windows c++ 服务器端它说它已成功发送 25 个字节，但“计数”始终返回 0。

C++ Winsock 服务器：

int  main(int argc, const char *argv[])
{
    WSADATA wsaData;
    int iResult;
    SOCKET ListenSocket = INVALID_SOCKET;
    SOCKET ClientSocket = INVALID_SOCKET;

    struct addrinfo *result = NULL;
    struct addrinfo hints;
    int valread;
    int iSendResult;
    char * recvbuf;
    char *recvstr;
    int recvbuflen = DEFAULT_BUFLEN;
    recvbuf = (char*)malloc((recvbuflen + 1) * sizeof(char));
    recvstr = (char*)malloc((recvbuflen + 1) * sizeof(char));
    char* AndroidID;
    char *sendbuf = "Client: sending data test";

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed with error: %d\n", iResult);

        return 1;
    }

    ZeroMemory(&hints, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
    hints.ai_flags = AI_PASSIVE;

    // Resolve the server address and port
    iResult = getaddrinfo(NULL, DEFAULT_PORT, &hints, &result);
    if (iResult != 0) {
        printf("getaddrinfo failed with error: %d\n", iResult);
        WSACleanup();

        return 1;
    }

    // Create a SOCKET for connecting to server
    ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
    if (ListenSocket == INVALID_SOCKET) {
        printf("socket failed with error: %ld\n", WSAGetLastError());
        freeaddrinfo(result);
        WSACleanup();

        return 1;
    }

    // Setup the TCP listening socket
    iResult = bind(ListenSocket, result->ai_addr, (int)result->ai_addrlen);
    if (iResult == SOCKET_ERROR) {
        printf("bind failed with error: %d\n", WSAGetLastError());
        freeaddrinfo(result);
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    freeaddrinfo(result);

    iResult = listen(ListenSocket, SOMAXCONN);
    if (iResult == SOCKET_ERROR) {
        printf("listen failed with error: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();

        return 1;
    }

    // Accept a client socket
    ClientSocket = accept(ListenSocket, NULL, NULL);
    if (ClientSocket == INVALID_SOCKET) {
        printf("accept failed with error: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();

        return 1;
    }

    if (ClientSocket != INVALID_SOCKET)
    {
        cout << "Start Receving" << endl;

        //------Start Receiving
        //-----------------------------------
        int lengthofrecv=recv(ClientSocket, recvbuf, recvbuflen, 0);
        recvbuf[lengthofrecv] = '\0';//append \0 to use with printf()
        AndroidID = recvbuf;
        printf("AndroidID - %s \n", recvbuf);
        cout << " \n Done ";

        //---Start Sending to android
        //-----------------------------------------
        iResult = send(ClientSocket, sendbuf, (int)strlen(sendbuf), 0);
        if (iResult == SOCKET_ERROR) 
        {
            wprintf(L"send failed with error: %d\n", WSAGetLastError());
            closesocket(ClientSocket);
            WSACleanup();
            return 1;
        }
        printf("Bytes Sent: %d\n", iResult);

        cout << WSAGetLastError() << endl;
    }

    // shutdown the connection since we're done
    iResult = shutdown(ClientSocket, SD_SEND);
    if (iResult == SOCKET_ERROR) {
        printf("shutdown failed with error: %d\n", WSAGetLastError());
        closesocket(ClientSocket);
        WSACleanup();
        return 1;
    }

    //cleanup
    closesocket(ClientSocket);
    WSACleanup();

    return 0;
}

服务器控制台输出：

开始接收

AndroidID - Hello World...

发送的完成字节数：25

0

按任意键继续。 . .

Answer 1

问题是您在将初始字符串发送到服务器后调用oos.close()。

DataOutputStream 扩展了FilterOutputStream，并记录了其close() 方法的行为：

FilterOutputStream.close()

FilterOutputStream的close方法调用其flush方法，然后调用其底层输出流的close方法。

在这种情况下，“底层输出流”是套接字的 outputStream，它的close() 行为也被记录在案：

Socket.getOutputStream()

关闭返回的 OutputStream 将关闭关联的套接字。

Socket.close()

关闭此套接字。

当前在此套接字上的 I/O 操作中阻塞的任何线程都将抛出 SocketException。

一旦套接字被关闭，它就不能用于进一步的网络使用（即不能重新连接或重新连接）。需要创建一个新的套接字。

关闭这个socket也会关闭这个socket的InputStream和OutputStream。

如果此套接字具有关联的通道，则该通道也将关闭。

因此，您的客户端在读取服务器的回复字符串之前关闭了套接字连接。您需要删除对oos.close() 的调用，以便保持连接打开，直到您完成阅读。

在服务器端，仅仅由于时间原因，您的代码可能能够在套接字检测到断开连接之前调用send() 并将回复字符串放入套接字的出站缓冲区。缓冲区实际上并不是由send() 自己传输的，它被排队到操作系统内核，它会在后台传输数据。所以send()如果在检测到断开连接之前缓冲了回复字符串，将返回成功而不是失败。