数据不在 QTcpSockets 和 Java Sockets 之间传输答案

【问题标题】：Data isn't transmitted between QTcpSockets and Java Sockets数据不在 QTcpSockets 和 Java Sockets 之间传输
【发布时间】：2019-08-14 10:22:50
【问题描述】：

所以我有两个应用程序，一个是使用 Qt5 用 C++ 编写的，另一个是用 Java 编写的。 C++ 应用程序充当客户端，连接到 java 应用程序中的 ServerSocket 对象，然后从连接中实例化一个套接字。然后，当我尝试向服务器发送字符串时，我要么必须重复发送字符串（例如 20000 次），要么服务器根本没有收到任何内容。

QString s = " This is a test string that will be sent to the server upon connection\n";
QTcpSocket *sock = new QTcpSocket;
sock->connectToHost(QHostAddress::LocalHost, 5000, QIODevice::ReadWrite);
sock->waitForConnected(5000);
QTextStream out(sock);
while(!sock->waitForBytesWritten(3000)) {
        out << s << endl;
}

如果上面的代码不会产生任何结果，下面会产生分段字符串以及服务器接收到的重复字符串：

QString s = " This is a test string that will be sent to the server upon connection\n";
QTcpSocket *sock = new QTcpSocket;
sock->connectToHost(QHostAddress::LocalHost, 5000, QIODevice::ReadWrite);
sock->waitForConnected(5000);
QTextStream out(sock);
do {
        out << s << endl;
} while(!sock->waitForBytesWritten(3000) | 1);

服务器是这样一个简单的java程序：

ServerSocket ss = new ServerSocket(5000);
Socket s = ss.accept();
DataInputStream in = new DataInputStream(s.getInputStream());
while (true){
        String tmp = in.readUTF();
        System.out.println(tmp);
        if (tmp.contains(" ")){
              break;
}

我希望输出是一个简单的This is a test string that will be sent to the server upon connection；然而，结果要么什么都没有，要么就是这样：

his is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

 This is a test string that will be sent to the server upon connection

您知道如何解决这个问题吗？

【问题讨论】：

我不知道“Q”，但如果我用 Java 编写客户端，我必须在调用 out 后发送一个“flush”，让它真正发送数据包.
冲洗没有区别
刷新会将消息推送出流的缓冲区并进入网络堆栈，但 TCP 不保证网络堆栈不会缓冲它或将其拆分为多个 TCP 数据包。如果要在 TCP 流中发送离散消息，则需要将消息包装在协议中。
你知道我将如何在 Qt 中做到这一点吗？
如果刷新没有任何区别，那么我认为您的协议堆栈已损坏。最好去问问 QT 的人他们的东西是如何工作的。虽然不能保证“刷新”，但协议栈应该尽最大努力将数据在线发送出去，而且实际上应该总是成功的。

标签： java c++ qt sockets tcp

【解决方案1】：

因此解决方案是将数据读入byte[]，然后使用字符串构造函数转换为这样的字符串：

ServerSocket ss = new ServerSocket(5000);

Socket s = ss.accept();

DataInputStream in = new DataInputStream(s.getInputStream());

byte[] b = new byte[1024];
in.read(b);

String tmp = new String(b, "UTF8");
System.out.println(b);
System.out.println(tmp);

我不知道为什么，但这是我得出的解决方案。尽管进行了细微的更改，但客户端几乎保持不变：

QString s = "This is a test string that will be sent to the server upon connection\n";

QTcpSocket *sock = new QTcpSocket;

sock->connectToHost(QHostAddress::LocalHost, 5000, QIODevice::ReadWrite);

sock->waitForConnected(5000);


do {
        sock->write(s.toUtf8());
        sock->flush();

        sock->waitForBytesWritten();
} while (sock->isValid() && sock->bytesToWrite() > 0);

【讨论】：

查看我的注释 (5) 以了解您的解决方案为何有效。

【解决方案2】：

(1) waitForBytesWritten 在 Windows 上可能会失败 - 最好使用信号 bytesWritten()

(2) 循环

while(!sock->waitForBytesWritten(3000) | 1);

在我看来就像一个无限循环，与 waitForBytesWritten 的返回码无关

(3) 在你的程序上下文中waitForBytesWritten 的概念是什么？它可能会在写入流的第一个字节后返回！

(4)

的思想是什么

if (tmp.contains(" ")){
              break;

对我来说，这看起来可能会在收到任何空白后中断 - 例如“This”之后的第一个空格。它可能会在几行之后中断，具体取决于 readUTF 提供了多少（我不是 Java 专家）。

(5) readUTF 需要修改后的 UTF8 格式的字符串，但 Qt 不会发送修改后的 UTF8 格式的字符串（前导 16 位整数包含长度）。因此，Java 会将前两个字符（'Th'）解释为长度，然后彩票可能会开始 - 根据这两个字符，解码将返回看似任意的结果。

【讨论】：

所以你的意思是，如果我将字符串的长度添加到一个字节数组中，其中包含你认为可以解决的长度？
根据您的字符串，readUTF 可能会产生意想不到的结果，例如Qt中nul和补充字符的编码是不同的。
但是不是UTF标准的字符集所以使用QString方法toUtf8()应该避免吗？
UTF 是标准化的，但 readUTF 不会读取标准化的 UTF8 而是“修改后的 UTF8”。 google这个词或者在这里阅读Java的接口说明！