问题描述

我需要创建一个应用程序，该应用程序需要使用 TCP/IP 与现有软件进行通信，其中我的应用程序和其他应用程序都将使用下面指定的端口号.

I need to create an application which requires communicating to an existent software using TCP/IP, where both mine and the other application will be using the port number specified below.

private void frmScan_Load(object sender, EventArgs e)
{
    clientSocket.Connect("100.100.100.30", 76545);
}

public void msg(string mesg)
{
    textBox1.Text = textBox1.Text + Environment.NewLine + " >> " + mesg;
}

private void cmdSCANok_Click(object sender, EventArgs e)
{

    msg("Client Started");
    NetworkStream serverStream = clientSocket.GetStream();
    byte[] outStream = Encoding.ASCII.GetBytes("PCK|SCAN|5025066840471");

    serverStream.Write(outStream, 0, outStream.Length);
    serverStream.Flush();

    byte[] inStream = new byte[10025];
    serverStream.Read(inStream, 0, (int)clientSocket.ReceiveBufferSize);
    string returndata = Encoding.ASCII.GetString(inStream, 0, inStream.Length);


    msg("Data from Server : " + returndata);
} 

发生的情况是，我正在与之通信的程序有一些内置语言，它可以理解我发送的代码，并根据我发送的代码返回数据.所以在上面的代码中，我发送了三位代码: ("PCK|SCAN|5025066840471") 它将在数据库中找到一个特定的项目.当它运行时，我得到一个错误:

What happens is, the program I am communicating with has some in-built language where it will understand the code that I send, and it will return data according to the code that I have sent. So in the code above, I sent three bits of code: ("PCK|SCAN|5025066840471") which will find a specific item in the database. When it runs, I get an error on the line:

serverStream.Read(inStream, 0, (int)clientSocket.ReceiveBufferSize);

错误显示如下:指定的参数超出了有效值的范围.参数名称:大小"

the error shows the following: "Specified argument was out of the range of valid values. Parameter name: size"

我按照我在这个网站上看到的教程进行操作:http://csharp.net-informations.com/communications/csharp-client-socket.htm - 但我的做法略有不同.所以不要放

I followed the tutorial I saw on this website: http://csharp.net-informations.com/communications/csharp-client-socket.htm - But I did slightly different. So instead of putting

string returndata = Encoding.ASCII.GetString(inStream);

我写道:

string returndata = Encoding.ASCII.GetString(inStream, 0, inStream.Length); 

我对为什么会遇到这些问题感到非常困惑，老实说，我不太了解代码在做什么，我只是有一个粗略的想法，但不足以解决这个问题.有人可以帮忙吗?

I am extremely confused on why I am getting those problems, and to be honest I am not understanding much of what the code is doing, I just have a rough idea, but not enough to troubleshoot this. Can someone help please?

非常感谢！

PS:我正在 Visual Studio 2010 上为 Windows CE(便携式设备)编程.

PS: I am programming for Windows CE (portable device) on Visual Studio 2010.

推荐答案

您的代码是如何不进行 TCP 通信的一个很好的例子.我已经多次看到这段代码被复制了很多次，我很乐意为您指出一个关于 TCP 的好教程 - 可惜我还没有看到一个:)

Your code is a great example of how not to do TCP communication. I've seen this code copied over and over many times, and I'd be very happy to point you to a good tutorial on TCP - too bad I haven't seen one yet :)

让我先指出一些错误:

• TCP 不保证数据包以一串字节的形式到达.因此(理论上)Write 操作可能会导致拆分，需要在另一侧进行两次读取.通过 TCP 发送没有标头的数据是一个非常糟糕的主意 - 接收方不知道它必须读取多少.所以你有两个选择——要么在数据本身之前写入整组数据的长度，要么使用控制字符来结束数据包"
• 第一点也应该澄清你的阅读也是错误的.读取整个命令"可能需要不止一次读取操作，或者一次读取操作可能会同时给您两个命令！
• 您正在将 ReceiveBufferSize 字节读入 10025 长缓冲区.ReceiveBufferSize 可能比您的缓冲区大.不要这样做 - 读取 inStream.Length 的最大计数.如果您使用 C++ 进行编码，这将是一个很好的缓冲区溢出示例.
• 当您将数据转换为字符串时，您预计整个缓冲区已满.很可能并非如此.相反，您必须存储 read 调用的返回值——它告诉您实际读取了多少字节.否则，您正在读取垃圾，并且基本上有 另一个 缓冲区溢出.

• TCP doesn't guarantee you the packet arrives as one bunch of bytes. So (theoretically) the Write operation could result in a split, requiring two reads on the other side. Sending data without headers over TCP is a very bad idea - the receiving side has no idea how much it has to read. So you've got two options - either write the length of the whole bunch of data before the data itself, or use a control character to end the "packet"
• The first point should also clarify that your reading is wrong as well. It may take more than a single read operation to read the whole "command", or a single read operation might give you two commands at once!
• You're reading ReceiveBufferSize bytes into a 10025 long buffer. ReceiveBufferSize might be bigger than your buffer. Don't do that - read a max count of inStream.Length. If you were coding in C++, this would be a great example of a buffer overflow.
• As you're converting the data to a string, you're expecting the whole buffer is full. That's most likely not the case. Instead, you have to store the return value of the read call - it tells you how many bytes were actually read. Otherwise, you're reading garbage, and basically having another buffer overflow.

因此，一个更好(尽管仍远非完美)的实现应该是这样的:

So a much better (though still far from perfect) implementation would be like this:

NetworkStream serverStream = clientSocket.GetStream();
byte[] outStream = Encoding.ASCII.GetBytes("PCK|SCAN|5025066840471");

// It would be much nicer to send a terminator or data length first, 
// but if your server doesn't expect that, you're out of luck.
serverStream.Write(outStream, 0, outStream.Length);

// When using magic numbers, at least use nice ones :)
byte[] inStream = new byte[4096];

// This will read at most inStream.Length bytes - it can be less, and it
// doesn't tell us how much data there is left for reading.
int bytesRead = serverStream.Read(inStream, 0, inStream.Length);

// Only convert bytesRead bytes - the rest is garbage
string returndata = Encoding.ASCII.GetString(inStream, 0, bytesRead);

哦，我不得不推荐 这篇关于 TCP 协议设计的文章.

它谈到了关于 TCP 的许多误解，最重要的是请参阅消息框架部分.

It talks about many of the misconceptions about TCP, most importantly see the Message Framing part.

这篇关于指定的参数超出了有效值的范围.参数名称:size &串口通讯的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！