byte []数组以可变长度的结构进行构造 [英] byte[] array to struct with variable length array

问题描述

我正在从套接字接收一个字节数组，字节的结构只是一个固定宽度字符串的大char数组.在某些情况下，最后一个字段是动态的(而不是固定长度)，而我试图将字节编组为结构.我读过，可变长度char数组需要为IntPtr，但是我还没有弄清楚如何用剩余的字节编组它.我还阅读了一些文章，可能需要第二种结构，但仍然无法弄清楚如何正确地将其编组.

I'm receiving an array of bytes from a socket and the structure of the bytes is simply a large char array of fixed width strings. In some cases, the last field is dynamic (instead of fixed length) and I'm trying to Marshal the bytes to a struct. I've read that the variable length char array needs to be IntPtr, but I haven't figured out how to Marshal it with the remaining bytes. I've also read in some articles that I might need a second structure, but still can't figure out how to Marshal it properly.

这是一个这样的站点

在结构中处理可变长度char数组的正确方法是什么?

What's the proper way to deal with variable length char arrays in structs?

结构:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct Header
{
    #region private member fields

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f1;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f2;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f3;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f4;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f5;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f6;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    private char[] _f7;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 12)]
    private char[] _f8;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
    private char[] _f9;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f10;

    // how would this get filled with a char[] array from the byte array?
    public IntPtr VariableLengthData;

    #endregion
}

功能:

public static Header FromArray(byte[] array)
{
    IntPtr buff = IntPtr.Zero;

    try
    {
        int objsize = Marshal.SizeOf(typeof(Header));
        buff = Marshal.AllocHGlobal(objsize);
        Marshal.Copy(array, 0, buff, objsize);
        var result = (Header)Marshal.PtrToStructure(buff, typeof(HostHeader));

        // the variable length data needs to be filled in somehow
        // but also note that an extra 4 bytes was added to the size
        // of the struct with the IntPtr
        if(objsize < array.Length)
        {
            Marshal.Copy(array, array.Length - objsize, result.VariableLengthData, array.Length - objsize);
        }

        return result;
    }
    finally
    {
        if (buff != IntPtr.Zero)
        {
            Marshal.FreeHGlobal(buff);
            buff = IntPtr.Zero;
        }
    }
}

这有效-但是现在Marshal.SizeOf(headerObj)说，它比我尝试将其转换回byte []数组时的实际尺寸要小.除此之外，此解决方案有什么问题吗?

This works - but now Marshal.SizeOf(headerObj) says it's smaller than it really is when I attempt to convert it back to a byte[] array. Other than that, anything wrong with this solution?

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct Header
{
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)] 
    public char[] Field1;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)] 
    public char[] Field2;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)] 
    public char[] Field3;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 1)]
    public char[] Field4;
}

public static Header DeserializeHeader(byte[] data)
{
    int objsize = Marshal.SizeOf(typeof(Header));
    IntPtr buff = Marshal.AllocHGlobal(objsize);
    Marshal.Copy(data, 0, buff, objsize);
    var header = (Header)Marshal.PtrToStructure(buff, typeof(Header));
    Marshal.FreeHGlobal(buff);

    // resize Field4 to hold all the remaining bytes
    if(objsize < data.Length)
    {
        header.Field4 = Encoding.ASCII.GetChars(data, objsize - header.Field4.Length, data.Length - objsize - header.Field4.Length);
    }
    return header;
}

推荐答案

请不要太努力使您的C#声明与数据包格式完全匹配.您希望这样做:

Just don't try too hard to make your C# declarations match the packet format exactly. You'd favor this:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
public class Header {
    //....
}

public class Packet {
    public Header Header;
    public byte[] VariableLengthData;
}

现在，它变得简单.您可以一口气将标头编组，然后复制存在的所有多余字节:

Now it becomes simple. You can marshal the header in one fell swoop and just copy whatever extra bytes are present:

static unsafe Packet FromArray(byte[] data) {
    var hdrsize = Marshal.SizeOf(typeof(Header));
    if (data.Length < hdrsize) throw new ArgumentException();
    Packet result = new Packet();
    // Marshal the header
    fixed (byte* pdata = &data[0]) {
        result.Header = (Header)Marshal.PtrToStructure(new IntPtr(pdata), typeof(Header)); 
    }
    // Copy the rest
    var varsize = data.Length - hdrsize;
    result.VariableLengthData = new byte[varsize];
    Array.Copy(data, hdrsize, result.VariableLengthData, 0, varsize);
    return result;
}

并根据需要修改Packet类，您可能想添加一堆属性来处理char [].

And modify the Packet class as you see fit, you probably want to add a bunch of properties to deal with the char[].

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