c# - byte[] array to struct with variable length 数组

Question

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字符数组。在某些情况下，最后一个字段是动态的(而不是固定长度)，我正在尝试将字节编码为结构。我读过可变长度的 char 数组需要是 IntPtr，但我还没有弄清楚如何用剩余的字节对其进行编码。我还在一些文章中读到我可能需要第二个结构，但仍然无法弄清楚如何正确地编码它。

这是一个这样的 site

在结构中处理可变长度字符数组的正确方法是什么？

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
}

函数:

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;
        }
    }
}

这行得通 - 但现在 Marshal.SizeOf(headerObj) 说它比我尝试将它转换回 byte[] 数组时实际要小。除此之外，这个解决方案还有什么问题吗？

[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;
}

Answer 1

只是不要太努力让您的 C# 声明与数据包格式完全匹配。你会喜欢这个:

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

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

现在变得简单了。您可以一口气编码 header ，只需复制存在的任何额外字节:

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，您可能想要添加一堆属性来处理 char[]。