c# - 尝试将结构转换为 byte[] 时的方法访问预期

Question

我需要将以下结构转换为字节数组:

[Serializable]
public struct newLeads
{
    public string id;
    public string first_name;
    public string last_name;
}

我正在尝试使用以下代码转换为字节数组:

public class ConvertStruct
{
    public static byte[] StructureToByteArray(object obj)
    {
        int Length = Marshal.SizeOf(obj);
        byte[] bytearray = new byte[Length];
        IntPtr ptr = Marshal.AllocHGlobal(Length);
        Marshal.StructureToPtr(obj, ptr, false);
        Marshal.Copy(ptr, bytearray, 0, Length);
        Marshal.FreeHGlobal(ptr);
        return bytearray;
    }
}

我在网上收到异常:

IntPtr ptr = Marshal.AllocHGlobal(Length);

Exception: Attempt by security transparent method 'Classes.ConvertStruct.ConvertStruct.StructureToByteArray(System.Object)' to access security critical method 'System.Runtime.InteropServices.Marshal.AllocHGlobal(Int32)' failed."}

我的问题是？我该如何解决这个问题以避免异常并将我的简单结构转换为 byte[]？

提前致谢!

更新:我在控制台应用程序中试过这个并且它有效。我是从 asp.net 页面代码隐藏中调用它的，所以这一定与它有关，但我不知道是什么!

Answer 1

1. 检查结构的大小，不要装箱。

2. 为字符串设置适当的编码(marshal)处理(取自 answer 的 goric )，如果不这样做，您将得到字节数组中字符串的内存地址(这不是一件好事)。

   [Serializable]
   public struct newLeads
   {
       [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 5000)]
       public string id;
       [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 5000)]
       public string first_name;
       [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 5000)]
       public string last_name;
   }
   
   [SecurityPermission(SecurityAction.Demand, UnmanagedCode = true)]
   public static byte[] ToByteArray(newLeads value)
   {
       int length = Marshal.SizeOf(typeof(newLeads));
       var result = new byte[length];
       IntPtr sourcePtr = Marshal.AllocHGlobal(length);
       Marshal.StructureToPtr(value, sourcePtr, false);
       Marshal.Copy(sourcePtr, result, 0, length);
       Marshal.FreeHGlobal(sourcePtr);
       return result;
   }
   

---

在您的评论中，您说过此代码会更快失败。好吧，它使用安全权限要求(如 .NET 4 所推荐的那样)，每次调用该方法时都会检查特定的权限。你可以尝试在没有它的情况下执行它，预期的结果就是你开始时得到的结果。

---

真正的答案

您必须在受限环境中运行，可能是某种沙箱或不支持指针的平台。在这种情况下，我们可能需要通过其他方式进行转换。

你说的是 ASP.NET？就是这样。

为了不使用指针进行转换，试试这个技巧:

//You will have to decide an encoding.
//If nto ASCII, try UTF8Encoding, UnicodeEncoding or (Hopefully not) UTF7Encoding
void Main()
{
    Encoding encoding = new ASCIIEncoding();
    newLeads target = GetNewLeads();
    byte[] id = EncodeString(target.id, encoding);
    byte[] first_name = EncodeString(target.first_name, encoding);
    byte[] last_name = EncodeString(target.last_name, encoding);
}

byte[] EncodeString(string str, Encoding encoding)
{
    byte[] data;
    if (ReferenceEquals(str, null))
    {
        data = new byte[0];
    }
    else
    {
        data = encoding.GetBytes(str);
    }
    return data;
}

在这一点上，我需要更多地了解您的情况，以便为您提供更好的解决方案，特别是谁或什么将读取该字节数组？。无论如何，您可以像这样对字符串的长度进行编码(为 null 保留 -1):

byte[] EncodeString(string str, Encoding encoding)
{
    byte[] data;
    byte[] data_length;
    Union union = new Union();
    if (ReferenceEquals(str, null))
    {
        data = new byte[0];
        union.data = -1;
    }
    else
    {
        data = encoding.GetBytes(str);
        union.data = str.Length;
    }
    data_length = new byte[]{union.a, union.b, union.c, union.c};
    int length = data.Length;
    byte[] result = new byte[4 + data.Length];
    System.Buffer.BlockCopy(data_length, 0, result, 0, 4);
    System.Buffer.BlockCopy(data, 0, result, 4, length);
    return result;
}

//I hope endianess doesn't bite
[StructLayout(LayoutKind.Explicit)] 
struct Union
{
    [FieldOffset(0)]
    public int data;
    [FieldOffset(0)] 
    public byte a;
    [FieldOffset(1)] 
    public byte b;
    [FieldOffset(2)] 
    public byte c;
    [FieldOffset(3)] 
    public byte d;
}

最后，我们需要连接这些数组。我知道这可以优化更多......(使用 MemoryStream 和 StreamWriter 的好主意)无论如何，这是我的第一个实现[测试]:

byte[] ToByteArray(newLeads value)
{
    Encoding encoding = new ASCIIEncoding(); //Choose some encoding
    byte[] id = EncodeString(value.id, encoding);
    byte[] first_name = EncodeString(value.first_name, encoding);
    byte[] last_name = EncodeString(value.last_name, encoding);
    byte[] result = new byte[id.Length + first_name.Length + last_name.Length];
    System.Buffer.BlockCopy(id, 0, result, 0, id.Length);
    System.Buffer.BlockCopy
        (
            first_name,
            0,
            result,
            id.Length,
            first_name.Length
        );
    System.Buffer.BlockCopy
        (
            last_name,
            0,
            result,
            id.Length + first_name.Length,
            last_name.Length
        );
    return result;
}

byte[] EncodeString(string str, Encoding encoding)
{
    byte[] data;
    byte[] data_length;
    Union union = new Union();
    if (ReferenceEquals(str, null))
    {
        data = new byte[0];
        union.data = -1;
    }
    else
    {
        data = encoding.GetBytes(str);
        union.data = str.Length;
    }
    data_length = new byte[]{union.a, union.b, union.c, union.c};
    int length = data.Length;
    byte[] result = new byte[4 + data.Length];
    System.Buffer.BlockCopy(data_length, 0, result, 0, 4);
    System.Buffer.BlockCopy(data, 0, result, 4, length);
    return result;
}

//I hope endianess doesn't bite
[StructLayout(LayoutKind.Explicit)] 
struct Union
{
    [FieldOffset(0)]
    public int data;
    [FieldOffset(0)] 
    public byte a;
    [FieldOffset(1)] 
    public byte b;
    [FieldOffset(2)] 
    public byte c;
    [FieldOffset(3)] 
    public byte d;
}

注意:我没有使用以 null 结尾的字符串，因为我不知道你最终会使用什么编码。

优化

相同的逻辑，但使用流实现(Union 没有改变)[已测试]。

byte[] ToByteArray(newLeads value)
{
    Encoding encoding = new ASCIIEncoding(); //Choose some encoding
    var stream = new MemoryStream();
    EncodeString(value.id, stream, encoding);
    EncodeString(value.first_name, stream, encoding);
    EncodeString(value.last_name, stream, encoding);
    int length = (int)stream.Length;
    byte[] result = new byte[(int)stream.Length];
    System.Buffer.BlockCopy(stream.GetBuffer(), 0, result, 0, length);
    stream.Close();
    return result;
}

void EncodeString(string str, Stream stream, Encoding encoding)
{
    Union union = new Union();
    if (ReferenceEquals(str, null))
    {
        union.data = -1;
        stream.Write(new byte[]{union.a, union.b, union.c, union.c}, 0, 4);
    }
    else
    {
        union.data = str.Length;
        stream.Write(new byte[]{union.a, union.b, union.c, union.c}, 0, 4);
        var tmp = encoding.GetBytes(str);
        stream.Write(tmp, 0, tmp.Length);
    }
}

---

将字符串还原

为了取回数据，我们首先读取字符串的长度(使用相同类型的 Union):

var newLeads = GetNewLeads();
var z= ToByteArray(newLeads); //we have the byteArray in z

var data = new MemoryStream(z); //Create an stream for convenience
//Use the union to get the length
var union = new Union()
    {
        a = (byte)data.ReadByte(),
        b = (byte)data.ReadByte(),
        c = (byte)data.ReadByte(),
        d = (byte)data.ReadByte()
    };
Console.WriteLine(union.data); //the length of the first string

我们的下一步是读取那么多字符，为此我们将使用 StreamReader:

var newLeads = GetNewLeads();
var z = ToByteArray(newLeads);

var data = new MemoryStream(z);
var union = new Union()
    {
        a = (byte)data.ReadByte(),
        b = (byte)data.ReadByte(),
        c = (byte)data.ReadByte(),
        d = (byte)data.ReadByte()
    };
var encoding = new ASCIIEncoding();
string result = null;
if (union.data != -1)
{
    char[] finalChars = new char[union.data];
    var reader = new StreamReader(data, encoding);
    reader.Read(finalChars, 0, union.data);
    result = new string(finalChars);
}
Console.WriteLine(result);

有了这个，我们构建了一个解码字符串的方法:

string DecodeString(Stream data, Encoding encoding)
{   
    //TODO: You may want to validate that data and encoding are not null
    //or make this private
    var union = new Union()
    {
        a = (byte)data.ReadByte(),
        b = (byte)data.ReadByte(),
        c = (byte)data.ReadByte(),
        d = (byte)data.ReadByte()
    };
    string result = null;
    if (union.data != -1)
    {
        char[] finalChars = new char[union.data];
        var reader = new StreamReader(data, encoding);
        reader.Read(finalChars, 0, union.data);
        result = new string(finalChars);
    }
    return result;
}

//Convenience method, not needed:

string DecodeString(byte[] data, Encoding encoding)
{
    //TODO: You may want to validate that data and encoding are not null
    //or make this private
    return DecodeString(new MemoryStream(data), encoding);
}

最后是恢复 newLeads 的方法(再次使用相同的 Union 类型)[已测试]:

newLeads FromByteArray(byte[] data)
{
    //TODO: Validate that data is not null
    Encoding encoding = new ASCIIEncoding(); //Choose the same encoding
    newLeads result = new newLeads();
    var reader = new StreamReader(new MemoryStream(data), encoding);
    result.id = DecodeString(reader);
    result.first_name = DecodeString(reader);
    result.last_name = DecodeString(reader);
    reader.Close();
    return result;
}


//Changed to reuse StreamReader...
//Because closing it will close the underlying stream
string DecodeString(StreamReader reader)
{
    //TODO: You may want to validate that reader is not null
    //or make this private
    var data = reader.BaseStream;
    var union = new Union()
    {
        a = (byte)data.ReadByte(),
        b = (byte)data.ReadByte(),
        c = (byte)data.ReadByte(),
        d = (byte)data.ReadByte()
    };
    string result = null;
    if (union.data != -1)
    {
        char[] finalChars = new char[union.data];
        reader.Read(finalChars, 0, union.data);
        result = new string(finalChars);
    }
    return result;
}

//Convenience method, not needed:

string DecodeString(byte[] data, Encoding encoding)
{
    //TODO: You may want to validate that data and encoding are not null
    //or make this private
    return DecodeString(new StreamReader(new MemoryStream(data), encoding));
}