c# - 使用 .net C# 在 SNMP 项目上编码错误

Question

我必须构建一个 SNMP 项目来与各种设备进行通信。遗憾的是，除了用于 SNMP 的 Windows dll(mgmtapi.dll、snmpapi.dll、wsnmp32.dll)之外，我不能使用任何库。我已经为那些库和这些库的功能所需的所有结构制作了包装器，但是在循环之后:

• SnmpMgrOpen(初始化并获取 session )。
• 创建 SnmpVarBindList(使用 SnmpMgrStrToOid、SnmpUtilMemAlloc 和其他编码)以创建 GET 请求。
• SnmpMgrRequest 发出请求并填充 SnmpVarBindList 结构。
• SnmpMgrClose 关闭 session 。

当我想使用

查看 SnmpVarBindList 中的 SnmpVarBind 中的内容时

Marshal.PtrToStringAnsi(varBind.value.asnValue.text.stream, (int)varBind.value.asnValue.text.length + 1)

我收到错误:试图读取或写入 protected 内存。这通常表明其他内存已损坏。

从头文件 snmp.h 翻译而来的结构是:

[StructLayout(LayoutKind.Sequential)]
public struct AsnOctetString
{
    public uint length;
    public int dynamic;
    public IntPtr stream;
}

[StructLayout(LayoutKind.Sequential)]
public struct AsnObjectIdentifier
{
    public uint idLength;
    public IntPtr ids;
}

[StructLayout(LayoutKind.Explicit)]
public struct AsnUnion
{
    [FieldOffset(0)]
    public int number;
    [FieldOffset(0)]
    public uint unsigned32;
    [FieldOffset(0)]
    public ulong counter64;
    [FieldOffset(0)]
    public AsnOctetString text;
    [FieldOffset(0)]
    public AsnOctetString bits;
    [FieldOffset(0)]
    public AsnObjectIdentifier objectID;
    [FieldOffset(0)]
    public AsnOctetString sequence;
    [FieldOffset(0)]
    public AsnOctetString address;
    [FieldOffset(0)]
    public uint counter;
    [FieldOffset(0)]
    public uint gauge;
    [FieldOffset(0)]
    public uint ticks;
    [FieldOffset(0)]
    public AsnOctetString arbitrary;
}

[StructLayout(LayoutKind.Sequential)]
public struct AsnAny
{
    public byte asnType;
    public AsnUnion asnValue;
}

[StructLayout(LayoutKind.Sequential)]
public struct SnmpVarBind
{
    public AsnObjectIdentifier name;
    public AsnAny value;
}

[StructLayout(LayoutKind.Sequential)]
public struct SnmpVarBindList
{
    public IntPtr list;
    public uint len;
}

有什么想法吗？我可以放你想要/需要的代码。

Answer 1

我知道这个答案已经很晚了，但我最近遇到了 SNMP API 的编码问题。我曾假设这些结构是按字节边界打包的，但这是错误的。如果你看Snmp.h , 你会看到 #include <pshpack4.h>这会打开 4 字节边界上的打包。这意味着字段偏移量不同。这就是我的 AsnAny看起来像:

[StructLayout(LayoutKind.Explicit)]
    private struct AsnAny
    {
        [FieldOffset(0)]
        public readonly byte Type;

        [FieldOffset(4)]
        public readonly Int32 Number;

        [FieldOffset(4)]
        public readonly UInt32 Unsigned32;

        [FieldOffset(4)]
        public readonly UInt64 Counter64;

        [FieldOffset(4)]
        public readonly AsnOctetString String;

        [FieldOffset(4)]
        public readonly AsnOctetString Bits;

        [FieldOffset(4)]
        public readonly AsnObjectIdentifier Object;

        [FieldOffset(4)]
        public readonly AsnOctetString Sequence;

        [FieldOffset(4)]
        public readonly AsnOctetString IPAddress;

        [FieldOffset(4)]
        public readonly UInt32 Counter32;

        [FieldOffset(4)]
        public readonly UInt32 Gauge32;

        [FieldOffset(4)]
        public readonly UInt32 Ticks;

        [FieldOffset(4)]
        public readonly AsnOctetString Arbitrary;
    }