c# - 无法导入.NET Core 3.0加载的DLL

Question

我有一个 .NET Core 3 项目，它使用一个包装器库，该库使用 Mosquitto 与 MQTT 代理进行通信。

包装器定义为:

public static class MosquittoWrapper
  {
    public const string MosquittoDll = "mosq";

    [StructLayout(LayoutKind.Sequential)]
    public struct mosquitto_message
    {
      public int mid;
      public string topic;
      public byte[] payload;
      public int payloadlen;
      public int qos;
      [MarshalAs(UnmanagedType.U1)]
      public bool retain;
    }

    public delegate void ConnectCallbackDelegate(int result);
    public delegate void MessageCallbackDelegate(mosquitto_message mesage);

    [DllImport(MosquittoDll, CallingConvention = CallingConvention.Cdecl)]
    public static extern int mosq_init();

    [DllImport(MosquittoDll, CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
    internal static extern int mosq_set_tls_psk(string psk, string identity, string? ciphers);

    [DllImport(MosquittoDll, CallingConvention = CallingConvention.Cdecl)]
    internal static extern void mosq_set_callback(ConnectCallbackDelegate? connect_callback, MessageCallbackDelegate? message_callback);

    [DllImport(MosquittoDll, CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
    internal static extern int mosq_connect(string host, int port, int keepalive);

    [DllImport(MosquittoDll, CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
    internal static extern int mosq_subscribe_topic(string topic);

    [DllImport(MosquittoDll, CallingConvention = CallingConvention.Cdecl)]
    internal static extern void mosq_runloop(int timeout, int max_packets, int sleep_on_reconnect);

    [DllImport(MosquittoDll, CallingConvention = CallingConvention.Cdecl)]
    internal static extern int mosq_destroy();
  }

header 定义为:

#pragma once

#ifndef MOSQUITTO_H_
#define MOSQUITTO_H_

#include <mosquitto.h>

#ifdef _WIN32
#    ifdef LIBRARY_EXPORTS
#        define LIBRARY_API __declspec(dllexport)
#    else
#        define LIBRARY_API __declspec(dllimport)
#    endif
#elif
#    define LIBRARY_API
#endif


typedef void (*CONNECT_CALLBACK)(int);
typedef void (*MESSAGE_CALLBACK)(const struct mosquitto_message*);

// return value 0 represents success. Or ENOMEM, EINVAL when error.
LIBRARY_API int mosq_init();
LIBRARY_API int mosq_set_tls_psk(char* psk, char* identity, char* ciphers);
LIBRARY_API void mosq_set_callback(CONNECT_CALLBACK connect_callback, MESSAGE_CALLBACK message_callback);
LIBRARY_API int mosq_connect(char* host, int port, int keepalive);
LIBRARY_API int mosq_subscribe_topic(char* topic);
LIBRARY_API void mosq_runloop(int timeout, int max_packets, int sleep_on_reconnect);
LIBRARY_API int mosq_destroy();

#endif // MOSQUITTO_H_

问题是当我尝试启动项目时，.NET Core 抛出异常。 System.DllNotFoundException:“无法加载 DLL 'mosq' 或其依赖项之一:找不到指定的模块。 (0x8007007E)'

这根本没有意义。该 dll 及其依赖项被复制到加载 mosq dll 的文件夹中。此外，运行的进程显式地写入有关相关dll加载的符号。我还尝试将 dll 放在不同的文件夹中，但没有用。可能会出现什么问题？

Answer 1

dotnet core 中的 DLL 导入有效 same as it did in .net framework 。

转到https://mosquitto.org/并下载(源/dll)。在这里，我获取了 Windows 二进制文件“mosquitto.dll”。

使用上述 dll 的包装器生成 C# 程序(API: https://mosquitto.org/api/files/mosquitto-h.html )。

这里我将仅使用 init 函数作为概念证明

using System;
using System.Runtime.InteropServices;

namespace aac
{
    class Program
    {
        static void Main(string[] args)
        {
            // Just test the init function
            MosquittoWrapper.mosquitto_lib_init();
            Console.WriteLine("success");
        }
    }

    public static class MosquittoWrapper
    {
        // Same name as DLL
        public const string MosquittoDll = "mosquitto";

        // https://mosquitto.org/api/files/mosquitto-h.html#mosquitto_lib_init
        [DllImport(MosquittoDll, CallingConvention = CallingConvention.Cdecl)]
        public static extern int mosquitto_lib_init();
    }
}

然后构建项目

PS C:\Users\bburns\code\scratch\aac\aac> dotnet build
Microsoft (R) Build Engine version 16.3.0+0f4c62fea for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restore completed in 20.94 ms for C:\Users\bburns\code\scratch\aac\aac\aac.csproj.
  aac -> C:\Users\bburns\code\scratch\aac\aac\bin\Debug\netcoreapp3.0\aac.dll

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:01.61

然后将 mosquitto.dll 放在与执行程序集相同的文件夹中

 bin\Debug\netcoreapp3.0

运行程序:

PS C:\Users\bburns\code\scratch\aac\aac> dotnet run
success 

请注意，如果名称不匹配或找不到 dll，您将生成 DllFileNotFoundException。

public const string MosquittoDll = "mosquittoz";

构建并运行

PS C:\Users\bburns\code\scratch\aac\aac> dotnet run
Unhandled exception. System.DllNotFoundException: Unable to load DLL 'mosquittoz' or one of its dependencies: The specified module could not be found. (0x8007007E)
   at aac.MosquittoWrapper.mosquitto_lib_init()
   at aac.Program.Main(String[] args) in C:\Users\bburns\code\scratch\aac\aac\Program.cs:line 10