通过 dbus-sharp 访问 NetworkManager 连接设置

Question

我是运行 Arch Linux，mcs 版本如下：

>mcs --version
Mono C# compiler version 4.0.4.0

以及以下版本的dbus-sharp

>pacman -Ss dbus-sharp
extra/dbus-sharp 0.8.1-1 [installed] C# implementation of D-Bus
extra/dbus-sharp-glib 0.6.0-1 [installed] C# GLib implementation of D-Bus

这是我的测试程序，基于此处找到的示例代码：https://gist.github.com/Ummon/4317268

我只是想访问当前活动连接的设置，它应该作为 'Dict of {String, Dict of {String, Variant}}' 返回，因为我已经在 org.freedesktop.NetworkManager.Settings.Connection 界面的 d-feet 工具中检查过

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Net;
using DBus;

namespace NetworkManagerDictTest {
    public class MyTest {
        [Interface("org.freedesktop.NetworkManager.Settings.Connection")]
        public interface IConnection {
            IDictionary<string, IDictionary<string, object>> GetSettings();
        }
        readonly static string BUS_NAME = "org.freedesktop.NetworkManager";

        public static void Main(string[] argv) {
            org.freedesktop.DBus.Properties NetworkManagerProps = Bus.System.GetObject<org.freedesktop.DBus.Properties>(BUS_NAME, new ObjectPath("/org/freedesktop/NetworkManager"));
            ObjectPath[] activeConnections = NetworkManagerProps.Get(BUS_NAME, "ActiveConnections") as ObjectPath[];
            if (activeConnections.Length > 0) {
                org.freedesktop.DBus.Properties ActiveConnectionProperties = Bus.System.GetObject<org.freedesktop.DBus.Properties>(BUS_NAME, activeConnections[0]);
                ObjectPath ActiveConnectionPath = ActiveConnectionProperties.Get("org.freedesktop.NetworkManager.Connection.Active", "Connection") as ObjectPath;
                Console.WriteLine("Using connection path: " + ActiveConnectionPath);
                IConnection connection = Bus.System.GetObject<IConnection>(BUS_NAME, ActiveConnectionPath);
                Console.WriteLine("Connection Object ok");
                IDictionary<string, IDictionary<string, object>> settings = connection.GetSettings();
                Console.WriteLine(settings);
            }
        }
    }
}

编译没有错误也没有警告：

mcs Test.cs -r:/usr/lib/mono/dbus-sharp-2.0/dbus-sharp.dll -r:/usr/lib/mono/dbus-sharp-glib-2.0/dbus-sharp-glib.dll

但是我的程序在执行过程中崩溃，输出如下：

>mono Test.exe
Using connection path: /org/freedesktop/NetworkManager/Settings/0
Connection Object ok

Unhandled Exception:
DBus.Protocol.MessageReader+PaddingException: Read non-zero byte at position 28 while expecting padding. Value given: 200
  at DBus.Protocol.MessageReader.ReadPad (Int32 alignment) [0x00000] in <filename unknown>:0 
  at DBus.Protocol.MessageReader.ReadStruct (System.Type type) [0x00000] in <filename unknown>:0 
  at DBus.Protocol.MessageReader.ReadValue (System.Type type) [0x00000] in <filename unknown>:0 
  at DBus.Protocol.MessageReader.ReadDictionary[String,IDictionary`2] () [0x00000] in <filename unknown>:0 
  at NetworkManagerDictTest.MyTest+IConnectionProxy.GetSettings () [0x00000] in <filename unknown>:0 
  at NetworkManagerDictTest.MyTest.Main (System.String[] argv) [0x00000] in <filename unknown>:0 

[ERROR] FATAL UNHANDLED EXCEPTION: DBus.Protocol.MessageReader+PaddingException: Read non-zero byte at position 28 while expecting padding. Value given: 200
  at DBus.Protocol.MessageReader.ReadPad (Int32 alignment) [0x00000] in <filename unknown>:0 
  at DBus.Protocol.MessageReader.ReadStruct (System.Type type) [0x00000] in <filename unknown>:0 
  at DBus.Protocol.MessageReader.ReadValue (System.Type type) [0x00000] in <filename unknown>:0 
  at DBus.Protocol.MessageReader.ReadDictionary[String,IDictionary`2] () [0x00000] in <filename unknown>:0 
  at NetworkManagerDictTest.MyTest+IConnectionProxy.GetSettings () [0x00000] in <filename unknown>:0 
  at NetworkManagerDictTest.MyTest.Main (System.String[] argv) [0x00000] in <filename unknown>:0

如何解决这个问题？我在使用 DBus 时犯了错误吗？似乎所有对 GetSettings 的方法调用都没有问题。我在尝试修复另一个项目中的错误时也遇到了类似的问题，其中 dbus-sharp 在调用 GetSettings 时会抛出异常。这可能是 dbus-sharp 的问题吗？

Answer 1

查看源代码，dbus-sharp 似乎直接从声明方法的签名中推断出 return 类型。不幸的是，它不检查我是否正在使用父 class 或字典的接口，最终它尝试读取 DBus 结构，因为后备情况导致异常，因为 DBus 结构在字典使用时填充了 8 字节4 个字节

用 Dictionary 替换所有 IDictionary 类型工作正常并解决了我的问题。

通过 dbus-sharp 访问 NetworkManager 连接设置

Accessing NetworkManager Connection Settings through dbus-sharp

c#

linux

mono

dbus