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Python DBus未知方法或接口

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提问于 2025-04-14 16:11

我正在按照一个关于Linux蓝牙开发的学习指南进行学习，链接在这里，而且我对DBus编程还很陌生。

这个指南使用Python来和系统的DBus进行交互，代码如下。

#!/usr/bin/python3
import dbus

bus = dbus.SystemBus()
proxy = bus.get_object('org.freedesktop.hostname1','/org/freedesktop/hostname1')
interface = dbus.Interface(proxy, 'org.freedesktop.Dbus.Properties')

print("----------------")
hostname = interface.Get('org.freedesktop.hostname1','Hostname')
print("The host name is ",hostname)

但是，当我调用interface.Get方法时，出现了以下错误。

dbus.exceptions.DBusException: org.freedesktop.DBus.Error.UnknownMethod: Unknown method Get or interface org.freedesktop.Dbus.Properties.

我可以使用d-feet工具对org.freedesktop.hostname1对象的org.freedesktop.Dbus.Properties接口运行Get方法，并且能够如预期那样返回主机名。我也尝试以root身份运行这个Python脚本，但仍然遇到同样的错误。

我使用dbus-monitor在Wireshark中捕获了数据包，并比较了d-feet的请求和Python的dbus请求，但我找不到问题所在。两个请求都是发送到同一个目标，看起来结构也一样，相关的细节也相同，只是字典元素的数组顺序似乎不同（不确定这是否重要）。

d-feet请求：

Frame 17: 197 bytes on wire (1576 bits), 197 bytes captured (1576 bits)
    Encapsulation type: D-Bus (146)
    Arrival Time: Mar 13, 2024 07:21:04.048618000 AEDT
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1710274864.048618000 seconds
    [Time delta from previous captured frame: 0.001328000 seconds]
    [Time delta from previous displayed frame: 0.001328000 seconds]
    [Time since reference or first frame: 2.546796000 seconds]
    Frame Number: 17
    Frame Length: 197 bytes (1576 bits)
    Capture Length: 197 bytes (1576 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: dbus]
D-Bus
    Endianness: little-endian
    Message Type: Method call
    Message Flags: 0x00
        .... ...0 = No Reply Expected: Expected
        .... ..0. = No Auto Start: Start
        .... .0.. = Allow Interactive Authorization: Don't allow
    Protocol Version: 1
    Message Body Length: 45
    Message Serial: 623
    Header Field Array
        Array Length: 134
        Dict Entry, 1, Path: /org/freedesktop/hostname1
            Field Code: Path (1)
            Variant: /org/freedesktop/hostname1
                Variant Signature: o
                Path: /org/freedesktop/hostname1
        Dict Entry, 2, Interface: org.freedesktop.DBus.Properties
            Field Code: Interface (2)
            Variant: org.freedesktop.DBus.Properties
                Variant Signature: s
                Interface: org.freedesktop.DBus.Properties
        Dict Entry, 6, Destination: :1.171
            Field Code: Destination (6)
            Variant: :1.171
                Variant Signature: s
                Destination: :1.171
        Dict Entry, 8, Signature: ss
            Field Code: Signature (8)
            Variant: ss
                Variant Signature: g
                Signature: ss
        Dict Entry, 3, Member: Get
            Field Code: Member (3)
            Variant: Get
                Variant Signature: s
                Member: Get
        Dict Entry, 7, Sender: :1.83
            Field Code: Sender (7)
            Variant: :1.83
                Variant Signature: s
                Sender: :1.83
    Body
        String: org.freedesktop.hostname1
        String: Hostname

d-feet的响应：

Frame 18: 86 bytes on wire (688 bits), 86 bytes captured (688 bits)
    Encapsulation type: D-Bus (146)
    Arrival Time: Mar 13, 2024 07:21:04.048994000 AEDT
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1710274864.048994000 seconds
    [Time delta from previous captured frame: 0.000376000 seconds]
    [Time delta from previous displayed frame: 0.000376000 seconds]
    [Time since reference or first frame: 2.547172000 seconds]
    Frame Number: 18
    Frame Length: 86 bytes (688 bits)
    Capture Length: 86 bytes (688 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: dbus]
D-Bus
    Endianness: little-endian
    Message Type: Method reply
    Message Flags: 0x01
        .... ...1 = No Reply Expected: Not expected
        .... ..0. = No Auto Start: Start
        .... .0.. = Allow Interactive Authorization: Don't allow
    Protocol Version: 1
    Message Body Length: 22
    Message Serial: 10
    Header Field Array
        Array Length: 47
        Dict Entry, 5, Reply serial: 623
            Field Code: Reply serial (5)
            Variant: 623
                Variant Signature: u
                Reply serial: 623
        Dict Entry, 6, Destination: :1.83
            Field Code: Destination (6)
            Variant: :1.83
                Variant Signature: s
                Destination: :1.83
        Dict Entry, 8, Signature: v
            Field Code: Signature (8)
            Variant: v
                Variant Signature: g
                Signature: v
        Dict Entry, 7, Sender: :1.171
            Field Code: Sender (7)
            Variant: :1.171
                Variant Signature: s
                Sender: :1.171
    Body
        Variant: Lenny-Leonard
            Variant Signature: s
            String: Lenny-Leonard

Python请求：

Frame 34: 197 bytes on wire (1576 bits), 197 bytes captured (1576 bits)
    Encapsulation type: D-Bus (146)
    Arrival Time: Mar 13, 2024 07:21:06.564106000 AEDT
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1710274866.564106000 seconds
    [Time delta from previous captured frame: 0.000312000 seconds]
    [Time delta from previous displayed frame: 0.000312000 seconds]
    [Time since reference or first frame: 5.062284000 seconds]
    Frame Number: 34
    Frame Length: 197 bytes (1576 bits)
    Capture Length: 197 bytes (1576 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: dbus]
D-Bus
    Endianness: little-endian
    Message Type: Method call
    Message Flags: 0x00
        .... ...0 = No Reply Expected: Expected
        .... ..0. = No Auto Start: Start
        .... .0.. = Allow Interactive Authorization: Don't allow
    Protocol Version: 1
    Message Body Length: 45
    Message Serial: 4
    Header Field Array
        Array Length: 135
        Dict Entry, 1, Path: /org/freedesktop/hostname1
            Field Code: Path (1)
            Variant: /org/freedesktop/hostname1
                Variant Signature: o
                Path: /org/freedesktop/hostname1
        Dict Entry, 6, Destination: :1.171
            Field Code: Destination (6)
            Variant: :1.171
                Variant Signature: s
                Destination: :1.171
        Dict Entry, 2, Interface: org.freedesktop.Dbus.Properties
            Field Code: Interface (2)
            Variant: org.freedesktop.Dbus.Properties
                Variant Signature: s
                Interface: org.freedesktop.Dbus.Properties
        Dict Entry, 3, Member: Get
            Field Code: Member (3)
            Variant: Get
                Variant Signature: s
                Member: Get
        Dict Entry, 8, Signature: ss
            Field Code: Signature (8)
            Variant: ss
                Variant Signature: g
                Signature: ss
        Dict Entry, 7, Sender: :1.173
            Field Code: Sender (7)
            Variant: :1.173
                Variant Signature: s
                Sender: :1.173
    Body
        String: org.freedesktop.hostname1
        String: Hostname

Python的响应：

Frame 35: 189 bytes on wire (1512 bits), 189 bytes captured (1512 bits)
    Encapsulation type: D-Bus (146)
    Arrival Time: Mar 13, 2024 07:21:06.564291000 AEDT
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1710274866.564291000 seconds
    [Time delta from previous captured frame: 0.000185000 seconds]
    [Time delta from previous displayed frame: 0.000185000 seconds]
    [Time since reference or first frame: 5.062469000 seconds]
    Frame Number: 35
    Frame Length: 189 bytes (1512 bits)
    Capture Length: 189 bytes (1512 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: dbus]
D-Bus
    Endianness: little-endian
    Message Type: Error reply
    Message Flags: 0x01
        .... ...1 = No Reply Expected: Not expected
        .... ..0. = No Auto Start: Start
        .... .0.. = Allow Interactive Authorization: Don't allow
    Protocol Version: 1
    Message Body Length: 69
    Message Serial: 12
    Header Field Array
        Array Length: 103
        Dict Entry, 5, Reply serial: 4
            Field Code: Reply serial (5)
            Variant: 4
                Variant Signature: u
                Reply serial: 4
        Dict Entry, 6, Destination: :1.173
            Field Code: Destination (6)
            Variant: :1.173
                Variant Signature: s
                Destination: :1.173
        Dict Entry, 4, Error name: org.freedesktop.DBus.Error.UnknownMethod
            Field Code: Error name (4)
            Variant: org.freedesktop.DBus.Error.UnknownMethod
                Variant Signature: s
                Error name: org.freedesktop.DBus.Error.UnknownMethod
        Dict Entry, 8, Signature: s
            Field Code: Signature (8)
            Variant: s
                Variant Signature: g
                Signature: s
        Dict Entry, 7, Sender: :1.171
            Field Code: Sender (7)
            Variant: :1.171
                Variant Signature: s
                Sender: :1.171
    Body
        String: Unknown method Get or interface org.freedesktop.Dbus.Properties.

我在这里漏掉了什么吗？有没有可能发送其他请求来发现所选接口可用的方法，或者验证它是否是正确的接口？

谢谢。

Linux 系统编程 方法调用 dbus bluetooth d-feet dbus-monitor interface

1 个回答

1

这个问题是通过修正一个拼写错误解决的，感谢ukBaz的指正。

原本写的是org.freedesktop.Dbus.Properties，正确的应该是org.freedesktop.DBus.Properties。

现在一切都正常了。

回答于 2025-04-14 由 Python大师
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