通过来自 Python 的 dbus 函数调用传递文件描述符(又名调用 flatpak 的 HostCommand)

Question

我想调用Flatpak的新Development DBus服务来在主机上生成进程，而不是在沙箱中。

为了调用DBus服务，我编写了以下代码:

#!/usr/bin/env python
import logging
import os
import sys
import dbus
def call_on_host(cmd):
    "Calls Flatpak via DBus to spawn a process"
    name = "org.freedesktop.Flatpak"
    path = "/org/freedesktop/Flatpak/Development"
    bus = dbus.SessionBus()
    proxy = bus.get_object(name, path)
    iface = "org.freedesktop.Flatpak.Development"
    fp_helper = dbus.Interface(proxy, iface)
    wd = '/tmp/'
    read_fd, write_fd = os.pipe()
    fds = {0:dbus.types.UnixFd(read_fd)}
    envs = {'FOO':'bar'}
    flags = 1
    # cwd, cmd, fds, env, flags = ('/', ['ls'], {0:dbus.types.UnixFd(open('/etc/passwd'))}, {'foo':'bar'}, 1)
    logging.info("Executing %r %r %r %r %r", wd, cmd, fds, envs, flags)
    ret = fp_helper.HostCommand(wd, cmd, fds, envs, flags)
    return ret

logging.basicConfig(level=logging.DEBUG)
print (call_on_host(sys.argv[1:]))

然而，这并不是很有效。Flatpak DBus helper不接收任何值，即它们都是NULL。

$ python execute_on_host.py  'ls' /
INFO:root:Executing '/tmp/' ['ls'] {0: <dbus.UnixFd object at 0x7f4b5ae6c120>} {'FOO': 'bar'} 1
Traceback (most recent call last):
  File "execute_on_host.py", line 42, in <module>
    print (call_on_host(sys.argv[1:]))
  File "execute_on_host.py", line 35, in call_on_host
    ret = fp_helper.HostCommand(wd, cmd, fds, envs, flags)
  File "/usr/lib/python2.7/dist-packages/dbus/proxies.py", line 70, in __call__
    return self._proxy_method(*args, **keywords)
  File "/usr/lib/python2.7/dist-packages/dbus/proxies.py", line 145, in __call__
    **keywords)
  File "/usr/lib/python2.7/dist-packages/dbus/connection.py", line 651, in call_blocking
    message, timeout)
dbus.exceptions.DBusException: org.freedesktop.DBus.Error.InvalidArgs: No command 19430 given!!1 - *arg_argv[0] == 0

我现在有点糊涂了。在调用代理对象上的gvariables函数之前，我需要包装我的类型吗?

为了测试我是否可以调用具有该签名的服务，我从这个问题中窃取了大部分内容，并得出以下结论:

import unittest
import os
import sys
import subprocess
import time
import dbus
import dbus.service
import dbus.glib
import gobject
class MyDBUSService(dbus.service.Object):
    def __init__(self):
        bus_name = dbus.service.BusName('test.helloservice', bus = dbus.SessionBus())
        dbus.service.Object.__init__(self, bus_name, '/test/helloservice')
    def listen(self):
        loop = gobject.MainLoop()
        loop.run()
    @dbus.service.method('test.helloservice', in_signature="ayaaya{uh}a{ss}u")
    def hello(self, cwd, cmd, fds, env, flags):
        print ([type(foo) for foo in (cwd, cmd, fds, env, flags)]  )
        print ("cwd: %s" % cwd)
        print ("cmd: %s" % cmd)
        print ("fsd: %s" % fds)
        r = os.fdopen(fds[0].take()).read()
        return r

class BaseTestCase(unittest.TestCase):
    def setUp(self):
        env = os.environ.copy()
        self.p = subprocess.Popen(['python', __file__, 'server'], env=env)
        # Wait for the service to become available
        time.sleep(1)
        assert self.p.stdout == None
        assert self.p.stderr == None
        open("/tmp/dbus-test", "w").write("Hello, World!")
    def testHelloService(self):
        bus = dbus.SessionBus()
        helloservice = bus.get_object('test.helloservice', '/test/helloservice')
        hello = helloservice.get_dbus_method('hello', 'test.helloservice')
        cwd, cmd, fds, env, flags = ('/', ['ls'], {0:dbus.types.UnixFd(open('/tmp/dbus-test'))}, {'foo':'bar'}, 1)
        r = hello(cwd, cmd, fds, env, flags)
        assert r == "Hello, World!"
    def tearDown(self):
        # terminate() not supported in Python 2.5
        #self.p.terminate()
        os.kill(self.p.pid, 15)

if __name__ == '__main__':
    arg = ""
    if len(sys.argv) > 1:
        arg = sys.argv[1]
    if arg == "server":
        myservice = MyDBUSService()
        myservice.listen()
    else:
        unittest.main()

很好。

所以我想知道:我如何从Python调用Flatpak开发服务?

Answer 1

为了调查我的代码是否导致通过总线发送相同的消息，我启动了dbus-monitor来检查如果已知良好的客户机发送该消息会发生什么。我得到了以下内容:

method call time=14743.5 sender=:1.6736 -> destination=org.freedesktop.Flatpak serial=8 path=/org/freedesktop/Flatpak/Development; interface=org.freedesktop.Flatpak.Development; member=HostCommand
   array of bytes "/" + 
   array [
      array of bytes "ls" + 
   ]
   array [
      dict entry(
         uint32 0
         file descriptor
               inode: 40
               type: char
      )
      dict entry(
         uint32 1
         file descriptor
               inode: 58091333
               type: fifo
      )
      dict entry(
         uint32 2
         file descriptor
               inode: 40
               type: char
      )
   ]
   array [
      dict entry(
         string "CLUTTER_IM_MODULE"
         string "xim"
      )
   ]
   uint32 1

然而，我自己的客户产生了:

array of bytes "/"
array [
  array of bytes "ls"
]
array [
  dict entry(
     uint32 0
     file descriptor
           inode: 1866322
           type: file
  )
]
array [
  dict entry(
     string "FOO"
     string "bar"
  )
]
uint32 1

区别在于空字节。当添加到我的代码，它工作。原来有关于这个问题的bug报告。