使用 python 浏览 avahi 服务会错过服务

Posted 2023-04-14

【中文标题】使用 python 浏览 avahi 服务会错过服务

【英文标题】：Browsing avahi services with python misses services

【发布时间】：2013-03-11 07:34:59

【问题描述】：

我需要一个类，它为我提供当前可用的某种类型的 avahi 服务列表。因此，我在一个单独的线程中运行gobject.MainLoop()（第 23-25 行），并为我感兴趣的每个服务添加一个浏览器（第 27,28 行）。原则上这是可行的。

我的问题是，我并不总是获得所有服务。有时列出所有可用的服务，有时没有列出，有时只列出几个。我的猜测是，浏览器在连接适当的信号（第 41-44 行）之前开始迭代服务（第 36 行），但我不知道如何解决这个问题。下面是一个显示失败的最小示例。

我在网上看到的大多数示例（例如：Stopping the Avahi service and return a list of elements）在设置好浏览器并连接信号后运行 MainLoop。当收到“AllForNow”信号时，循环退出。这对我来说不是一个选项，因为浏览器应该继续运行并监听新的或已删除的服务（顺便说一句，这很可靠，只是初始查询有问题）。

#!/usr/bin/python
import dbus
from dbus.mainloop.glib import DBusGMainLoop
import avahi
import gobject
import threading

gobject.threads_init()
dbus.mainloop.glib.threads_init()

class ZeroconfBrowser:
    def __init__(self):
        self.service_browsers = set()
        self.services = 
        self.lock = threading.Lock()

        loop = DBusGMainLoop(set_as_default=True)
        self._bus = dbus.SystemBus(mainloop=loop)
        self.server = dbus.Interface(
                self._bus.get_object(avahi.DBUS_NAME, avahi.DBUS_PATH_SERVER), 
                avahi.DBUS_INTERFACE_SERVER)

        thread = threading.Thread(target=gobject.MainLoop().run)
        thread.daemon = True
        thread.start()

        self.browse("_ssh._tcp")
        self.browse("_http._tcp")

    def browse(self, service):
        if service in self.service_browsers:
            return
        self.service_browsers.add(service)

        with self.lock:
            browser = dbus.Interface(self._bus.get_object(avahi.DBUS_NAME, 
                    self.server.ServiceBrowserNew(avahi.IF_UNSPEC, 
                            avahi.PROTO_UNSPEC, service, 'local', dbus.UInt32(0))),
                    avahi.DBUS_INTERFACE_SERVICE_BROWSER)

            browser.connect_to_signal("ItemNew", self.item_new)
            browser.connect_to_signal("ItemRemove", self.item_remove)
            browser.connect_to_signal("AllForNow", self.all_for_now)
            browser.connect_to_signal("Failure", self.failure)

    def resolved(self, interface, protocol, name, service, domain, host, 
            aprotocol, address, port, txt, flags):
        print "resolved", interface, protocol, name, service, domain, flags

    def failure(self, exception):
        print "Browse error:", exception

    def item_new(self, interface, protocol, name, stype, domain, flags):
        with self.lock:
            self.server.ResolveService(interface, protocol, name, stype,
                    domain, avahi.PROTO_UNSPEC, dbus.UInt32(0),
                    reply_handler=self.resolved, error_handler=self.resolve_error)

    def item_remove(self, interface, protocol, name, service, domain, flags):
        print "removed", interface, protocol, name, service, domain, flags

    def all_for_now(self):
        print "all for now"

    def resolve_error(self, *args, **kwargs):
        with self.lock:
            print "Resolve error:", args, kwargs

import time
def main():
    browser = ZeroconfBrowser()
    while True:
        time.sleep(3)
        for key, value in browser.services.items():
            print key, str(value)

if __name__ == '__main__':
    main()

【参考方案1】：

我找不到可安装的 python-dbus 包。不过我确实找到了一个很好用的示例 Avahi 浏览器——avahi.py

pip install python-tdbus

来源

#!/usr/bin/env python
#
# This file is part of python-tdbus. Python-tdbus is free software
# available under the terms of the MIT license. See the file "LICENSE" that
# was provided together with this source file for the licensing terms.
#
# Copyright (c) 2012 the python-tdbus authors. See the file "AUTHORS" for a
# complete list.

# This example shows how to access Avahi on the D-BUS.


from tdbus import SimpleDBusConnection, DBUS_BUS_SYSTEM, DBusHandler, signal_handler, DBusError

import logging

logging.basicConfig(level=logging.DEBUG)

CONN_AVAHI = 'org.freedesktop.Avahi'
PATH_SERVER = '/'
IFACE_SERVER = 'org.freedesktop.Avahi.Server'

conn = SimpleDBusConnection(DBUS_BUS_SYSTEM)

try:
    result = conn.call_method(PATH_SERVER, 'GetVersionString',
                        interface=IFACE_SERVER, destination=CONN_AVAHI)
except DBusError:
    print 'Avahi NOT available.'
    raise

print 'Avahi is available at %s' % CONN_AVAHI
print 'Avahi version: %s' % result.get_args()[0]
print
print 'Browsing service types on domain: local'
print 'Press CTRL-c to exit'
print

result = conn.call_method('/', 'ServiceTypeBrowserNew', interface=IFACE_SERVER,
                    destination=CONN_AVAHI, format='iisu', args=(-1, 0, 'local', 0))
browser = result.get_args()[0]
print browser
class AvahiHandler(DBusHandler):

    @signal_handler()
    def ItemNew(self, message):
    args = message.get_args()
        print 'service %s exists on domain %s' % (args[2], args[3])

conn.add_handler(AvahiHandler())
conn.dispatch()

输出

Avahi is available at org.freedesktop.Avahi
Avahi version: avahi 0.6.31

Browsing service types on domain: local
Press CTRL-c to exit

/Client1/ServiceTypeBrowser1
service _udisks-ssh._tcp exists on domain local
service _workstation._tcp exists on domain local
service _workstation._tcp exists on domain local
service _udisks-ssh._tcp exists on domain local