python - 使用 Twisted 模拟 DNS 服务器

Question

我正在尝试编写一个基于 Twisted 的模拟 DNS 服务器来做一些测试。

从 this guide 中汲取灵感我写了一个非常简单的服务器，它只是将所有内容解析为 127.0.0.1 :

from twisted.internet import defer, reactor
from twisted.names import dns, error, server


class MockDNSResolver:

    def _doDynamicResponse(self, query):
        name = query.name.name
        record = dns.Record_A(address=b"127.0.0.1")
        answer = dns.RRHeader(name=name, payload=record)
        authority = []
        additional = []
        return [answer], authority, additional

    def query(self, query, timeout=None):
        print("Incoming query for:", query.name)
        if query.type == dns.A:
            return defer.succeed(self._doDynamicResponse(query))
        else:
            return defer.fail(error.DomainError())


if __name__ == "__main__":
    clients = [MockDNSResolver()]
    factory = server.DNSServerFactory(clients=clients)
    protocol = dns.DNSDatagramProtocol(controller=factory)
    reactor.listenUDP(10053, protocol)
    reactor.listenTCP(10053, factory)
    reactor.run()

以上与 dig 一起工作得很好和 nslookup (来自不同的终端):

$ dig -p 10053 @localhost something.example.org A +short
127.0.0.1

$ nslookup something.else.example.org 127.0.0.1 -port=10053
Server:     127.0.0.1
Address:    127.0.0.1#10053

Non-authoritative answer:
Name:   something.else.example.org
Address: 127.0.0.1

我还在运行服务器的终端上获得了相应的点击:

Incoming query for: something.example.org
Incoming query for: something.else.example.org

然后，我基于 this section about making requests 编写了以下代码段和 this section about installing a custom resolver :

from twisted.internet import reactor
from twisted.names.client import createResolver
from twisted.web.client import Agent


d = Agent(reactor).request(b'GET', b'http://does.not.exist')
reactor.installResolver(createResolver(servers=[('127.0.0.1', 10053)]))


def callback(result):
    print('Result:', result)


d.addBoth(callback)
d.addBoth(lambda _: reactor.stop())

reactor.run()

但这失败了(并且我在服务器终端中没有线路)。看起来好像查询不会发送到模拟服务器，而是发送到系统定义的服务器:

Result: [Failure instance: Traceback: <class 'twisted.internet.error.DNSLookupError'>: DNS lookup failed: no results for hostname lookup: does.not.exist.
/.../venv/lib/python3.6/site-packages/twisted/internet/_resolver.py:137:deliverResults
/.../venv/lib/python3.6/site-packages/twisted/internet/endpoints.py:921:resolutionComplete
/.../venv/lib/python3.6/site-packages/twisted/internet/defer.py:460:callback
/.../venv/lib/python3.6/site-packages/twisted/internet/defer.py:568:_startRunCallbacks
--- <exception caught here> ---
/.../venv/lib/python3.6/site-packages/twisted/internet/defer.py:654:_runCallbacks
/.../venv/lib/python3.6/site-packages/twisted/internet/endpoints.py:975:startConnectionAttempts
]

我正在使用:

macOS 10.14.6 Python 3.6.6，扭曲 18.9.0

Linux Mint 19.1、Python 3.6.9、Twisted 19.7.0

感谢您的帮助，如果需要其他信息，请告诉我。

谢谢!

Answer 1

解决方案是:

(客户端)按照@Hadus 的建议，交换安装解析器的行的顺序并为请求创建延迟。我认为这无关紧要，因为 react 堆还没有运行。

(服务器)工具 lookupAllRecords ，重用现有的 _doDynamicResponse方法。

# server
from twisted.internet import defer, reactor
from twisted.names import dns, error, server


class MockDNSResolver:
    """
    Implements twisted.internet.interfaces.IResolver partially
    """

    def _doDynamicResponse(self, name):
        print("Resolving name:", name)
        record = dns.Record_A(address=b"127.0.0.1")
        answer = dns.RRHeader(name=name, payload=record)
        return [answer], [], []

    def query(self, query, timeout=None):
        if query.type == dns.A:
            return defer.succeed(self._doDynamicResponse(query.name.name))
        return defer.fail(error.DomainError())

    def lookupAllRecords(self, name, timeout=None):
        return defer.succeed(self._doDynamicResponse(name))


if __name__ == "__main__":
    clients = [MockDNSResolver()]
    factory = server.DNSServerFactory(clients=clients)
    protocol = dns.DNSDatagramProtocol(controller=factory)
    reactor.listenUDP(10053, protocol)
    reactor.listenTCP(10053, factory)
    reactor.run()

# client
from twisted.internet import reactor
from twisted.names.client import createResolver
from twisted.web.client import Agent


reactor.installResolver(createResolver(servers=[('127.0.0.1', 10053)]))
d = Agent(reactor).request(b'GET', b'http://does.not.exist:8000')


def callback(result):
    print('Result:', result)


d.addBoth(callback)
d.addBoth(lambda _: reactor.stop())

reactor.run()

$ python client.py
Result: <twisted.web._newclient.Response object at 0x101077f98>

(我正在另一个终端中运行一个带有 python3 -m http.server 的简单 Web 服务器，否则我会得到一个合理的 twisted.internet.error.ConnectionRefusedError 异常)。