Finger 的演变：迁移到基于组件的架构

介绍

这是 Twisted 教程的第四部分 从零开始的 Twisted，或 Finger 的演变 。

在本节教程中，我们将把代码迁移到基于组件的架构，以便添加新功能变得轻而易举。请参阅 接口和适配器 以获取有关组件的更完整讨论。

编写可维护的代码

在最后一个版本中，服务类比任何其他类都长三倍，而且难以理解。这是因为它承担了多个责任。它必须知道如何访问用户信息，通过每半分钟重新读取文件，但也必须知道如何在各种协议中显示自己。在这里，我们使用了 Twisted 提供的基于组件的架构来实现关注点分离。现在，服务只负责支持 getUser /getUsers 。它通过 zope.interface.implementer 装饰器声明其支持。然后，使用适配器使该服务看起来像适合各种事物的类：为 TCPServer 提供 Finger 工厂，为站点的构造函数提供资源，以及为 TCPClient 提供 IRC 客户端工厂。所有适配器使用的只是在 FingerService 中声明要使用的 getUser /getUsers 方法。当然，我们可以跳过接口，让配置代码直接使用诸如 FingerFactoryFromService(f) 之类的东西。但是，使用接口提供了与继承相同的灵活性：未来的子类可以覆盖适配器。

finger19.tac

# Do everything properly, and componentize
import html

from zope.interface import Interface, implementer

from twisted.application import internet, service, strports
from twisted.internet import defer, endpoints, protocol, reactor
from twisted.protocols import basic
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc
from twisted.words.protocols import irc


class IFingerService(Interface):
    def getUser(user):
        """
        Return a deferred returning L{bytes}.
        """

    def getUsers():
        """
        Return a deferred returning a L{list} of L{bytes}.
        """


class IFingerSetterService(Interface):
    def setUser(user, status):
        """
        Set the user's status to something.
        """


def catchError(err):
    return b"Internal error in server"


class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)

        def writeValue(value):
            self.transport.write(value + b"\r\n")
            self.transport.loseConnection()

        d.addCallback(writeValue)


class IFingerFactory(Interface):
    def getUser(user):
        """
        Return a deferred returning L{bytes}
        """

    def buildProtocol(addr):
        """
        Return a protocol returning L{bytes}
        """


@implementer(IFingerFactory)
class FingerFactoryFromService(protocol.ServerFactory):
    protocol = FingerProtocol

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)


components.registerAdapter(FingerFactoryFromService, IFingerService, IFingerFactory)


class FingerSetterProtocol(basic.LineReceiver):
    def connectionMade(self):
        self.lines = []

    def lineReceived(self, line):
        self.lines.append(line)

    def connectionLost(self, reason):
        if len(self.lines) == 2:
            self.factory.setUser(*self.lines)


class IFingerSetterFactory(Interface):
    def setUser(user, status):
        """
        Return a deferred returning L{bytes}.
        """

    def buildProtocol(addr):
        """
        Return a protocol returning L{bytes}.
        """


@implementer(IFingerSetterFactory)
class FingerSetterFactoryFromService(protocol.ServerFactory):
    protocol = FingerSetterProtocol

    def __init__(self, service):
        self.service = service

    def setUser(self, user, status):
        self.service.setUser(user, status)


components.registerAdapter(
    FingerSetterFactoryFromService, IFingerSetterService, IFingerSetterFactory
)


class IRCReplyBot(irc.IRCClient):
    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)

    def privmsg(self, user, channel, msg):
        user = user.split("!")[0]
        if self.nickname.lower() == channel.lower():
            d = self.factory.getUser(msg.encode("ascii"))
            d.addErrback(catchError)
            d.addCallback(lambda m: f"Status of {msg}: {m}")
            d.addCallback(lambda m: self.msg(user, m))


class IIRCClientFactory(Interface):
    """
    @ivar nickname
    """

    def getUser(user):
        """
        Return a deferred returning a string.
        """

    def buildProtocol(addr):
        """
        Return a protocol.
        """


@implementer(IIRCClientFactory)
class IRCClientFactoryFromService(protocol.ClientFactory):
    protocol = IRCReplyBot
    nickname = None

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)


components.registerAdapter(
    IRCClientFactoryFromService, IFingerService, IIRCClientFactory
)


@implementer(resource.IResource)
class UserStatusTree(resource.Resource):
    def __init__(self, service):
        resource.Resource.__init__(self)
        self.service = service
        self.putChild("RPC2", UserStatusXR(self.service))

    def render_GET(self, request):
        d = self.service.getUsers()

        def formatUsers(users):
            l = [f'<li><a href="{user}">{user}</a></li>' for user in users]
            return "<ul>" + "".join(l) + "</ul>"

        d.addCallback(formatUsers)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET

    def getChild(self, path, request):
        if path == "":
            return UserStatusTree(self.service)
        else:
            return UserStatus(path, self.service)


components.registerAdapter(UserStatusTree, IFingerService, resource.IResource)


class UserStatus(resource.Resource):
    def __init__(self, user, service):
        resource.Resource.__init__(self)
        self.user = user
        self.service = service

    def render_GET(self, request):
        d = self.service.getUser(self.user)
        d.addCallback(html.escape)
        d.addCallback(lambda m: "<h1>%s</h1>" % self.user + "<p>%s</p>" % m)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET


class UserStatusXR(xmlrpc.XMLRPC):
    def __init__(self, service):
        xmlrpc.XMLRPC.__init__(self)
        self.service = service

    def xmlrpc_getUser(self, user):
        return self.service.getUser(user)


@implementer(IFingerService)
class FingerService(service.Service):
    def __init__(self, filename):
        self.filename = filename
        self.users = {}

    def _read(self):
        self.users.clear()
        with open(self.filename, "rb") as f:
            for line in f:
                user, status = line.split(b":", 1)
                user = user.strip()
                status = status.strip()
                self.users[user] = status
        self.call = reactor.callLater(30, self._read)

    def getUser(self, user):
        return defer.succeed(self.users.get(user, b"No such user"))

    def getUsers(self):
        return defer.succeed(list(self.users.keys()))

    def startService(self):
        self._read()
        service.Service.startService(self)

    def stopService(self):
        service.Service.stopService(self)
        self.call.cancel()


application = service.Application("finger", uid=1, gid=1)
f = FingerService("/etc/users")
serviceCollection = service.IServiceCollection(application)
f.setServiceParent(serviceCollection)
strports.service("tcp:79", IFingerFactory(f)).setServiceParent(serviceCollection)
strports.service("tcp:8000", server.Site(resource.IResource(f))).setServiceParent(
    serviceCollection
)
i = IIRCClientFactory(f)
i.nickname = "fingerbot"
internet.ClientService(
    endpoints.clientFromString(reactor, "tcp:irc.freenode.org:6667"), i
).setServiceParent(serviceCollection)

最新版本的优势

• 可读性 - 每个类都很短

• 可维护性 - 每个类只了解接口

• 代码部分之间的依赖关系降至最低

• 示例：编写新的 IFingerService 很容易

finger19a_changes.py

class IFingerSetterService(Interface):
    def setUser(user, status):
        """Set the user's status to something"""


# Advantages of latest version


@implementer(IFingerService, IFingerSetterService)
class MemoryFingerService(service.Service):
    def __init__(self, users):
        self.users = users

    def getUser(self, user):
        return defer.succeed(self.users.get(user, b"No such user"))

    def getUsers(self):
        return defer.succeed(list(self.users.keys()))

    def setUser(self, user, status):
        self.users[user] = status


f = MemoryFingerService({b"moshez": b"Happy and well"})
serviceCollection = service.IServiceCollection(application)
strports.service(
    "tcp:1079:interface=127.0.0.1", IFingerSetterFactory(f)
).setServiceParent(serviceCollection)

完整的源代码在这里

finger19a.tac

# Do everything properly, and componentize
import html

from zope.interface import Interface, implementer

from twisted.application import internet, service, strports
from twisted.internet import defer, endpoints, protocol, reactor
from twisted.protocols import basic
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc
from twisted.words.protocols import irc


class IFingerService(Interface):
    def getUser(user):
        """Return a deferred returning L{bytes}"""

    def getUsers():
        """Return a deferred returning a L{list} of L{bytes}"""


class IFingerSetterService(Interface):
    def setUser(user, status):
        """Set the user's status to something"""


def catchError(err):
    return "Internal error in server"


class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)

        def writeValue(value):
            self.transport.write(value + b"\r\n")
            self.transport.loseConnection()

        d.addCallback(writeValue)


class IFingerFactory(Interface):
    def getUser(user):
        """Return a deferred returning L{bytes}"""

    def buildProtocol(addr):
        """Return a protocol returning L{bytes}"""


@implementer(IFingerFactory)
class FingerFactoryFromService(protocol.ServerFactory):
    protocol = FingerProtocol

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)


components.registerAdapter(FingerFactoryFromService, IFingerService, IFingerFactory)


class FingerSetterProtocol(basic.LineReceiver):
    def connectionMade(self):
        self.lines = []

    def lineReceived(self, line):
        self.lines.append(line)

    def connectionLost(self, reason):
        if len(self.lines) == 2:
            self.factory.setUser(*self.lines)


class IFingerSetterFactory(Interface):
    def setUser(user, status):
        """Return a deferred returning L{bytes}"""

    def buildProtocol(addr):
        """Return a protocol returning L{bytes}"""


@implementer(IFingerSetterFactory)
class FingerSetterFactoryFromService(protocol.ServerFactory):
    protocol = FingerSetterProtocol

    def __init__(self, service):
        self.service = service

    def setUser(self, user, status):
        self.service.setUser(user, status)


components.registerAdapter(
    FingerSetterFactoryFromService, IFingerSetterService, IFingerSetterFactory
)


class IRCReplyBot(irc.IRCClient):
    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)

    def privmsg(self, user, channel, msg):
        user = user.split("!")[0]
        if self.nickname.lower() == channel.lower():
            d = self.factory.getUser(msg)
            d.addErrback(catchError)
            d.addCallback(lambda m: f"Status of {msg}: {m}")
            d.addCallback(lambda m: self.msg(user, m))


class IIRCClientFactory(Interface):

    """
    @ivar nickname
    """

    def getUser(user):
        """Return a deferred returning a string"""

    def buildProtocol(addr):
        """Return a protocol"""


@implementer(IIRCClientFactory)
class IRCClientFactoryFromService(protocol.ClientFactory):
    protocol = IRCReplyBot
    nickname = None

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)


components.registerAdapter(
    IRCClientFactoryFromService, IFingerService, IIRCClientFactory
)


@implementer(resource.IResource)
class UserStatusTree(resource.Resource):
    def __init__(self, service):
        resource.Resource.__init__(self)
        self.service = service
        self.putChild("RPC2", UserStatusXR(self.service))

    def render_GET(self, request):
        d = self.service.getUsers()

        def formatUsers(users):
            l = [f'<li><a href="{user}">{user}</a></li>' for user in users]
            return "<ul>" + "".join(l) + "</ul>"

        d.addCallback(formatUsers)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET

    def getChild(self, path, request):
        if path == "":
            return UserStatusTree(self.service)
        else:
            return UserStatus(path, self.service)


components.registerAdapter(UserStatusTree, IFingerService, resource.IResource)


class UserStatus(resource.Resource):
    def __init__(self, user, service):
        resource.Resource.__init__(self)
        self.user = user
        self.service = service

    def render_GET(self, request):
        d = self.service.getUser(self.user)
        d.addCallback(html.escape)
        d.addCallback(lambda m: "<h1>%s</h1>" % self.user + "<p>%s</p>" % m)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET


class UserStatusXR(xmlrpc.XMLRPC):
    def __init__(self, service):
        xmlrpc.XMLRPC.__init__(self)
        self.service = service

    def xmlrpc_getUser(self, user):
        return self.service.getUser(user)


@implementer(IFingerService, IFingerSetterService)
class MemoryFingerService(service.Service):
    def __init__(self, users):
        self.users = users

    def getUser(self, user):
        return defer.succeed(self.users.get(user, b"No such user"))

    def getUsers(self):
        return defer.succeed(list(self.users.keys()))

    def setUser(self, user, status):
        self.users[user] = status


application = service.Application("finger", uid=1, gid=1)
f = MemoryFingerService({b"moshez": b"Happy and well"})
serviceCollection = service.IServiceCollection(application)
strports.service("tcp:79", IFingerFactory(f)).setServiceParent(serviceCollection)
strports.service("tcp:8000", server.Site(resource.IResource(f))).setServiceParent(
    serviceCollection
)
i = IIRCClientFactory(f)
i.nickname = "fingerbot"
internet.ClientService(
    endpoints.clientFromString(reactor, "tcp:irc.freenode.org:6667"), i
).setServiceParent(serviceCollection)
strports.service(
    "tcp:1079:interface=127.0.0.1", IFingerSetterFactory(f)
).setServiceParent(serviceCollection)

面向切面编程

最后，一个面向切面编程的例子，它不是关于日志记录或计时。这段代码实际上很有用！看看面向切面编程如何帮助你编写更少的代码，并减少依赖关系！