在twisted中实现重新连接http客户端

Question

我正在实现一个库模块作为 couchdb 更改通知的客户端。我想让库处于“连续”模式，也就是说，连接必须永远保持打开状态，或者至少如果连接已关闭，它必须重新连接，以便couchdb有一个通道来通知库中发生的任何新更改数据库。然后我将处理这些通知以生成某些事件（这尚未实现）。

我选择的方法是使用 ReconnectingClientFactory （它根据详细的算法自动重新连接）作为我的协议工厂的基础。每当建立连接时，都会调用 buildProtocol 方法。在此方法中，我创建协议实例，并（立即）触发 callLater 以表示连接已准备就绪。在 cdConnected 函数中，我发送请求并添加回调来处理接收到的数据 (cbReceived)。

代码按预期重新连接，但我遇到两个不同的问题：

• 请求失败（没有通过 tcp 连接发送数据），但我不知道为什么。
• 即使连接完全关闭，也会生成错误。

也许有人知道我做错了什么？

谢谢！

（编辑：“连接已完全关闭。”错误是由我自己打印的，因此可以忽略）

这是代码：

from   twisted.internet              import defer
from   twisted.internet.protocol     import ReconnectingClientFactory
from   twisted.web._newclient        import HTTP11ClientProtocol
from   twisted.web._newclient        import Request
from   twisted.web.client            import _parse

class MyReconnectingClientFactory(ReconnectingClientFactory):

    def __init__(self, reactor, cbConnected):
        self.reactor      = reactor
        self.cbConnected  = cbConnected

    def startedConnecting(self, connector):
        print 'Started to connect ...'

    def buildProtocol(self, addr):
        print 'Resetting reconnection delay'
        self.resetDelay()
        proto = HTTP11ClientProtocol()
        self.reactor.callLater(0, self.cbConnected, proto)
        return proto

    def clientConnectionLost(self, connector, reason):
        print 'Lost connection.  Reason:', reason
        ReconnectingClientFactory.clientConnectionLost(self, connector, reason)

    def clientConnectionFailed(self, connector, reason):
        print 'Connection failed. Reason:', reason
        ReconnectingClientFactory.clientConnectionFailed(self, connector, reason)

def cbReceived(response):
    print response

def printError(failure):
    print "printError > %s" % (str(failure))

def cbConnected(proto):
    print "Sending request ..."
    req = Request(method, path, headers, bodyProducer)
    d = proto.request(req)
    d.addCallback(cbReceived).addErrback(printError)
    return d

from twisted.internet import reactor

uri='http://localhost:5984/cn/_changes?feed=continuous'
method='GET'
headers=None
bodyProducer=None

scheme, host, port, path = _parse(uri)
factory = MyReconnectingClientFactory(reactor, cbConnected)
reactor.connectTCP(host, port, factory)
reactor.run()

这是输出：

Started to connect ...
Resetting reconnection delay
Sending request ...
printError > [Failure instance: Traceback (failure with no frames): <class 'twisted.web._newclient.RequestGenerationFailed'>: [<twisted.python.failure.Failure <type 'exceptions.AttributeError'>>]
]
Lost connection.  Reason: [Failure instance: Traceback (failure with no frames): <class 'twisted.internet.error.ConnectionDone'>: Connection was closed cleanly.
]
Started to connect ...
Resetting reconnection delay
Sending request ...
printError > [Failure instance: Traceback (failure with no frames): <class 'twisted.web._newclient.RequestGenerationFailed'>: [<twisted.python.failure.Failure <type 'exceptions.AttributeError'>>]
]
Lost connection.  Reason: [Failure instance: Traceback (failure with no frames): <class 'twisted.internet.error.ConnectionDone'>: Connection was closed cleanly.
]

Answer 1

您应该查看生成的故障。 _newclient 有抛出复合失败的习惯；这些包含进一步的失败。

我稍微调整了你的代码：

def printError(failure):
print "printError > %r" % failure

from twisted.web import _newclient
if failure.check(_newclient.RequestGenerationFailed):
    print "printError: RequestGenerationFailed"
    for f in failure.value.reasons:
        print "printError > %r" % f
        print f.getTraceback()

你在失败时执行了 str() ，这不是获取有关异常信息的好方法。让 repr 来处理它，这就是它的工作。

使用 %r，我发现它实际上给了我一个 RequestGenerationFailed。这是一个更有趣的失败。失败值是有原因的。

经过我的修改，脚本给出了以下内容：

Started to connect ...
Resetting reconnection delay
Sending request ...
printError > <twisted.python.failure.Failure <class 'twisted.web._newclient.RequestGenerationFailed'>>
printError: RequestGenerationFailed
printError > <twisted.python.failure.Failure <type 'exceptions.AttributeError'>>
Traceback (most recent call last):
  File "/usr/lib64/python2.7/site-packages/twisted/internet/base.py", line 1174, in mainLoop
    self.runUntilCurrent()
  File "/usr/lib64/python2.7/site-packages/twisted/internet/base.py", line 796, in runUntilCurrent
    call.func(*call.args, **call.kw)
  File "so.py", line 50, in cbConnected
    d = proto.request(req)
  File "/usr/lib64/python2.7/site-packages/twisted/web/_newclient.py", line 1266, in request
    _requestDeferred = maybeDeferred(request.writeTo, self.transport)
--- <exception caught here> ---
  File "/usr/lib64/python2.7/site-packages/twisted/internet/defer.py", line 125, in maybeDeferred
    result = f(*args, **kw)
  File "/usr/lib64/python2.7/site-packages/twisted/web/_newclient.py", line 703, in writeTo
    self._writeHeaders(transport, None)
  File "/usr/lib64/python2.7/site-packages/twisted/web/_newclient.py", line 535, in _writeHeaders
    hosts = self.headers.getRawHeaders('host', ())
exceptions.AttributeError: 'NoneType' object has no attribute 'getRawHeaders'

Lost connection.  Reason: [Failure instance: Traceback (failure with no frames): <class 'twisted.internet.error.ConnectionDone'>: Connection was closed cleanly.
]

这应该为您提供一个很好的线索，告诉您在哪里寻找实际问题。

顺便说一句，看看 Paisley，CouchDB 的 Twisted 客户端： paisley

有几个分支，并且特别是 我的更改分支 有一些您可能会收到的更改通知内容我制作了一个桌面小程序，向我显示添加到基于 CouchDB 的待办事项系统中的任务。

听起来您的更改 a) 已经在那里或 b) 应该进入那里； c) 您应该考虑与佩斯利合作并为其做出贡献。

祝你好运！