Question

我正在使用python asynchat来实现网络协议。在连接时，我需要发送命令，服务器应答会话。

我的主要问题是我需要等到我得到会话响应。但不知道如何实现这一点。我应该使用socket.recv进行连接设置吗？是一个好主意？

Answer 1

使用异步技术编写网络应用程序时，通过在某处记录您的状态然后让主循环继续来等待。在将来的某个时间，您正在等待的数据将变为可用，主循环将通知您该事实，并且您可以将新数据与记录状态组合以完成您正在处理的任何任务。根据具体任务，您可能需要在实际完成任务之前多次完成此循环。

无论您使用什么异步系统，这些想法基本相同。但是，Twisted为a vastly superior system到asynchat，因此我不会尝试解释任何异步详细信息。相反，这是一个使用Twisted来做你要问的事情的例子：

from twisted.internet.defer import Deferred
from twisted.internet.protocol import Protocol, Factory
from twisted.internet.endpoints import TCP4ClientEndpoint
from twisted.internet import reactor

# Stream-oriented connections like TCP are handled by an instance 
# of a Protocol subclass
class SomeKindOfClient(Protocol):

     # When a new connection is established, the first thing that
     # happens is this method is called.
     def connectionMade(self):
         # self.transport is set by the superclass, and lets us 
         # send data over the connection
         self.transport.write("GREETING")

         # a Deferred is a generic, composable API for specifying
         # callbacks
         self.greetingComplete = Deferred()

         # Here's some local state
         self._buffer = ""

     # Whenever bytes arrive on the TCP connection, they're passed
     # to this method
     def dataReceived(self, bytes):

         # Incorportate the network event data into our local state.
         #  This kind of buffering is always necessary with TCP, because
         # there's no guarantees about how many bytes will be delivered
         # at once (except that it will be at least 1), regardless of
         # the size of the send() the peer did.
         self._buffer += bytes

         # Figure out if we're done - let's say the server response is 32
         # bytes of something
         if len(self._buffer) >= 32:
             # Deliver it to whomever is waiting, by way of the Deferred
             # object
             greeting, self._buffer = self._buffer[:32], self._buffer[32:]
             complete = self.greetingComplete
             self.greetingComplete = None
             complete.callback(greeting)

         # Otherwise we'll keep waiting until dataReceived is called again
         # and we have enough bytes.


# One of the normal ways to create a new client connection
f = Factory()
f.protocol = SomeKindOfClient
e = TCP4ClientEndpoint(reactor, "somehost", 1234)

# Connect returns one of those Deferreds - letting us specify a function
# to call when the connection is established.  The implementation of
# connect is also doing basically the same kind of thing as you're asking
# about.
d = e.connect(f)

# Execution continues to this point before the connection has been
# established.  Define a function to use as a callback when the connection
# does get established.
def connected(proto):
    # proto is an instance of SomeKindOfClient.  It has the 
    # greetingComplete attribute, which we'll attach a callback to so we
    # can "wait" for the greeting to be complete.
    d = proto.greetingComplete

    def gotGreeting(greeting):
        # Note that this is really the core of the answer.  This function
        # is called *only* once the protocol has decided it has received
        # some necessary data from the server.  If you were waiting for a
        # session identifier of some sort, this is where you might get it
        # and be able to proceed with the remainder of your application
        # logic.
        print "Greeting arrived", repr(greeting)

    # addCallback is how you hook a callback up to a Deferred - now
    # gotGreeting will be called when d "fires" - ie, when its callback
    # method is invoked by the dataReceived implementation above.
    d.addCallback(gotGreeting)

# And do the same kind of thing to the Deferred we got from 
# TCP4ClientEndpoint.connect
d.addCallback(connected)

# Start the main loop so network events can be processed
reactor.run()

要了解其行为，您可以启动一个简单的服务器（例如nc -l 1234）并将客户端指向该服务器。你会看到问候语到达，你可以发回一些字节。一旦你发回30，客户端将打印它们（然后无限期地挂起，因为我在该协议中没有实现其他逻辑）。

python网络：asynchat握手

1 个答案: