浅析python中socketserver模块使用

         虽然说用python编写简单的网络程序狠方便，但是复杂一点的网络程序还是用现成的框架比较好，这样就可以专心事物逻辑，而不是套接字的各种细节。Socketserver模块简化了编写网络服务程序，同时socketserver模块也是python标准库中很多服务器框架的基础。

socketserver模块类介绍

      SocketServer内部使用 IO多路复用 以及 “多线程” 和 “多进程” ，从而实现并发处理多个客户端请求的Socket服务端。即：每个客户端请求连接到服务器时，Socket服务端都会在服务器是创建一个“线程”或者“进 程” 专门负责处理当前客户端的所有请求。

        socketserver模块可以简化网络服务器的编写，python把网络服务抽象成两个主要的类，一个是server类，用于处理连接相关的网络操作，另一个是RequestHandler类，用于处理数据相关的操作。并且提供两个Mixln类，用于扩展server，实现多进程或者多线程。

Server类

   它包含了五种server类，分别是  Baseserver（不直接对外服务）；TCPServer（使用TCP协议） ；UDPServer（使用UDP协议），UinixStreamServer    和UnixDatagramServer（后面两个仅仅在unix环境下游泳，一般不常用）

他们五个的关系如下：

BaseServer的源码：

class BaseServer:

    """Base class for server classes.

    Methods for the caller:

    - __init__(server_address, RequestHandlerClass)
    - serve_forever(poll_interval=0.5)
    - shutdown()
    - handle_request()  # if you do not use serve_forever()
    - fileno() -> int   # for select()

    Methods that may be overridden:

    - server_bind()
    - server_activate()
    - get_request() -> request, client_address
    - handle_timeout()
    - verify_request(request, client_address)
    - server_close()
    - process_request(request, client_address)
    - shutdown_request(request)
    - close_request(request)
    - service_actions()
    - handle_error()

    Methods for derived classes:

    - finish_request(request, client_address)

    Class variables that may be overridden by derived classes or
    instances:

    - timeout
    - address_family
    - socket_type
    - allow_reuse_address

    Instance variables:

    - RequestHandlerClass
    - socket

    """

    timeout = None

    def __init__(self, server_address, RequestHandlerClass):
        """Constructor.  May be extended, do not override."""
        self.server_address = server_address
        self.RequestHandlerClass = RequestHandlerClass
        self.__is_shut_down = threading.Event()
        self.__shutdown_request = False

    def server_activate(self):
        """Called by constructor to activate the server.

        May be overridden.

        """
        pass

    def serve_forever(self, poll_interval=0.5):
        """Handle one request at a time until shutdown.

        Polls for shutdown every poll_interval seconds. Ignores
        self.timeout. If you need to do periodic tasks, do them in
        another thread.
        """
        self.__is_shut_down.clear()
        try:
            while not self.__shutdown_request:
                # XXX: Consider using another file descriptor or
                # connecting to the socket to wake this up instead of
                # polling. Polling reduces our responsiveness to a
                # shutdown request and wastes cpu at all other times.
                r, w, e = _eintr_retry(select.select, [self], [], [],
                                       poll_interval)
                if self in r:
                    self._handle_request_noblock()

                self.service_actions()
        finally:
            self.__shutdown_request = False
            self.__is_shut_down.set()

    def shutdown(self):
        """Stops the serve_forever loop.

        Blocks until the loop has finished. This must be called while
        serve_forever() is running in another thread, or it will
        deadlock.
        """
        self.__shutdown_request = True
        self.__is_shut_down.wait()

    def service_actions(self):
        """Called by the serve_forever() loop.

        May be overridden by a subclass / Mixin to implement any code that
        needs to be run during the loop.
        """
        pass

    # The distinction between handling, getting, processing and
    # finishing a request is fairly arbitrary.  Remember:
    #
    # - handle_request() is the top-level call.  It calls
    #   select, get_request(), verify_request() and process_request()
    # - get_request() is different for stream or datagram sockets
    # - process_request() is the place that may fork a new process
    #   or create a new thread to finish the request
    # - finish_request() instantiates the request handler class;
    #   this constructor will handle the request all by itself

    def handle_request(self):
        """Handle one request, possibly blocking.

        Respects self.timeout.
        """
        # Support people who used socket.settimeout() to escape
        # handle_request before self.timeout was available.
        timeout = self.socket.gettimeout()
        if timeout is None:
            timeout = self.timeout
        elif self.timeout is not None:
            timeout = min(timeout, self.timeout)
        fd_sets = _eintr_retry(select.select, [self], [], [], timeout)
        if not fd_sets[0]:
            self.handle_timeout()
            return
        self._handle_request_noblock()

    def _handle_request_noblock(self):
        """Handle one request, without blocking.

        I assume that select.select has returned that the socket is
        readable before this function was called, so there should be
        no risk of blocking in get_request().
        """
        try:
            request, client_address = self.get_request()
        except OSError:
            return
        if self.verify_request(request, client_address):
            try:
                self.process_request(request, client_address)
            except:
                self.handle_error(request, client_address)
                self.shutdown_request(request)

    def handle_timeout(self):
        """Called if no new request arrives within self.timeout.

        Overridden by ForkingMixIn.
        """
        pass

    def verify_request(self, request, client_address):
        """Verify the request.  May be overridden.

        Return True if we should proceed with this request.

        """
        return True

    def process_request(self, request, client_address):
        """Call finish_request.

        Overridden by ForkingMixIn and ThreadingMixIn.

        """
        self.finish_request(request, client_address)
        self.shutdown_request(request)

    def server_close(self):
        """Called to clean-up the server.

        May be overridden.

        """
        pass

    def finish_request(self, request, client_address):
        """Finish one request by instantiating RequestHandlerClass."""
        self.RequestHandlerClass(request, client_address, self)

    def shutdown_request(self, request):
        """Called to shutdown and close an individual request."""
        self.close_request(request)

    def close_request(self, request):
        """Called to clean up an individual request."""
        pass

    def handle_error(self, request, client_address):
        """Handle an error gracefully.  May be overridden.

        The default is to print a traceback and continue.

        """
        print('-'*40)
        print('Exception happened during processing of request from', end=' ')
        print(client_address)
        import traceback
        traceback.print_exc() # XXX But this goes to stderr!
        print('-'*40)

RequestHandler类

所有requestHandler都继承BaseRequestHandler基类。

请求的基类是baserequesthandler，其中一般需要重写的方法就是handle方法，主要就是如何处理接下里的请求，在这个类中，主要有三个方法，分别是setup ,handle ,finish方法，在调用这个类的时候，先调用setup进行一些初始化的工作，然后调用handle方法进行处理请求，然后调用finish方法，做一些关闭连接什么的，在这个里面最主要的参数就是self.request，也就是请求的socket对象，其中可以发送消息sendall或者send,接受消息就是recv

在请求处理的子类中有两个，一个是SreamRequestHandle和DatagramRequestHandle，在这个里面重写了基类的setup方法和finish方法，handle方法没有重写，因为这个是留给用户做处理请求的方法

requestHandler源码：

class BaseRequestHandler:

    """Base class for request handler classes.

    This class is instantiated for each request to be handled.  The
    constructor sets the instance variables request, client_address
    and server, and then calls the handle() method.  To implement a
    specific service, all you need to do is to derive a class which
    defines a handle() method.

    The handle() method can find the request as self.request, the
    client address as self.client_address, and the server (in case it
    needs access to per-server information) as self.server.  Since a
    separate instance is created for each request, the handle() method
    can define arbitrary other instance variariables.

    """

    def __init__(self, request, client_address, server):
        self.request = request
        self.client_address = client_address
        self.server = server
        self.setup()
        try:
            self.handle()
        finally:
            self.finish()

    def setup(self):
        pass

    def handle(self):
        pass

    def finish(self):
        pass

源码

混合类（并发类）

两个混合类，一个是ForkingMixin，主要是用fork的，产生一个新的进程去处理；一个是ThreadingMixin，产生一个新的线程，主要是用来提供异步处理的能力，其余tcpserver和udpserver组合，又产生了新的四个类，从而提供异步处理的能力。

    （在使用混合类和服务器类的时候，注意混合类需要写在前面，因为混合类重写了服务器类的方法，从而需要放在第一个位置。）

class socketserver.ForkingTCPServer
 
class socketserver.ForkingUDPServer
 
class socketserver.ThreadingTCPServer
 
class socketserver.ThreadingUDPServer

 

下面主要举例说一下socketserver服务器端和客户端的代码

scoketserver服务器端

            在socketserver模块中，主要就是使用一些服务器类，从而简化socket网络编程的方法，先上一段基本的服务器代码：

import socketserver

ip_port = ('127.0.0.1',8888)
class Myhandler(socketserver.BaseRequestHandler):
    def handle(self):
        while True:
            data = self.request.recv(1024)
            print(data,self.client_address)
            if data == 'exit':
                break
if __name__ == '__main__':
    s =socketserver.ThreadingTCPServer((ip_port),Myhandler)
    s.serve_forever()

        在上述代码中，首先定义了一个类，也就是处理请求的类，从基类baserequesthandler继承，主要就是重写了其中的handle方法，告知服务器如何来处理客户端的请求。然后建立了一个线程的TCP服务器类，也就是通过多线程来进行应答客户端，然后通过使用一直运行的方法就是serve_forever

scoketserver客户端

import socket


ip_port = ('127.0.0.1',8888)
sk = socket.socket()
sk.connect(ip_port)
print ("客户端启动：")
while True:
    inp = input('>>>')
    sk.sendall(bytes(inp,"utf8"))
    server_response=sk.recv(1024)
    print (str(server_response,"utf8"))
    if inp == 'exit':
        break
sk.close()

      客户端的代码和socket编程的代码基本相同，因为在socketserver模块中，主要是创建socke的服务端，而不涉及到客户端，从而客户端不需要修改代码即可进行运行。

class socketserver.ForkingTCPServer
 
class socketserver.ForkingUDPServer
 
class socketserver.ThreadingTCPServer
 
class socketserver.ThreadingUDPServer

socketserver内部调用程序

• 启动服务端程序
• 执行 TCPServer.init 方法，创建服务端Socket对象并绑定 IP 和 端口
• 执行 BaseServer.init 方法，将自定义的继承自SocketServer.BaseRequestHandler 的类 - MyRequestHandle赋值给 self.RequestHandlerClass
• 执行 BaseServer.server_forever 方法，While 循环一直监听是否有客户端请求到达 ...
  当客户端连接到达服务器
• 执行 ThreadingMixIn.process_request 方法，创建一个 “线程” 用来处理请求
• 执行 ThreadingMixIn.process_request_thread 方法
• 执行 BaseServer.finish_request 方法，执行 self.RequestHandlerClass() 即：执行 自定义 MyRequestHandler 的构造方法（自动调用基类BaseRequestHandler的构造方法，在该构造方法中又会调用 MyRequestHandler的handle方法）