SocketServer 中非常重要的两个基类就是：BaseServer 和 BaseRequestHandler
在SocketServer 中也提供了对TCP以及UDP的高级封装，这次我们主要通过分析关于TCP的处理逻辑来对SocketServer模块进行一个很好的理解和学习
TCPServer
TCPServer 继承了BaseServer，初始化的时候，进行了socket套接字的创建。
def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True):
"""Constructor. May be extended, do not override."""
BaseServer.__init__(self, server_address, RequestHandlerClass)
self.socket = socket.socket(self.address_family,
self.socket_type)
if bind_and_activate:
try:
self.server_bind()
self.server_activate()
except:
self.server_close()
raise
在这里我们看到了我们非常熟悉的关于socket的创建的内容：
self.socket = socket.socket(self.address_family, self.socket_type)
通过socket模块创建了socket对象，接着调用了server_bind和server_activate
server_bind
源码内容如下：
def server_bind(self):
"""Called by constructor to bind the socket. May be overridden. """
if self.allow_reuse_address:
self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
self.socket.bind(self.server_address)
self.server_address = self.socket.getsockname()
这里我们看到了非常熟悉的操作socket.bind方法，以及设置了socket的相关属性
server_activate
源码内容如下：
def server_activate(self):
"""Called by constructor to activate the server. May be overridden. """
self.socket.listen(self.request_queue_size)
同样的这里的调用也非常简单就是执行了socket.listen
get_request
在TCPServer类中我们还看到了get_request方法，源码内容如下：
def get_request(self):
"""Get the request and client address from the socket. May be overridden. """
return self.socket.accept()
这个的调用其实我们可以在BaseServer这个基类中看到，我们之前看过关于BaseServer中这个基类的源码
我们可以从我们调用BaseServer基类中的serve_forever方法查看，这里是调用了_handle_request_noblock方法，我继续查看_handle_request_noblock这个源码
def _handle_request_noblock(self):
"""Handle one request, without blocking. I assume that selector.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)
else:
self.shutdown_request(request)
可以看到这里最后是调用了process_request来处理请求，继续查看源码：
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 finish_request(self, request, client_address):
"""Finish one request by instantiating RequestHandlerClass."""
self.RequestHandlerClass(request, client_address, self)
从上面的代码我们可以到最后是在finish_request中实例化了RequestHandlerClass
我们 这个时候查看一下BaseRequestHandler这个基类的源码如下:
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 other arbitrary instance variables.
"""
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
在初始化函数里我们看到了调用setup()方法，这setup在StreamRequestHandler会被重写
StreamRequestHandler
TCPServer实现了使用tcp套接字的网络服务，Handler方面则是对应的StreamRequestHandler。它继承了BaseRequestHandler。基类的setup方法和finish方法被它重写，用于通过连接实现缓存文件的读写操作。
setup方法
源码内容如下：
def setup(self):
self.connection = self.request
if self.timeout is not None:
self.connection.settimeout(self.timeout)
if self.disable_nagle_algorithm:
self.connection.setsockopt(socket.IPPROTO_TCP,
socket.TCP_NODELAY, True)
self.rfile = self.connection.makefile('rb', self.rbufsize)
self.wfile = self.connection.makefile('wb', self.wbufsize)
这里主要设置了对应连接的属性，其中创建了两个对象非常重要:
一个可读（rfile）和一个可写（wfile）的“文件”对象
但是实际并不是创建了文件，而是封装了读取数据和发送数据的操作，抽象成了对文件的操作
可以理解：
self.rfile 就是读取客户端数据的对象，它有一些方法可以读取数据。self.wfile则是用来发送数据给客户端的对象。
整理流程(TCP)
实现TCP服务需要使用TCPServer和StreamRequestHandler共同协作
