SocketServer源码学习(二)

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