提起网络编程,不同于web编程,它主要是C/S架构,也就是服务器、客户端结构的。对于初学者而言,最需要理解的不是网络的概念,而是python对于网络编程都提供了些什么模块和功能。不同于计算机发展的初级阶段,程序员走到今天,已经脱离了手工打造一切,要自己实现所有细节的年代。现在提倡的是不要重复造*,而是学习别人的*怎么用,只有那些有需求或能专研的人才去设计*甚至汽车,so,这是一个速成的年代。
因此,对于一个面向工作的python程序员,学习python的网络编程,其实学的就是那么几个模块,和你学习打游戏,word、excel没什么两样,本质上不是创造而是拿来主义,千万不要以为你需要从TCP/IP网络协议最底层开始一点一点实现所有的功能,它们都被封装在socket这个模块里。
socket概念
我相信,所有的初学者都曾经被各种各样的标准模块和第三方模块所困扰,不知道该用哪个。同时,每个模块也包含许许多多的类,继承关系复杂,更是让人挠头。读源码看官方文档研究高手的文章更是一个漫长的过程。为什么就没有人将这些模块和类给梳理一下呢???难道这就是编程界的自我封闭和筛选机制?
在谈及socket编程,必须知道这么几个概念:阻塞与非阻塞,同步与异步,多线程与多进程,IO多路复用与事件驱动。但是本文不打算讲这些。实际上你只需要知道两个模块三个类,就OK了,绝对速成!(以下为python3.5)
socket模块:socket类
socketserver模块:ThreadingTCPServer、ForkingTCPServer类
对于socket模块你必须透彻其原理,了熟于胸。但它是一个同步阻塞类型的模块,只能进行一对一的通信,在现今的计算机世界,属于最落后被淘汰的东西,基本不在实际中应用。
socketserver模块稍微有点用,它能通过多线程或多进程的方式与多个用户同时进行通信。从字面就能看出ThreadingTCPServer类是实现的多线程,ForkingTCPServer是实现的多进程。
socket模块
再怎么说它没用,它也是基础中的基础,不理解它的原理,那么更高级的模块就会掌握不透彻。
socket(套接字)是什么?socket就是两个节点为了互相通信,而在各自家里装的一部”电话“
socket模块是什么?socket模块是python内置的为了方便简单快速进行网络编程而提供的现成的”*“。它将TCP/IP协议进行了封装,你不需要知道如何进行网络通信,你只需要import socket,然后直接使用它提供的功能就好了。可以用下图来表示:
socket是基于C/S架构的,它的通信逻辑如下图:(借用图)
进行socket编程,必须写两个py文件,一个服务端,一个客户端。但是有两点必须强调:
1. python3以后,socket传递的都是bytes类型的数据,string需要先转换一下,string.encode()即可;
另一端接收到的bytes数据想转换成string,只要bytes.decode()一下就可以。
2. 在正常通信时,accept和recv方法是阻塞的,程序会暂停在那,一直等到有数据过来。
下面是一个例子:
#!/usr/bin/env python # -*- coding:utf-8 -*- import socket ip_port = ('127.0.0.1',9999) sk = socket.socket() sk.bind(ip_port) sk.listen(5) while True: print('server waiting...') conn,addr = sk.accept() client_data = conn.recv(1024) print(client_data) conn.sendall('我是黄河!') conn.close()
socket server
#!/usr/bin/env python # -*- coding:utf-8 -*- import socket ip_port = ('127.0.0.1',9999) s = socket.socket() s.connect(ip_port) s.sendall('我是长江') server_reply = s.recv(1024) print(server_reply) s.close()
socket client
方法分析:
sk = socket.socket(socket.AF_INET,socket.SOCK_STREAM,0) 实例化socket类的一个对象
参数一:地址簇
socket.AF_INET IPv4(默认)
socket.AF_INET6 IPv6
socket.AF_UNIX 只能够用于单一的Unix系统进程间通信
参数二:类型
socket.SOCK_STREAM 流式socket , for TCP (默认)
socket.SOCK_DGRAM 数据报式socket , for UDP
socket.SOCK_RAW 原始套接字,普通的套接字无法处理ICMP、IGMP等网络报文,而SOCK_RAW可以;其次,SOCK_RAW也可以处理特殊的IPv4报文;此外,利用原始套接字,可以通过IP_HDRINCL套接字选项由用户构造IP头。
socket.SOCK_RDM 是一种可靠的UDP形式,即保证交付数据报但不保证顺序。SOCK_RAM用来提供对原始协议的低级访问,在需要执行某些特殊操作时使用,如发送ICMP报文。SOCK_RAM通常仅限于高级用户或管理员运行的程序使用。
socket.SOCK_SEQPACKET 可靠的连续数据包服务
参数三:协议
0 (默认)与特定的地址家族相关的协议,如果是 0 ,则系统就会根据地址格式和套接类别,自动选择一个合适的协议
下面是一个UDP协议的例子,注意其中没有accept和connect的概念。
# 服务端 import socket ip_port = ('127.0.0.1',9999) sk = socket.socket(socket.AF_INET,socket.SOCK_DGRAM,0) sk.bind(ip_port) while True: data = sk.recv(1024) print(data) # 客户端 import socket ip_port = ('127.0.0.1',9999) sk = socket.socket(socket.AF_INET,socket.SOCK_DGRAM,0) while True: inp = input('数据:').strip() if inp == 'exit': break sk.sendto(inp,ip_port) sk.close()
UDP Demo
sk.bind(address)
s.bind(address) 将套接字绑定到地址。address地址的格式取决于地址族。在AF_INET下,以元组(host,port)的形式表示地址。
sk.listen(backlog)
开始监听传入连接。backlog指定在拒绝连接之前,可以挂起的最大连接数量,也就是除了当前正在和服务器进行通信的连接外,还可以
进入链接池的连接个数。超过这个数的连接将被服务器积极拒绝,无法建立连接。backlog等于5,表示内核已经接到了连接请求,但服务器
还没有调用accept进行处理的连接个数最大为5,这个值不能无限大,因为要在内核中维护连接队列
sk.setblocking(bool)
是否阻塞(默认True),如果设置False,那么accept和recv时一旦无数据,则报错。socket由阻塞变成非阻塞模式的关键参数!
sk.accept()
接受连接并返回(conn,address),其中conn是新的套接字对象,可以用来接收和发送数据。address是连接客户端的地址。
接收TCP 客户的连接(阻塞式)等待连接的到来
sk.connect(address)
连接到address处的套接字。一般,address的格式为元组(hostname,port),如果连接出错,返回socket.error错误。
sk.connect_ex(address)
同上,只不过会有返回值,连接成功时返回 0 ,连接失败时候返回编码,例如:10061
sk.close()
关闭套接字
sk.recv(bufsize[,flag])
接受套接字的数据。数据以字符串形式返回,bufsize指定最多可以接收的数量。flag提供有关消息的其他信息,通常可以忽略。
sk.recvfrom(bufsize[.flag])
与recv()类似,但返回值是(data,address)。其中data是包含接收数据的字符串,address是发送数据的套接字地址。
sk.send(string[,flag])
将string中的数据发送到连接的套接字。返回值是要发送的字节数量,该数量可能小于string的字节大小。即:可能未将指定内容全部发送。
sk.sendall(string[,flag])
将string中的数据发送到连接的套接字,但在返回之前会尝试发送所有数据。成功返回None,失败则抛出异常。
内部通过递归调用send,将所有内容发送出去。
sk.sendto(string[,flag],address)
将数据发送到套接字,address是形式为(ipaddr,port)的元组,指定远程地址。返回值是发送的字节数。该函数主要用于UDP协议。
sk.settimeout(timeout)
设置套接字操作的超时期,timeout是一个浮点数,单位是秒。值为None表示没有超时期。一般,超时期应该在刚创建套接字时设置,
因为它们可能用于连接的操作(如 client 连接最多等待5s )
sk.getpeername()
返回连接套接字的远程地址。返回值通常是元组(ipaddr,port)。
sk.getsockname()
返回套接字自己的地址。通常是一个元组(ipaddr,port)
sk.fileno()
套接字的文件描述符
SocketServer模块
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内创建一个“线程”或者“进程” 专门负责处理当前客户端的所有请求。
ThreadingTCPServer(多线程)
ThreadingTCPServer实现的Soket服务器内部会为每个client创建一个 “线程”,该线程用来和客户端进行交互。服务器相当于一个总管,在接收连接并创建新的线程后,就撒手不管了,后面的通信就是线程和客户端之间的连接了,理解这一点很重要!
1、ThreadingTCPServer基础
使用ThreadingTCPServer:
- 创建一个继承自 SocketServer.BaseRequestHandler 的类
- 类中必须定义一个名称为 handle 的方法
- 启动ThreadingTCPServer
#!/usr/bin/env python # -*- coding:utf-8 -*- import socketserver class MyServer(socketserver.BaseRequestHandler): def handle(self): # print self.request,self.client_address,self.server conn = self.request conn.sendall('欢迎致电 10086,请输入1xxx,0转人工服务.') Flag = True while Flag: data = conn.recv(1024) data = str(data, encoding="utf-8") if data == 'exit': Flag = False ': conn.sendall(bytes('通过可能会被录音.balabala一大推',encoding="utf-8")) else: conn.sendall(bytes('请重新输入',encoding="utf-8")) if __name__ == '__main__': server = socketserver.ThreadingTCPServer(('127.0.0.1',8009),MyServer) server.serve_forever()
SocketServer 服务器
#!/usr/bin/env python # -*- coding:utf-8 -*- import socket ip_port = ('127.0.0.1',8009) sk = socket.socket() sk.connect(ip_port) sk.settimeout(5) while True: data = sk.recv(1024) print('receive:',data) inp = input('please input:') sk.sendall(bytes(inp, encoding="utf-8")) if inp == 'exit': break sk.close()
socketserver 客户端
分析一下服务器端的代码,核心要点有这些:
- 连接对象不再是socket模块中的socket.socket()了,而是self.request,这是固定语法,不可变!以后调用send和recv方法都是使用self.request
- handle方法是整个连接的处理核心,一旦它运行结束,整个连接也就断了(但其他的线程和其他的客户端还正常),因此一般在此设置一个无限循环。
- 在server = SocketServer.ThreadingTCPServer(('127.0.0.1',8009),MyServer)这个实例化的过程中,必须将自己创建的类,作为参数传递进去
- server.serve_forever()表示该服务器在正常情况下将永远运行
2、ThreadingTCPServer源码剖析
ThreadingTCPServer类的继承关系如下:
内部调用流程为:
- 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)
ThreadingTCPServer相关源码:
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) - 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() 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() # 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 socket.error: 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', print client_address import traceback traceback.print_exc() # XXX But this goes to stderr! print '-'*40
BaseServer
class TCPServer(BaseServer): """Base class for various socket-based server classes. Defaults to synchronous IP stream (i.e., TCP). Methods for the caller: - __init__(server_address, RequestHandlerClass, bind_and_activate=True) - serve_forever(poll_interval=0.5) - shutdown() - handle_request() # if you don't 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) - process_request(request, client_address) - shutdown_request(request) - close_request(request) - 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 - request_queue_size (only for stream sockets) - allow_reuse_address Instance variables: - server_address - RequestHandlerClass - socket """ address_family = socket.AF_INET socket_type = socket.SOCK_STREAM request_queue_size = 5 allow_reuse_address = False 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 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() def server_activate(self): """Called by constructor to activate the server. May be overridden. """ self.socket.listen(self.request_queue_size) def server_close(self): """Called to clean-up the server. May be overridden. """ self.socket.close() def fileno(self): """Return socket file number. Interface required by select(). """ return self.socket.fileno() def get_request(self): """Get the request and client address from the socket. May be overridden. """ return self.socket.accept() def shutdown_request(self, request): """Called to shutdown and close an individual request.""" try: #explicitly shutdown. socket.close() merely releases #the socket and waits for GC to perform the actual close. request.shutdown(socket.SHUT_WR) except socket.error: pass #some platforms may raise ENOTCONN here self.close_request(request) def close_request(self, request): """Called to clean up an individual request.""" request.close()
TCPServer
class ThreadingMixIn: """Mix-in class to handle each request in a new thread.""" # Decides how threads will act upon termination of the # main process daemon_threads = False def process_request_thread(self, request, client_address): """Same as in BaseServer but as a thread. In addition, exception handling is done here. """ try: self.finish_request(request, client_address) self.shutdown_request(request) except: self.handle_error(request, client_address) self.shutdown_request(request) def process_request(self, request, client_address): """Start a new thread to process the request.""" t = threading.Thread(target = self.process_request_thread, args = (request, client_address)) t.daemon = self.daemon_threads t.start()
ThreadingMixIn
class ThreadingTCPServer(ThreadingMixIn, TCPServer): pass # 还有比这更简单,更NB的类吗
ThreadingTCPServer
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
SocketServer.BaseRequestHandler
ForkingTCPServer
ForkingTCPServer和ThreadingTCPServer的使用和执行流程基本一致,只不过在内部分别为请求者建立 “线程” 和 “进程”。
基本使用:
#!/usr/bin/env python # -*- coding:utf-8 -*- import socketserver class MyServer(socketserver.BaseRequestHandler): def handle(self): # print self.request,self.client_address,self.server conn = self.request conn.sendall(bytes('欢迎致电 10086,请输入1xxx,0转人工服务.',encoding="utf-8")) Flag = True while Flag: data = conn.recv(1024) data = str(data,encoding="utf-8") if data == 'exit': Flag = False ': conn.sendall(bytes('通过可能会被录音.balabala一大推',encoding="utf-8")) else: conn.sendall(bytes('请重新输入.',encoding="utf-8")) if __name__ == '__main__': server = socketserver.ForkingTCPServer(('127.0.0.1',8009),MyServer) server.serve_forever()
多进程socket服务器
客户端不需要修改。所有的变化都是在服务器端。以上ForkingTCPServer只是将 ThreadingTCPServer 实例中的代码:
server = socketserver.ThreadingTCPServer(('127.0.0.1',8009),MyRequestHandler) 变更为: server = socketserver.ForkingTCPServer(('127.0.0.1',8009),MyRequestHandler)