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-introduction

The original meaning of Socket is "hole" or "socket", which is also called "socket" in the process communication mechanism of Unix. Sockets are actually not complex; they consist of an ip address and a port number. Socket, as it originally meant in English, is like a porous socket. A mainframe is like a room full of all kinds of sockets (ip addresses). Each socket has many sockets (ports) through which we can boil water, watch TV and play computer.

Applications usually send requests to or respond to network requests through "sockets".

One of the functions of sockets is to distinguish between different application processes. When a process binds to a port of native ip, all data sent to this port on this ip address will be sent by the kernel to that process for processing.

-socket in python

Python provides two basic socket modules.

The first is Socket, which provides a standard BSD Sockets API.

The second is SocketServer, which provides server-centric classes that simplify the development of web servers.

-socket

Let's start with the first one.

As we know, most of today's applications are based on CPX S architecture, which is divided into client / server side.

Server-side: the server-side process needs to apply for a socket, bind it to the socket itself, and listen to the socket. When a client sends data, it accepts the data for processing, and responds to the client after the processing is completed.

Client: the client is relatively simple. The client only needs to apply for a socket and then connect to the socket on the server side through this socket. After the connection is established, the subsequent operation can be carried out.

To write the server side of the python:

1 create a socket

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2 bind socket

S1.bind (address) # A socket created by AF_INET, the address address must be a two-element tuple in the format (host,port). Host represents the host and port represents the port number.

# if the port number is in use, the hostname is incorrect, or the port is reserved, the bind method throws a socket.error exception. # examples: ('192.168.1.1)

3 monitoring sockets

S1.listen (backlog) # backlog specifies the maximum number of clients allowed to connect to the server. Its value is at least 1. When connection requests are received, they need to be queued, and if the queue is full, the request is rejected.

4 waiting for the connection to be accepted

Connection, address = s1.accept () # when the accept method is called, the socket will enter the "waiting" state, that is, it is in the blocking state. When the client requests a connection, the method establishes the connection and returns to the server. The # accept method returns a connection,address with two elements. # the first element, connection, is the socket object (actually the memory address of the connected client) through which the server must communicate with the client; # the second element, address, is the client's Internet address.

5 processing stage

Connection.recv (bufsize [, flag])

# Note that socket data is accepted for connection#. The data is returned as a string, and the bufsize specifies the maximum number that can be received. Flag provides additional information about the message, and you can usually ignore connection.send (string [, flag]) # to send data from string to the socket of the connection. The return value is the number of bytes to be sent, which may be less than the byte size of string. That is, the specified content may not be all sent.

6 transfer is over, close the connection

S1.close () # close the socket

Python authoring client

1 create a socket object

Import sockets2=socket.socket ()

2 connect to the server side

S2.connect (address) # connects to the socket at address. In general, the format of address is tuple (hostname,port). If there is an error in the connection, an socket.error error is returned.

3 processing stage

S2.recv (bufsize [, flag]) # accepts socket data. The data is returned as a string, and the bufsize specifies the maximum number that can be received. Flag provides additional information about the message, and you can usually ignore s2.send (string [, flag]) # to send data from string to the socket of the connection. The return value is the number of bytes to be sent, which may be less than the byte size of string. That is, the specified content may not be all sent.

4 connection ends, close socket

S2.close ()

There are many other methods in socket:

Socket.getaddrinfo (host, port, family=0, type=0, proto=0, flags=0) 10061 0, count=

All right, after introducing socket, it's time to introduce socketserver.

-socketserver

Although it is convenient to write simple network programs with Python, it is better to use off-the-shelf frameworks for complex network programs. This allows you to focus on the transaction logic rather than the details of the socket. The SocketServer module simplifies the task of writing network service programs. At the same time, the SocketServer module is the basis of many server frameworks in the Python standard library.

Socketserver is SocketServer in python2 and uncapitalized in python3 and renamed to socketserver.

Socketserver contains two categories, one is the service class (server class), and the other is the request processing class (request handle class). The former provides many methods: such as binding, listening, running. (that is, the process of establishing a connection) the latter focuses on how to handle the data sent by the user (that is, transaction logic).

In general, all services first establish a connection, that is, to establish an instance of the service class, and then start to process user requests, that is, to establish an instance of the request processing class.

Let's analyze the source code to see how the service class is associated with the request processing class.

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Let's introduce these two classes next.

Let's first take a look at the service category:

There are 5 types: BaseServer,TCPServer,UnixStreamServer,UDPServer,UnixDatagramServer.

BaseServer does not provide direct external services.

TCPServer is for TCP socket streams

UDPServer for UDP Datagram sockets

UnixStreamServer and UnixDatagramServer are not commonly used for UNIX domain sockets.

The inheritance between them:

Methods of the service class:

View Code

All of these service classes process requests synchronously: one request cannot be processed until it is finished. To support the asynchronous model, you can use multiple inheritance to have the server class inherit ForkingMixIn or ThreadingMixIn mix-in classes.

ForkingMixIn uses multiple processes (bifurcations) to achieve asynchronism.

ThreadingMixIn uses multithreading to achieve asynchronism.

Request handler class:

To implement a service, you must also derive a handler class request handling class and override the handle () method of the parent class. The handle method is used specifically to process requests. The module processes requests through a combination of service classes and request processing classes.

The request handling classes provided by the SocketServer module are BaseRequestHandler and its derived classes StreamRequestHandler and DatagramRequestHandler. You can see from the name that one handles streaming sockets and the other deals with Datagram sockets.

There are three methods for the request processing class:

Setup ()

Called before the handle () method to perform any initialization actions required. The default implementation does nothing.

That is, it is called before handle (), and the main function is to perform all kinds of initialization-related work before processing the request. Nothing will be done by default. (if you want it to do something, programmers should override this method in their request handlers (because custom request handlers inherit the BaseRequestHandler,ps provided in python: mentioned below), and then add something to it.)

Handle ()

This function must do all the work required to service a request. The default implementation does nothing. Several instance attributes are available to it; the request is available as self.request; the client address as self.client_address; and the server instance as self.server, in case it needs access to per-server information.

The type of self.request is different for datagram or stream services. For stream services,self.request is a socket object; for datagram services,self.request is a pair of string and socket.

The job of handle () is to do all the work related to processing the request. I won't do anything by default. He has several instance parameters: self.request self.client_address self.server

Finish ()

Called after the handle () method to perform any clean-up actions required. The default implementation does nothing. If setup () raises an exception, this function will not be called.

After the handle () method is called, its function is to perform the cleanup after the request has been processed, and nothing will be done by default

Handler source code

As you can see from the source code, setup () / handle () / finish () in BaseRequestHandler has no definition, while his two derived classes, StreamRequestHandler and DatagramRequestHandler, override setup () / finish ().

So when we need to write our own socketserver program, we only need to reasonably choose one of StreamRequestHandler and DatagramRequestHandler as the parent class, then customize a request handling class and override the handle () method in it.

To create a service with socketserver:

1 create a request handler class (request processing class), reasonably choose one of StreamRequestHandler and DatagramRequestHandler as the parent class (or, of course, use BaseRequestHandler as the parent class), and override its handle () method.

Instantiate a server class object and pass it the address of the service and the request handler class you created earlier.

3 call the handle_request () or serve_forever () method of the server class object to start processing the request.

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