[Zhengdian Atomic Alpha IMX6ULL Linux Development Board] Chapter 12 TCP Programming Test (Linux C Programming)

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[Zhengdian Atomic Alpha IMX6ULL Linux Development Board] Chapter 12 TCP Programming Test (Linux C Programming) [Copy link]

1. Basic Concepts of SOCKET

The following comes from "Linux Advanced Programming"

Socket is a mechanism for realizing inter-process communication on a network host. From the user space point of view, a socket is a file descriptor. The operation on a socket is equivalent to the operation on a normal file descriptor, that is, it can be operated using functions such as read, write, and close. Once the necessary initialization of the socket is completed, data interaction with the other end is realized through the socket.

For example

1. To send data to the other party, just write the data to the socket
2. To receive data, just read the data on the socket in a blocking manner.

TCP implementation flow chart:

2. Socket function

After a rough look, it is actually similar to Python's TCP. Python provides a module

C provides library functions

#include <sys/socket.h> header file

The library functions included in the header file are:

Function prototype	int socket(int domain, int type, int protocol)
Function passed value	domain	AF_INET: IPv4 protocol
		AF_INET6: IPv6 protocol
		AF_LOCAL: Unix domain protocol
		AF_ROUTE: Routing socket
		AF_KEY: Key socket
	type	SOCKET_STREAM: bidirectional reliable data stream, corresponding to TCP
		SOCKET_DGRAM: bidirectional unreliable datagram, corresponding to UDP
		SOCKET_RAW: Provides protocols below the transport layer and can access internal network interfaces, such as receiving and sending ICMP messages
	protocol	When type is SOCKET_RAW, you need to set this value to indicate the protocol type. For other types, just set it to 0
Function return value	Success: socket file descriptor
	Failure: -1, the reason for failure is stored in error

bind (associate a local protocol address with a socket file descriptor)
Function Description	Associates a protocol address with a socket file descriptor
Function prototype	int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen)
Function passed value	sockfd	Socket file descriptor
	addr	my_addr points to the sockaddr structure, which contains information such as IP address and port
	addrlen	The size of the sockaddr structure can be set to sizeof(struct sockaddr)
Function return value	Success: 0
	Failure: -1, the reason for failure is stored in error

listen (wait for connection)
Function Description	Waiting for connection
Function prototype	int listen(int sockfd, int backlog)
Function passed value	sockfd	Listening socket file descriptor
	backlog	The maximum number of connections that the socket queues
Function return value	Success: 0
	Failure: -1, the reason for failure is stored in error
Special Notes	For the listening socket file descriptor sockfd, the kernel maintains two queues, one for unfinished connections and the other for completed connections. The sum of these two queues does not exceed the backlog.

connect (establish a socket connection)
illustrate	Establishing a socket connection
prototype	int connect(int sockfd, const struct sockaddr *serv_addr, socklen_t addrlen)
Incoming Value	sockfd	Socket file descriptor
	serv_addr	The network address and port to connect to
	addrlen	The size of the sockaddr structure can be set to sizeof(struct sockaddr)
Function return value	Success: 0
	Failure: -1, the reason for failure is stored in error

function	int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen)
Passing in parameters	sockfd: socket file descriptor
	addrlen: the size of addr, which can be set to sizeof(struct sockaddr)
Outgoing parameters	addr: fill in the address data of the remote host
Function return value	Success: The actual number of bytes read
	Failure: -1, the error code is stored in error

Function prototype	int close(int sockfd)
Incoming Value	sockfd: socket file descriptor
function Return Value	Success: 0
	Failure: -1, the reason for failure is stored in error

3. Programming

Socket address data type

Server Program

Client Program

4. Test:

Server.c and client.c

If any of them need to be run on a development board, cross-compilation is required.

Compile command: arm-linux-gnueabihf-gcc server.c -o server

The development board runs ./server

Ububtu system operation: ./client

Forgot to take a screenshot, it's very simple anyway

淡漠

Good stuff, learn from it.