TCP server communication process (important)

1.TCP Introduce

Transmission control protocol
characteristic ：
Error re threading , Each time you send data, the other party will reply ACK
Safe and reliable

2. Server client TCP Communication model

client ： Call model （ Establishing a connection , Use connections , Close the connection ）
Create socket （ Customer phone ）– Connect to server （ Connect , dial ）– Sending and receiving data （ Reading and writing is right socket File operations ）（ Talking and communicating ）– close （ Hang up ）

Correlation function description

1. socket function – Semantics ： Create socket

#include <sys/types.h> / See NOTES /
#include <sys/socket.h>
int socket(int domain, int type, int protocol);
Specific parameters

domain:（socket Choice of agreement ）

AF_INET This is most used to produce socket The agreement , Use TCP or UDP To transmit , use IPv4 The address of
AF_INET6 Similar to the above , It's just for use IPv6 The address of
AF_UNIX Local agreement , Use in Unix and Linux On the system , Generally, it is used when the client and server are on the same platform and on it

type:（ Socket type ）

SOCK_STREAM The agreement is in order 、 reliable 、 Data complete connection based on byte stream . This is one of the most used socket type , This socket It's using TCP To transmit .
SOCK_DGRAM This protocol is connectionless 、 Fixed length transfer calls . It's not a reliable agreement , Use UDP To connect it .
SOCK_SEQPACKET The agreement is two-way 、 Reliable connection , Sending packets of fixed length for transmission . The package must be fully accepted before it can be read .
SOCK_RAW socket Type provides a single network access , This socket Type used ICMP Public agreement .（ping、traceroute Use this Agreement ）
SOCK_RDM This type is rarely used , It's not implemented on most operating systems , It is provided to the data link layer for use , The order of packets is not guaranteed

protocol:
Pass on 0 Indicates that the default protocol is used .
Return value ：
success ： Returns to the newly created socket File descriptor for sockdf, For later use ,
Failure ： return -1, Set up errno

describe

socket() Open a network communication port , If it works , It's like open() Also returns a file descriptor , Applications can be used just like reading and writing files read/write Sending and receiving data on the Internet , If socket() Call error, return -1. about IPv4,domain Parameter specified as AF_INET. about TCP agreement ,type Parameter specified as SOCK_STREAM, Represents a stream oriented transport protocol . If it is UDP agreement , be type Parameter specified as SOCK_DGRAM, Represents a datagram oriented transport protocol .protocol The introduction of parameters is omitted , Designated as 0 that will do .

2.connect function – Semantics ： Connect to server

#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
sockdf:
socket File descriptor , The descriptor just created
addr:
Pass in the parameter ,ipv4/ipv6 General socket structure address （ Specify server-side address information , contain IP Address and port number ） If the type is wrong, force it , Turn to the general structure address
addrlen:
Pass in the parameter , Pass in sizeof(addr) size , The length of the incoming socket structure
Return value ：
Successfully returns 0, Failure to return -1, Set up errno
The client needs to call connect() Connect to server ,connect and bind The form of the parameter is consistent , The difference lies in bind The parameter of is its own address , and connect Is the address of the other party .connect() Successfully returns 0, Error return -1

Example of procedure code （ a key ）

#include <unistd.h>
#include <stdio.h>
#include <arpa/inet.h>
#include <sys/socket.h>

int main(int argc, char *argv[])
{
    
	// Create socket 
	int sock_fd;
	sock_fd = socket(AF_INET,SOCK_STREAM,0);
	// establish ipv4 Socket structure -- Assign the three elements of the server to the client 
	struct sockaddr_in addr;
	addr.sin_family = AF_INET;// Set up ipv4 Address format 
	addr.sin_port = htons(8080);// Host byte order to network byte order 
	inet_pton(AF_INET,"192.168.21.29",&addr.sin_addr.s_addr);// Convert dotted decimal string into network big end 
	// Connect to server 
	connect(sock_fd,(struct sockaddr *)&addr,sizeof(addr));//connect To convert to a generic socket structure type 
	
	char buf[1024]="";
	while(1)
	{
    
		int n = read(STDIN_FILENO,buf,sizeof(buf));
		write(sock_fd,buf,n);// Writing data 
		n = read(sock_fd,buf,sizeof(buf));// Reading data 
		write(STDOUT_FILENO,buf,n);
		printf("\n");
	
	}1

	
	
// Close socket 
	close(sock_fd);

	return 0;
}