1. Input man socket into the terminal to check the contents of socket
2. Create socket on the server side

/*
First parameter domain (network type): pf? INET IPv4 / PF? Inet6 IPv6
 The second parameter type (socket type): sock'stream connection oriented -- TCP protocol / sock'dgram connectionless -- UDP protocol
 The third parameter, protocol:
*/
int serverSocket = socket(PF_INET, SOCK_STREAM, 0);
if (serverSocket == -1) {
    NSLog(@"Create failure");
}else{
    NSLog(@"Create success");
}

2. Bind port number

int bind(SOCKET sock, const struct sockaddr *addr, int addrlen);

• First parameter: created socket file descriptor,
• Second parameter: the address structure passed in. To be compatible with the old system, the function declaration type is struct sockaddr *, but we usually use sockaddr_in, which is easier to use.

//Create SOCKADDR? In structure variable
struct sockaddr_in addr;
addr.sin_family = AF_INET;//Use ipv4 address
addr.sin_addr.s_addr = htonl(INADDR_ANY);//Binding ip address to any
addr.sin_port = htons(1234);//Port number

int result = bind(serverSocket, (const struct sockaddr *)&addr, sizeof(addr));
if (result == -1) {
    NSLog(@"Bind error");
}else{
    NSLog(@"Binding success");
}

3. Start monitoring

int listen(SOCKET sock, int backlog);

• The socket is the socket that needs to enter the listening state, and the backlog is the maximum length of the request queue.

result = listen(serverSocket, 5);
if (result == -1) {
    NSLog(@"Monitoring failed");
}else{
    NSLog(@"Start monitoring");
}

4. accept

SOCKET accept(SOCKET sock, struct sockaddr *addr, int *addrlen);

• sock is the server socket, addr is the SOCKADDR in structure variable, addrlen is the length of parameter addr, which can be obtained by sizeof().

//Save client information
struct sockaddr c_addr;
socklen_t len;
//Save received data buffer
char *buff[1024];
while (1) {
    int newSocket = accept(serverSocket, (struct sockaddr *)&c_addr, &len);
    if (newSocket == -1) {
        NSLog(@"Failed to receive data");
    }else{
        NSLog(@"Start talking");
        //receive data
        size_t length = recv(newSocket, buff, 1024, 0);
        NSLog(@"Received%zu Byte:%s",length ,buff);
        
        //send data
        char *msg = "hello";
        length = send(newSocket, msg, strlen(msg), 0);
        NSLog(@"Successfully sent to client%zu byte",length);
    }
}

5. Client creates socket

• Import header file

#import <sys/socket.h>
#import<netinet/in.h>
#import <arpa/inet.h>
#import <sys/types.h>

	int clientSocket = socket(PF_INET, SOCK_STREAM, 0);
    if (clientSocket == -1) {
        NSLog(@"Create failure");
    }else{
        NSLog(@"Create success");
    }

6. Initiate connection

int connect(SOCKET sock, const struct sockaddr *serv_addr, int addrlen);

struct sockaddr_in addr;
addr.sin_family = AF_INET;//ipv4 
addr.sin_addr.s_addr = inet_addr("127.0.0.1");//Binding specific ip address
addr.sin_port = htons(1234);//Binding port number

int result = connect(clientSocket, (const struct sockaddr *)&addr, sizeof(addr));
if (result == -1) {
    NSLog(@"link error");
}else{
    NSLog(@"Successful connection");
}

7. Send data

//send data
char *msg = "hello world";
ssize_t len = send(clientSocket, msg, strlen(msg), 0);
NSLog(@"Successful transmission %zd byte",len);

char buff[1024];
len = recv(clientSocket, buff, 1024, 0);
NSLog(@"Successful reception%zd byte",len,buff);

8. results