Socket socket programming -- UDP

UDP communication socket Programming
because UDP It's for connectionless 、 unreliable , So it's easy to implement , Just indicate where to send the data when sending it , and UDP It supports multi client connection .

API Function introduction

 receive messages （ Be similar to accept+recv）
ssize_t recvfrom(int sockfd, void* buf, size_t len, int flags, 
				struct sockaddr* src_addr, socklen_t* addrlen);
param:
	sockfd:  Socket 
	buf:  Buffer to accept 
	len:  Length of buffer 
	flags:  Sign a , General filling 0
	src_addr:  The original address , Out parameter 
	addrlen:  Sender address length 
return:
	 success ： Returns the number of bytes read 
	 Failure ： return -1


ssize_t sendto(int sockfd, const void* buf, size_t len, int flags, 
				const struct sockaddr* dest_addr, socklen_t addrlen);
param:
	sockfd:  Socket 
	buf:  Buffer to send 
	len:  Length of buffer 
	flags:  Sign a , General filling 0
	dest_addr:  Destination address 
	addrlen:  Length of destination address 
return:
	 success ： Returns the number of bytes written 
	 Failure ： return -1

use nc Command test UDP when ,nc -u 127.1 8888

Server code

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/types.h>
#include<unistd.h>
#include<arpa/inet.h>
#include<netinet/in.h>
#include<ctype.h>

int main()
{
    
    int fd = socket(AF_INET, SOCK_DGRAM, 0);
    if(fd < 0)
    {
    
        perror("socket error\n");
        return -1;
    }

    struct sockaddr_in serv;
    struct sockaddr_in client;
    bzero(&serv, sizeof(serv));
    serv.sin_family = AF_INET;
    serv.sin_port = htons(8888);
    serv.sin_addr.s_addr = htonl(INADDR_ANY);
    bind(fd, (struct sockaddr*)&serv, sizeof(serv));

    int n;
    socklen_t len;
    char buf[1024] = {
    0};
    while(1)
    {
    
        memset(buf, 0, sizeof(buf));
        len = sizeof(client);
        n = recvfrom(fd, buf, sizeof(buf), 0, (struct sockaddr*)&client, &len);
        printf("port==[%d], n==[%d], buf==[%s]\n", ntohs(client.sin_port), n, buf);
        
        for(int j=0; j<n; j++)
        {
    
            buf[j] = toupper(buf[j]);
        }

        sendto(fd, buf, n, 0, (struct sockaddr*)&client, len);
    }

    close(fd);
    return 0;
}

Client code

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/types.h>
#include<unistd.h>
#include<arpa/inet.h>
#include<netinet/in.h>
#include<ctype.h>

int main()
{
    
    int fd = socket(AF_INET, SOCK_DGRAM, 0);
    if(fd < 0)
    {
    
        perror("socket error\n");
        return -1;
    }

    int n;

    char buf[1024] = {
    0};
    struct sockaddr_in serv;
    serv.sin_family = AF_INET;
    serv.sin_port = htons(8888);
    inet_pton(AF_INET, "127.0.0.1", &serv.sin_addr.s_addr);

    while(1)
    {
    
        memset(buf, 0, sizeof(buf));
        n = read(STDIN_FILENO, buf, sizeof(buf));
        sendto(fd, buf, n, 0, (struct sockaddr*)&serv, sizeof(serv));

        memset(buf, 0, sizeof(buf));
        n = recvfrom(fd, buf, sizeof(buf), 0, NULL, NULL);// Can write NULL
        printf("n==[%d], buf==[%s]\n", n, buf);
    }

    close(fd);
    return 0;
}