Linux网络编程 - UDP发送/接受数据

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YOLO晴 2021-11-02 21:11:00

文章标签 网络编程 #include 数据客户端 #define 文章分类 代码人生

UDP （User Datagram Protocol）：用户数据报协议。

UDP 是一个不可靠的通信协议，没有重传和确认，没有有序控制，也没有拥塞控制。可以简单地理解为，在 IP 报文的基础上，UDP 增加的能力有限。

UDP编程

UDP中客户端和服务器端交互的图解：

UDP Server :

Create UDP socket.

Bind the socket to server address.

Wait until datagram packet arrives from client.

Process the datagram packet and send a reply to client.

Go back to Step 3.

UDP Client :

Create UDP socket.

Send message to server.

Wait until response from server is received.

Process reply and go back to step 2, if necessary.

Close socket descriptor and exit.

主要是使用以下函数：

#include <sys/socket.h>
 
ssize_t recvfrom(int sockfd, void *buff, size_t nbytes, int flags, 
　　　　　　　　　　struct sockaddr *from, socklen_t *addrlen); 
 
ssize_t sendto(int sockfd, const void *buff, size_t nbytes, int flags,
                const struct sockaddr *to, socklen_t *addrlen);

recvfrom的参数含义：

sockfd ：本地创建的套接字描述符
buff ：指向本地缓存的指针
nbytes ：最大接收数据字节
flags ：与 I/O 相关的参数
from 和 addrlen：返回对端发送方的地址和端口等信息

返回值：实际接收的字节数。

sendto的参数意义：

sockfd ：本地创建的套接字描述符
buff ：指向本地缓存的指针
nbytes ：最大接收数据字节
flags ：与 I/O 相关的参数
to 和 addrlen，表示发送的对端地址和端口等信息。

UDP例子

UDP Server:

// Server side implementation of UDP client-server model

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
  
#define PORT    8080
#define MAXLINE 1024
  
// Driver code
int main() {
    int sockfd;
    char buffer[MAXLINE];
    char sendbuffer[MAXLINE];
    struct sockaddr_in servaddr, cliaddr;
      
    // Creating socket file descriptor
    if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
        perror("socket creation failed");
        exit(EXIT_FAILURE);
    }
      
    memset(&servaddr, 0, sizeof(servaddr));
    memset(&cliaddr, 0, sizeof(cliaddr));
      
    // Filling server information
    servaddr.sin_family    = AF_INET; // IPv4
    servaddr.sin_addr.s_addr = INADDR_ANY;
    servaddr.sin_port = htons(PORT);
      
    // Bind the socket with the server address
    if ( bind(sockfd, (const struct sockaddr *)&servaddr, 
            sizeof(servaddr)) < 0 )
    {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }
      
    int n;
    socklen_t len = (socklen_t)sizeof(cliaddr);  //len is value/resuslt
  


    for (;;) {
        n = recvfrom(sockfd, (char *)buffer, MAXLINE, 
                    MSG_WAITALL, ( struct sockaddr *) &cliaddr,
                    &len);
        buffer[n] = '\0';
        printf("Client : %s\n", buffer);
        
        sprintf(sendbuffer, "have recieve %d bytes", strlen(buffer));
        sendto(sockfd, (const char *)sendbuffer, strlen(sendbuffer), 0, 
                (const struct sockaddr *) &cliaddr, len);
        fprintf(stdout, "%s\n", sendbuffer);
    }

    return 0;
}

UDP Client:

// Client side implementation of UDP client-server model

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

#define PORT     8080
#define MAXLINE 1024
  
// Driver code
int main() {
    int sockfd;
    char buffer[MAXLINE];
    char *hello = "Hello from client";
    struct sockaddr_in     servaddr;
  
    // Creating socket file descriptor
    if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
        perror("socket creation failed");
        exit(EXIT_FAILURE);
    }
  
    memset(&servaddr, 0, sizeof(servaddr));
      
    // Filling server information
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(PORT);
    servaddr.sin_addr.s_addr = INADDR_ANY;
      
    socklen_t len = (socklen_t)sizeof(servaddr);  //len is value/resuslt
  
    // send msg
    while (fgets(buffer, MAXLINE, stdin) != NULL) {
        int i = strlen(buffer);
        if (buffer[i - 1] == '\n') {
            buffer[i - 1] = 0;
        }
        sendto(sockfd, (const char *)buffer, strlen(buffer), 0, 
                (const struct sockaddr *) &servaddr, len);
        fprintf(stdout, "message: %s have sent.\n", buffer);
        int n = recvfrom(sockfd, (char *)buffer, MAXLINE, MSG_WAITALL, 
                    (struct sockaddr *) &servaddr, &len);
        buffer[n] = '\0';
        printf("Server : %s\n", buffer);   
    }
  
    close(sockfd);
    return 0;
}