接收端编程、UDP编程练习、wireshrak抓包工具、UDP包头

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学习笔记

接收端

recvfrom

#include <sys/types.h>
#include <sys/socket.h>

ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags,
struct sockaddr *src_addr, socklen_t *addrlen);

功能：从套接字中接收数据

参数：

sockfd：套接字文件描述符

buf：存放数据空间首地址

flags：属性，默认为0；

src_addr：存放IP地址信息空间的首地址

addrlen：存放接收到ip地址大小空间的首地址、

返回值：成功返回实际接收字节数，失败返回-1；

inet_ntoa

功能：将二进制转换为字符串

ntohs

功能：将大端字节序转换为本地字节序

#include "head.h"

int main(void)
{
    int sockfd = 0;
    struct sockaddr_in recvaddr;
    struct sockaddr_in tmpaddr;
    char tmpbuff[1024] = {0};
    ssize_t nsize = 0;
    ssize_t nsize1 = 0;
    char recvbuff[1024] = {0};
    socklen_t recvbufflen;
    recvbufflen = sizeof(tmpaddr);

    fgets(tmpbuff, sizeof(tmpbuff), stdin);
    
   // while (1)
    {

        /*创建用来通信的UDP套接字*/
        sockfd = socket(AF_INET, SOCK_DGRAM, 0);//通信使用的协议族(AF_INET是IPv4协议族)，套接字类型：数据报套接字；默认0
        if (-1 == sockfd)
        {
            perror("fail to socket");
            return -1;
        }

        /*对接收方地址赋值*/
        recvaddr.sin_family = AF_INET;
        recvaddr.sin_port = htons(50001);//本地字节序转换为网络的大端字节序
        recvaddr.sin_addr.s_addr = inet_addr("192.168.1.101");//函数接口inet_addr将字符串的ip地址转换为内存当中的IP地址
        //前面是ip地址转换为32位之后的变量名

        /*发送信息*/
        nsize = sendto(sockfd, tmpbuff, strlen(tmpbuff), 0, (struct sockaddr *)&recvaddr, sizeof(recvaddr));
        //0为发送的属性，默认为0，发送到哪里(那个空间的首地址)，那个地方的空间大小
        if (-1 == nsize)
        {
            perror("fail to sendto");
            return -1;
        }
        //printf("成功发送%ld字节！\n", nsize);
        

        /*接收信息*/
        nsize1 = recvfrom(sockfd, recvbuff, sizeof(recvbuff), 0, (struct sockaddr *)&tmpaddr, &recvbufflen);
        if (-1 == nsize1)
        {
            perror("fail to recvform");
            return -1;
        }
        printf("RECV ASCII FROM %s:%d  %s\n", inet_ntoa(tmpaddr.sin_addr), ntohs(tmpaddr.sin_port), recvbuff);
    }
    close(sockfd);

    return 0;
}

bind

#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>

int bind(int sockfd, const struct sockaddr *addr,socklen_t addrlen);

功能：在套接字绑定一个IP地址和端口号

参数：

sockfd：套接字的文件描述符

addr：绑定的IP地址空间的首地址

addrlen：绑定IP地址的长度

返回值：成功0，失败-1；

UDP编程

发端：

socket -> sendto -> close

收端：

socket -> bind -> recvfrom -> close

发端：

#include "head.h"

int main(void)
{
    int sockfd = 0;
    char tmpbuff[1024] = {0};
    struct sockaddr_in myaddr;
    struct sockaddr_in recvaddr;
    ssize_t nsize = 0;
    int ret = 0;

    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (-1 == sockfd)
    {
        perror("fail to socket");
        return -1;
    }

    myaddr.sin_family = AF_INET;
    myaddr.sin_port = htons(54321);
    myaddr.sin_addr.s_addr = inet_addr("192.168.1.172");
    ret = bind(sockfd, (struct sockaddr *)&myaddr, sizeof(myaddr));
    if (ret == -1)
    {
        perror("fail to bind");
        return -1;
    }

    fgets(tmpbuff, sizeof(tmpbuff), stdin);
    
    recvaddr.sin_family = AF_INET;
    recvaddr.sin_port = htons(30000);
    recvaddr.sin_addr.s_addr = inet_addr("192.168.1.167");

    nsize = sendto(sockfd, tmpbuff, strlen(tmpbuff), 0, (struct sockaddr *)&recvaddr, sizeof(recvaddr));
    if (-1 == nsize)
    {
        perror("fail to sendto");
        return -1;
    }

    printf("成功发送%ld字节数据\n", strlen(tmpbuff));
    
    close(sockfd);

    return 0;
}

收端：

#include "head.h"

int main(void)
{
    int sockfd = 0;
    struct sockaddr_in myaddr;
    int ret = 0;
    size_t nsize = 0;
    char tmpbuff[1024] = {0};
    struct sockaddr_in sendaddr;
    socklen_t sendaddrlen;
    sendaddrlen = sizeof(sendaddr);   
 
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (-1 == sockfd)
    {
        perror("fail to sockfd");
        return -1;
    }

    myaddr.sin_family = AF_INET;
    myaddr.sin_port = htons(33333);
    myaddr.sin_addr.s_addr = inet_addr("192.168.1.172");
    ret = bind(sockfd, (struct sockaddr *)&myaddr, sizeof(myaddr));
    if (-1 == ret)
    {
        perror("fail to bind");
        return -1;
    }

    nsize = recvfrom(sockfd, tmpbuff, sizeof(tmpbuff), 0, (struct sockaddr *)&sendaddr, &sendaddrlen);
    if (-1 == nsize)
    {
        perror("fail to recvfrom");
        return -1;
    }

    printf("RECV ASCII FROM %s:%d  %s", inet_ntoa(sendaddr.sin_addr), ntohs(sendaddr.sin_port), tmpbuff);

    return 0;
}