UDP服务器客户端

1. UDP的特点

UDP服务器在调用bind()函数之后就可以接受任何UDP客户端发来的数据，不需要像TCP一样建立一对一连接，UDP是面向无连接的。

2. UDP服务器客户端收发过程

3. sendto() 与recvfrom() 函数

1）sendto()函数，调用者为发送方

头文件：#include <sys/types.h>

       #include <sys/socket.h>

函数原型：ssize_t sendto(int sockfd, const void*buf, size_t len, int flags,

                      const struct sockaddr*dest_addr, socklen_t addrlen);

功能：向dest_addr 表示的接收方发送数据，该函数不是阻塞的，

参数：int sockfd  发送方套接字  

const void *buf   要发送的数据的地址

size_t len         发送数据的长度

int flags          通常为0

const struct sockaddr *dest_addr   接收方的ip+port

socklen_t   addrlen                地址长度

返回值：成功   实际发送字节的个数

失败   -1

2）recvfrom() 函数，调用者为接收方

头文件：#include<sys/types.h>

        #include <sys/socket.h>

函数原型：ssize_t recvfrom(intsockfd, void *buf, size_t len, int flags, structsockaddr *src_addr, socklen_t *addrlen);

功能：从发送方接收数据，该函数是阻塞函数

参数：int sockfd 接收方套接字

  void *buf  接受数据的缓冲区地址

  size_tlen  缓冲区大小

int flags    通常为0

struct sockaddr *src_addr     发送方的 ip+port

socklen_t *addrlen               

返回值：成功 实际接收的字节的个数

失败 -1

示例代码：

Client.c文件代码

/*************************************************************************

 @Author: wanghao

 @Created Time : Fri 25 May 2018 08:09:19 PM PDT

 @File Name: client.c

 @Description:

 ************************************************************************/

#include <stdio.h>

#include <sys/types.h>     

#include <sys/socket.h>

#include <sys/socket.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <unistd.h>

#include <string.h>

#include <pthread.h>

#define N 36

#define MAXSIZE 36

void *func(void *arg)

{

       intsocketfd;

       intaddrlen;

       structsockaddr_in server_addr;

       charbufread[MAXSIZE] = {0};

       socketfd= *(int *)arg;

       addrlen= sizeof(struct sockaddr);

       while(1)

       {

      recvfrom(socketfd, bufread, sizeof(bufread), 0, (struct sockaddr*)(&server_addr), &addrlen);

          printf("server ip = %s port =%d\n", inet_ntoa(server_addr.sin_addr), ntohs(server_addr.sin_port));

          printf("%s\n",bufread);

       }

}

int main(int argc, const char *argv[])

{

       intsocketfd;

       intclient_fd;

       intaddrlen;

       u_shortport;

       pthread_ta_thread;

       charbufwrite[MAXSIZE] = "hello every!";

       structsockaddr_in server_addr;

       structsockaddr_in client_addr;

       if(argc< 3)

       {

              printf("usage:%s <IPadd> <Port>\n",argv[0]);

              return-1;

       }

       socketfd= socket(PF_INET, SOCK_DGRAM, 0);

       if(socket< 0)

       {

              perror("");

              return-1;

       }

       port= (u_short)atol(argv[2]);

       server_addr.sin_family= PF_INET;

       server_addr.sin_port= htons(port);

       server_addr.sin_addr.s_addr= inet_addr(argv[1]);

       addrlen= sizeof(struct sockaddr_in);

       pthread_create(&a_thread,NULL, func, (void *)(&socketfd));

       while(1)

       {

                     /*Thisfunction is a non-blocking function*/

                     sendto(socketfd,bufwrite, sizeof(bufwrite), 0, (struct sockaddr*)(&server_addr), addrlen);

                     sleep(1);

       }

       close(socketfd);

       return0;

}

Server.c文件代码：

/*************************************************************************

 @Author: wanghao

 @Created Time : Fri 25 May 2018 08:09:19 PM PDT

 @File Name: server.c

 @Description:

 ************************************************************************/

#include <stdio.h>

#include <sys/types.h>     

#include <sys/socket.h>

#include <sys/socket.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <unistd.h>

#include <string.h>

#include <pthread.h>

#include <unistd.h>

#include <fcntl.h>

#define N 36

#define MAXSIZE 128

typedef struct client_mem

{

       intflags;

       structsockaddr_in client_addr;

}Client_mem;

int main(int argc, const char *argv[])

{

       intsocketfd;

       intclient_fd;

       intaddrlen;

       intflag;

       u_shortport;

       pthread_ta_thread;

       charbuf[MAXSIZE] = {0};

       structsockaddr_in my_addr;

       structsockaddr_in client_addr;

       if(argc< 3)

       {

              printf("usage:%s <IPadd> <Port>\n",argv[0]);

              return-1;

       }

       socketfd= socket(PF_INET, SOCK_DGRAM, 0);

       if(socket< 0)

       {

              perror("");

              return-1;

       }

       port= (u_short)atol(argv[2]);

       my_addr.sin_family= PF_INET;

       my_addr.sin_port= htons(port);

       my_addr.sin_addr.s_addr= inet_addr(argv[1]);

       addrlen= sizeof(struct sockaddr_in);

       if(bind(socketfd,(struct sockaddr *)(&my_addr), addrlen) < 0)

       {

              perror("");

              return-2;

       }

       while(1)

       {

                     if(recvfrom(socketfd,buf, sizeof(buf), 0, (struct sockaddr*)(&client_addr), &addrlen) <0)

                     {

                            perror("receiveerror!\n");

                            sleep(2);

                            continue;

                     }

                     buf[strlen(buf)]= '\0';

                     printf("clientip = %s port = %d\n", inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port));

                     printf("%s",buf);

                     if(sendto(socketfd,buf, sizeof(buf), 0, (struct sockaddr*)(&client_addr), addrlen) < 0)

                     {

                            perror("sendtoerror");

                     }

       }

       close(socketfd);

       return0;

}