【LINUX/UNIX网络编程】之使用SOCKET进行UDP编程

先看任务需求：

实验二 UDP数据发送与接收

【实验目的】

1、熟练掌握套接字函数的使用方法。

2、应用套接字函数完成基本UDP通讯，实现服务器与客户端的文件传送

【实验学时】

4学时

【实验内容】

要求：

（1）客户可以从服务器下载文件、或向服务器上传文件。

（2）客户可向服务器发送多种指令：DOWNLOAD、UPLOAD、YES、NO、START、END、SHUTDOWN、CONTENT、OKDOWLOAD格式：DOWLOAD [filename]表示从服务器下载filename文件，如果服务器存在该文件，返回YES，否则返回NO；客户接收如果是YES，可发送START表示开始下载，之后，服务器将文件传送给客户，客户接收并保存；UPLOAD格式：UPLOAD [filename]表示向服务器上传filename文件，服务器发送NO表示拒绝接收。服务器发送START表示开始传送，之后向服务器传输文件；END:表示文件传送结束SHUTDOWN:表示通讯结束，双方退出。

先画一下流程图方便理顺思路：

下面上代码：

1.定义了一个protocol结构体方便传输信息和信息校验等；

 #ifndef _protocol
 #define _protocol

 #define INFOLEN 1000
 #define SHUTDOWN 0
 #define DOWNLOAD 1
 #define UPLOAD 2
 #define YES 3
 #define NO 4
 #define START 5
 #define END 6
 #define CONTENT 7
 #define OK 8

 struct protocol
 {
     int command;
     int len;  //length of buf
     int no;
     char buf[INFOLEN];
 };
 #endif

2.客户端程序：

 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <sys/types.h>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include "protocol.h"

 /*-----------------------变量声明区------------------*/
     int socketfd;
     int addrlen;
     struct sockaddr_in server;
     struct protocol sentbuf;
     struct protocol recvbuf;
     int num;
     char ip[];
     int port;
     int choice;
     char filename[];
 /*------------------------函数声明区------------------*/
 void ShowMenu();
 void DownLoad();
 void UpLoad();
 void ShutDown();

 int main() {

     /*-------------create UDP socket------------*/
     if((socketfd = socket(AF_INET,SOCK_DGRAM,)) == -){
         perror("socket error\n");
         exit();
     }

     /*-----------------IO-----------------------*/
     printf("Please input the ip:\n");
     scanf("%s",ip);
     printf("Please input the port:\n");
     scanf("%d",&port);

     /*--------------------recvfrom and sendto----------*/
     bzero(&server,sizeof(server));
     server.sin_family = AF_INET;
     server.sin_port = htons(port);
     server.sin_addr.s_addr = inet_addr(ip);
     addrlen = sizeof(server);

     /*--------------------调试信息---------------------------
     recvbuf.command = DOWNLOAD;
     recvbuf.no =0;
     printf("input the message:\n");
     scanf("%s",recvbuf.buf);
     recvbuf.len = strlen(recvbuf.buf);
     sendto(socketfd,&recvbuf,sizeof(recvbuf),0,(struct sockaddr *)&server,sizeof(server)); */

     while (){
     ShowMenu();
     scanf("%d",&choice);
     if(choice == SHUTDOWN){
         ShutDown();
         break;
     }
     else if(choice == DOWNLOAD){
         DownLoad();
     }
     else if(choice == UPLOAD){
         UpLoad();
     }
     else{
         printf("Please make a right choice!\n");
     }
 } 

     /*-----------------close------------------------*/
     close(socketfd);
     return ;
 }

 void ShowMenu(){
     printf("=====================================\n");
     printf("         Please make a choice:       \n");
     printf("         0:  ||shutdown||            \n");
     printf("         1:  ||download||            \n");
     printf("         2:  || upload ||            \n");
     printf("=====================================\n");
 }
 void DownLoad(){
     bzero(&recvbuf,sizeof(recvbuf));
     bzero(&sentbuf,sizeof(sentbuf));
     bzero(filename,sizeof(filename));
     printf("Please input the file name:\n");
     scanf("%s",sentbuf.buf);
     sentbuf.command = DOWNLOAD;
     sendto(socketfd,&sentbuf,sizeof(sentbuf),,(struct sockaddr *)&server,sizeof(server));
     bcopy(sentbuf.buf,filename,strlen(sentbuf.buf));
     recvfrom(socketfd,&recvbuf,sizeof(recvbuf),,(struct sockaddr *)&server,&addrlen);
     if(recvbuf.command == YES){
         printf("YES!\n");
         printf("Start  to transmission!\n");
             sentbuf.command = START;
             sendto(socketfd,&sentbuf,sizeof(sentbuf),,(struct sockaddr *)&server,sizeof(server));
             int no =;
             int fd =open(filename,O_CREAT | O_TRUNC |O_WRONLY,);
             if(fd < ){
                 perror("create file error\n");
                 exit();
             }
             bzero(&recvbuf,sizeof(recvbuf));
             while((num = recvfrom(socketfd,&recvbuf,sizeof(recvbuf),,(struct sockaddr *)&server,&addrlen)) >){
                 if(recvbuf.command == CONTENT){
                     if(no == recvbuf.no){
                     write(fd,recvbuf.buf,recvbuf.len);
                     //printf("kkk%s\n",recvbuf.buf );
                     no++;
                     bzero(&recvbuf,sizeof(recvbuf));
                 }
                 else{
                     perror("The file no is not same.Some message is missed! error occured! \n");
                     break;
                 }
                 }
                 if(recvbuf.command == END){
                     close(fd);
                     printf("transmission is successful!\n");
                     break;
                 }
             }
     }
     else if(recvbuf.command ==NO){
         perror("NO such file on server!\n");
     }
     else{
         perror("recvbuf.command error\n");
         exit();
     }
 }
 void UpLoad(){
     bzero(&recvbuf,sizeof(recvbuf));
     bzero(&sentbuf,sizeof(sentbuf));
     bzero(filename,sizeof(filename));
     printf("Please input the file name:\n");
     scanf("%s",sentbuf.buf);
     sentbuf.command = UPLOAD;
     sendto(socketfd,&sentbuf,sizeof(sentbuf),,(struct sockaddr *)&server,sizeof(server));
     bcopy(sentbuf.buf,filename,strlen(sentbuf.buf));
     //判断要传输的文件是否存在
     int fd;
     fd = open(filename,O_RDONLY);
     if(fd < ){
         perror("The file you want to trans is not exist!\n");
         exit();
     }
     recvfrom(socketfd,&recvbuf,sizeof(recvbuf),,(struct sockaddr *)&server,&addrlen);
     if(recvbuf.command == START){
             int no =;
             while((num = read(fd,sentbuf.buf,INFOLEN)) >){
                 sentbuf.no = no;
                 sentbuf.command = CONTENT;
                 sentbuf.len = strlen(sentbuf.buf);
                 sendto(socketfd,&sentbuf,sizeof(sentbuf),,(struct sockaddr *)&server,sizeof(server));
                 no++;
                 bzero(&sentbuf,sizeof(sentbuf));
             }
             bzero(&sentbuf,sizeof(sentbuf));
             sentbuf.command = END;
             sendto(socketfd,&sentbuf,sizeof(sentbuf),,(struct sockaddr *)&server,sizeof(server));
     }
     else if(recvbuf.command == NO){
         printf("not transmission\n");
         printf("The file is exist!\n");
     }
     else {
         perror("error! wrong choice!\n");
     }
 }

 void ShutDown(){
     printf("client is shutdown now!\n");
     bzero(&sentbuf,sizeof(sentbuf));
     sentbuf.command == SHUTDOWN;
     sendto(socketfd,&sentbuf,sizeof(sentbuf),,(struct sockaddr *)&server,sizeof(server));
 }

3.服务器端程序：

 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <sys/types.h>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include "protocol.h"

 /*-----------------------变量声明区------------------*/
     int socketfd;
     int addrlen;
     struct sockaddr_in server;
     struct sockaddr_in client;
     struct protocol sentbuf;
     struct protocol recvbuf;
     int num;
     char ip[];
     int port;
     int choice;

 int main(){

     /*-------------create UDP socket------------*/
     if((socketfd = socket(AF_INET,SOCK_DGRAM,)) == -){
         perror("socket error\n");
         exit();
     }

     /*-----------------IO-----------------------*/
     printf("Please input the ip:\n");
     scanf("%s",ip);
     printf("Please input the port:\n");
     scanf("%d",&port);

     /*-----------------bind----------------------*/
     bzero(&server,sizeof(server));
     server.sin_family = AF_INET;
     server.sin_port = htons(port);
     server.sin_addr.s_addr = inet_addr(ip);
     if (bind(socketfd,(struct sockaddr *)&server,sizeof(server)) == -){
         perror("bind error\n");
         exit();
     }

     /*---------------------调试信息------------
     addrlen = sizeof(client);
     recvfrom(socketfd,&recvbuf,sizeof(recvbuf),0,(struct sockaddr *)&client,&addrlen);
     num = strlen(recvbuf.buf);
     recvbuf.buf[num] = '\0';
     printf("command %d\n",recvbuf.command );
     printf("len %d\n",recvbuf.len );
     printf("no %d\n", recvbuf.no);
     printf("buf %s\n",recvbuf.buf ); */

     addrlen = sizeof(client);
     while(){
     bzero(&recvbuf,sizeof(recvbuf));
     num =recvfrom(socketfd,&recvbuf,sizeof(recvbuf),,(struct sockaddr *)&client,&addrlen);
     choice = recvbuf.command;
     if(choice == DOWNLOAD){
         char buf[];
         int fd;
         fd = open((recvbuf.buf),O_RDONLY);
         if(fd <){
             sentbuf.command = NO;
             sendto(socketfd,&sentbuf,sizeof(sentbuf),,(struct sockaddr *)&client,sizeof(client));
             printf("no such file!\n");
             exit();
         }
         else{
             sentbuf.command = YES;
             sendto(socketfd,&sentbuf,sizeof(sentbuf),,(struct sockaddr *)&client,sizeof(client));
             recvfrom(socketfd,&recvbuf,sizeof(recvbuf),,(struct sockaddr *)&client,&addrlen);
             if(recvbuf.command == START){
                 int no =;
                 while((num = read(fd,sentbuf.buf,INFOLEN)) >){
                     sentbuf.no = no;
                     sentbuf.command = CONTENT;
                     sentbuf.len = strlen(sentbuf.buf);
                     sendto(socketfd,&sentbuf,sizeof(sentbuf),,(struct sockaddr *)&client,sizeof(client));
                     no++;
                     bzero(&sentbuf,sizeof(sentbuf));
                 }
                 bzero(&sentbuf,sizeof(sentbuf));
                 sentbuf.command = END;
                 sendto(socketfd,&sentbuf,sizeof(sentbuf),,(struct sockaddr *)&client,sizeof(client));
             }
         }
     }
     else if(choice == UPLOAD){
         int fd1= open(recvbuf.buf,O_RDONLY);
         if (fd1 < ){
             sentbuf.command = START;
         }
         else{
             sentbuf.command = NO;
         }
         close(fd1);
         sendto(socketfd,&sentbuf,sizeof(sentbuf),,(struct sockaddr *)&client,sizeof(client));
         if(sentbuf.command ==START){
             int no =;
             int fd =open(recvbuf.buf,O_CREAT | O_TRUNC |O_WRONLY,);
             if(fd < ){
                 perror("create file error\n");
                 exit();
             }
             bzero(&recvbuf,sizeof(recvbuf));
             while((num = recvfrom(socketfd,&recvbuf,sizeof(recvbuf),,(struct sockaddr *)&server,&addrlen)) >){
                 if(recvbuf.command == CONTENT){
                     if(no == recvbuf.no){
                     write(fd,recvbuf.buf,recvbuf.len);
                     //printf("kkk%s\n",recvbuf.buf );
                     bzero(&recvbuf,sizeof(recvbuf));
                 }
                 else{
                     perror("The file no is not same.Some message is missed! error occured! \n");
                     break;
                 }
                 }
                 if(recvbuf.command == END){
                     close(fd);
                     printf("transmission is successful!\n");
                     break;
                 }
             }
         }
         else if(sentbuf.command == NO){
             printf("Not to trans the file\n");
             printf("The file is exist!\n");
         }
         else{
             perror("error! wrong choice!\n");
             exit();
         }

     }
     else if (recvbuf.command == SHUTDOWN){
         printf("Now the server is shutdown!\n");
         break;
     }
 }

     /*----------------------close ----------*/
     close(socketfd);
     return ;
 }

4.makefile文件；

 main:udpserver.o udpclient.o
     gcc -o udpserver udpserver.o
     gcc -o udpclient udpclient.o
 udpserver.o:udpserver.c protocol.h
     gcc -c udpserver.c
 udpclient.o: udpclient.c protocol.h
     gcc -c udpclient.c
 clean:
     rm -rf *.o

代码写的挺烂的，里面有很多重复的代码和功能，完全可以抽取出来做成一个函数的。以后慢慢再改吧。先完成功能，把上机考试过了再说。