【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[20];
    int port;
    int choice;
    char filename[100];
/*------------------------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,0)) == -1){
        perror("socket error
");
        exit(1);
    }

    /*-----------------IO-----------------------*/
    printf("Please input the ip:
");
    scanf("%s",ip);
    printf("Please input the port:
");
    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:
");
    scanf("%s",recvbuf.buf);
    recvbuf.len = strlen(recvbuf.buf);
    sendto(socketfd,&recvbuf,sizeof(recvbuf),0,(struct sockaddr *)&server,sizeof(server)); */


    while (1){
    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!
");
    }
} 

    /*-----------------close------------------------*/
    close(socketfd);
    return 0;
}


void ShowMenu(){
    printf("=====================================
");
    printf("         Please make a choice:       
");
    printf("         0:  ||shutdown||            
");
    printf("         1:  ||download||            
");
    printf("         2:  || upload ||            
");
    printf("=====================================
");
}
void DownLoad(){
    bzero(&recvbuf,sizeof(recvbuf));
    bzero(&sentbuf,sizeof(sentbuf));
    bzero(filename,sizeof(filename));
    printf("Please input the file name:
");
    scanf("%s",sentbuf.buf);
    sentbuf.command = DOWNLOAD;
    sendto(socketfd,&sentbuf,sizeof(sentbuf),0,(struct sockaddr *)&server,sizeof(server));
    bcopy(sentbuf.buf,filename,strlen(sentbuf.buf));
    recvfrom(socketfd,&recvbuf,sizeof(recvbuf),0,(struct sockaddr *)&server,&addrlen);
    if(recvbuf.command == YES){
        printf("YES!
");
        printf("Start  to transmission!
");
            sentbuf.command = START;
            sendto(socketfd,&sentbuf,sizeof(sentbuf),0,(struct sockaddr *)&server,sizeof(server));
            int no =0;
            int fd =open(filename,O_CREAT | O_TRUNC |O_WRONLY,0644);
            if(fd < 0){
                perror("create file error
");
                exit(1);
            }
            bzero(&recvbuf,sizeof(recvbuf));
            while((num = recvfrom(socketfd,&recvbuf,sizeof(recvbuf),0,(struct sockaddr *)&server,&addrlen)) >0){
                if(recvbuf.command == CONTENT){
                    if(no == recvbuf.no){
                    write(fd,recvbuf.buf,recvbuf.len);
                    //printf("kkk%s
",recvbuf.buf );
                    no++;
                    bzero(&recvbuf,sizeof(recvbuf));
                }
                else{
                    perror("The file no is not same.Some message is missed! error occured! 
");
                    break;
                }
                }
                if(recvbuf.command == END){
                    close(fd);
                    printf("transmission is successful!
");
                    break;
                }
            }
    }
    else if(recvbuf.command ==NO){
        perror("NO such file on server!
");
    }
    else{
        perror("recvbuf.command error
");
        exit(1);
    }
}
void UpLoad(){
    bzero(&recvbuf,sizeof(recvbuf));
    bzero(&sentbuf,sizeof(sentbuf));
    bzero(filename,sizeof(filename));
    printf("Please input the file name:
");
    scanf("%s",sentbuf.buf);
    sentbuf.command = UPLOAD;
    sendto(socketfd,&sentbuf,sizeof(sentbuf),0,(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 < 0){
        perror("The file you want to trans is not exist!
");
        exit(1);
    }
    recvfrom(socketfd,&recvbuf,sizeof(recvbuf),0,(struct sockaddr *)&server,&addrlen);
    if(recvbuf.command == START){
            int no =0;
            while((num = read(fd,sentbuf.buf,INFOLEN)) >0){
                sentbuf.no = no;
                sentbuf.command = CONTENT;
                sentbuf.len = strlen(sentbuf.buf);
                sendto(socketfd,&sentbuf,sizeof(sentbuf),0,(struct sockaddr *)&server,sizeof(server));
                no++;
                bzero(&sentbuf,sizeof(sentbuf));
            }
            bzero(&sentbuf,sizeof(sentbuf));
            sentbuf.command = END;
            sendto(socketfd,&sentbuf,sizeof(sentbuf),0,(struct sockaddr *)&server,sizeof(server));
    }
    else if(recvbuf.command == NO){
        printf("not transmission
");
        printf("The file is exist!
");
    }
    else {
        perror("error! wrong choice!
");
    }
}

void ShutDown(){
    printf("client is shutdown now!
");
    bzero(&sentbuf,sizeof(sentbuf));
    sentbuf.command == SHUTDOWN;
    sendto(socketfd,&sentbuf,sizeof(sentbuf),0,(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[20];
    int port;
    int choice;

int main(){

    /*-------------create UDP socket------------*/
    if((socketfd = socket(AF_INET,SOCK_DGRAM,0)) == -1){
        perror("socket error
");
        exit(1);
    }

    /*-----------------IO-----------------------*/
    printf("Please input the ip:
");
    scanf("%s",ip);
    printf("Please input the port:
");
    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)) == -1){
        perror("bind error
");
        exit(1);
    }

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

    addrlen = sizeof(client);
    while(1){
    bzero(&recvbuf,sizeof(recvbuf));
    num =recvfrom(socketfd,&recvbuf,sizeof(recvbuf),0,(struct sockaddr *)&client,&addrlen);
    choice = recvbuf.command;
    if(choice == DOWNLOAD){
        char buf[100];
        int fd;
        fd = open((recvbuf.buf),O_RDONLY);
        if(fd <0){
            sentbuf.command = NO;
            sendto(socketfd,&sentbuf,sizeof(sentbuf),0,(struct sockaddr *)&client,sizeof(client));
            printf("no such file!
");
            exit(1);
        }
        else{
            sentbuf.command = YES;
            sendto(socketfd,&sentbuf,sizeof(sentbuf),0,(struct sockaddr *)&client,sizeof(client));
            recvfrom(socketfd,&recvbuf,sizeof(recvbuf),0,(struct sockaddr *)&client,&addrlen);
            if(recvbuf.command == START){
                int no =0;
                while((num = read(fd,sentbuf.buf,INFOLEN)) >0){
                    sentbuf.no = no;
                    sentbuf.command = CONTENT;
                    sentbuf.len = strlen(sentbuf.buf);
                    sendto(socketfd,&sentbuf,sizeof(sentbuf),0,(struct sockaddr *)&client,sizeof(client));
                    no++;
                    bzero(&sentbuf,sizeof(sentbuf));
                }
                bzero(&sentbuf,sizeof(sentbuf));
                sentbuf.command = END;
                sendto(socketfd,&sentbuf,sizeof(sentbuf),0,(struct sockaddr *)&client,sizeof(client));
            }
        }
    }
    else if(choice == UPLOAD){
        int fd1= open(recvbuf.buf,O_RDONLY);
        if (fd1 < 0){
            sentbuf.command = START;
        }
        else{
            sentbuf.command = NO;
        }
        close(fd1);
        sendto(socketfd,&sentbuf,sizeof(sentbuf),0,(struct sockaddr *)&client,sizeof(client));
        if(sentbuf.command ==START){
            int no =0;
            int fd =open(recvbuf.buf,O_CREAT | O_TRUNC |O_WRONLY,0644);
            if(fd < 0){
                perror("create file error
");
                exit(1);
            }
            bzero(&recvbuf,sizeof(recvbuf));
            while((num = recvfrom(socketfd,&recvbuf,sizeof(recvbuf),0,(struct sockaddr *)&server,&addrlen)) >0){
                if(recvbuf.command == CONTENT){
                    if(no == recvbuf.no){
                    write(fd,recvbuf.buf,recvbuf.len);
                    //printf("kkk%s
",recvbuf.buf );
                    bzero(&recvbuf,sizeof(recvbuf));
                }
                else{
                    perror("The file no is not same.Some message is missed! error occured! 
");
                    break;
                }
                }
                if(recvbuf.command == END){
                    close(fd);
                    printf("transmission is successful!
");
                    break;
                }
            }
        }
        else if(sentbuf.command == NO){
            printf("Not to trans the file
");
            printf("The file is exist!
");
        }
        else{
            perror("error! wrong choice!
");
            exit(1);
        }

    }
    else if (recvbuf.command == SHUTDOWN){
        printf("Now the server is shutdown!
");
        break;
    }
}
    
    /*----------------------close ----------*/
    close(socketfd);
    return 0;
}

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。