首先对文件按内容分块（有块大小的约束），然后对于每个chunk构造单独的一个UDP 数据报进行传输，在应用层的开始是自定义的包头，有块号，块长度，块指纹等元数据信息，这些信息便于接收端能够按序正确接收。

/*--vonzhou
 ---this project is to upload file after chunking using 
    rabin fingerprint, here use UDP so that every packet nodelay.
    but we need to ensure the reliability.

*/

#include "global.h"

#define SERV_PORT 2500

typedef struct {
        unsigned char fp[20];
        int chunk_id;
        short flags;
        short chunk_len; // The max is 32767 enough
        char data[MAX_CHUNK_SIZE];
}TransferUnit;

// some flags for this chunk transfered.
enum{
        CHUNK_NEED_DEDU = 0x0001,   // need deduplication
        CHUNK_OTHER = 0x0002      // other for extension
};

FileInfo *fi;

int sendUDP(FileInfo *fi,int sockfd,struct sockaddr *pservaddr,socklen_t servlen){
    char buf[sizeof(TransferUnit)];
    fd_set wrset;
    struct timeval tv;
    int rlen,wlen, len = 1;
    int fd;
    int ret;
    int i,j;
    FingerChunk *p;
    TransferUnit unit;

    //connect to server
    if(connect(sockfd,(struct sockaddr *)pservaddr,servlen) == -1)
        err_quit("connet error");
    else
        printf("connect server ok!\n");

    fd = open(fi->file_path, O_RDONLY);
    if(fd==-1)
        err_quit("fopen error %s\n",strerror(errno));

    // begin to transfer the file to the server;            
    i=0;
    p = fi->first;

    while(1){
        tv.tv_sec = 1;// tell select to wait 1 second;
        tv.tv_usec = 0;

        FD_ZERO(&wrset);
        FD_SET(sockfd,&wrset);
        // wait for the socket can write        
        ret = select(sockfd+1,NULL,&wrset,NULL,&tv);
        if(ret == -1)
            err_quit("select error %s\n",strerror(errno));
        else if(ret==0){
            printf("select timeout,continue circle\n");
            continue;
        }

        //prepare for writing the socket        
        memset(&unit, 0, sizeof(unit));
        if(FD_ISSET(sockfd,&wrset)){
            /* we should first transfer some medadata,like filename,filter feature vector,
            *FIXME: file fingerprint to controller? to make a packetin,
            *here just let the fp = 20 1s
            */
            if(i == 0){
                for(j=0;j<20;j++)
                    unit.fp[j] = 0xff;
                unit.chunk_id = 0;
                //need not dedu
                unit.chunk_len = strlen(fi->file_path);
                wlen = write(sockfd, &unit, 28 + strlen(fi->file_path));
                if(wlen != (28 + strlen(fi->file_path)))
                     err_quit("write data to sockfd error:%s\n",strerror(errno));
                memset(&unit, 0, sizeof(unit));
            }

            if(p != NULL)
                len = p->chunklen;
            // the last read , p is null, so cannnot use p->chu
            rlen = read(fd, unit.data, len);
            if(rlen < 0)
                err_quit("fread data error %s\n",strerror(errno));
            else if(rlen==0){
                //indicate the transfer completed
                for(j=0;j<20;j++)
                    unit.fp[j] = 0xff;
                unit.chunk_id = 0;
                //need not dedu
                unit.chunk_len = 3;
                strncpy(unit.data,"end", 3);
                wlen = write(sockfd,&unit,28 + 3);
                if(wlen !=31)
                    err_quit("write end flag error:%s\n",strerror(errno));

                printf("File %s Transfer Success!\n", fi->file_path);
                close(fd);
                return 0;
            }
            // construct this tranfer unit we cannot before read
            //bcos the following p pointer used.
            for(j=0; j< 20;j++)
                unit.fp[j] = p->chunk_hash[j];// 20B fingerprint;
            unit.chunk_id = i; // 4B chunk ID
            unit.chunk_len = p->chunklen;
            unit.flags = CHUNK_NEED_DEDU;
            //write to socket
            wlen = write(sockfd, &unit, 28+p->chunklen);
            if(wlen != (rlen + 28))
                err_quit("write data to sockfd error:%s\n",strerror(errno));

            i++;
            p = p->next;
            memset(&unit, 0, sizeof(unit));
            usleep(500);
            printf("The %d times read\n",i);
        }
    }// end while(1)
}


int main(int argc ,char *argv[])
{
        char *fh;
        struct sysinfo s_info;
        long time1,time2;
        int error1,error2;
        int sockfd;
        struct stat fsize;
        struct sockaddr_in servaddr;
        error1= sysinfo(&s_info);
        time1 = s_info.uptime;
        int r;
        //  FileInfo *fi;
        fi = file_new();

        if(argc != 3)
        err_quit("useage:udpclient<IPaddress>;\n");
        bzero(&servaddr,sizeof(servaddr));
        servaddr.sin_family= AF_INET;
        servaddr.sin_port = htons(SERV_PORT);

        if(inet_pton(AF_INET,argv[1],&servaddr.sin_addr) <= 0)
            err_quit("[%s]is not a valid IPaddress\n",argv[1]);

        sockfd =socket(AF_INET,SOCK_DGRAM,0);

        r = fcntl(sockfd, F_GETFL, 0);
        fcntl(sockfd, F_SETFL, r & ~O_NONBLOCK);

        // chunking file 
        strcpy(fi->file_path, argv[2]);
        chunk_file(fi);
        printf("File size : %lld\n",fi->file_size);
        printf("Chunk Num : %d\n",fi->chunknum);

        sendUDP(fi, sockfd, (struct sockaddr *)&servaddr,sizeof(servaddr));
        close(sockfd);

        fprintf(stderr,"ServerIP:\t%s\n",argv[1]);
        if(stat(argv[2],&fsize) == -1)
                perror("failed to get fiel statusi\n");
        else
                fprintf(stderr,"file name:\t%s\nfile size:\t%dK\n",argv[2],fsize.st_size/1024);
        error2=sysinfo(&s_info);
        time2 = s_info.uptime;
        printf("tranfice file time =%ld seconds\n",(time2-time1));
}