#include<sys/types.h>

#include<sys/socket.h>

#include<sys/ioctl.h>

#include<netinet/in.h>

#include<unistd.h>

#include<stdio.h>



#include″tftpdfunc.h″



#define PACKSIZE BLOCKSIZE+4



struct bf{

  int counter;   /*數據緩沖區的長度或是標志*/

  char buf[PACKSIZE];   /*數據緩沖區*/

}buffers[2];



/*bf.counter的標志*/

#define BF_ALLOC-3    /*bf.buf已被分配，但尚未填入數據*/

#define BF_FREE  -2    /*bf.buf尚未被分配*/



static int next; /*下一個可用緩沖區*/

static int current;   /*當前正在使用的緩沖區*/



/*用于轉換文件傳輸格式的兩個變量*/

int newline=0;

int prevchar=-1;   /*前一個字符*/



void read_block(FILE*file,int convert);

int write_block(FILE*file,int convert);

struct tftphdr*rwrite_init(int);



struct tftphdr *write_init(void){return rwrite_init(0);}

struct tftphdr *read_init(void){return rwrite_init(1);}



struct tftpdr*

rwrite_init(int x)

{

  newline=0;

  prevchar=-1;

  buffers[0].counter=BF_ALLOC;   /*分配第一塊緩沖區*/

  current=0;

  buffers[1].counter=BF_FREE;

  next=x;

  return (struct tftphdr*)buffers[0].buf;

}



int my_read(FILE*file,struct tftphdr **dpp,

	    int convert/*convert值為1，需轉換成netascii碼*/)

{

  struct bf *b;

  

  buffers[current].counter=BF_FREE;

  current=!current;

  

  b=&buffers[current];

  if(b->counter==BF_FREE)   /*緩沖區空*/

    read_block(file.convert);

  

  dpp=(struct tftphdr)b->buf;

  return b->counter;

}



void read_block(FILE*file,int convert   /*值為1， 需轉換成ascii碼*/)

{

  int i;

  char *p;

  int c;

  struct bf *b;

  struct tftphdr *dp;

  

  b=&buffers[next];

  if(b->counter !=BF_FREE)

    return;

	next=!next;

	

	dp=(struct tftpdr*)b->buf;

	

	if(convert ==0){    /*直接以二進制碼讀出，不需轉換，直接讀出*/

	  b->counter=read(fileno(file),dp->th_data,BLOCKSIZE);

	  return;

	}

	/*需轉換成ascii碼，逐個讀出字符并處理行尾的換行符*/

	p=dp->th_data;

	for(i=0;i<BLOCKSIZE;i++){

	  if (newline){

	    if(prevchar==′\n′)

	      c=′\n′;

	    else  c=′\0′;

	    newline=0;

	  }

	  else{

	    c=getc(file);

	    if(c==EOF)break;

	    if(c==′\n′||c==′\r′){

	      prevchar=c;

	      c=′\r′;

	      newline=1;

	    }

	  }

	  *p++=c;

	}

	b->counter=(int)(p-dp->th_data);

}





int my_write(FILE*file,struct tftphdr** dpp,int ct, int convert)

{

  buffers[current].counter=ct;    /*數據塊的長度*/

  current=!current;

  if(buffers[current].counter!=BF_FREE)/*有數據*/

    write_block(file,convert);   /*寫入數據，刷新緩沖區*/

  buffers[current].counter=BF_ALLOC; /*標志該緩沖區已分配*/

  *dpp=(struct tftphdr)buffers[current].buf;

  return ct;

}



int write_block(FILE*file,int convert)

{

  char*buf;

  int count;

  int ct;

  char*p;

  int c;  /*當前讀出的字符*/

  struct bf*b;

  struct tftphdr*dp;



  b=&buffers[next];

  if(b->counte <-1)      /*數據塊長度*/

  b->counter=BF_FREE;

  dp=(struct tftphdr*)b->buf;

  next=!next;

  140	buf=dp->th_data;

  

  if(count<0)

    return-1;

  if(convert==0)/*不需轉換*/

    return= write(fileno(file);buf, count);

  

  p=buf;

  ct=count;

  while(ct--)

  c=*p++;

  if(prevchar==′\r′)

    if(c==′\n′)   /*回車后是換行*/

      fseek(file ,-1,1);

    else

      if(c==′\0′)   /*回車后是空字符*/

	goto   skipit;   /*空字符不寫入文件*/

  putc(c,file);

  skipit;

  prevchar=c;



  return count;

}



int synch(int f/*套接字*/)

{

  int i,j=0;

  char rbuf[PACKSIZE];

  struct sockaddr_in from;

  size_t fromlen;

  

while(1){

  (void) ioctl(f,FIONREAD,&i);

  if(i){

    j++;

    fromlen=sizeof from;

    (void)recvfrom(f,rbuf,sizeof(rbuf),0,

		   (struct sockaddr*)&from,&fromlen);

  }else{

    return(j);

  }

}