* "DCP" a uucp clone. Copyright Richard H. Lamb 1985,1986,1987 */
/* original 1-window "g" protocol */
#include "dcp.h"
#define PKTSIZE         64
#define PKTSIZ2         2
#define HDRSIZE         6
#define MAXTRY			10

static int      pkrec,pksent;
/*<FF>*/
/******************SUB SUB SUB PACKET HANDLER************/
gclosepk()
{
char tmp[PKTSIZE];
gspack(1,0,0,0,tmp);
gspack(1,0,0,0,tmp);
return(0);
}

gopenpk()
{
int i,j,n1,n2,len;
char tmp[PKTSIZE];
pkrec=0; pksent=1;
pktsize=PKTSIZE;
msgtime=MSGTIME;
j=7;
gsta:
if(j == 4 ) return(0); /* if ok */
for(i=0;i<MAXTRY;i++)
{gspack(j,0,0,0,tmp); if(grpack(&n1,&n2,&len,tmp)==j) {j--; goto gsta;} }
return(-1); /* fail */
}

/*
 *
 * ggetpkt
 ***** description: Gets no more than a packet's worth of data from
****               the "packet i/o state machine". May have to
****               periodically run the pkt machine to get some
****               packets.
* on input: dont care   getpkt(data,&len)  char *data int len
* on return: data+\0 and length in len. ret(0) if alls well
* ret(-1) if problems.(fail)
 */
ggetpkt(data,len)
int *len;
char data[];
{
int npkrec,npksent,i,nlen;
char tmp[PKTSIZE];
for(i=0;i<MAXTRY;i++)
{
switch(grpack(&npkrec,&npksent,&nlen,data))
{
case 0: /*if(npksent != ((pkrec+1)%8)) {
                gspack(2,pkrec,0,0,tmp);
                if(debug > 0) printmsg(" send REJ %d ",pkrec);
                break;
        }    */
        pkrec = (pkrec+1)%8;
        *len = nlen;
        gspack(4,pkrec,0,0,tmp);
        return(0);
/*case 2:
        if(debug > 0) printmsg(" extra REJ %d ",npkrec);
        return(0);
case 4:
        if(debug > 0) printmsg(" extra RR %d ",npkrec);
        return(0);
case -1: gspack(4,pkrec,0,0,tmp);
        if(debug > 0) printmsg(" unknown rec packet - send ack ");
        break;
case -2: gspack(2,pkrec,0,0,tmp);
        if(debug > 0) printmsg(" send REJ %d ",pkrec);
        break;    */
default: break;
}
}
return(-1);
}
/*
 *
 *  sendpkt
 *
*****   description:    Put at most a packet's worth of data  in the pkt state
*****                   machine for xmission.
*****                   May have to run the pkt machine a few times to get
*****                   an available output slot.
 *
 * on input: char *data int len,flg; len=length of data in data.
 *           flg=2 just send the packet with no wait for ack.
 *           flg>0 zero out the unused part of the buffer. (for UUCP "msg"
 *                                                                   pkts)
 *           flg=0 normal data
 * return:   ret(0) if alls well ret(-1) if problems (fail)
 *
*/
gsendpkt(data,len,msg)
int len,msg;
char data[];
{
int nlen,npkrec,npksent,i;
char tmp[PKTSIZE];
if(msg) {len=PKTSIZE; for(i=strlen(data);i<len;i++) data[i] = '\0'; }
for(i=0;i<MAXTRY;i++)
{
gspack(0,pkrec,pksent,len,data); if(msg == 2) return(0);
switch(grpack(&npkrec,&npksent,&nlen,tmp))
{
case 4: /*if(npkrec != pksent) {
        if(debug > 0) printmsg(" wrong RR %d (%d) ",pksent,npkrec);
        break;
        }   */
        pksent = (1+pksent)%8;
        return(0);
/*case 2: if(debug > 0) printmsg(" REJ %d ",npkrec);
        break;
case 0: return(0);
case -1: break;  */
default: break;
}
}
return(-1);
}

/*<FF>*/
/*************** FRAMMING *****************************/
/*
 *
 *
 *      send a packet
 * nt2=type nt3=pkrec nt4=pksent len=length<=PKTSIZE cnt1= data * ret(0) always
 */
gspack(nt2,nt3,nt4,len,cnt1)
int nt2,nt3,nt4,len;
char cnt1[];
{
unsigned int check,i;
unsigned char c2,pkt[HDRSIZE];
if(len > 64) len = 64;
if(len == 0) cnt1[0] = '\0';
if(debug > 0) {
printmsg("send packet type %d",nt2);
printmsg("  num = %d n = %d",nt3,nt4);
printmsg("  len = %d data =\n|%s|",len,cnt1);
}
c2 = '\0';
pkt[0] = '\020';
pkt[4] = nt2<<3;
nt2 &= 7;
switch(nt2)
{
case 1:      break;                  /* stop protocol */
case 2:      pkt[4] += nt3; break;   /* reject        */
case 3:      break;
case 4:      pkt[4] += nt3; break;   /* ack          */
case 5:      pkt[4] += 3;   break;   /* 3 windows */
case 6:      pkt[4] += 1;   break;   /* pktsiz = 64 (1) */
case 7:      pkt[4] += 3;   break;   /* 3 windows */
case 0:      pkt[4] += 0x80 + nt3 + (nt4<<3);
                c2 = (PKTSIZE - len)&0xff;
                if(c2)
                {
                        pkt[4] += 0x40;   /* if len < PKTSIZE */
                        for(i=PKTSIZE-1;i>0;i--) cnt1[i]=cnt1[i-1];
                        cnt1[0]=c2;
                }
                break;
}
pkt[4] &= 0xff;
if(nt2)
{
        pkt[1] = 9;             /* control packet size = 0 (9) */
        check = (0xaaaa - pkt[4])&0xffff;
}
else
{
        pkt[1] = PKTSIZ2;             /* data packet size = 64 (2) */
        check = checksum(cnt1,PKTSIZE);
i = pkt[4];/* got to do this on PC for ex-or high bits */
i &= 0xff;
check = (check ^ i) & 0xffff;
        check = (0xaaaa - check) & 0xffff;
}
        pkt[2] = check & 0xff;
        pkt[3] = (check>>8) & 0xff;
        pkt[5] = (pkt[1]^pkt[2]^pkt[3]^pkt[4])&0xff;
        swrite(pkt,HDRSIZE);       /* header is 6-bytes long */
/*      write(flog,pkt,HDRSIZE);   */
        if(pkt[1] != 9) { swrite(cnt1,PKTSIZE);     /* data is always 64
bytes long */       /*    write(flog,cnt1,PKTSIZE);   */
}
}

/*<FF>*/
/*
 *
 *      read packet
 * on return: nt3=pkrec nt4=pksent len=length <=PKTSIZE  cnt1=data *
ret(type) ok; ret(-1) input buf empty; ret(-2) bad header;
 *              ret(-3) lost pkt timeout; ret(-4) checksum error;ret(-5) ?
 */
grpack(nt3,nt4,len,cnt1)
int *nt3,*nt4,*len;
char cnt1[];
{
unsigned int nt1,check,checkchk,i;
unsigned char c,c2,pkt[HDRSIZE];
int ii;
c = '\0';
while((c & 0x7f) != '\020') if(sread(&c,1,msgtime) < 1) return(-1);

if(sread(&pkt[1],HDRSIZE-1,msgtime) < (HDRSIZE-1)) return(-1);
/*write(flog,&c,1); write(flog,&pkt[1],HDRSIZE-1); */
/* header is 6-bytes long */
i = pkt[1]^pkt[2]^pkt[3]^pkt[4]^pkt[5];
i &= 0xff;
if(i)
{                        /*  bad header */
        printmsg("****bad header****");
      return(-2);
}
if((pkt[1] &=0x7f) == 9)
{       /* control packet */
        *len = 0;
        c = pkt[4] & 0xff;
        nt1  = c>>3;
        *nt3 = c & 7;
        *nt4 = 0;
        check = 0;
        checkchk = 0;
        cnt1[*len] = '\0';
}
else
{       /* data packet */
        if(pkt[1] != PKTSIZ2) return(-5);   /* cant handle other than 64*/
        nt1  = 0;
        c2 = pkt[4] & 0xff;
        c = c2&0x3f;
        *nt4 = c>>3;
        *nt3 = c & 7;
        if(sread(cnt1,PKTSIZE,msgtime) < PKTSIZE) return(-3);
/*        write(flog,cnt1,PKTSIZE);     */
        /* 64 byte packets even if partial */
i = pkt[3];
i = (i<<8)&0xff00;
check = pkt[2];
check = i|(check&0xff);
        checkchk = checksum(cnt1,PKTSIZE);
i = pkt[4]|0x80;
i &= 0xff;
        checkchk = 0xaaaa - (checkchk^i);
        checkchk &= 0xffff;
        if(checkchk != check) {
                printmsg("***checksum error***");
                return(-4);
        }
        *len = PKTSIZE;
        if(c2&0x40)
        {
                ii = (cnt1[0]&0xff);
                *len = (*len-ii)&0xff;
                for(ii=0;ii<*len;ii++) cnt1[ii] = cnt1[ii+1];
        }
        cnt1[*len] = '\0';
}
if(debug > 0) {
        printmsg("receive packet type %d ",nt1);
        printmsg("  num = %d n = %d",*nt3,*nt4);
        printmsg("  checksum rec = %x comp = %x",check,checkchk);
        printmsg("  len = %d data =\n|%s|",*len,cnt1);
}
        ii = nt1;
        return(ii);
}

unsigned checksum(data,len)
int len;
char data[];
{
unsigned int i,j,tmp,chk1,chk2;
chk1 = 0xffff;
chk2 = 0;
j = len;
for(i=0;i<len;i++)
{
        if(chk1&0x8000) { chk1 <<= 1; chk1++; }
        else { chk1 <<= 1; }
        tmp = chk1;
        chk1 += (data[i]&0xff);
        chk2 += chk1^j;
        if((chk1&0xffff) <= (tmp&0xffff)) chk1 ^= chk2;
        j--;
}
return(chk1&0xffff);
}