/* IP header conversion routines
 * Copyright 1991 Phil Karn, KA9Q
 */
#include "global.h"
#include "mbuf.h"
#include "ip.h"
#include "internet.h"
  
/* Convert IP header in host format to network mbuf
 * If cflag != 0, take checksum from structure,
 * otherwise compute it automatically.
 */
struct mbuf *
htonip(ip,data,cflag)
register struct ip *ip;
struct mbuf *data;
int cflag;
{
    int16 hdr_len;
    struct mbuf *bp;
    register char *cp;
    int16 fl_offs;
  
    hdr_len = IPLEN + ip->optlen;
    if(hdr_len > IPLEN + IP_MAXOPT)
        hdr_len = IPLEN + IP_MAXOPT;
    if((bp = pushdown(data,hdr_len)) == NULLBUF){
        free_p(data);
        return NULLBUF;
    }
    cp = bp->data;
  
    *cp++ = (ip->version << 4) | (hdr_len >> 2);
    *cp++ = ip->tos;
    cp = put16(cp,ip->length);
    cp = put16(cp,ip->id);
    fl_offs = ip->offset >> 3;
    if(ip->flags.congest)
        fl_offs |= 0x8000;
    if(ip->flags.df)
        fl_offs |= 0x4000;
    if(ip->flags.mf)
        fl_offs |= 0x2000;
  
    cp = put16(cp,fl_offs);
    *cp++ = ip->ttl;
    *cp++ = ip->protocol;
    if(cflag){
        /* Use checksum from host structure */
        cp = put16(cp,ip->checksum);
    } else {
        /* Clear checksum for later recalculation */
        *cp++ = 0;
        *cp++ = 0;
    }
    cp = put32(cp,ip->source);
    cp = put32(cp,ip->dest);
    if(ip->optlen != 0)
        memcpy(cp,ip->options,min(ip->optlen,IP_MAXOPT));
  
    /* If requested, recompute checksum and insert into header */
    if(!cflag)
        put16(&bp->data[10],cksum(NULLHEADER,bp,hdr_len));
  
    return bp;
}
/* Extract an IP header from mbuf */
int
ntohip(ip,bpp)
register struct ip *ip;
struct mbuf **bpp;
{
    int ihl;
    int16 fl_offs;
    char ipbuf[IPLEN];
  
    if(pullup(bpp,ipbuf,IPLEN) != IPLEN)
        return -1;
  
    ip->version = (ipbuf[0] >> 4) & 0xf;
    ip->tos = ipbuf[1];
    ip->length = get16(&ipbuf[2]);
    ip->id = get16(&ipbuf[4]);
    fl_offs = get16(&ipbuf[6]);
    ip->offset = (fl_offs & 0x1fff) << 3;
    ip->flags.mf = (fl_offs & 0x2000) ? 1 : 0;
    ip->flags.df = (fl_offs & 0x4000) ? 1 : 0;
    ip->flags.congest = (fl_offs & 0x8000) ? 1 : 0;
    ip->ttl = ipbuf[8];
    ip->protocol = ipbuf[9];
    ip->checksum = get16(&ipbuf[10]);
    ip->source = get32(&ipbuf[12]);
    ip->dest = get32(&ipbuf[16]);
  
    ihl = (ipbuf[0] & 0xf) << 2;
    if(ihl < IPLEN){
        /* Bogus packet; header is too short */
        ip->optlen = 0;
        return -1;
    }
    if ( (ip->optlen = ihl - IPLEN) != 0 ) {
        if ( pullup(bpp,ip->options,ip->optlen) < ip->optlen )
            return -1;
    }
    return ihl;
}
/* Perform end-around-carry adjustment */
int16
eac(sum)
register int32 sum; /* Carries in high order 16 bits */
{
    register int16 csum;
  
    while((csum = sum >> 16) != 0)
        sum = csum + (sum & 0xffffL);
    return (int16) (sum & 0xffffl); /* Chops to 16 bits */
}
/* Checksum a mbuf chain, with optional pseudo-header */
int16
cksum(ph,m,len)
struct pseudo_header *ph;
register struct mbuf *m;
int16 len;
{
    register int16 cnt, total;
    register int32 sum, csum;
    register char *up;
    int16 csum1;
    int swap = 0;
  
    sum = 0l;
  
    /* Sum pseudo-header, if present */
    if(ph != NULLHEADER){
        sum = hiword(ph->source);
        sum += loword(ph->source);
        sum += hiword(ph->dest);
        sum += loword(ph->dest);
        sum += uchar(ph->protocol);
        sum += ph->length;
    }
    /* Now do each mbuf on the chain */
    for(total = 0; m != NULLBUF && total < len; m = m->next) {
        cnt = min(m->cnt, len - total);
        up = (char *)m->data;
        csum = 0;
  
        if(((long)up) & 1){
            /* Handle odd leading byte */
            if(swap)
                csum = uchar(*up++);
            else
                csum = (int16)(uchar(*up++) << 8);
            cnt--;
            swap = !swap;
        }
        if(cnt > 1){
            /* Have the primitive checksumming routine do most of
             * the work. At this point, up is guaranteed to be on
             * a short boundary
             */
            csum1 = lcsum((unsigned short *)up, (int16)(cnt >> 1));
            if(swap)
                csum1 = (csum1 << 8) | (csum1 >> 8);
            csum += csum1;
        }
        /* Handle odd trailing byte */
        if(cnt & 1){
            if(swap)
                csum += uchar(up[--cnt]);
            else
                csum += (int16)(uchar(up[--cnt]) << 8);
            swap = !swap;
        }
        sum += csum;
        total += m->cnt;
    }
    /* Do final end-around carry, complement and return */
    return (int16)(~eac(sum) & 0xffff);
}
  
