static u08 ip_receive_packet( ip_header * p, u16 len )
{
// log_printf( "ip: got ip packet, proto=%d\n", p->proto );
if (!__ip_validate_header( p ))
{
log_printf( "ip: bad ip checksum\n" );
return 1;
}
switch( p->proto )
{
case IPPROTO_ICMP: return icmp_receive_packet( p, len );
case IPPROTO_UDP: return udp_receive_packet( p, len );
case IPPROTO_TCP: return tcp_receive_packet( p, len );
}
return 1; // did we eat it? yes we did...
}
int32 udp_receive (DEVICE *dptr, int32 link, uint16 *pdata, uint16 maxbuf)
{
// Receive an IMP packet from the virtual modem. pdata is a pointer usually
// directly into H316 simulated memory) to where the IMP packet data should
// be stored, and maxbuf is the maximum length of that buffer in H316 words
// (not bytes!). If a message is successfully received then this routine
// returns the length, again in H316 words, of the IMP packet. The caller
// can detect buffer overflows by comparing this result to maxbuf. If no
// packets are waiting right now then zero is returned, and -1 is returned
// in the event of any fatal socket I/O error.
//
// This routine also handles checking for unsolicited messages and duplicate
// or out of sequence messages. All of these are unceremoniously discarded.
//
// One final note - it's explicitly allowed for pdata to be null and/or
// maxbuf to be zero. In either case the received package is discarded, but
// the actual length of the discarded package is still returned.
UDP_PACKET pkt; int32 pktlen, explen, implen, i; uint32 magic, pktseq;
if ((link < 0) || (link >= MAXLINKS)) return SCPE_IERR;
if (!udp_links[link].used) return SCPE_IERR;
while ((pktlen = udp_receive_packet(link, &pkt)) > 0) {
// First do some header checks for a valid UDP packet ...
if (pktlen < UDP_HEADER_LEN) {
sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet w/o header (length=%d)\n", link, pktlen);
continue;
}
magic = ntohl(pkt.magic);
if (magic != MAGIC) {
sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet w/bad magic number (magic=%08x)\n", link, magic);
continue;
}
implen = ntohs(pkt.count);
explen = UDP_HEADER_LEN + implen*sizeof(uint16);
if (explen != pktlen) {
sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet length wrong (expected=%d received=%d)\n", link, explen, pktlen);
continue;
}
// Now the hard part = check the sequence number. The rxsequence value is
// the number of the next packet we expect to receive - that's the number
// this packet should have. If this packet's sequence is less than that,
// then this packet is out of order or a duplicate and we discard it. If
// this packet is greater than that, then we must have missed one or two
// packets. In that case we MUST update rxsequence to match this one;
// otherwise the two ends could never resynchronize after a lost packet.
pktseq = ntohl(pkt.sequence);
if (pktseq < udp_links[link].rxsequence) {
sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet out of sequence 1 (expected=%d received=%d\n", link, udp_links[link].rxsequence, pktseq);
continue;
}
if (pktseq != udp_links[link].rxsequence) {
sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet out of sequence 2 (expected=%d received=%d\n", link, udp_links[link].rxsequence, pktseq);
}
udp_links[link].rxsequence = pktseq+1;
// It's a valid packet - if there's no buffer then just discard it.
if ((pdata == NULL) || (maxbuf == 0)) {
sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet discarded (no buffer available)\n", link);
return implen;
}
// Copy the data to the H316 memory and we're done!
sim_debug(IMP_DBG_UDP, dptr, "link %d - packet received (sequence=%d, length=%d)\n", link, pktseq, pktlen);
for (i = 0; i < (implen < maxbuf ? implen : maxbuf); ++i)
*pdata++ = ntohs(pkt.data[i]);
return implen;
}
// Here if pktlen <= 0 ...
return pktlen;
}
int udp_receive (int link, uint8_t * pdata, uint16_t maxbuf)
{
// Receive an packet from the virtual modem. pdata is a pointer to where
// the IMP packet data should be stored, and maxbuf is the maximum length
// of that buffer in bytes. If a message is
// successfully received then this routine returns the length, again in
// bytes, of the packet. The caller can detect buffer overflows by
// comparing this result to maxbuf. If no packets are waiting right now
// then zero is returned, and -1 is returned in the event of any fatal
// socket I/O error.
//
// This routine also handles checking for unsolicited messages and
// duplicate or out of sequence messages. All of these are
// unceremoniously discarded.
//
// One final note - it's explicitly allowed for pdata to be null and/or
// maxbuf to be zero. In either case the received package is discarded, but
// the actual length of the discarded package is still returned.
UDP_PACKET pkt;
int32_t pktlen, explen, implen, i;
uint32_t magic, pktseq;
if ((link < 0) || (link >= MAXLINKS))
return -1;
if (!udp_links [link] . used)
return -1;
//if (dptr != udp_links [link] . dptr)
//return SCPE_IERR;
while ((pktlen = udp_receive_packet (link, & pkt, sizeof (pkt))) > 0)
{
// First do some header checks for a valid UDP packet ...
if (((size_t) pktlen) < UDP_HEADER_LEN)
{
//sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet w/o header (length=%d)\n", link, pktlen);
continue;
}
magic = pkt . magic;
if (magic != MAGIC)
{
//sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet w/bad magic number (magic=%08x)\n", link, magic);
continue;
}
implen = pkt . count;
explen = UDP_HEADER_LEN + implen * sizeof (uint8_t);
if (explen != pktlen)
{
//sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet length wrong (expected=%d received=%d)\n", link, explen, pktlen);
continue;
}
// Now the hard part = check the sequence number. The rxsequence value
// is the number of the next packet we expect to receive - that's the
// number this packet should have. If this packet's sequence is less
// than that, then this packet is out of order or a duplicate and we
// discard it. If this packet is greater than that, then we must have
// missed one or two packets. In that case we MUST update rxsequence
// to match this one; otherwise the two ends could never resynchronize
// after a lost packet./ And there's one final complication to worry
// about - if the simh on the other end is restarted for some reason,
// then his sequence numbers will reset to zero. In that case we'll
// never recover synchronization without special efforts. The hack is
// to check for a packet sequence number of zero and, if we find it,
// force synchronization. This improves the situation, but I freely
// admit that it's possible to think of a number of cases where this
// also fails. The only absolute solution is to implement a more
// complicated system with non-IMP control messages exchanged between
// the modem emulation on both ends. That'd be nice, but I'll leave it
// as an exercise for later.
pktseq = pkt . sequence;
if ((pktseq == 0) && (udp_links [link] . rxsequence != 0))
{
//sim_debug(IMP_DBG_UDP, dptr, "link %d - remote modem restarted\n", link);
}
else if (pktseq < udp_links [link] . rxsequence)
{
//sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet out of sequence 1 (expected=%d received=%d\n", link, udp_links[link].rxsequence, pktseq);
continue; // discard this packet!
}
else if (pktseq != udp_links [link] . rxsequence)
{
//sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet out of sequence 2 (expected=%d received=%d\n", link, udp_links[link].rxsequence, pktseq);
}
udp_links [link] . rxsequence = pktseq + 1;
// It's a valid packet - if there's no buffer then just discard it.
if ((pdata == NULL) || (maxbuf == 0))
{
//sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet discarded (no buffer available)\n", link);
return implen;
}
// Copy the data and we're done!
//sim_debug (IMP_DBG_UDP, dptr, "link %d - packet received (sequence=%d, length=%d)\n", link, pktseq, pktlen);
printf ("link %d - packet received (sequence=%d, length=%d)\n", link, pktseq, pktlen);
for (i = 0; i < (implen < maxbuf ? implen : maxbuf); ++ i)
* pdata ++ = pkt . data [i];
return implen;
}
// Here if pktlen <= 0 ...
return pktlen;
}
