xref: /plan9/sys/src/cmd/ip/snoopy/hdlc.c (revision ed397113cdcf7aafea372b730bbcd17b05ee3f60)

#include <u.h>
#include <libc.h>
#include <ip.h>
#include "dat.h"
#include "protos.h"

enum {
	HDLC_frame=	0x7e,
	HDLC_esc=	0x7d,

	/* PPP frame fields */
	PPP_addr=	0xff,
	PPP_ctl=	0x3,
	PPP_initfcs=	0xffff,
	PPP_goodfcs=	0xf0b8,
};

/*
 * Calculate FCS - rfc 1331
 */
ushort fcstab[256] =
{
      0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
      0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
      0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
      0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
      0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
      0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
      0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
      0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
      0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
      0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
      0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
      0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
      0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
      0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
      0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
      0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
      0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
      0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
      0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
      0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
      0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
      0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
      0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
      0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
      0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
      0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
      0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
      0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
      0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
      0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
      0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
      0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
};

static uchar inbuf[16*1024];
static int inlen;

static Mux p_mux[] =
{
	{"ppp",		(PPP_addr<<8)|PPP_ctl,	} ,
	{0}
};

enum
{
	Ot = 1
};

static void
p_compile(Filter *f)
{
	Mux *m;

	for(m = p_mux; m->name != nil; m++)
		if(strcmp(f->s, m->name) == 0){
			f->pr = m->pr;
			f->ulv = m->val;
			f->subop = Ot;
			return;
		}
	sysfatal("unknown ethernet field or protocol: %s", f->s);
}

static int
p_filter(Filter *f, Msg *m)
{
	ulong t;

	if(m->pe-m->ps < 2)
		return 0;

	switch(f->subop){
	case Ot:
		t = (m->ps[0]<<8)|m->ps[1];
		if(t != f->ulv)
			return 0;
		break;
	}
	return 1;
}

static int
p_seprint(Msg *m)
{
	ulong t;

	if(m->pe-m->ps < 2)
		return -1;

	t = (m->ps[0]<<8)|m->ps[1];
	m->ps += 2;
	demux(p_mux, t, t, m, &dump);

	return 0;
}

static int
p_framer(int fd, uchar *pkt, int pktlen)
{
	ushort fcs;
	uchar *from, *efrom, *to, *eto;
	int n;
	ulong c;

	eto = pkt+pktlen;
	for(;;){
		efrom = memchr(inbuf, HDLC_frame, inlen);
		if(efrom == nil){
			if(inlen >= sizeof(inbuf))
				inlen = 0;
			n = read(fd, inbuf+inlen, sizeof(inbuf)-inlen);
			if(n <= 0)
				break;
			inlen += n;
			continue;
		}

		/* checksum and unescape the frame */
		fcs = PPP_initfcs;
		to = pkt;
		for(from = inbuf; from < efrom;){
			c = *from++;
			if(c == HDLC_esc)
				c = (*from++) ^ 0x20;
			if(to < eto)
				*to++ = c;
			fcs = (fcs >> 8) ^ fcstab[(fcs ^ c) & 0xff];
		}

		/* move down anything that's left */
		inlen -= efrom+1-inbuf;
		memmove(inbuf, efrom+1, inlen);

		/* accept if this is a good packet */
		if(fcs != PPP_goodfcs)
			print("bad frame %ld %2.2ux %2.2ux!\n", to-pkt, pkt[0], pkt[1]);
		else
			return to-pkt;
	}
	return -1;
}

Proto hdlc =
{
	"hdlc",
	p_compile,
	p_filter,
	p_seprint,
	p_mux,
	"%#.4lux",
	nil,
	p_framer,
};