eapol.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

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

typedef struct Hdr	Hdr;
struct Hdr
{
	uchar	vi;		/* version */
	uchar	type;
	uchar	len[2];	/* length of data following this header */
};

enum
{
	EAPOLHDR=	4,		/* sizeof(Hdr) */

	/* eapol types */
	Eap = 0,
	Start,
	Logoff,
	Key,
	AsfAlert,
};

enum
{
	Ot,	/* type */
};

static Mux p_mux[] =
{
	{ "eap", Eap, },
	{ "eapol_start", Start, },
	{ "eapol_logoff", Logoff, },
	{ "eapol_key", Key, },
	{ "asf_alert", AsfAlert, },
	{ 0 }
};

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 eapol field or type: %s", f->s);
}

static int
p_filter(Filter *f, Msg *m)
{
	Hdr *h;

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

	h = (Hdr*)m->ps;

	/* len does not include header */
	m->ps += EAPOLHDR;

	switch(f->subop){
	case Ot:
		return h->type == f->ulv;
	}
	return 0;
}

static char*
op(int i)
{
	static char x[20];

	switch(i){
	case Eap:
		return "Eap";
	case Start:
		return "Start";
	case Logoff:
		return "Logoff";
	case Key:
		return "Key";
	case AsfAlert:
		return "AsfAlert";
	default:
		sprint(x, "%1d", i);
		return x;
	}
}

static int
p_seprint(Msg *m)
{
	Hdr *h;
	int len;

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

	h = (Hdr*)m->ps;

	/* len does not include header */
	m->ps += EAPOLHDR;

	/* truncate the message if there's extra */
	len = NetS(h->len);
	if(m->ps + len < m->pe)
		m->pe = m->ps + len;
	else if(m->ps+len > m->pe)
		return -1;

	/* next protocol  depending on type*/
	demux(p_mux, h->type, h->type, m, &dump);

	m->p = seprint(m->p, m->e, "type=%s version=%1d datalen=%1d",
			op(h->type), h->vi, len);
	return 0;
}

Proto eapol =
{
	"eapol",
	p_compile,
	p_filter,
	p_seprint,
	p_mux,
	"%lud",
	nil,
	defaultframer,
};