ipmux.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 "../port/lib.h"
#include "mem.h"
#include "dat.h"
#include "fns.h"
#include "../port/error.h"

#include "ip.h"
#define DPRINT if(0)print

typedef struct Ipmuxrock  Ipmuxrock;
typedef struct Ipmux      Ipmux;
typedef struct Ip4hdr     Ip4hdr;
typedef struct Ip6hdr     Ip6hdr;

enum
{
	IPHDR		= 20,		/* sizeof(Ip4hdr) */
};

struct Ip4hdr
{
	uchar	vihl;		/* Version and header length */
	uchar	tos;		/* Type of service */
	uchar	length[2];	/* packet length */
	uchar	id[2];		/* ip->identification */
	uchar	frag[2];	/* Fragment information */
	uchar	ttl;		/* Time to live */
	uchar	proto;		/* Protocol */
	uchar	cksum[2];	/* Header checksum */
	uchar	src[4];		/* IP source */
	uchar	dst[4];		/* IP destination */
	uchar	data[1];	/* start of data */
};
Ip4hdr *ipoff = 0;

struct Ip6hdr
{
	uchar vcf[4];		/* version, class label, and flow label */ 
	uchar ploadlen[2];	/* payload length */
	uchar proto;		/* next header, i.e. proto */
	uchar ttl;		/* hop limit, i.e. ttl */
	uchar src[16];		/* IP source */
	uchar dst[16];		/* IP destination */
};


enum
{
	Tproto,
	Tdata,
	Tiph,
	Tdst,
	Tsrc,
	Tifc,

	Cother = 0,
	Cbyte,		/* single byte */
	Cmbyte,		/* single byte with mask */
	Cshort,		/* single short */
	Cmshort,	/* single short with mask */
	Clong,		/* single long */
	Cmlong,		/* single long with mask */
	Cifc,
	Cmifc,
};

char *ftname[] = 
{
[Tproto]	"proto",
[Tdata]		"data",
[Tiph]	 	"iph",
[Tdst]		"dst",
[Tsrc]		"src",
[Tifc]		"ifc",
};

/*
 *  a node in the decision tree
 */
struct Ipmux
{
	Ipmux	*yes;
	Ipmux	*no;
	uchar	type;		/* type of field(Txxxx) */
	uchar	ctype;		/* tupe of comparison(Cxxxx) */
	uchar	len;		/* length in bytes of item to compare */
	uchar	n;		/* number of items val points to */
	short	off;		/* offset of comparison */
	short	eoff;		/* end offset of comparison */
	uchar	skiphdr;	/* should offset start after ipheader */
	uchar	*val;
	uchar	*mask;
	uchar	*e;		/* val+n*len*/

	int	ref;		/* so we can garbage collect */
	Conv	*conv;
};

/*
 *  someplace to hold per conversation data
 */
struct Ipmuxrock
{
	Ipmux	*chain;
};

static int	ipmuxsprint(Ipmux*, int, char*, int);
static void	ipmuxkick(void *x);

static char*
skipwhite(char *p)
{
	while(*p == ' ' || *p == '\t')
		p++;
	return p;
}

static char*
follows(char *p, char c)
{
	char *f;

	f = strchr(p, c);
	if(f == nil)
		return nil;
	*f++ = 0;
	f = skipwhite(f);
	if(*f == 0)
		return nil;
	return f;
}

static Ipmux*
parseop(char **pp)
{
	char *p = *pp;
	int type, off, end, len;
	Ipmux *f;

	p = skipwhite(p);
	if(strncmp(p, "dst", 3) == 0){
		type = Tdst;
		off = (ulong)(ipoff->dst);
		len = IPv4addrlen;
		p += 3;
	}
	else if(strncmp(p, "src", 3) == 0){
		type = Tsrc;
		off = (ulong)(ipoff->src);
		len = IPv4addrlen;
		p += 3;
	}
	else if(strncmp(p, "ifc", 3) == 0){
		type = Tifc;
		off = -IPv4addrlen;
		len = IPv4addrlen;
		p += 3;
	}
	else if(strncmp(p, "proto", 5) == 0){
		type = Tproto;
		off = (ulong)&(ipoff->proto);
		len = 1;
		p += 5;
	}
	else if(strncmp(p, "data", 4) == 0 || strncmp(p, "iph", 3) == 0){
		if(strncmp(p, "data", 4) == 0) {
			type = Tdata;
			p += 4;
		}
		else {
			type = Tiph;
			p += 3;
		}
		p = skipwhite(p);
		if(*p != '[')
			return nil;
		p++;
		off = strtoul(p, &p, 0);
		if(off < 0 || off > (64-IPHDR))
			return nil;
		p = skipwhite(p);
		if(*p != ':')
			end = off;
		else {
			p++;
			p = skipwhite(p);
			end = strtoul(p, &p, 0);
			if(end < off)
				return nil;
			p = skipwhite(p);
		}
		if(*p != ']')
			return nil;
		p++;
		len = end - off + 1;
	}
	else
		return nil;

	f = smalloc(sizeof(*f));
	f->type = type;
	f->len = len;
	f->off = off;
	f->val = nil;
	f->mask = nil;
	f->n = 1;
	f->ref = 1;
	if(type == Tdata)
		f->skiphdr = 1;
	else
		f->skiphdr = 0;

	return f;	
}

static int
htoi(char x)
{
	if(x >= '0' && x <= '9')
		x -= '0';
	else if(x >= 'a' && x <= 'f')
		x -= 'a' - 10;
	else if(x >= 'A' && x <= 'F')
		x -= 'A' - 10;
	else
		x = 0;
	return x;
}

static int
hextoi(char *p)
{
	return (htoi(p[0])<<4) | htoi(p[1]);
}

static void
parseval(uchar *v, char *p, int len)
{
	while(*p && len-- > 0){
		*v++ = hextoi(p);
		p += 2;
	}
}

static Ipmux*
parsemux(char *p)
{
	int n, nomask;
	Ipmux *f;
	char *val;
	char *mask;
	char *vals[20];
	uchar *v;

	/* parse operand */
	f = parseop(&p);
	if(f == nil)
		return nil;

	/* find value */
	val = follows(p, '=');
	if(val == nil)
		goto parseerror;

	/* parse mask */
	mask = follows(p, '&');
	if(mask != nil){
		switch(f->type){
		case Tsrc:
		case Tdst:
		case Tifc:
			f->mask = smalloc(f->len);
			v4parseip(f->mask, mask);
			break;
		case Tdata:
		case Tiph:
			f->mask = smalloc(f->len);
			parseval(f->mask, mask, f->len);
			break;
		default:
			goto parseerror;
		}
		nomask = 0;
	} else {
		nomask = 1;
		f->mask = smalloc(f->len);
		memset(f->mask, 0xff, f->len);
	}

	/* parse vals */
	f->n = getfields(val, vals, sizeof(vals)/sizeof(char*), 1, "|");
	if(f->n == 0)
		goto parseerror;
	f->val = smalloc(f->n*f->len);
	v = f->val;
	for(n = 0; n < f->n; n++){
		switch(f->type){
		case Tsrc:
		case Tdst:
		case Tifc:
			v4parseip(v, vals[n]);
			break;
		case Tproto:
		case Tdata:
		case Tiph:
			parseval(v, vals[n], f->len);
			break;
		}
		v += f->len;
	}

	f->eoff = f->off + f->len;
	f->e = f->val + f->n*f->len;
	f->ctype = Cother;
	if(f->n == 1){
		switch(f->len){
		case 1:
			f->ctype = nomask ? Cbyte : Cmbyte;
			break;
		case 2:
			f->ctype = nomask ? Cshort : Cmshort;
			break;
		case 4:
			if(f->type == Tifc)
				f->ctype = nomask ? Cifc : Cmifc;
			else
				f->ctype = nomask ? Clong : Cmlong;
			break;
		}
	}
	return f;

parseerror:
	if(f->mask)
		free(f->mask);
	if(f->val)
		free(f->val);
	free(f);
	return nil;
}

/*
 *  Compare relative ordering of two ipmuxs.  This doesn't compare the
 *  values, just the fields being looked at.  
 *
 *  returns:	<0 if a is a more specific match
 *		 0 if a and b are matching on the same fields
 *		>0 if b is a more specific match
 */
static int
ipmuxcmp(Ipmux *a, Ipmux *b)
{
	int n;

	/* compare types, lesser ones are more important */
	n = a->type - b->type;
	if(n != 0)
		return n;

	/* compare offsets, call earlier ones more specific */
	n = (a->off+((int)a->skiphdr)*(ulong)ipoff->data) - 
		(b->off+((int)b->skiphdr)*(ulong)ipoff->data);
	if(n != 0)
		return n;

	/* compare match lengths, longer ones are more specific */
	n = b->len - a->len;
	if(n != 0)
		return n;

	/*
	 *  if we get here we have two entries matching
	 *  the same bytes of the record.  Now check
	 *  the mask for equality.  Longer masks are
	 *  more specific.
	 */
	if(a->mask != nil && b->mask == nil)
		return -1;
	if(a->mask == nil && b->mask != nil)
		return 1;
	if(a->mask != nil && b->mask != nil){
		n = memcmp(b->mask, a->mask, a->len);
		if(n != 0)
			return n;
	}
	return 0;
}

/*
 *  Compare the values of two ipmuxs.  We're assuming that ipmuxcmp
 *  returned 0 comparing them.
 */
static int
ipmuxvalcmp(Ipmux *a, Ipmux *b)
{
	int n;

	n = b->len*b->n - a->len*a->n;
	if(n != 0)
		return n;
	return memcmp(a->val, b->val, a->len*a->n);
} 

/*
 *  add onto an existing ipmux chain in the canonical comparison
 *  order
 */
static void
ipmuxchain(Ipmux **l, Ipmux *f)
{
	for(; *l; l = &(*l)->yes)
		if(ipmuxcmp(f, *l) < 0)
			break;
	f->yes = *l;
	*l = f;
}

/*
 *  copy a tree
 */
static Ipmux*
ipmuxcopy(Ipmux *f)
{
	Ipmux *nf;

	if(f == nil)
		return nil;
	nf = smalloc(sizeof *nf);