domain.c

早期freebsd实现

		int c = *host++;

		if (isascii(c) && isupper(c))
			c = tolower(c);
		hfunc = ((hfunc << 1) ^ c) % 2003;
	}

	hfunc &= 0xff;

	if (tTd(17, 9))
		printf(" = %d\n", hfunc);
	return hfunc;
}
/*
**  GETCANONNAME -- get the canonical name for named host
**
**	This algorithm tries to be smart about wildcard MX records.
**	This is hard to do because DNS doesn't tell is if we matched
**	against a wildcard or a specific MX.
**	
**	We always prefer A & CNAME records, since these are presumed
**	to be specific.
**
**	If we match an MX in one pass and lose it in the next, we use
**	the old one.  For example, consider an MX matching *.FOO.BAR.COM.
**	A hostname bletch.foo.bar.com will match against this MX, but
**	will stop matching when we try bletch.bar.com -- so we know
**	that bletch.foo.bar.com must have been right.  This fails if
**	there was also an MX record matching *.BAR.COM, but there are
**	some things that just can't be fixed.
**
**	Parameters:
**		host -- a buffer containing the name of the host.
**			This is a value-result parameter.
**		hbsize -- the size of the host buffer.
**		trymx -- if set, try MX records as well as A and CNAME.
**
**	Returns:
**		TRUE -- if the host matched.
**		FALSE -- otherwise.
*/

bool
getcanonname(host, hbsize, trymx)
	char *host;
	int hbsize;
	bool trymx;
{
	extern int h_errno;
	register u_char *eom, *ap;
	register char *cp;
	register int n; 
	HEADER *hp;
	querybuf answer;
	int ancount, qdcount;
	int ret;
	char **domain;
	int type;
	char **dp;
	char *mxmatch;
	bool amatch;
	bool gotmx;
	int qtype;
	int loopcnt;
	char *xp;
	char nbuf[MAX(PACKETSZ, MAXDNAME*2+2)];
	char *searchlist[MAXDNSRCH+2];
	extern char *gethostalias();

	if (tTd(8, 2))
		printf("getcanonname(%s)\n", host);

	if ((_res.options & RES_INIT) == 0 && res_init() == -1)
		return (FALSE);

	/*
	**  Initialize domain search list.  If there is at least one
	**  dot in the name, search the unmodified name first so we
	**  find "vse.CS" in Czechoslovakia instead of in the local
	**  domain (e.g., vse.CS.Berkeley.EDU).
	**
	**  Older versions of the resolver could create this
	**  list by tearing apart the host name.
	*/

	loopcnt = 0;
cnameloop:
	for (cp = host, n = 0; *cp; cp++)
		if (*cp == '.')
			n++;

	if (n == 0 && (xp = gethostalias(host)) != NULL)
	{
		if (loopcnt++ > MAXCNAMEDEPTH)
		{
			syserr("loop in ${HOSTALIASES} file");
		}
		else
		{
			strncpy(host, xp, hbsize);
			host[hbsize - 1] = '\0';
			goto cnameloop;
		}
	}

	dp = searchlist;
	if (n > 0)
		*dp++ = "";
	if (n >= 0 && *--cp != '.' && bitset(RES_DNSRCH, _res.options))
	{
		for (domain = _res.dnsrch; *domain != NULL; )
			*dp++ = *domain++;
	}
	else if (n == 0 && bitset(RES_DEFNAMES, _res.options))
	{
		*dp++ = _res.defdname;
	}
	else if (*cp == '.')
	{
		*cp = '\0';
	}
	*dp = NULL;

	/*
	**  Now run through the search list for the name in question.
	*/

	mxmatch = NULL;
	qtype = T_ANY;

	for (dp = searchlist; *dp != NULL; )
	{
		if (qtype == T_ANY)
			gotmx = FALSE;
		if (tTd(8, 5))
			printf("getcanonname: trying %s.%s (%s)\n", host, *dp,
				qtype == T_ANY ? "ANY" : qtype == T_A ? "A" :
				qtype == T_MX ? "MX" : "???");
		ret = res_querydomain(host, *dp, C_IN, qtype,
				      &answer, sizeof(answer));
		if (ret <= 0)
		{
			if (tTd(8, 7))
				printf("\tNO: errno=%d, h_errno=%d\n",
					errno, h_errno);

			if (errno == ECONNREFUSED || h_errno == TRY_AGAIN)
			{
				/* the name server seems to be down */
				h_errno = TRY_AGAIN;
				return FALSE;
			}

			if (h_errno != HOST_NOT_FOUND)
			{
				/* might have another type of interest */
				if (qtype == T_ANY)
				{
					qtype = T_A;
					continue;
				}
				else if (qtype == T_A && !gotmx && trymx)
				{
					qtype = T_MX;
					continue;
				}
			}

			if (mxmatch != NULL)
			{
				/* we matched before -- use that one */
				break;
			}

			/* otherwise, try the next name */
			dp++;
			qtype = T_ANY;
			continue;
		}
		else if (tTd(8, 7))
			printf("\tYES\n");

		/*
		**  This might be a bogus match.  Search for A or
		**  CNAME records.  If we don't have a matching
		**  wild card MX record, we will accept MX as well.
		*/

		hp = (HEADER *) &answer;
		ap = (u_char *) &answer + HEADERSZ;
		eom = (u_char *) &answer + ret;

		/* skip question part of response -- we know what we asked */
		for (qdcount = ntohs(hp->qdcount); qdcount--; ap += ret + QFIXEDSZ)
		{
			if ((ret = dn_skipname(ap, eom)) < 0)
			{
				if (tTd(8, 20))
					printf("qdcount failure (%d)\n",
						ntohs(hp->qdcount));
				return FALSE;		/* ???XXX??? */
			}
		}

		amatch = FALSE;
		for (ancount = ntohs(hp->ancount); --ancount >= 0 && ap < eom; ap += n)
		{
			n = dn_expand((u_char *) &answer, eom, ap,
				      (u_char *) nbuf, sizeof nbuf);
			if (n < 0)
				break;
			ap += n;
			GETSHORT(type, ap);
			ap += SHORTSIZE + LONGSIZE;
			GETSHORT(n, ap);
			switch (type)
			{
			  case T_MX:
				gotmx = TRUE;
				if (**dp != '\0')
				{
					/* got a match -- save that info */
					if (trymx && mxmatch == NULL)
						mxmatch = *dp;
					continue;
				}

				/* exact MX matches are as good as an A match */
				/* fall through */

			  case T_A:
				/* good show */
				amatch = TRUE;

				/* continue in case a CNAME also exists */
				continue;

			  case T_CNAME:
				if (loopcnt++ > MAXCNAMEDEPTH)
				{
					/*XXX should notify postmaster XXX*/
					message("DNS failure: CNAME loop for %s",
						host);
					if (CurEnv->e_message == NULL)
					{
						char ebuf[MAXLINE];

						sprintf(ebuf, "Deferred: DNS failure: CNAME loop for %s",
							host);
						CurEnv->e_message = newstr(ebuf);
					}
					h_errno = NO_RECOVERY;
					return FALSE;
				}

				/* value points at name */
				if ((ret = dn_expand((u_char *)&answer,
				    eom, ap, (u_char *)nbuf, sizeof(nbuf))) < 0)
					break;
				(void)strncpy(host, nbuf, hbsize); /* XXX */
				host[hbsize - 1] = '\0';

				/*
				**  RFC 1034 section 3.6 specifies that CNAME
				**  should point at the canonical name -- but
				**  urges software to try again anyway.
				*/

				goto cnameloop;

			  default:
				/* not a record of interest */
				continue;
			}
		}

		if (amatch)
		{
			/* got an A record and no CNAME */
			mxmatch = *dp;
			break;
		}

		/*
		**  If this was a T_ANY query, we may have the info but
		**  need an explicit query.  Try T_A, then T_MX.
		*/

		if (qtype == T_ANY)
			qtype = T_A;
		else if (qtype == T_A && !gotmx && trymx)
			qtype = T_MX;
		else
		{
			/* really nothing in this domain; try the next */
			qtype = T_ANY;
			dp++;
		}
	}

	if (mxmatch == NULL)
		return FALSE;

	/* create matching name and return */
	(void) sprintf(nbuf, "%.*s%s%.*s", MAXDNAME, host,
			*mxmatch == '\0' ? "" : ".",
			MAXDNAME, mxmatch);
	strncpy(host, nbuf, hbsize);
	host[hbsize - 1] = '\0';
	return TRUE;
}


char *
gethostalias(host)
	char *host;
{
	char *fname;
	FILE *fp;
	register char *p;
	char buf[MAXLINE];
	static char hbuf[MAXDNAME];

	fname = getenv("HOSTALIASES");
	if (fname == NULL || (fp = fopen(fname, "r")) == NULL)
		return NULL;
	while (fgets(buf, sizeof buf, fp) != NULL)
	{
		for (p = buf; p != '\0' && !(isascii(*p) && isspace(*p)); p++)
			continue;
		if (*p == 0)
		{
			/* syntax error */
			continue;
		}
		*p++ = '\0';
		if (strcasecmp(buf, host) == 0)
			break;
	}

	if (feof(fp))
	{
		/* no match */
		fclose(fp);
		return NULL;
	}

	/* got a match; extract the equivalent name */
	while (*p != '\0' && isascii(*p) && isspace(*p))
		p++;
	host = p;
	while (*p != '\0' && !(isascii(*p) && isspace(*p)))
		p++;
	*p = '\0';
	strncpy(hbuf, host, sizeof hbuf - 1);
	hbuf[sizeof hbuf - 1] = '\0';
	return hbuf;
}


#else /* not NAMED_BIND */

#include <netdb.h>

bool
getcanonname(host, hbsize, trymx)
	char *host;
	int hbsize;
	bool trymx;
{
	struct hostent *hp;

	hp = gethostbyname(host);
	if (hp == NULL)
		return (FALSE);

	if (strlen(hp->h_name) >= hbsize)
		return (FALSE);

	(void) strcpy(host, hp->h_name);
	return (TRUE);
}

#endif /* not NAMED_BIND */