From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <f0350d8cfafc8751c821b0434be0066e@plan9.jp>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] csipinfo
From: Joel “chesky” Salomon <chesky@plan9.jp>
Date: Wed, 18 Oct 2006 16:17:19 -0400
In-Reply-To: <365a3b8e0ce821506adb926ac1001503@plan9.jp>
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Topicbox-Message-UUID: cd0b0ad4-ead1-11e9-9d60-3106f5b1d025

I think I have a working gethostbyaddr:

char*
gethostbyaddr(char *net, char *addr)
{
	// Thanks to erik and rog for their help with this code
	char buf[1024], errbuf[ERRMAX], *dq[4], *host;
	int fd, l;

	if(net == nil)
		net = "/net";
	snprint(buf, sizeof buf, "%s/dns", net);
	if((fd = open(buf, ORDWR)) < 0){
		l = snprint(errbuf, ERRMAX, "gethostbyaddr: can't open %s: %r", buf);
		errstr(errbuf, l);
		return nil;
	}
	if(getfields(addr, dq, 4, 1, ".") != 4){
		close(fd);
		werrstr("gethostbyaddr: malformed address");
		return nil;
	}
	l = snprint(buf, sizeof buf, "%s.%s.%s.%s.in-addr.arpa ptr",
		dq[3], dq[2], dq[1], dq[0]);
	if(write(fd, buf, l) != l){
		l = snprint(errbuf, ERRMAX,
			"gethostbyaddr: write error resolving %s.%s.%s.%s: %s/dns: %r",
			dq[0], dq[1], dq[2], dq[3], net);
		close(fd);
		errstr(errbuf, l);
		return nil;
	}
	if(read(fd, buf, sizeof buf) <= 0){
		l = snprint(errbuf, ERRMAX,
			"gethostbyaddr: read error resolving %s.%s.%s.%s: %s/dns: %r",
			dq[0], dq[1], dq[2], dq[3], net);
		close(fd);
		errstr(errbuf, l);
		return nil;
	}
	close(fd);
	host = strstr(buf, " ptr ");
	if(host == nil){
		werrstr("gethostbyaddr: dns lookup failed");
		return nil;
	}
	return strdup(host);
}

--Joel