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From: peiffer@umn-cs.CS.UMN.EDU (Tim J. Peiffer)
Newsgroups: gnu.bash.bug
Subject: Re: gethostent call in readline.c
Message-ID: <13429@umn-cs.CS.UMN.EDU>
Date: 11 Jun 89 03:55:36 GMT
References: <126@unmvax.unm.edu>
Reply-To: peiffer@umn-cs.cs.umn.edu (Tim J. Peiffer)
Organization: CSci Dept., University of Minnesota, Mpls.
Lines: 53

In article <126@unmvax.unm.edu> mike@unmvax.cs.unm.edu writes:
>Hostname completions are a good idea, but there is a problem.  With
>the resolv library (which BSD uses by DEFAULT, thank god), there is no
>gethostent function.  Even if it were implemented (perhaps doing a
>depth-first search on the entire DNS), it would be far too slow when
>hooked up to the internet with named.  Just too many hosts to page
>through.
	Uh, I hate to burst your bubble, but that is not exactly what 
	happens.  If the system implements gethostbyname(3N) properly,
	it first looks in the host tables to see if it exists there.
	Consider the name 'host' and a domain name of 'sub.sub_domain.domain'.
	
	Then the resolvers request an address - the resolver makes
	use of what is called a sliding window match.  The resolver then,
	if name is not fully qualified (e.g. ends with a '.'), pulls 
	off a domain name from /etc/resolv.conf.  Then the name is presented
	to the DNS - fully qualified as host.sub.sub_domain.domain.
	(remember the terminating '.').  If the data is not found, a 
	NXDOMAIN signal is returned.  Then the domain name is pruned 
	from the left -> host.sub_domain.domain.  The name is resubmitted
	to the server and repruned until 'host.' fails.

	If the domain is not the same as the zone that the server is
	responsible for, the query is forwarded to an upline server until
	it either receives an authoritative answer or it reaches a root
	server and receives a NXDOMAIN response.  Typically there are
	only 3-6 servers upline until you contact a root server.  In
	my application, for any query, 6 queries is all that are done.
	This takes place inside of 10 seconds - tops at the worst of 
	network conditions.
	
>Has anyone else thought of this?

	No need.  By the way, gethostent returns a pointer to a 
	structure hostent in netdb.h.  The object has the following 
	structure containing the broken-out fields of a line in the 
	network host data base, /etc/hosts.

          struct    hostent {
               char *h_name;  /* official name of host */
               char **h_aliases;   /* alias list */
               int  h_addrtype;    /* address type */
               int  h_length; /* length of address */
               char *h_addr;  /* address */
          };
	This structure is used in *every* transaction that the 
	resolver goes through.

Tim Peiffer	peiffer@umn-cs.cs.umn.edu
Computer Science Department
University of Minnesota, MPLS MN

P.S.  I thought this spot was reserved for bashing out GNU bugs..