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nslookup: handle replies without RRs

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Under some circumstances, a DNS reply might contain no resource records,
e.g. when a valid domain is queried that does not have records of the
requested type.

Example with nslookup from BIND dnsutils:

    $ nslookup -q=SRV example.org
    Server:	10.11.12.13
    Address:	10.11.12.13#53

    Non-authoritative answer:
    *** Can't find example.org: No answer

Currently the busybox nslookup applet simply prints nothing after the
"Non-authoritative answer:" line in the same situation.

This change modifies nslookup to either print "Parse error" or "No answer"
diagnostics, depending on the parse_reply() return value.

function                                             old     new   delta
send_queries                                        1676    1711     +35

Signed-off-by: Jo-Philipp Wich <jo@mein.io>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Jo-Philipp Wich 2019-06-27 17:27:28 +02:00 committed by Denys Vlasenko
parent caf5ee0dd9
commit 8c3b520d4f
1 changed files with 7 additions and 1 deletions
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8
networking/nslookup.c
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@ -615,9 +615,15 @@ static int send_queries(struct ns *ns)
G.query[qn].name, rcodes[rcode]);
G.exitcode = EXIT_FAILURE;
} else {
if (parse_reply(reply, recvlen) < 0) {
switch (parse_reply(reply, recvlen)) {
case -1:
printf("*** Can't find %s: Parse error\n", G.query[qn].name);
G.exitcode = EXIT_FAILURE;
break;
case 0:
printf("*** Can't find %s: No answer\n", G.query[qn].name);
break;
}
}
bb_putchar('\n');