nslookup: handle replies without RRs

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>

1 files changed, 7 insertions, 1 deletions

diff --git a/networking/nslookup.c b/networking/nslookup.c
index 8adde14b8..a7dd823f0 100644
--- a/networking/nslookup.c
+++ b/networking/nslookup.c
@@ -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');