json dns: do not use array to output answer

Without this patch DNS answers for a single query are stored in a
single json event. The result is an array in the object like this one:
 {"type":"answer","id":45084,"rrname":"s-static.ak.facebook.com","rrtype":"CNAME","ttl":734},
 {"type":"answer","id":45084,"rrname":"s-static.ak.facebook.com.edgekey.net","rrtype":"CNAME","ttl":1710},
This type of output is not well supported in logstash. It is
displayed as it is written above and it is not possible to
query the fields.

I think the reason is that this is not logical if we consider search
query. For example if we search for "rrname" equal "s-static.ak.facebook.com"
we got one entry with two values in it. That's against the logic
of event. Furthermore, if we want to get a complete query, we can
used the id.

This patch splits the answer part in mulitple message. The result
is then accepted by logstash and fields can be queried easily.

src/output-json-dns.c

@@ -135,7 +135,8 @@ static void LogQuery(LogDnsLogThread *aft, json_t *js, DNSTransaction *tx, DNSQu
     json_object_del(js, "dns");
 }
 
-static void AppendAnswer(json_t *djs, DNSTransaction *tx, DNSAnswerEntry *entry) {
+static void OutputAnswer(LogDnsLogThread *aft, json_t *djs, DNSTransaction *tx, DNSAnswerEntry *entry) {
+    MemBuffer *buffer = (MemBuffer *)aft->buffer;
     json_t *js = json_object();
     if (js == NULL)
         return;
@@ -179,40 +180,34 @@ static void AppendAnswer(json_t *djs, DNSTransaction *tx, DNSAnswerEntry *entry)
             json_object_set_new(js, "rdata", json_string(""));
         }
     }
-    json_array_append_new(djs, js);
+
+    /* reset */
+    MemBufferReset(buffer);
+    json_object_set_new(djs, "dns", js);
+    OutputJSONBuffer(djs, aft->dnslog_ctx->file_ctx, buffer);
+    json_object_del(djs, "dns");
+
+    return;
 }
 
 static void LogAnswers(LogDnsLogThread *aft, json_t *js, DNSTransaction *tx) {
-    MemBuffer *buffer = (MemBuffer *)aft->buffer;
 
     SCLogDebug("got a DNS response and now logging !!");
 
-    json_t *djs = json_array();
-    if (djs == NULL) {
-        return;
-    }
-
-    /* reset */
-    MemBufferReset(buffer);
-
     if (tx->no_such_name) {
-        AppendAnswer(djs, tx, NULL);
+        OutputAnswer(aft, js, tx, NULL);
     }
 
     DNSAnswerEntry *entry = NULL;
     TAILQ_FOREACH(entry, &tx->answer_list, next) {
-        AppendAnswer(djs, tx, entry);
+        OutputAnswer(aft, js, tx, entry);
     }
 
     entry = NULL;
     TAILQ_FOREACH(entry, &tx->authority_list, next) {
-        AppendAnswer(djs, tx, entry);
+        OutputAnswer(aft, js, tx, entry);
     }
 
-    /* dns */
-    json_object_set_new(js, "dns", djs);
-    OutputJSONBuffer(js, aft->dnslog_ctx->file_ctx, buffer);
-    json_object_del(js, "dns");
 }
 
 static int JsonDnsLogger(ThreadVars *tv, void *thread_data, const Packet *p, Flow *f, void *alstate, void *txptr, uint64_t tx_id)