try fix #180

src/dns.c

@@ -356,7 +356,7 @@ u16 dns_empty_reply(void *noalias msg, int qnamelen) {
     h->answer_count = 0;
     h->authority_count = 0;
     h->additional_count = 0;
-    return msg_minlen(qnamelen);
+    return qnamelen > 0 ? msg_minlen(qnamelen) : sizeof(struct dns_header);
 }
 
 // return newlen (0 if failed)

src/server.zig

@@ -389,7 +389,7 @@ fn on_query(qmsg: *RcMsg, fdobj: *EvLoop.Fd, src_addr: *const cc.SockAddr, in_qf
 
     if (!dns.check_query(msg, p_ascii_namebuf, &qnamelen)) {
         log.warn(@src(), "dns.check_query(fd:%d) failed: invalid query msg", .{fdobj.fd});
-        return;
+        return send_reply_xxx(msg, fdobj, src_addr, in_qflags); // make the requester happy
     }
 
     const id = dns.get_id(msg);
@@ -818,6 +818,17 @@ fn send_reply(msg: []const u8, fdobj: *EvLoop.Fd, src_addr: *const cc.SockAddr,
     );
 }
 
+/// [async]
+fn send_reply_xxx(msg: []u8, fdobj: *EvLoop.Fd, src_addr: *const cc.SockAddr, qflags: QueryCtx.Flags) void {
+    if (msg.len >= dns.header_len())
+        _ = dns.empty_reply(msg, 0);
+
+    if (qflags.has(.from_tcp))
+        g.evloop.send(fdobj, msg, 0) orelse {} // TODO: error handling
+    else
+        _ = cc.sendto(fdobj.fd, msg, 0, src_addr) orelse 0; // TODO: error handling
+}
+
 // =========================================================================
 
 /// qctx will be free()