proxy: add query duration

proxy/dnscontext.go

@@ -17,6 +17,9 @@ type DNSContext struct {
 	// StartTime is the moment when request processing started.
 	StartTime time.Time
 
+	// QueryDuration is the time duration of the successfull query.
+	QueryDuration time.Duration
+
 	// Conn is the underlying client connection.  It is nil if Proto is
 	// ProtoDNSCrypt, ProtoHTTPS, or ProtoQUIC.
 	Conn net.Conn

proxy/proxy.go

@@ -523,6 +523,9 @@ func (p *Proxy) replyFromUpstream(d *DNSContext) (ok bool, err error) {
 	if err != nil && p.Fallbacks != nil {
 		log.Debug("proxy: replying from upstream: using fallback due to %s", err)
 
+		// Reset the timer.
+		start = time.Now()
+
 		upstreams = p.Fallbacks.getUpstreamsForDomain(req.Question[0].Name)
 		if len(upstreams) == 0 {
 			return false, fmt.Errorf("selecting fallback upstream: %w", upstream.ErrNoUpstreams)
@@ -531,6 +534,10 @@ func (p *Proxy) replyFromUpstream(d *DNSContext) (ok bool, err error) {
 		resp, u, err = upstream.ExchangeParallel(upstreams, req)
 	}
 
+	if resp != nil {
+		d.QueryDuration = time.Since(start)
+	}
+
 	p.handleExchangeResult(d, req, resp, u)
 
 	return resp != nil, err