Add ExchangeCache api

client.go

@@ -152,6 +152,39 @@ func (c *Client) exchange(ctx context.Context, transport Transport, message *dns
 	return response, err
 }
 
+func (c *Client) ExchangeCache(ctx context.Context, message *dns.Msg) (*dns.Msg, bool) {
+	response, cached := c.exchangeCache(ctx, message)
+	if !cached {
+		return nil, false
+	}
+	if rewriteTTL, loaded := RewriteTTLFromContext(ctx); loaded {
+		for _, recordList := range [][]dns.RR{response.Answer, response.Ns, response.Extra} {
+			for _, record := range recordList {
+				record.Header().Ttl = rewriteTTL
+			}
+		}
+	}
+	return response, true
+}
+
+func (c *Client) exchangeCache(ctx context.Context, message *dns.Msg) (*dns.Msg, bool) {
+	if c.independentCache || len(message.Question) != 1 {
+		return nil, false
+	}
+	question := message.Question[0]
+	disableCache := c.disableCache || DisableCacheFromContext(ctx)
+	if disableCache {
+		return nil, false
+	}
+	response, ttl := c.loadResponse(question, nil)
+	if response == nil {
+		return nil, false
+	}
+	logCachedResponse(c.logger, ctx, response, ttl)
+	response.Id = message.Id
+	return response, true
+}
+
 func (c *Client) Lookup(ctx context.Context, transport Transport, domain string, strategy DomainStrategy) ([]netip.Addr, error) {
 	if dns.IsFqdn(domain) {
 		domain = domain[:len(domain)-1]