Pull request: dnsforward: preserve domain name case

Updates #3194.

Squashed commit of the following:

commit 42a363c56b9b7441f9dc4bfc9d881b1b1e8f6b57
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon May 31 15:15:59 2021 +0300

    dnsforward: preserve domain name case

CHANGELOG.md

@@ -37,6 +37,7 @@ released by then.
 
 ### Fixed
 
+- Domain name case in responses ([#3194]).
 - Custom upstreams selection for clients with client IDs in DNS-over-TLS and
   DNS-over-HTTP ([#3186]).
 - Incorrect client-based filtering applying logic ([#2875]).
@@ -48,6 +49,7 @@ released by then.
 [#3184]: https://github.com/AdguardTeam/AdGuardHome/issues/3184
 [#3185]: https://github.com/AdguardTeam/AdGuardHome/issues/3185
 [#3186]: https://github.com/AdguardTeam/AdGuardHome/issues/3186
+[#3194]: https://github.com/AdguardTeam/AdGuardHome/issues/3194
 [#3198]: https://github.com/AdguardTeam/AdGuardHome/issues/3198
 
 

internal/dnsforward/access.go

@@ -129,10 +129,12 @@ func (a *accessCtx) IsBlockedIP(ip net.IP) (bool, string) {
 }
 
 // IsBlockedDomain - return TRUE if this domain should be blocked
-func (a *accessCtx) IsBlockedDomain(host string) bool {
+func (a *accessCtx) IsBlockedDomain(host string) (ok bool) {
 	a.lock.Lock()
-	_, ok := a.blockedHostsEngine.Match(host)
-	a.lock.Unlock()
+	defer a.lock.Unlock()
+
+	_, ok = a.blockedHostsEngine.Match(strings.ToLower(host))
+
 	return ok
 }
 

internal/dnsforward/filter.go

@@ -20,13 +20,10 @@ func (s *Server) beforeRequestHandler(_ *proxy.Proxy, d *proxy.DNSContext) (bool
 	}
 
 	if len(d.Req.Question) == 1 {
-		// It's lowercased here since this handler is called before any
-		// other one.
-		name := strings.ToLower(d.Req.Question[0].Name)
-		d.Req.Question[0].Name = name
-		host := strings.TrimSuffix(name, ".")
+		host := strings.TrimSuffix(d.Req.Question[0].Name, ".")
 		if s.access.IsBlockedDomain(host) {
-			log.Tracef("Domain %s is blocked by settings", host)
+			log.Tracef("domain %s is blocked by access settings", host)
+
 			return false, nil
 		}
 	}