From 75b864f25ec5f762d6cbfc07d3dce7d77ca0629c Mon Sep 17 00:00:00 2001
From: Simon Zolin <s.zolin@adguard.com>
Date: Fri, 20 Sep 2019 13:48:22 +0300
Subject: [PATCH] * dnsforward: create dnsfilter asynchronously

---
 dnsforward/dnsforward.go | 83 +++++++++++++++++++++++++++++++++++++---
 home/dns.go              |  1 +
 2 files changed, 79 insertions(+), 5 deletions(-)

diff --git a/dnsforward/dnsforward.go b/dnsforward/dnsforward.go
index 862bf162..8c95eff4 100644
--- a/dnsforward/dnsforward.go
+++ b/dnsforward/dnsforward.go
@@ -44,6 +44,12 @@ type Server struct {
 	queryLog  querylog.QueryLog    // Query log instance
 	stats     stats.Stats
 
+	// How many times the server was started
+	// While creating a dnsfilter object,
+	//  we use this value to set s.dnsFilter property only with the most recent settings.
+	startCounter         uint32
+	dnsfilterCreatorChan chan dnsfilterCreatorParams
+
 	AllowedClients         map[string]bool // IP addresses of whitelist clients
 	DisallowedClients      map[string]bool // IP addresses of clients that should be blocked
 	AllowedClientsIPNet    []net.IPNet     // CIDRs of whitelist clients
@@ -54,6 +60,11 @@ type Server struct {
 	conf ServerConfig
 }
 
+type dnsfilterCreatorParams struct {
+	conf    dnsfilter.Config
+	filters map[int]string
+}
+
 // NewServer creates a new instance of the dnsforward.Server
 // Note: this function must be called only once
 func NewServer(stats stats.Stats, queryLog querylog.QueryLog) *Server {
@@ -73,6 +84,12 @@ func (s *Server) Close() {
 // FilteringConfig represents the DNS filtering configuration of AdGuard Home
 // The zero FilteringConfig is empty and ready for use.
 type FilteringConfig struct {
+	// Create dnsfilter asynchronously.
+	// Requests won't be filtered until dnsfilter is created.
+	// If "restart" command is received while we're creating an old dnsfilter object,
+	//  we delay creation of the new object until the old one is created.
+	AsyncStartup bool
+
 	ProtectionEnabled          bool   `yaml:"protection_enabled"`      // whether or not use any of dnsfilter features
 	FilteringEnabled           bool   `yaml:"filtering_enabled"`       // whether or not use filter lists
 	FiltersUpdateIntervalHours uint32 `yaml:"filters_update_interval"` // time period to update filters (in hours)
@@ -254,8 +271,6 @@ func (s *Server) startInternal(config *ServerConfig) error {
 
 // Initializes the DNS filter
 func (s *Server) initDNSFilter(config *ServerConfig) error {
-	log.Tracef("Creating dnsfilter")
-
 	if config != nil {
 		s.conf = *config
 	}
@@ -280,13 +295,71 @@ func (s *Server) initDNSFilter(config *ServerConfig) error {
 		s.conf.SafeBrowsingBlockHost = safeBrowsingBlockHost
 	}
 
-	s.dnsFilter = dnsfilter.New(&s.conf.Config, filters)
-	if s.dnsFilter == nil {
-		return fmt.Errorf("could not initialize dnsfilter")
+	if s.conf.AsyncStartup {
+		params := dnsfilterCreatorParams{
+			conf:    s.conf.Config,
+			filters: filters,
+		}
+		s.startCounter++
+		if s.startCounter == 1 {
+			s.dnsfilterCreatorChan = make(chan dnsfilterCreatorParams, 1)
+			go s.dnsfilterCreator()
+		}
+
+		// remove all pending tasks
+		stop := false
+		for !stop {
+			select {
+			case <-s.dnsfilterCreatorChan:
+				//
+			default:
+				stop = true
+			}
+		}
+
+		s.dnsfilterCreatorChan <- params
+	} else {
+		log.Debug("creating dnsfilter...")
+		f := dnsfilter.New(&s.conf.Config, filters)
+		if f == nil {
+			return fmt.Errorf("could not initialize dnsfilter")
+		}
+		log.Debug("created dnsfilter")
+		s.dnsFilter = f
 	}
 	return nil
 }
 
+func (s *Server) dnsfilterCreator() {
+	for {
+		params := <-s.dnsfilterCreatorChan
+
+		s.Lock()
+		counter := s.startCounter
+		s.Unlock()
+
+		log.Debug("creating dnsfilter...")
+		f := dnsfilter.New(&params.conf, params.filters)
+		if f == nil {
+			log.Error("could not initialize dnsfilter")
+			continue
+		}
+
+		set := false
+		s.Lock()
+		if counter == s.startCounter {
+			s.dnsFilter = f
+			set = true
+		}
+		s.Unlock()
+		if set {
+			log.Debug("created and activated dnsfilter")
+		} else {
+			log.Debug("created dnsfilter")
+		}
+	}
+}
+
 // Stop stops the DNS server
 func (s *Server) Stop() error {
 	s.Lock()
diff --git a/home/dns.go b/home/dns.go
index c9f199e1..bf5a2daa 100644
--- a/home/dns.go
+++ b/home/dns.go
@@ -104,6 +104,7 @@ func generateServerConfig() (dnsforward.ServerConfig, error) {
 		FilteringConfig: config.DNS.FilteringConfig,
 		Filters:         filters,
 	}
+	newconfig.AsyncStartup = true
 	bindhost := config.DNS.BindHost
 	if config.DNS.BindHost == "0.0.0.0" {
 		bindhost = "127.0.0.1"