Support server refresh concurrency (#2537)

* simultaneously refresh all servers

* Add `cert_refresh_concurrency`

---------

Co-authored-by: YX Hao <lifenjoiner@163.com>

dnscrypt-proxy/config.go

@@ -42,6 +42,7 @@ type Config struct {
 	Timeout                  int            `toml:"timeout"`
 	KeepAlive                int            `toml:"keepalive"`
 	Proxy                    string         `toml:"proxy"`
+	CertRefreshConcurrency   int            `toml:"cert_refresh_concurrency"`
 	CertRefreshDelay         int            `toml:"cert_refresh_delay"`
 	CertIgnoreTimestamp      bool           `toml:"cert_ignore_timestamp"`
 	EphemeralKeys            bool           `toml:"dnscrypt_ephemeral_keys"`
@@ -116,6 +117,7 @@ func newConfig() Config {
 		LocalDoH:                 LocalDoHConfig{Path: "/dns-query"},
 		Timeout:                  5000,
 		KeepAlive:                5,
+		CertRefreshConcurrency:   10,
 		CertRefreshDelay:         240,
 		HTTP3:                    false,
 		CertIgnoreTimestamp:      false,
@@ -437,6 +439,7 @@ func ConfigLoad(proxy *Proxy, flags *ConfigFlags) error {
 	if config.ForceTCP {
 		proxy.mainProto = "tcp"
 	}
+	proxy.certRefreshConcurrency = Max(1, config.CertRefreshConcurrency)
 	proxy.certRefreshDelay = time.Duration(Max(60, config.CertRefreshDelay)) * time.Minute
 	proxy.certRefreshDelayAfterFailure = time.Duration(10 * time.Second)
 	proxy.certIgnoreTimestamp = config.CertIgnoreTimestamp

dnscrypt-proxy/example-dnscrypt-proxy.toml

@@ -183,6 +183,12 @@ keepalive = 30
 # use_syslog = true
 
 
+## The maximum concurrency to reload certificates from the resolvers.
+## Default is 10.
+
+# cert_refresh_concurrency = 10
+
+
 ## Delay, in minutes, after which certificates are reloaded
 
 cert_refresh_delay = 240

dnscrypt-proxy/proxy.go

@@ -74,6 +74,7 @@ type Proxy struct {
 	certRefreshDelayAfterFailure  time.Duration
 	timeout                       time.Duration
 	certRefreshDelay              time.Duration
+	certRefreshConcurrency        int
 	cacheSize                     int
 	logMaxBackups                 int
 	logMaxAge                     int

dnscrypt-proxy/serversInfo.go

@@ -224,17 +224,34 @@ func (serversInfo *ServersInfo) refresh(proxy *Proxy) (int, error) {
 	dlog.Debug("Refreshing certificates")
 	serversInfo.RLock()
 	// Appending registeredServers slice from sources may allocate new memory.
-	registeredServers := make([]RegisteredServer, len(serversInfo.registeredServers))
+	serversCount := len(serversInfo.registeredServers)
+	registeredServers := make([]RegisteredServer, serversCount)
 	copy(registeredServers, serversInfo.registeredServers)
 	serversInfo.RUnlock()
+	countChannel := make(chan struct{}, proxy.certRefreshConcurrency)
+	errorChannel := make(chan error, serversCount)
+	for i := range registeredServers {
+		countChannel <- struct{}{}
+		go func(registeredServer *RegisteredServer) {
+			err := serversInfo.refreshServer(proxy, registeredServer.name, registeredServer.stamp)
+			if err == nil {
+				proxy.xTransport.internalResolverReady = true
+			}
+			errorChannel <- err
+			<-countChannel
+		}(&registeredServers[i])
+	}
 	liveServers := 0
 	var err error
-	for _, registeredServer := range registeredServers {
-		if err = serversInfo.refreshServer(proxy, registeredServer.name, registeredServer.stamp); err == nil {
+	for i := 0; i < serversCount; i++ {
+		err = <-errorChannel
+		if err == nil {
 			liveServers++
-			proxy.xTransport.internalResolverReady = true
 		}
 	}
+	if liveServers > 0 {
+		err = nil
+	}
 	serversInfo.Lock()
 	sort.SliceStable(serversInfo.inner, func(i, j int) bool {
 		return serversInfo.inner[i].initialRtt < serversInfo.inner[j].initialRtt