Dynamically reduce the timeout as we get closer to the cnx limit

Similar to what pf does

Author: jedisct1

dnscrypt-proxy/config.go

@@ -82,6 +82,7 @@ type Config struct {
 	SourceIPv4               bool                        `toml:"ipv4_servers"`
 	SourceIPv6               bool                        `toml:"ipv6_servers"`
 	MaxClients               uint32                      `toml:"max_clients"`
+	TimeoutLoadReduction     float64                     `toml:"timeout_load_reduction"`
 	BootstrapResolversLegacy []string                    `toml:"fallback_resolvers"`
 	BootstrapResolvers       []string                    `toml:"bootstrap_resolvers"`
 	IgnoreSystemDNS          bool                        `toml:"ignore_system_dns"`
@@ -147,6 +148,7 @@ func newConfig() Config {
 		SourceDoH:                true,
 		SourceODoH:               false,
 		MaxClients:               250,
+		TimeoutLoadReduction:     0.5,
 		BootstrapResolvers:       []string{DefaultBootstrapResolver},
 		IgnoreSystemDNS:          false,
 		LogMaxSize:               10,

dnscrypt-proxy/config_loader.go

@@ -171,6 +171,11 @@ func configureServerParams(proxy *Proxy, config *Config) {
 	proxy.blockedQueryResponse = config.BlockedQueryResponse
 	proxy.timeout = time.Duration(config.Timeout) * time.Millisecond
 	proxy.maxClients = config.MaxClients
+	proxy.timeoutLoadReduction = config.TimeoutLoadReduction
+	if proxy.timeoutLoadReduction < 0.0 || proxy.timeoutLoadReduction > 1.0 {
+		dlog.Warnf("timeout_load_reduction must be between 0.0 and 1.0, using default 0.5")
+		proxy.timeoutLoadReduction = 0.5
+	}
 	proxy.mainProto = "udp"
 	if config.ForceTCP {
 		proxy.mainProto = "tcp"

dnscrypt-proxy/proxy.go

@@ -86,6 +86,7 @@ type Proxy struct {
 	cacheMaxTTL                   uint32
 	clientsCount                  uint32
 	maxClients                    uint32
+	timeoutLoadReduction          float64
 	cacheMinTTL                   uint32
 	cacheNegMaxTTL                uint32
 	cloakTTL                      uint32
@@ -474,7 +475,8 @@ func (proxy *Proxy) tcpListener(acceptPc *net.TCPListener) {
 		go func() {
 			defer clientPc.Close()
 			defer proxy.clientsCountDec()
-			if err := clientPc.SetDeadline(time.Now().Add(proxy.timeout)); err != nil {
+			dynamicTimeout := proxy.getDynamicTimeout()
+			if err := clientPc.SetDeadline(time.Now().Add(dynamicTimeout)); err != nil {
 				return
 			}
 			start := time.Now()
@@ -686,6 +688,25 @@ func (proxy *Proxy) clientsCountDec() {
 	}
 }
 
+func (proxy *Proxy) getDynamicTimeout() time.Duration {
+	if proxy.timeoutLoadReduction <= 0.0 || proxy.maxClients == 0 {
+		return proxy.timeout
+	}
+
+	currentClients := atomic.LoadUint32(&proxy.clientsCount)
+	utilization := float64(currentClients) / float64(proxy.maxClients)
+
+	factor := 1.0 - (utilization * utilization * proxy.timeoutLoadReduction)
+	if factor < 0.1 {
+		factor = 0.1
+	}
+
+	dynamicTimeout := time.Duration(float64(proxy.timeout) * factor)
+	dlog.Debugf("Dynamic timeout: %v (utilization: %.2f%%, factor: %.2f)", dynamicTimeout, utilization*100, factor)
+
+	return dynamicTimeout
+}
+
 func (proxy *Proxy) processIncomingQuery(
 	clientProto string,
 	serverProto string,