Make semtech_udp cache expiration and cleanup interval configurable. (#244)

Co-authored-by: Orne Brocaar <info@brocaar.com>

Author: lukaskirner

cmd/chirpstack-gateway-bridge/cmd/configfile.go

@@ -94,6 +94,18 @@ type="{{ .Backend.Type }}"
   # disconnected and it will unsubscribe from the gateway MQTT topic and cleanup the UDP docket. 
   connection_timeout_duration={{ .Backend.SemtechUDP.CleanupDuration }}
 
+  # Cache expiration
+  #
+  # ChirpStack Gateway Bridge temporarily store downlinks. If a gateway does not send any
+  # UDP data within the configured timeout the downlink is discarded.
+  cache_default_expiration="{{ .Backend.SemtechUDP.CacheDefaultExpiration }}"
+
+  # Cache cleanup interval
+  #
+  # ChirpStack Gateway Bridge temporarily store downlinks in a cache. The cache is cleaned in 
+  # the configured interval.
+  cache_cleanup_interval="{{ .Backend.SemtechUDP.CacheCleanupInterval }}"
+
 
   # Basic Station backend.
   [backend.basic_station]

cmd/chirpstack-gateway-bridge/cmd/root.go

@@ -41,6 +41,9 @@ func init() {
 	viper.SetDefault("backend.semtech_udp.udp_bind", "0.0.0.0:1700")
 	viper.SetDefault("backend.semtech_udp.cleanup_duration", time.Minute)
 
+	viper.SetDefault("backend.semtech_udp.cache_default_expiration", 15*time.Second)
+	viper.SetDefault("backend.semtech_udp.cache_cleanup_interval", 15*time.Second)
+
 	viper.SetDefault("backend.concentratord.crc_check", true)
 	viper.SetDefault("backend.concentratord.event_url", "ipc:///tmp/concentratord_event")
 	viper.SetDefault("backend.concentratord.command_url", "ipc:///tmp/concentratord_command")

internal/backend/semtechudp/backend.go

@@ -72,7 +72,10 @@ func NewBackend(conf config.Config) (*Backend, error) {
 		},
 		fakeRxTime:   conf.Backend.SemtechUDP.FakeRxTime,
 		skipCRCCheck: conf.Backend.SemtechUDP.SkipCRCCheck,
-		cache:        cache.New(15*time.Second, 15*time.Second),
+		cache: cache.New(
+			conf.Backend.SemtechUDP.CacheDefaultExpiration,
+			conf.Backend.SemtechUDP.CacheCleanupInterval,
+		),
 	}
 
 	go func() {

internal/config/config.go

@@ -21,10 +21,12 @@ type Config struct {
 		Type string `mapstructure:"type"`
 
 		SemtechUDP struct {
-			UDPBind         string `mapstructure:"udp_bind"`
-			SkipCRCCheck    bool   `mapstructure:"skip_crc_check"`
-			FakeRxTime      bool   `mapstructure:"fake_rx_time"`
-			CleanupDuration int    `mapstructure:"connection_timeout_duration"`
+			UDPBind                string        `mapstructure:"udp_bind"`
+			SkipCRCCheck           bool          `mapstructure:"skip_crc_check"`
+			FakeRxTime             bool          `mapstructure:"fake_rx_time"`
+			CleanupDuration        int           `mapstructure:"connection_timeout_duration"`
+			CacheDefaultExpiration time.Duration `mapstructure:"cache_default_expiration"`
+			CacheCleanupInterval   time.Duration `mapstructure:"cache_cleanup_interval"`
 		} `mapstructure:"semtech_udp"`
 
 		BasicStation struct {