Implement config option to override ICE candidates port

config/config.sample.toml

@@ -52,6 +52,16 @@ enable_ipv6 = false
 # For more advanced usage this value can also be a comma separated list of
 # NAT mappings in the form of "external IP / internal IP" pairs, e.g. "8.8.8.8/10.0.2.2,8.8.4.4/10.0.2.1".
 ice_host_override = ""
+
+# An optional port number to be used as an override for host candidates in
+# place of the one used to listen on (ice_port_udp/ice_port_tcp).
+# This can be useful in case there are additional network components (e.g. NLBs)
+# in front of this service that may route the traffic through a different port.
+#
+# Note: this port will apply to both UDP and TCP host candidates.
+#
+# ice_host_port_override = 30443
+
 # A list of ICE servers (STUN/TURN) to be used by the service. It supports
 # advanced configurations.
 # Example

docs/env_config.md

@@ -15,6 +15,7 @@ RTCD_RTC_ICEPORTUDP                                 Integer
 RTCD_RTC_ICEADDRESSTCP                              String
 RTCD_RTC_ICEPORTTCP                                 Integer
 RTCD_RTC_ICEHOSTOVERRIDE                            String
+RTCD_RTC_ICEHOSTPORTOVERRIDE                        Integer
 RTCD_RTC_ICESERVERS                                 Comma-separated list of 
 RTCD_RTC_TURNCONFIG_STATICAUTHSECRET                String
 RTCD_RTC_TURNCONFIG_CREDENTIALSEXPIRATIONMINUTES    Integer

service/rtc/config.go

@@ -22,6 +22,9 @@ type ServerConfig struct {
 	// ICEHostOverride optionally specifies an IP address (or hostname)
 	// to be used as the main host ICE candidate.
 	ICEHostOverride string `toml:"ice_host_override"`
+	// ICEHostPortOverride optionally specifies a port number to override the one
+	// used to listen on when sharing host candidates.
+	ICEHostPortOverride int `toml:"ice_host_port_override"`
 	// A list of ICE server (STUN/TURN) configurations to use.
 	ICEServers ICEServers `toml:"ice_servers"`
 	TURNConfig TURNConfig `toml:"turn"`
@@ -54,6 +57,10 @@ func (c ServerConfig) IsValid() error {
 		return fmt.Errorf("invalid TURNConfig: %w", err)
 	}
 
+	if c.ICEHostPortOverride != 0 && (c.ICEHostPortOverride < 80 || c.ICEHostPortOverride > 49151) {
+		return fmt.Errorf("invalid ICEHostPortOverride value: %d is not in allowed range [80, 49151]", c.ICEHostPortOverride)
+	}
+
 	return nil
 }
 

service/rtc/config_test.go

@@ -69,6 +69,20 @@ func TestServerConfigIsValid(t *testing.T) {
 		require.Equal(t, "invalid TURNConfig: invalid CredentialsExpirationMinutes value: should be less than 1 week", err.Error())
 	})
 
+	t.Run("invalid ICEHostPortOverride", func(t *testing.T) {
+		var cfg ServerConfig
+		cfg.ICEPortUDP = 8443
+		cfg.ICEPortTCP = 8443
+		cfg.ICEHostPortOverride = 45
+		err := cfg.IsValid()
+		require.Error(t, err)
+		require.Equal(t, "invalid ICEHostPortOverride value: 45 is not in allowed range [80, 49151]", err.Error())
+		cfg.ICEHostPortOverride = 65000
+		err = cfg.IsValid()
+		require.Error(t, err)
+		require.Equal(t, "invalid ICEHostPortOverride value: 65000 is not in allowed range [80, 49151]", err.Error())
+	})
+
 	t.Run("valid", func(t *testing.T) {
 		var cfg ServerConfig
 		cfg.ICEAddressUDP = "127.0.0.1"

service/rtc/sfu.go

@@ -249,6 +249,17 @@ func (s *Server) InitSession(cfg SessionConfig, closeCb func() error) error {
 		if candidate == nil {
 			return
 		}
+
+		if s.cfg.ICEHostPortOverride != 0 && candidate.Typ == webrtc.ICECandidateTypeHost {
+			s.log.Debug("overriding host candidate port",
+				mlog.String("sessionID", cfg.SessionID),
+				mlog.Uint("port", candidate.Port),
+				mlog.Int("override", s.cfg.ICEHostPortOverride),
+				mlog.String("addr", candidate.Address),
+				mlog.Int("protocol", candidate.Protocol))
+			candidate.Port = uint16(s.cfg.ICEHostPortOverride)
+		}
+
 		msg, err := newICEMessage(us, candidate)
 		if err != nil {
 			s.log.Error("failed to create ICE message", mlog.Err(err), mlog.String("sessionID", cfg.SessionID))