Add an engine for global webrtc settings

* hook up UDP limitation to it.
This was Michiel De Backker's suggestion

relates to #281

pkg/ice/agent.go

@@ -91,9 +91,13 @@ func (a *Agent) getErr() error {
 	return ErrClosed
 }
 
+// AgentConfig collects the arguements to ice.Agent construction into
+// a single structure, for future-proofness of the interface
 type AgentConfig struct {
 	Urls     []*URL
 	Notifier func(ConnectionState)
+
+	// PortMin and PortMax are optional. Leave them 0 for the default UDP port allocation strategy.
 	PortMin uint16
 	PortMax uint16
 }

rtcconfiguration.go

@@ -44,11 +44,6 @@ type RTCConfiguration struct {
 
 	// IceCandidatePoolSize describes the size of the prefetched ICE pool.
 	IceCandidatePoolSize uint8
-
-	// MinLocalPort and MaxLocalPort, if nonzero, set limits to local ephemeral
-	// UDP ports that are allocated by the ICE agent.
-	MinLocalPort uint16
-	MaxLocalPort uint16
 }
 
 func (c RTCConfiguration) getIceServers() (*[]*ice.URL, error) {

rtcpeerconnection.go

@@ -158,7 +158,7 @@ func New(configuration RTCConfiguration) (*RTCPeerConnection, error) {
 		}
 	}
 
-	pc.networkManager, err = network.NewManager(urls, pc.generateChannel, pc.iceStateChange, configuration.MinLocalPort, configuration.MaxLocalPort)
+	pc.networkManager, err = network.NewManager(urls, pc.generateChannel, pc.iceStateChange, defaultSettingEngine.EphemeralUDP.PortMin, defaultSettingEngine.EphemeralUDP.PortMax)
 	if err != nil {
 		return nil, err
 	}

settingengine.go

@@ -0,0 +1,28 @@
+package webrtc
+
+import "github.com/pions/webrtc/pkg/ice"
+
+var defaultSettingEngine = newSettingEngine()
+
+type settingEngine struct {
+	EphemeralUDP struct {
+		PortMin uint16
+		PortMax uint16
+	}
+}
+
+// SetEphemeralUDPPortRange limits the pool of ephemeral ports that
+// ICE UDP connections can allocate from
+func SetEphemeralUDPPortRange(portMin, portMax uint16) error {
+	if portMax < portMin {
+		return ice.ErrPort
+	}
+
+	defaultSettingEngine.EphemeralUDP.PortMin = portMin
+	defaultSettingEngine.EphemeralUDP.PortMax = portMax
+	return nil
+}
+
+func newSettingEngine() *settingEngine {
+	return new(settingEngine)
+}