Add IOStream readyState delegate observer

Examples/iOS/NetStreamSwitcher.swift

@@ -162,4 +162,12 @@ extension NetStreamSwitcher: IOStreamDelegate {
     /// Tells the receiver to the stream opened.
     func streamDidOpen(_ stream: IOStream) {
     }
+
+    /// Tells the receiver that the ready state will change.
+    func stream(_ stream: IOStream, willChange readyState: IOStream.ReadyState) {
+    }
+
+    /// Tells the receiver that the ready state did change.
+    func stream(_ stream: IOStream, didChange readyState: IOStream.ReadyState) {
+    }
 }

Sources/IO/IOStream.swift

@@ -34,6 +34,10 @@ public protocol IOStreamDelegate: AnyObject {
     func stream(_ stream: IOStream, audioErrorOccurred error: IOAudioUnitError)
     /// Tells the receiver to the stream opened.
     func streamDidOpen(_ stream: IOStream)
+    /// Tells the receiver that the ready state will change.
+    func stream(_ stream: IOStream, willChange readyState: IOStream.ReadyState)
+    /// Tells the receiver that the ready state did change.
+    func stream(_ stream: IOStream, didChange readyState: IOStream.ReadyState)
 }
 
 @available(*, deprecated, renamed: "IOStream")
@@ -458,6 +462,7 @@ open class IOStream: NSObject {
     /// A handler that receives stream readyState will update.
     /// - Warning: Please do not call this method yourself.
     open func readyStateWillChange(to readyState: ReadyState) {
+        delegate?.stream(self, willChange: readyState)
         switch self.readyState {
         case .playing:
             mixer.stopRunning()
@@ -487,6 +492,7 @@ open class IOStream: NSObject {
         default:
             break
         }
+        delegate?.stream(self, didChange: readyState)
     }
 
     #if os(iOS) || os(tvOS)