[Amazon] StopConnect for UDC in Android tv-casting-app

Updated JNI and Android tv-casting-app to use CharToStringUTF
util function to create jstring and handle NULL JNIEnv interface

Changes
* JNI to use CharToStringUTF util function to create jstring
* Updated documentation for new JNI functions

Test
1. Manually verified UDC attempt is successful both Android iOS for following
   1. Attempt UDC attempt (both commissionee & commissioner generated passcode)
   2. Navigate back to discovery page
   3. Start new UDC attempt (both commissionee & commissioner generated passcode)

2. Manually verified UDC attempt is successful both Android iOS for following. UDC will finish in the background.
   1. Attempt UDC attempt (both commissionee & commissioner generated passcode)
   2. Confirm passcode on TV app or casting app depending on who
      generated passcode
   3. Navigate back before commission fnishes.

3. Manual regression test following
   * UDC attempt happy path (no navigate back) for both commissinee &
     commissioner generated passcode

Author: yuenton-amazon

examples/tv-casting-app/android/App/app/src/main/jni/com/matter/casting/core/CastingPlayer.java

@@ -30,9 +30,15 @@
  */
 public interface CastingPlayer {
 
+  /** @brief CastingPlayer's Conenction State */
   public enum ConnectionState {
+    /** State when CastingPlayer is not connected */
     NOT_CONNECTED,
+
+    /** State when CastingPlayer is attempting to connect */
     CONNECTING,
+
+    /** State when CastingPlayer is connnected */
     CONNECTED,
   }
 
@@ -161,10 +167,14 @@ MatterError verifyOrEstablishConnection(
   void disconnect();
 
   /**
-   * @return true if this CastingPlayer is still pending pass code from user and therefore is not
-   *     ready
+   * @brief Get CastingPlayer's current ConnectionState.
+   * @return Current ConnectionState.
    */
   ConnectionState getConnectionState();
 
+  /**
+   * @brief Get the Current ConnectionState of a CastingPlayer from the native layer.
+   * @returns A String representation of the CastingPlayer's current connectation.
+   */
   String getConnectionStateNative();
 }

examples/tv-casting-app/android/App/app/src/main/jni/com/matter/casting/core/MatterCastingPlayer.java

@@ -269,10 +269,27 @@ public MatterError continueConnecting() {
   @Override
   public native void disconnect();
 
+  /**
+   * @brief Get CastingPlayer's current ConnectionState.
+   * @throws IllegalArgumentException or NullPointerException when native layer returns invalid
+   *     state.
+   * @return Current ConnectionState.
+   */
   @Override
   public ConnectionState getConnectionState() {
     return ConnectionState.valueOf(getConnectionStateNative());
   }
 
+  /*
+   * @brief Get the Current ConnectionState of a CastingPlayer from the native layer.
+   *
+   * @returns A String representation of the CastingPlayer's current connectation.
+   *          Possible return values are
+   *            - "NOT_CONNECTED"
+   *            - "CONNECTING"
+   *            - "CONNECTED"
+   *            - Error message or NULL on error
+   */
+  @Override
   public native String getConnectionStateNative();
 }

examples/tv-casting-app/android/App/app/src/main/jni/cpp/core/MatterCastingPlayer-JNI.cpp

@@ -168,6 +168,14 @@ JNI_METHOD(void, disconnect)
 JNI_METHOD(jstring, getConnectionStateNative)
 (JNIEnv * env, jobject thiz)
 {
+    if (NULL == env)
+    {
+        jobject err_jstr = nullptr;
+        LogErrorOnFailure(
+            chip::JniReferences::GetInstance().CharToStringUTF(CharSpan::fromCharString("JNIEnv interface is NULL"), err_jstr));
+        return static_cast<jstring>(err_jstr);
+    }
+
     chip::DeviceLayer::StackLock lock;
     ChipLogProgress(AppServer, "MatterCastingPlayer-JNI::getConnectionState()");
 
@@ -186,7 +194,10 @@ JNI_METHOD(jstring, getConnectionStateNative)
     default: {
         char error_str[50];
         snprintf(error_str, sizeof(error_str), "Unsupported Connection State: %d", state);
-        return env->NewStringUTF(error_str);
+
+        jobject err_jstr = nullptr;
+        LogErrorOnFailure(chip::JniReferences::GetInstance().CharToStringUTF(CharSpan::fromCharString(error_str), err_jstr));
+        return static_cast<jstring>(err_jstr);
     }
     }
 }