Adds API for resynchronizing sleepy child with its parent

include/openthread/thread.h

@@ -285,6 +285,22 @@ otError otThreadSetJoinerAdvertisement(otInstance *   aInstance,
 
 #define OT_JOINER_ADVDATA_MAX_LENGTH 64 ///< Maximum AdvData Length of Joiner Advertisement
 
+/**
+ * Resynchronize a sleepy child with its parent, in case the Keep-alives
+ * are getting erroneously acknowledged. This function will send a child
+ * update request to the parent, if the device is a rx-off-when-idle (i.e. sleepy)
+ * child.
+ *
+ * @param aInstance A pointer to an OpenThread instance.
+ *
+ * @retval OT_ERROR_NONE           Successfully attempted to resynchronize with the parent.
+ * @retval OT_ERROR_REJECTED       The device is not a rx-off-when-idle child, so
+ *                                 no attempt to resynchronize was made
+ * @retval OT_ERROR_NO_BUFS        Insufficient buffers to generate the MLE Child Update Request.
+ *
+ */
+otError otThreadSleepyChildResynchronize(otInstance *aInstance);
+
 /**
  * Get the Thread Child Timeout used when operating in the Child role.
  *

src/core/api/thread_api.cpp

@@ -43,7 +43,21 @@
 
 using namespace ot;
 
-uint32_t otThreadGetChildTimeout(otInstance *aInstance)
+uint32_t otError otThreadSleepyChildResynchronize(otInstance *aInstance)
+{
+    Error     error    = kErrorNone;
+    Instance &instance = AsCoreType(aInstance);
+
+    VerifyOrExit(instance.Get<Mle::MleRouter>().IsChild(), error = kErrorRejected);
+    VerifyOrExit(instance.Get<MeshForwarder>().GetRxOnWhenIdle() == false, error = kErrorRejected);
+
+    error = AsCoreType(aInstance).Get<Mle::MleRouter>().SendChildUpdateRequest();
+
+exit:
+    return error;
+}
+
+otThreadGetChildTimeout(otInstance *aInstance)
 {
     return AsCoreType(aInstance).Get<Mle::MleRouter>().GetTimeout();
 }