Sending notifications as Flow more reliably

ble-ktx/src/main/java/no/nordicsemi/android/ble/ktx/ValueChangedCallbackExt.kt

@@ -2,9 +2,13 @@
 
 package no.nordicsemi.android.ble.ktx
 
+import android.util.Log
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.channels.awaitClose
+import kotlinx.coroutines.channels.onFailure
+import kotlinx.coroutines.channels.trySendBlocking
 import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.buffer
 import kotlinx.coroutines.flow.callbackFlow
 import no.nordicsemi.android.ble.ValueChangedCallback
 import no.nordicsemi.android.ble.callback.profile.ProfileReadResponse
@@ -17,6 +21,11 @@ import no.nordicsemi.android.ble.response.ReadResponse
  * Usage:
  *
  *     val hrmMeasurementsData = setNotificationCallback(hrmCharacteristic).asFlow()  // Flow<Data>
+ *
+ * Use the [buffer] operator on the resulting flow to specify a user-defined value and to control
+ * what happens when data is produced faster than consumed, i.e. to control the back-pressure behavior.
+ *
+ *      val hrmMeasurementsData = setNotificationCallback(hrmCharacteristic).asFlow().buffer()
  * @return The flow.
  * @since 2.3.0
  */
@@ -25,7 +34,8 @@ fun ValueChangedCallback.asFlow(): Flow<Data> = callbackFlow {
     // Make sure the callbacks are called without unnecessary delay.
     setHandler(null)
     with { _, data ->
-        trySend(data)
+        trySendBlocking(data)
+            .onFailure { t -> Log.w("ValueChangeCallback", "Sending data to Flow failed with: $t") }
     }
     awaitClose {
         // There's no way to unregister the callback from here.
@@ -41,6 +51,9 @@ fun ValueChangedCallback.asFlow(): Flow<Data> = callbackFlow {
  *     val hrmMeasurementsData: Flow<HeartRateMeasurementResponse> =
  *         setNotificationCallback(hrmCharacteristic)
  *             .asResponseFlow()
+ *
+ * Use the [buffer] operator on the resulting flow to specify a user-defined value and to control
+ * what happens when data is produced faster than consumed, i.e. to control the back-pressure behavior.
  * @return The flow.
  * @since 2.4.0
  */
@@ -49,7 +62,10 @@ inline fun <reified T: ReadResponse> ValueChangedCallback.asResponseFlow(): Flow
     // Make sure the callbacks are called without unnecessary delay.
     setHandler(null)
     with { device, data ->
-        trySend(T::class.java.getDeclaredConstructor().newInstance().apply { onDataReceived(device, data) })
+        val response = T::class.java.getDeclaredConstructor().newInstance()
+            .apply { onDataReceived(device, data) }
+        trySendBlocking(response)
+            .onFailure { t -> Log.w("ValueChangeCallback", "Sending response to Flow failed with: $t") }
     }
     awaitClose {
         // There's no way to unregister the callback from here.
@@ -66,6 +82,9 @@ inline fun <reified T: ReadResponse> ValueChangedCallback.asResponseFlow(): Flow
  *     val hrmMeasurementsData: Flow<HeartRateMeasurementResponse> =
  *         setNotificationCallback(hrmCharacteristic)
  *             .asValidResponseFlow()
+ *
+ * Use the [buffer] operator on the resulting flow to specify a user-defined value and to control
+ * what happens when data is produced faster than consumed, i.e. to control the back-pressure behavior.
  * @return The flow.
  * @since 2.4.0
  */
@@ -74,10 +93,12 @@ inline fun <reified T: ProfileReadResponse> ValueChangedCallback.asValidResponse
     // Make sure the callbacks are called without unnecessary delay.
     setHandler(null)
     with { device, data ->
-        T::class.java.getDeclaredConstructor().newInstance()
+        val response = T::class.java.getDeclaredConstructor().newInstance()
             .apply { onDataReceived(device, data) }
-            .takeIf { it.isValid }
-            ?.let { trySend(it) }
+        if (response.isValid) {
+            trySendBlocking(response)
+                .onFailure { t -> Log.w("ValueChangeCallback", "Sending response to Flow failed with: $t") }
+        }
     }
     awaitClose {
         // There's no way to unregister the callback from here.