Add default callbacks in broadcast & scan operations

PiperOrigin-RevId: 484029311

presence/data_types.h

@@ -25,33 +25,49 @@ namespace presence {
 
 // Holds the callback of stop scan for client to invoke later.
 struct ScanSession {
-  std::function<void(Status)> stop_scan_callback;
+  // Nearby library would provide the implementation of this callback in
+  // runtime. Assigning with a default value NotImplemented to surface potential
+  // issue where library failed to provide the implementation.
+  std::function<Status(void)> stop_scan_callback = []() {
+    return Status{Status::Value::kNotImplemented};
+  };
 };
 
+// Callers would provide the implementation of these callbacks. If callers
+// don't need these signal updates, they can skip with the provided default
+// empty functions.
 struct ScanCallback {
   // Updates client with the result of start scanning.
-  std::function<void(Status)> start_scan_cb;
+  std::function<void(Status)> start_scan_cb = [](Status) {};
 
   // Reports a {@link PresenceDevice} being discovered.
-  std::function<void(PresenceDevice)> on_discovered_cb;
+  std::function<void(PresenceDevice)> on_discovered_cb = [](PresenceDevice) {};
 
   // Reports a {@link PresenceDevice} information(distance, and etc)
   // changed.
-  std::function<void(PresenceDevice)> on_updated_cb;
+  std::function<void(PresenceDevice)> on_updated_cb = [](PresenceDevice) {};
 
   // Reports a {@link PresenceDevice} is no longer within range.
-  std::function<void(PresenceDevice)> on_lost_cb;
+  std::function<void(PresenceDevice)> on_lost_cb = [](PresenceDevice) {};
 };
 
 /**
  * Holds the callback of stop broadcast for client to invoke later.
  */
 struct BroadcastSession {
-  std::function<void(Status)> stop_broadcast_callback;
+  // Nearby library would provide the implementation of this callback in
+  // runtime. Assiging with a default value NotImplemented to surface potential
+  // issue where library failed to provide the implementation.
+  std::function<Status(void)> stop_broadcast_callback = []() {
+    return Status{Status::Value::kNotImplemented};
+  };
 };
 
+// Callers would provide the implementation of these callbacks. If callers
+// don't need these signal updates, they can skip with the provided default
+// empty functions.
 struct BroadcastCallback {
-  std::function<void(Status)> start_broadcast_cb;
+  std::function<void(Status)> start_broadcast_cb = [](Status) {};
 };
 
 }  // namespace presence

presence/presence_service_test.cc

@@ -33,11 +33,15 @@ TEST(PresenceServiceTest, StartScan) {
   PresenceService presence_service;
   PresenceClient client = presence_service.CreatePresenceClient();
 
-  auto scan_session = client.StartScan({}, {
-      .start_scan_cb = [&](Status status) { scan_result = status; },
-  });
+  auto scan_session = client.StartScan(
+      {}, {
+              .start_scan_cb = [&](Status status) { scan_result = status; },
+          });
+  auto scan_session_with_default_params =
+      client.StartScan(ScanRequest(), ScanCallback());
 
-  ASSERT_EQ(scan_session, nullptr);
+  EXPECT_EQ(scan_session, nullptr);
+  EXPECT_EQ(scan_session_with_default_params, nullptr);
 }
 
 }  // namespace

presence/status.h

@@ -26,6 +26,7 @@ struct Status {
   enum class Value {
     kError = 0,
     kSuccess,
+    kNotImplemented,
   };
   Value value{Value::kError};
   bool Ok() const { return value == Value::kSuccess; }