Runtime approach

Author: ncooke3

FirebaseCore/Extension/FIRHeartbeatLogger.h

@@ -40,8 +40,7 @@ typedef NS_ENUM(NSInteger, FIRDailyHeartbeatCode) {
 
 #ifndef FIREBASE_BUILD_CMAKE
 /// Returns the header value for the heartbeat logger via the given completion handler..
-- (void)asyncHeaderValueWithCompletionHandler:(void (^)(NSString *_Nullable))completionHandler
-    API_AVAILABLE(ios(13.0), macosx(10.15), macCatalyst(13.0), tvos(13.0), watchos(6.0));
+- (void)asyncHeaderValueWithCompletionHandler:(void (^)(NSString *_Nullable))completionHandler;
 
 /// Return the header value for the heartbeat logger.
 - (NSString *_Nullable)headerValue;
@@ -87,8 +86,7 @@ NSString *_Nullable FIRHeaderValueFromHeartbeatsPayload(FIRHeartbeatsPayload *he
 /// @note This API is thread-safe.
 /// @param completionHandler A completion handler to process the flushed payload of heartbeats.
 - (void)flushHeartbeatsIntoPayloadWithCompletionHandler:
-    (void (^)(FIRHeartbeatsPayload *))completionHandler
-    API_AVAILABLE(ios(13.0), macosx(10.15), macCatalyst(13.0), tvos(13.0), watchos(6.0));
+    (void (^)(FIRHeartbeatsPayload *))completionHandler;
 #endif  // FIREBASE_BUILD_CMAKE
 
 /// Gets today's corresponding heartbeat code.

FirebaseCore/Sources/FIRHeartbeatLogger.m

@@ -74,11 +74,15 @@ - (NSString *_Nullable)headerValue {
   return FIRHeaderValueFromHeartbeatsPayload([self flushHeartbeatsIntoPayload]);
 }
 
-- (void)asyncHeaderValueWithCompletionHandler:(void (^)(NSString *_Nullable))completionHandler
-    API_AVAILABLE(ios(13.0), macosx(10.15), macCatalyst(13.0), tvos(13.0), watchos(6.0)) {
-  [self flushHeartbeatsIntoPayloadWithCompletionHandler:^(FIRHeartbeatsPayload *payload) {
-    completionHandler(FIRHeaderValueFromHeartbeatsPayload(payload));
-  }];
+- (void)asyncHeaderValueWithCompletionHandler:(void (^)(NSString *_Nullable))completionHandler {
+  if (@available(iOS 13.0, macOS 10.15, macCatalyst 13.0, tvOS 13.0, watchOS 6.0, *)) {
+    [self flushHeartbeatsIntoPayloadWithCompletionHandler:^(FIRHeartbeatsPayload *payload) {
+      completionHandler(FIRHeaderValueFromHeartbeatsPayload(payload));
+    }];
+  } else {
+    // no-op
+    completionHandler(nil);
+  }
 }
 
 - (FIRHeartbeatsPayload *)flushHeartbeatsIntoPayload {
@@ -87,11 +91,15 @@ - (FIRHeartbeatsPayload *)flushHeartbeatsIntoPayload {
 }
 
 - (void)flushHeartbeatsIntoPayloadWithCompletionHandler:
-    (void (^)(FIRHeartbeatsPayload *))completionHandler
-    API_AVAILABLE(ios(13.0), macosx(10.15), macCatalyst(13.0), tvos(13.0), watchos(6.0)) {
-  [_heartbeatController flushAsyncWithCompletionHandler:^(FIRHeartbeatsPayload *payload) {
-    completionHandler(payload);
-  }];
+    (void (^)(FIRHeartbeatsPayload *))completionHandler {
+  if (@available(iOS 13.0, macOS 10.15, macCatalyst 13.0, tvOS 13.0, watchOS 6.0, *)) {
+    [_heartbeatController flushAsyncWithCompletionHandler:^(FIRHeartbeatsPayload *payload) {
+      completionHandler(payload);
+    }];
+  } else {
+    // no-op
+    completionHandler(nil);
+  }
 }
 #endif  // FIREBASE_BUILD_CMAKE