Do not write empty files

lofar_stingray/aggregate.py

@@ -69,7 +69,7 @@ def _round_datetime_ms(timestamp: datetime) -> datetime:
     return timestamp - timedelta(microseconds=subtract_us)
 
 
-def main():
+def main() -> int:
     """Parser main method"""
     logger.debug("Starting hdf5 converter")
 
@@ -93,9 +93,12 @@ def main():
 
     # wait for data to arrive on S3
     logger.info("Waiting for metadata to arrive on S3 for %s", args.begin)
-    _ = metadata_storage.wait_for_packets(args.begin)
+    if not metadata_storage.wait_for_packets(args.begin):
+        logger.error("Metadata not available on S3")
     logger.info("Waiting for statistics to arrive on S3 for %s", args.end)
-    _ = statistics_storage.wait_for_packets(args.end)
+    if not statistics_storage.wait_for_packets(args.end):
+        logger.error("Statistics not available on S3")
+        return 1  # this is fatal
 
     # aggregate data
     aggregator_args = (
@@ -151,7 +154,10 @@ def main():
         logger.info("Upload completed for %s", args.destination)
 
     logger.info("Shutting down.")
+    return 0
 
 
 if __name__ == "__main__":
-    main()
+    import sys
+
+    sys.exit(main())