Merge pull request #270 from flashbots/only-write-if-newly-empty

Only export empty blocks if there's an existing non-empty one

mev_inspect/s3_export.py

@@ -1,7 +1,8 @@
+import itertools
 import json
 import logging
 import os
-from typing import Optional
+from typing import Iterator, Optional, Tuple, TypeVar
 
 import boto3
 
@@ -26,6 +27,7 @@ logger = logging.getLogger(__name__)
 def export_block(inspect_db_session, block_number: int) -> None:
     export_bucket_name = get_export_bucket_name()
     client = get_s3_client()
+    object_key = f"mev_summary/flashbots_{block_number}.json"
 
     mev_summary_json_results = inspect_db_session.execute(
         statement=MEV_SUMMARY_EXPORT_QUERY,
@@ -34,19 +36,37 @@ def export_block(inspect_db_session, block_number: int) -> None:
         },
     )
 
+    first_value, mev_summary_json_results = _peek(mev_summary_json_results)
+    if first_value is None:
+        existing_object_size = _get_object_size(client, export_bucket_name, object_key)
+        if existing_object_size is None or existing_object_size == 0:
+            logger.info(f"Skipping block {block_number} - no data")
+            return
+
     mev_summary_json_fileobj = BytesIteratorIO(
         (f"{json.dumps(row)}\n".encode("utf-8") for (row,) in mev_summary_json_results)
     )
 
-    key = f"mev_summary/flashbots_{block_number}.json"
-
     client.upload_fileobj(
         mev_summary_json_fileobj,
         Bucket=export_bucket_name,
-        Key=key,
+        Key=object_key,
     )
 
-    logger.info(f"Exported to {key}")
+    logger.info(f"Exported to {object_key}")
+
+
+def _get_object_size(client, bucket: str, key: str) -> Optional[int]:
+    response = client.list_objects_v2(
+        Bucket=bucket,
+        Prefix=key,
+    )
+
+    for obj in response.get("Contents", []):
+        if obj["Key"] == key:
+            return obj["Size"]
+
+    return None
 
 
 def get_s3_client():
@@ -78,3 +98,15 @@ def get_export_aws_access_key_id() -> Optional[str]:
 
 def get_export_aws_secret_access_key() -> Optional[str]:
     return os.environ.get(EXPORT_AWS_SECRET_ACCESS_KEY_ENV)
+
+
+_T = TypeVar("_T")
+
+
+def _peek(iterable: Iterator[_T]) -> Tuple[Optional[_T], Iterator[_T]]:
+    try:
+        first = next(iterable)
+    except StopIteration:
+        return None, iter([])
+
+    return first, itertools.chain([first], iterable)