most_recent_message as reusable function

1 files changed, 25 insertions, 0 deletions

diff --git a/python/fatcat_tools/workers/worker_common.py b/python/fatcat_tools/workers/worker_common.py
index 77ea2c15..66150644 100644
--- a/python/fatcat_tools/workers/worker_common.py
+++ b/python/fatcat_tools/workers/worker_common.py
@@ -9,6 +9,31 @@ from pykafka import KafkaClient
 from fatcat_client.rest import ApiException
 
 
+def most_recent_message(topic):
+    """
+    Tries to fetch the most recent message from a given topic.
+    This only makes sense for single partition topics, though could be
+    extended with "last N" behavior.
+
+    Following "Consuming the last N messages from a topic"
+    from https://pykafka.readthedocs.io/en/latest/usage.html#consumer-patterns
+    """
+    consumer = topic.get_simple_consumer(
+        auto_offset_reset=OffsetType.LATEST,
+        reset_offset_on_start=True)
+    offsets = [(p, op.last_offset_consumed - 1)
+                for p, op in consumer._partitions.items()]
+    offsets = [(p, (o if o > -1 else -2)) for p, o in offsets]
+    if -2 in [o for p, o in offsets]:
+        return None
+    else:
+        consumer.reset_offsets(offsets)
+        msg = islice(consumer, 1)
+        if msg:
+            return list(msg)[0].value
+        else:
+            return None
+
 class FatcatWorker:
     """
     Common code for for Kafka producers and consumers.