fix: handle empty bucket

s3-age-metric/src/lambda_function.py

@@ -42,12 +42,12 @@ def lambda_handler(event, context):
             logger.fatal(str(e))
             raise e
 
-        s3_contents = sorted(s3_objects["Contents"], key= lambda i: i['LastModified'] )
-
-        oldest_item_in_set = s3_contents[0]['LastModified']
-        if oldest_item_in_set < oldest_item:
-            oldest_item = oldest_item_in_set
-            oldest_item_key = s3_contents[0]['Key']
+        if 'Contents' in s3_objects:
+            s3_contents = sorted(s3_objects['Contents'], key= lambda i: i['LastModified'] )
+            oldest_item_in_set = s3_contents[0]['LastModified']
+            if oldest_item_in_set < oldest_item:
+                oldest_item = oldest_item_in_set
+                oldest_item_key = s3_contents[0]['Key']
 
         if s3_objects['IsTruncated']:
             continuation_token = s3_objects['NextContinuationToken']

s3-age-metric/src/test_lambda_function.py

@@ -9,6 +9,24 @@
 
 from lambda_function import lambda_handler
 
+@mock_cloudwatch
+@mock_s3
+def test_no_object_in_bucket():
+
+    bucket_name = 'test_bucket'
+    bucket_prefix = ''
+    oldest_object_key = 'single_object'
+
+    s3_client = boto3.client('s3', region_name='us-east-1')
+    s3_client.create_bucket(Bucket=bucket_name)
+
+    with mock.patch.dict(os.environ, {'BUCKET_NAME': bucket_name, 'BUCKET_PREFIX': bucket_prefix}) as env:
+        result = lambda_handler({}, {})
+
+    assert result['bucket_name'] == 'test_bucket'
+    assert result['bucket_prefix'] == ''
+    assert result['oldest_item_key'] == None
+
 @mock_cloudwatch
 @mock_s3
 def test_single_object_in_bucket():
@@ -37,6 +55,41 @@ def test_single_object_in_bucket():
     assert result['oldest_item_key'] == 'single_object'
 
 
+@mock_cloudwatch
+@mock_s3
+def test_small_set_of_objects_in_bucket():
+
+    bucket_name = 'test_bucket'
+    bucket_prefix = ''
+
+    s3_client = boto3.client('s3', region_name='us-east-1')
+    s3_client.create_bucket(Bucket=bucket_name)
+
+    # Create a single item first which should be the oldest item
+    oldest_object_key = 'oldest_object'
+    s3_client.put_object(
+        Body='test content',
+        Bucket=bucket_name,
+        Key=oldest_object_key
+    )
+
+    time.sleep(1)
+
+    # Create a lot of items to ensure pagination works as expected
+    for i in range(10):
+        s3_client.put_object(
+            Body='test content',
+            Bucket=bucket_name,
+            Key=f'object_{i}'
+        )
+
+    with mock.patch.dict(os.environ, {'BUCKET_NAME': bucket_name, 'BUCKET_PREFIX': bucket_prefix}) as env:
+        result = lambda_handler({}, {})
+
+    assert result['bucket_name'] == 'test_bucket'
+    assert result['bucket_prefix'] == ''
+    assert result['oldest_item_key'] == 'oldest_object'
+
 @mock_cloudwatch
 @mock_s3
 def test_large_set_of_objects_in_bucket():