fix(s3_vectors): reject a store id with an empty bucket or index part

A "bucket:" or ":index" id split into an empty name, so ingestion silently
generated a fresh index and search sent the empty name to AWS. Both sides now
raise the existing format error through the shared helper.

litellm/llms/s3_vectors/vector_stores/transformation.py

@@ -33,12 +33,12 @@ S3_VECTORS_STORE_ID_ERROR: Final = (
 
 
 def split_s3_vectors_store_id(vector_store_id: str, fallback_bucket_name: object) -> tuple[str, str]:
-    if ":" in vector_store_id:
-        bucket_name, index_name = vector_store_id.split(":", 1)
-        return bucket_name, index_name
-    if not isinstance(fallback_bucket_name, str) or not fallback_bucket_name:
+    id_bucket_name, separator, id_index_name = vector_store_id.partition(":")
+    bucket_name: Final = id_bucket_name if separator else fallback_bucket_name
+    index_name: Final = id_index_name if separator else vector_store_id
+    if not isinstance(bucket_name, str) or not bucket_name or not index_name:
         raise ValueError(S3_VECTORS_STORE_ID_ERROR)
-    return fallback_bucket_name, vector_store_id
+    return bucket_name, index_name
 
 
 class S3VectorsVectorStoreConfig(BaseQueryEmbeddingVectorStoreConfig, BaseAWSLLM):

tests/test_litellm/llms/s3_vectors/vector_stores/test_s3_vectors_transformation.py

@@ -236,6 +236,22 @@ class TestS3VectorsVectorStoreConfig:
 
         assert executor.calls == []
 
+    @pytest.mark.parametrize("vector_store_id", ["test-bucket:", ":test-index"])
+    def test_transform_search_request_rejects_an_empty_bucket_or_index_in_the_id(self, vector_store_id):
+        config = S3VectorsVectorStoreConfig()
+        executor = _RecordingExecutor()
+
+        with pytest.raises(ValueError, match="vector_store_id must be in format 'bucket_name:index_name'"):
+            config.transform_search_vector_store_request(
+                **_search_kwargs(
+                    vector_store_id=vector_store_id,
+                    litellm_params={"vector_bucket_name": "test-bucket"},
+                    embedding_executor=executor,
+                )
+            )
+
+        assert executor.calls == []
+
     def test_transform_search_request_bucket_from_litellm_params(self):
         config = S3VectorsVectorStoreConfig()
 

tests/test_litellm/rag/ingestion/test_s3_vectors_ingestion.py

@@ -50,3 +50,16 @@ def test_bucket_alone_leaves_the_index_to_be_generated():
 def test_no_bucket_anywhere_is_rejected(vector_store):
     with pytest.raises(ValueError, match=STORE_ID_FORMAT_ERROR):
         _ingestion(**vector_store)
+
+
+@pytest.mark.parametrize(
+    "vector_store",
+    [
+        {"vector_store_id": "my-embeddings:"},
+        {"vector_store_id": ":my-index"},
+        {"vector_store_id": "my-embeddings:", "vector_bucket_name": "my-embeddings"},
+    ],
+)
+def test_an_empty_bucket_or_index_in_the_store_id_is_rejected_instead_of_generating_an_index(vector_store):
+    with pytest.raises(ValueError, match=STORE_ID_FORMAT_ERROR):
+        _ingestion(**vector_store)