[object_store] Fix empty Multipart Upload for AWS S3 (#5405)

* Fix empty multipart put for AWS S3

* Fix lint

Author: andrebsguedes

object_store/src/aws/client.rs

@@ -538,6 +538,16 @@ impl S3Client {
         upload_id: &str,
         parts: Vec<PartId>,
     ) -> Result<PutResult> {
+        let parts = if parts.is_empty() {
+            // If no parts were uploaded, upload an empty part
+            // otherwise the completion request will fail
+            let part = self
+                .put_part(location, &upload_id.to_string(), 0, Bytes::new())
+                .await?;
+            vec![part]
+        } else {
+            parts
+        };
         let request = CompleteMultipartUpload::from(parts);
         let body = quick_xml::se::to_string(&request).unwrap();
 

object_store/src/lib.rs

@@ -2200,6 +2200,21 @@ mod tests {
 
         let meta = storage.head(&path).await.unwrap();
         assert_eq!(meta.size, chunk_size * 2);
+
+        // Empty case
+        let path = Path::from("test_empty_multipart");
+
+        let id = multipart.create_multipart(&path).await.unwrap();
+
+        let parts = vec![];
+
+        multipart
+            .complete_multipart(&path, &id, parts)
+            .await
+            .unwrap();
+
+        let meta = storage.head(&path).await.unwrap();
+        assert_eq!(meta.size, 0);
     }
 
     #[cfg(any(feature = "azure", feature = "aws"))]