| bucket | string | no | no | The name of the GCS bucket. |
| prefix | string | yes | no | Optional prefix to filter objects by. The value defaults to ``. |
| credentials_json | string | no | no | JSON credentials for authenticating with GCP. |
| scanner | scanner | no | no | The scanner by which the stream of bytes consumed will be broken out into individual messages. Scanners are useful for processing large sources of data without holding the entirety of it within memory. For example, the csv scanner allows you to process individual CSV rows without loading the entire CSV file in memory at once. |
