The gateway package that can be found at github.com/pydio/cells/gateway/data/ provides a S3 API compatible gateway that provides the main access point to files and folders stored in Pydio.
It is based on a Minio server with a custom gateway and is registered as a Pydio Cells' microservice with id pydio.grpc.gateway.data.
Overview
The custom gateway provides access to the tree service and the various Pydio Datasources:
for all "stat" and "list" related queries, it uses the NodeProvider interface of Tree service,
for all "content" related queries (various GET and PUT request), it directly proxies to the underlying S3 server of each datasource.