How are objects (files) submitted to Swarm storage?

A subset of HTTP/1.1 called SCSP (Simple Content Storage Protocol) is used for all client communications. A complete implementation of the SCSP protocol in multiple common languages is available in the Swarm Software Development Kit (SDK). The Content Gateway (formerly Cloudscaler) allows communication via S3 from your application client to the Gateway which translates the requests (via SCSP) to the Swarm nodes. In this case, your application needs only speak the S3 protocol.