Motile: Reflecting an Architectural Style in a Mobile Code Language

Decentralized services, that is, services distributed across multiple, distinct spheres of authority, offer substantial challenges; particularly when we demand that they be both adaptive and secure. We consider decentralized services in the context of COmputAtional State Transfer (COAST), an architectural style for which service adaptivity and security are principal concerns, and discuss how the style is reflected in our reference implementation: MOTILE, a mobile code language, and ISLAND, a complementary peering infrastructure. We analyze both COAST and MOTILE/ISLAND from the perspectives of safety and security, detailing how these goals influenced the language, its supporting infrastructure, and the extent to which MOTILE/ISLAND conforms to the COAST style. We then evaluate a portion of COASTCAST, a decentralized service for the distribution, sharing, and manipulation of soft, real-time, high-definition video written in MOTILE/ISLAND, to illustrate the security and safety that the COAST style conveys. The deep interplay between style and language is instructive. Our combined analyses and evaluation demonstrate that the three principal mechanisms of the style—mobile code, execution sites, and Capability URLs (CURLs)—act in concert to provide effective security and safety for decentralized services, with language-specific mechanisms playing a critical role.