  Publish-subscribe systems are a popular approach for edge-based IoT use
cases: Heterogeneous, constrained edge devices can be integrated easily, with
message routing logic offloaded to edge message brokers. Message processing,
however, is still done on constrained edge devices. Complex content-based
filtering, the transformation between data representations, or message
extraction place a considerable load on these systems, and resulting
superfluous message transfers strain the network.
  In this paper, we propose Lotus, adding in-transit data processing to an edge
publish-subscribe middleware in order to offload basic message processing from
edge devices to brokers. Specifically, we leverage the Function-as-a-Service
paradigm, which offers support for efficient multi-tenancy, scale-to-zero, and
real-time processing. With a proof-of-concept prototype of Lotus, we validate
its feasibility and demonstrate how it can be used to offload sensor data
transformation to the publish-subscribe messaging middleware.
