TransOra: A Transaction-preserving and Transparent Distributed Oracle on Permissioned Blockchain For Hybrid Smart Contracts

Abstract

Hybrid transaction in blockchain enlarges the application domain of smart contracts by enabling off-chain data access. In support of the hybrid transaction, blockchain oracle is an indispensable middleware responsible for receiving data-request tasks and pushing the result back to chain. Though solutions supporting hybrid transactions do exist, they are less featured or applicable for both contract and application developers. On one hand, the racing-condition among several concurrent hybrid transactions should be manually resolved by contract developers. On the other hand, application developers have to associate each individual task with its parent hybrid transaction in order to obtain the result. In this paper, a novel block-chain oracle platform with a set of simple but unified API for both hybrid and traditional transactions is proposed. Firstly, we design and implement a transactional storage layer and a transaction scheduler for transaction preservation and ordering. Secondly, with the help of an automatic result tracing mechanism, application developers are able to acquire transaction results transparently without awareness of oracles and underlying task execution. Experiments are conducted on one of current prevalent permissioned blockchain platforms, RepChain, and the result shows that all of the system design goals are fulfilled with merely an acceptable loss of performance.