Private protocols, whose specifications are agnostic, are widely used in the Industrial Internet. While providing customized service, they also raise essential security concerns as well, due to their agnostic nature. The Protocol Reverse Analysis (PRA) techniques are developed to infer the specifications of private protocols. However, the conventional PRA techniques are far from perfection for the following reasons: (i) Error propagation: Canonical solutions strictly follow the "from keyword extraction to message clustering" serial structure, which deteriorates the performance for ignoring the interplay between the sub-tasks, and the error will flow and accumulate through the sequential workflow. (ii) Increasing diversity: As the protocols’ diversities of characteristics increase, tailoring for specific types of protocols becomes infeasible. To address these issues, we design a novel dual-track framework SPRA, and propose Share Learning, a new concept of protocol reverse analysis. Particularly, based on the share layer for protocol learning, SPRA builds a parallel workflow to co-optimize both the generative model for keyword extraction and the probability-based model for message clustering, which delivers automatic and robust syntax inference across diverse protocols and greatly improves the performance. Experiments on five real-world datasets demonstrate that the proposed SPRA achieves better performance compared with the state-of-art PRA methods.