gRPC Transaction Simulation Service

[aaronc]

Summary

As discussed in #5894 (comment), we need an approach for REST/gRPC-based transaction generation to either upgrade or replace the existing REST tx routes. The approach adopted here is to provide a gRPC tx simulation service (see #5922 (comment))

• Add simulation gRPC service definition #6872 Define the simulation service
• Implement cosmos.tx.Service gRPC service

[github-actions]

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[aaronc]

I started working on a protobuf service definition for this. Initially, I started by just copying the current transaction generation BaseReq and creating a service that took a BaseReq and some Msgs and does basically what the existing REST endpoints do.

In discussing with my team, I am rethinking this altogether.

My assessment is that REST transaction generation is basically an anti-pattern. Clients now have the full protobuf Tx schema and should have no problem constructing a Tx. What they need is basically simulation.

Signing transaction content returned from a possibly untrusted service should be avoided at all costs. Maybe the current REST tx endpoints were needed given the situation with amino. But all of the users I talked with when designing the current Tx understood the dangers of signing untrusted content. So I don't feel there is actually a huge benefit to adding this functionality and actually some downsides in that it adds something that could be used to exploit less savvy users.

I propose instead that we create a simple gRPC service for Tx simulation and gas/fee estimation. As I understand it, this should satisfy the core need.

How does this sound as an alternative?

[alexanderbez]

ACK from me @aaronc -- less work as well 👍