State-only versions of the Filecoin Actors (smart-contracts)

These crates may be used to inspect and validate the internal state of Filecoin Actors.

For the smart-contracts, see: https://github.com/filecoin-project/builtin-actors
NOTE: The code in actors/ and fil_actors_shared/ is copy-pasted from the above repository. Therefore, it's advised to avoid refactoring such code in order to facilitate a smoother version upgrade process and potentially automate it. fil_actor_interface/ can be modified according to project's needs.

Why the copy-paste?

Given the copy-paste nature of the code, it's important to understand the reasons behind it, as it's not obvious at first glance.

Maintenance

We copy only a small subset of the code, strictly around actor releases which happen ~3 times a year. This is not a huge burden to maintain.

Note that the approach here is similar to the one in go-state-types.

Versioning

The builtin-actors are not following semver and in the current structure it would be hard to do so. Dependency update in a particular actor version might require a major version bump. Dependencies of the actors code not unified and so actors vX might use completely different version of cid than actors vX+1. This creates compilation and linking issues in the downstream projects that depend on the actors code.

Security

In the builtin-actors, the prior versions of the actors are not maintained. Any security issues found in the actors code are fixed in the latest version and the older versions are not updated. This creates a security risk for the projects that depend on the actors code (and not the smart-contracts). By copying the code, the projects can maintain the security of the actors code by updating the code to the latest version.

Tradeoff

Given the current approach, the code that exists here might not be exactly the same as the one released in the WASM bundles. This shouldn't be an issue, as most of it is not used for calculations but as state definitions.

Alternative approaches

The existence of most of the code in the actors/ and fil_actors_shared/ directories could be avoided by having different versioning in the builtin-actors. Each actor release, e.g., actors_v14, would be a separate directory in the repository. As such, it would allow the release to follow semver and keep the dependencies across all actors up-to-date. On the other hand, the code would still need to be copied on new releases so it's shifting the problem rather than solving it. That said, it's a valid approach and could be considered in the future.