RPC Compatibility

A running Lotus node can be accessed through an RPC interface. The RPC methods are listed here:

• V0 methods (stable): https://github.com/filecoin-project/lotus/blob/master/documentation/en/api-v0-methods.md
• V1 methods (unstable): https://github.com/filecoin-project/lotus/blob/master/documentation/en/api-v1-unstable-methods.md

The current status of compatibility can be checked by comparing a running Forest node with a running Lotus node:

1. Build Lotus with support for Calibnet and sync to HEAD. Run Lotus with LOTUS_FEVM_ENABLEETHRPC=1 to enable the Eth RPC methods.
2. Run Forest against Calibnet and sync to HEAD.
3. Run forest-tool api compare

The output will look like this:

If an entry for Lotus is not marked as Valid, this indicates that the Forest RPC client is buggy and incorrectly communicates with Lotus.

Limitations

Forest aims at being a drop-in replacement for Lotus and have support for all of the RPC methods. Note, some methods (like Filecoin.ChainHotGC) are Lotus-specific and are meaningless in Forest. Such methods should be no-ops in Forest.

Forest does not yet support mining and none of the mining-related RPC calls will be implemented in the foreseeable future.

Gateway

The lotus-gateway executable is a reverse-proxy that sanitizes RPC calls before they're forwarded to a Filecoin node. The forest-tool api compare command will fail if run against a gateway rather than directly against a node. This means API compatiblity testing has to be done with a local node rather than api.node.glif.io.

Use mitmproxy

Inspecting RPC calls is best done with a reverse proxy. If Lotus listens to port 1234 and Forest listens to port 2345, run the API compatibility tests through reverse proxies:

1. mitmproxy --mode reverse:http://localhost:2345 --listen-port 8080
2. mitmproxy --mode reverse:http://localhost:1234 --listen-port 8081
3. forest-tool api compare --forest /ip4/127.0.0.1/tcp/8080/http --lotus /ip4/127.0.0.1/tcp/8081/http

Request / Response pairs will show up in the mitmproxy windows.

Adding a new method

Checklist for adding a new RPC method:

1. Add method name in src/rpc_api/mod.rs and set the access level.
2. Add request/response data types to src/rpc_api/data_types.rs as needed.
3. Add RpcRequest in the appropriate file in src/rpc_client/.
4. Test the method in src/tool/subcommands/api_cmd.rs. The method should show up as Valid for Lotus and MissingMethod for Forest. Use mitmproxy to debug.
5. Implement Forest endpoint in src/rpc/, add it to the method list in src/rpc/mod.rs
6. Verify that the test from step 4 shows Valid for Forest.