WASM API

The WASM API is currently semi-stable. A lot is in place and likely to not change or at least not change much. Until the WASM API is truly stable, the best documentation for it is the Rust reference implementation. When it is stable, this documentation will be updated.

In general the API provides you some functions you can call to read or manipulate state in the simulator. You are also expected to provide a few methods that the simulator can call in your script. See lotus-script-sys lib.rs and lotus-script script! macro for a complete list.

Parameter / return value passing

Simple types that fit in up to 64 bits are directly passed as is. Strings and complex data types are serialized with MessagePack. These are passed as a u64, containing two u32 where the first is the pointer to the serialized data and the second is the length of the data.

When passing from a script to the simulator, the data has only to be valid for the call itself. After that the script can deallocate.

When the simulator returns such a type, it first calls the allocate function in the script, which returns a pointer where the simulator will put the serialized data. The script then gets passed the corresponding u64 containing the pointer and length. The script is responsible for deallocating.

Calls with serialized parameters