Sdk prototype

[charlag]

#6427

[charlag]

It seems like we are in a pickle with wasm:

• to load wasm reliably we need import.meta.url
• it is only available in module context
• we cannot run worker as a module because of Safari
• we cannot dynamically import worker entry point because we need to set message handler right away
• we can postpone message handling by initiating the start from the worker side but we need to build some queue until the proper startup

[charlag]

Results for SDK prototype in Rust:

• on all platforms it is possible:
  • to call functions and methods on class-like objects, also async
  • to pass primitives around
  • to have error handling
  • to generate wrappers for methods & classes
• lessons learned:
  • We need to manage lifetimes of Rust objects (read: objects with behavior/classes) for all
    targets except Swift
    • this can be possibly avoided in JS/WASM with weak reference support
  • we can bundle WASM in a more automatic way than we do now but we need to change worker bootstrap a bit
  • wasm-bindgen can generate the whole npm module for us
  • wasm-bindgen doesn't have a good story for passing data structures around
    • it supports either classes with lifetimes or we have to convert data to/from JsValue
  • uniffi can be integrated into mobile app build but would probably be the best to distribute separate
    packages
  • uniffi can be described with both UDL and/or annotations, wasm-bindgen with annotations
  • uniffi and wasm-bindgen may conflict in some cases, e.g. constructor has different signatures
• unanswered questions:
  • what is the module structure?
    • we can look at how matrix sdk works with module for cryptography and more
  • how do we facilitate passing plain objects for wasm target?
    • do we need to do that? If there are a few places we might do it by hand
    • see #[wasm_bindgen(...)] pragma to convert to plain Object instead of Class rustwasm/wasm-bindgen#2645
    • see https://github.com/hamza1311/ducktor
  • what is the cutoff point for Rust code?
    • Do we want idiomatic wrappers in each language or do we just provide generated mappings?
  • how do we distribute the API metadata (entities & such)
    • does it make sense to only generate them in the target language and have generic/untyped API for Rust?
      • reducing number of types that need to be bridged/converted will reduce the code size a lot
  • do we want to include both WASM & native copy of SDK for mobile apps?