Crate faucet_transform_wasm 

WebAssembly-as-transform for faucet-stream.

Loads a user-provided, precompiled .wasm module through wasmtime and invokes an exported function once per record. Any language that compiles to core WebAssembly (Rust, TinyGo, AssemblyScript, Zig, C/C++, …) can express arbitrary per-record logic in a faucet pipeline without forking the project.

WasmTransformConfig is the user-facing config; WasmTransform is the compiled runtime that owns the wasmtime engine + module and runs it per page via WasmTransform::into_page_stage.

Sandbox

Modules run in a strict sandbox. Each record call is bounded by fuel (a deterministic CPU limit) and by memory (linear-memory cap). The only host imports are faucet_v1::log and faucet_v1::now_ns — there is no filesystem, network, clock, or environment access in v1.

ABI (v1)

The module must export:

• alloc(len: i32) -> i32 — allocate len bytes of linear memory, return the offset. The host writes the input JSON there before each call.
• <function>(ptr: i32, len: i32) -> i64 — the transform entry point (name from WasmTransformConfig::function, default "transform"). Input is UTF-8 JSON at [ptr, ptr+len). The packed return value is (out_ptr as u64) << 32 | (out_len as u64):
  • 0 → drop the record (filter it out).
  • u64::MAX → error; the host reads the message from the optional error_ptr() / error_len() exports.
  • otherwise → the output UTF-8 JSON at [out_ptr, out_ptr+out_len).
• memory — the exported linear memory (standard name).

Optional exports: free(ptr: i32, len: i32) (host calls it after copying output out), error_ptr() -> i32 / error_len() -> i32 (error message).

See the crate README and the docs/book cookbook page for full details and reference modules.

Structs

WasmTransform

A compiled WASM transform. The engine + module are compiled once and reused across the row’s pages; each page gets a fresh instance.

WasmTransformConfig

Configuration for the wasm transform.

Enums

WasmOnError

Policy for a per-record module failure.