Crate uni_plugin_rhai 

Rhai-script loader for the uni-db plugin framework.

uni-plugin-rhai is the host-embedded scripting loader. It sits parallel to uni-plugin-extism (Extism bytes-in/bytes-out WASM) and uni-plugin-wasm (Component Model WIT) but takes a fundamentally different shape: there is no WASM wrapper, no IPC, no instance pool — the Rhai rhai::Engine is embedded directly in the host process.

Why Rhai

Rhai fills the “dynamic AND sandboxed” loader quadrant:

• Pure Rust — no C toolchain, no WASM wrapper, no separate runtime. Builds anywhere uni-db builds.
• Sandboxed by language design — Rhai has no built-in I/O. Every effectful operation comes from a host-registered function. Registering a function is opt-in; absence is the default and matches the framework’s capability-gating contract (proposal §10.2).
• Resource limits are first-class on the Engine: set_max_operations, set_max_call_levels, set_max_string_size, set_max_array_size, set_max_map_size. No ad-hoc instruction-count shim.
• Actively maintained on crates.io 1.x.

Capability gating — Engine-import absence

The capability-enforcement layer 2 for Rhai is Engine-import absence: the loader registers a host function (uni.fs.read, uni.http.get, uni.query, …) on the per-plugin Engine only when the corresponding capability is in the effective grant set. A plugin without Capability::Filesystem cannot call uni.fs.read — Rhai raises ErrorFunctionNotFound at parse-resolution time. This is the in-host analogue of Component Model’s linker-absence guarantee.

Crate status

Implemented in phases. Phase 1 (this) ships the crate scaffold; phases 2+ wire the Engine factory, manifest parser, adapters, and Uni::load_rhai_plugin.

Modules

adapter

Scalar function adapter — turns a Rhai callable into an uni_plugin::traits::scalar::ScalarPluginFn.

adapter_aggregate

Aggregate function adapter — Rhai-side aggregate via four named fns.

adapter_procedure

Procedure adapter — Rhai-side procedure returning a stream of yield rows.

columns

Vectorized column userdata for Rhai plugins.

dynamic_bridge

Bridge between Rhai’s Dynamic and Arrow / DataFusion scalar types.

engine

Per-plugin rhai::Engine factory.

error

Error types for the Rhai loader.

host_fn_impls

Capability-gated host fns surfaced to Rhai scripts.

host_fns

Host function registration surface for Rhai plugins.

loader

Rhai loader — three-phase load mirroring ExtismLoader::load.

manifest

Rhai-side manifest reader.

runtime

Shared per-plugin runtime — the Engine + AST adapters hold by reference.

wire_translate

Translate wire-level type strings into internal Arrow DataTypes and uni_plugin signature types.

Structs

AggregateEntry

One aggregate fn entry.

LoadOutcome

Outcome of a successful Rhai plugin load.

ProcedureEntry

One procedure entry.

RhaiAccumulator

Per-group accumulator backed by a rhai::Dynamic state value.

RhaiAggregateFn

Aggregate fn adapter — implements AggregatePluginFn by dispatching to four Rhai callables.

RhaiHostFnRegistry

Registry of host functions available to Rhai plugins.

RhaiHostFnSpec

Metadata + registrar describing a single host function exposed to Rhai plugins.

RhaiLoader

Rhai loader.

RhaiManifest

Result of parsing a uni_manifest() return value.

RhaiPluginRuntime

Per-plugin runtime state shared across every adapter the plugin registers.

RhaiProcedure

Per-procedure Rhai callable adapter.

RhaiScalarFn

Per-row Rhai scalar function adapter.

ScalarEntry

One scalar fn entry from the Rhai manifest.

Enums

RhaiError

Errors specific to the Rhai loader.

Constants

DEFAULT_MAX_CALL_LEVELS

Default maximum recursion depth for Rhai scripts. Overridable by scripts via the loader’s per-plugin engine configuration; future: expose a Capability::MaxCallLevels(N) so plugins can request more.

Functions

build_engine

Build a Rhai engine pre-configured for a single plugin’s effective capability set.