Crate uni_plugin_extism 

Extism loader for the uni-db plugin framework.

uni-plugin-extism is the user-facing WASM loader. It sits parallel to uni-plugin-wasm (the Component Model loader). It follows the “Option C” hybrid pattern:

• Component Model (uni-plugin-wasm) — typed WIT contracts, capability gating by linker absence, used for the Lua-host, trusted built-ins, and plugins where soundness is load-bearing.
• Extism (this crate) — bytes-in / bytes-out, runtime-checked capabilities, used for user-authored UDFs that benefit from Extism’s mature 13-language host SDK story.

Trust is a property of the granted CapabilitySet, not of which ABI a plugin happens to use. A user can author a “trusted” plugin in Extism by granting it broad capabilities; a built-in can author against Extism if the structural advantages of CM aren’t load-bearing for its use case. The framework intentionally decouples ABI choice from trust tier.

Crate status

Loader is wired through the extism-sdk. ExtismLoader::load runs a two-pass instantiation (manifest probe, then plugin build) and surfaces failures as ExtismError::Instantiate. The host-fn registration surface (HostFnRegistry) and capability gating model are in place; the NotYetImplemented placeholder has been retired.

Why two WASM loaders

The proposal’s loader matrix (§5.1) keeps the four authoring categories (compile-time Rust, WASM, PyO3, Lua) but splits the WASM row into two ABIs. Both ABIs converge on the same PluginRegistrar — the executor cannot tell whether a registered ScalarPluginFn was authored against WIT or Extism. The two loaders share the wasmtime runtime (Extism is itself wasmtime-backed), so the runtime cost is one wasmtime process, not two.

Modules

adapter

Adapters bridging Extism plugin exports to the uni_plugin capability traits.

adapter_aggregate

Aggregate adapter — bridges Extism aggregate plugins to AggregatePluginFn / PluginAccumulator.

adapter_common

Shared helpers for the three Extism adapter modules.

adapter_procedure

Procedure adapter — bridges Extism procedure plugins to ProcedurePlugin.

error

Error types for the Extism loader.

exports

Plugin-export readers — manifest and register.

host_fns

Host function registration surface for Extism plugins.

host_svc

Capability-gated host services for Extism plugins.

ipc

Arrow IPC bridge — re-exported from uni-plugin-wasm-rt.

loader

ExtismLoader — top-level entry point for loading Extism plugins.

pool

Instance pool — re-exported from uni-plugin-wasm-rt.

wire_translate

Wire → internal type translation.

Structs

ExtismAggregateFn

AggregatePluginFn adapter wrapping an Extism plugin pool.

ExtismLoader

Top-level Extism plugin loader.

ExtismProcedure

ProcedurePlugin adapter wrapping an Extism plugin pool.

ExtismScalarFn

ScalarPluginFn adapter wrapping an Extism plugin pool.

HostFnRegistry

Registry of host functions available to Extism plugins.

RegistrationManifest

Top-level register export payload.

WireFnSignature

Wire-level scalar / aggregate / procedure signature shipped by a plugin’s register export.

Enums

ExtismError

Errors specific to the Extism loader.

RegistrationEntry

One registration entry — a single qname plus its kind + signature.

WireArgType

Wire-level argument type shipped by a plugin.

Functions

arrow_name_to_datatype

Map an Arrow primitive name (lowercase, as plugins write it) to arrow_schema::DataType.

parse_manifest_json

Parse the bytes returned by a plugin’s manifest export into an ExtismPluginManifest.

parse_registration_json

Parse the bytes returned by a plugin’s register export into a RegistrationManifest.

read_manifest_export

Call a live plugin’s manifest export and parse the response.

read_register_export

Call a live plugin’s register export and parse the response.

register_default_host_svc

Register the default capability-gated host-service surface on a loader.

wire_arg_to_internal

Translate a wire WireArgType into the internal ArgType.

wire_fn_sig_to_internal

Translate a full wire scalar/window signature into the internal FnSignature.

wire_null_handling_to_internal

Translate a wire null-handling string into the internal enum.

wire_volatility_to_internal

Translate a wire volatility string into the DataFusion enum.