Struct RuntimeExecutor 

pub struct RuntimeExecutor { /* private fields */ }

Runtime executor for executing Substrate runtime calls.

This struct wraps smoldot’s executor to run WASM runtime code against lazy-loaded storage via LocalStorageLayer.

Thread Safety

RuntimeExecutor is Send + Sync and can be shared across async tasks. Each call to RuntimeExecutor::call creates a new VM instance, so multiple calls can safely execute concurrently (though they will each have independent storage views).

Example

let executor = RuntimeExecutor::new(runtime_code, None)?;
let version = executor.runtime_version()?;
let result = executor.call("Metadata_metadata", &[], &storage).await?;

Cloning

RuntimeExecutor is cheap to clone. The runtime code is stored in an Arc<[u8]>, so cloning only increments a reference count. Multiple executors can share the same runtime code without copying.

Implementations

impl RuntimeExecutor

pub fn new( runtime_code: impl Into<Arc<[u8]>>, heap_pages: Option<u32>, ) -> Result<Self, ExecutorError>

Create a new executor with runtime WASM code.

Arguments

• runtime_code - The WASM runtime code (can be zstd-compressed). Accepts Vec<u8>, Arc<[u8]>, or any type that implements Into<Arc<[u8]>>.
• heap_pages - Number of heap pages. Use None to read from storage or use default.

Errors

Returns an error if the WASM code is invalid.

Example

// From Vec<u8> (takes ownership, no copy if Arc is created)
let executor = RuntimeExecutor::new(runtime_code_vec, None)?;

// From Arc<[u8]> (cheap clone, shares the same allocation)
let executor = RuntimeExecutor::new(runtime_code_arc.clone(), None)?;

pub fn with_config( runtime_code: impl Into<Arc<[u8]>>, heap_pages: Option<u32>, config: ExecutorConfig, ) -> Result<Self, ExecutorError>

Create a new executor with custom configuration.

Arguments

• runtime_code - The WASM runtime code (can be zstd-compressed).
• heap_pages - Number of heap pages. Use None to use the default.
• config - Custom execution configuration.

pub fn create_prototype(&self) -> Result<HostVmPrototype, ExecutorError>

Create a new HostVmPrototype optimized for repeated execution.

Uses ExecHint::ValidateAndCompile which enables ahead-of-time compilation, making subsequent calls faster. This is ideal for block building where the same runtime is called multiple times (initialize, apply extrinsics, finalize).

pub async fn call_with_prototype( &self, prototype: Option<HostVmPrototype>, method: &str, args: &[u8], storage: &LocalStorageLayer, ) -> (Result<RuntimeCallResult, ExecutorError>, Option<HostVmPrototype>)

Execute a runtime call, optionally reusing an existing VM prototype.

When prototype is Some, it is reused instead of creating a new one from raw WASM bytes. This avoids re-parsing and re-validating the WASM module on each call, which is significant for large runtimes (~2.5MB for Asset Hub).

Returns the call result along with the recovered prototype (if available) for reuse in subsequent calls.

Arguments

• prototype - An existing VM prototype to reuse, or None to create a fresh one.
• method - The runtime method to call.
• args - SCALE-encoded arguments for the method.
• storage - Storage layer for reading state from the forked chain.

pub async fn call( &self, method: &str, args: &[u8], storage: &LocalStorageLayer, ) -> Result<RuntimeCallResult, ExecutorError>

Execute a runtime call.

Arguments

• method - The runtime method to call (e.g., “Core_version”, “Metadata_metadata”).
• args - SCALE-encoded arguments for the method.
• storage - Storage layer for reading state from the forked chain.

Returns

Returns the call result including output bytes and storage diff.

Common Runtime Methods

Method	Purpose
Core_version	Get runtime version
Core_initialize_block	Initialize a new block
BlockBuilder_apply_extrinsic	Apply a transaction
BlockBuilder_finalize_block	Finalize block, get header
Metadata_metadata	Get runtime metadata

pub fn runtime_version(&self) -> Result<RuntimeVersion, ExecutorError>

Get the runtime version from the WASM code.

This reads the version from the WASM custom sections without executing any code.

Trait Implementations

impl Clone for RuntimeExecutor

fn clone(&self) -> RuntimeExecutor

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.