WASM Tool API

Overview

The WASM tool system provides secure sandboxed execution for untrusted tools using Wasmtime. It follows patterns from NEAR blockchain and modern WASM best practices:

Compile once, instantiate fresh: Tools are validated and compiled at registration time. Each execution creates a fresh instance.
Fuel metering: CPU usage is limited via Wasmtime’s fuel system.
Memory limits: Memory growth is bounded via ResourceLimiter.
Capability-based security: Features are opt-in via Capabilities.
Extended host API: Log, time, workspace, HTTP, tool invoke, secrets.

Architecture

┌─────────────────────────────────────────────────────────────────────────────┐
│                              WASM Tool Execution                             │
│                                                                              │
│   WASM Tool ──▶ Host Function ──▶ Allowlist ──▶ Credential ──▶ Execute     │
│   (untrusted)   (boundary)        Validator     Injector       Request      │
│                                                                    │        │
│                                                                    ▼        │
│                              ◀────── Leak Detector ◀────── Response        │
│                          (sanitized, no secrets)                            │
└─────────────────────────────────────────────────────────────────────────────┘

Security Constraints

Threat	Mitigation
CPU exhaustion	Fuel metering
Memory exhaustion	ResourceLimiter, 10MB default
Infinite loops	Epoch interruption + tokio timeout
Filesystem access	No WASI FS, only host workspace_read
Network access	Allowlisted endpoints only
Credential exposure	Injection at host boundary only
Secret exfiltration	Leak detector scans all outputs
Log spam	Max 1000 entries, 4KB per message
Path traversal	Validate paths (no `..`, no `/` prefix)
Trap recovery	Discard instance, never reuse
Side channels	Fresh instance per execution
Rate abuse	Per-tool rate limiting
WASM tampering	BLAKE3 hash verification on load

WasmToolRuntime

The runtime manages WASM compilation and execution.

Constructor

src/tools/wasm/runtime.rs

pub fn new(config: WasmRuntimeConfig) -> Result<Self, WasmError>

Creates a new WASM runtime with the specified configuration.

config

WasmRuntimeConfig

required

Runtime configuration including engine settings and security limits

Returns: Result<WasmToolRuntime, WasmError>

prepare

src/tools/wasm/runtime.rs

pub async fn prepare(
    &self,
    name: &str,
    wasm_bytes: &[u8],
    limits: Option<ResourceLimits>,
) -> Result<PreparedModule, WasmError>

Validates and compiles a WASM component. This is done once at registration time.

name

&str

required

Tool name for error messages

wasm_bytes

&[u8]

required

Raw WASM component bytes

limits

Option<ResourceLimits>

Optional resource limits (uses defaults if None)

Returns: Result<PreparedModule, WasmError> - Compiled module ready for execution

WasmToolWrapper

Wraps a WASM component as a Tool implementation.

Constructor

src/tools/wasm/wrapper.rs

pub fn new(
    runtime: Arc<WasmToolRuntime>,
    prepared: PreparedModule,
    capabilities: Capabilities,
) -> Self

Creates a new WASM tool wrapper.

runtime

Arc<WasmToolRuntime>

required

Shared runtime for execution

prepared

PreparedModule

required

Pre-compiled module from runtime.prepare()

capabilities

Capabilities

required

Security capabilities to grant the tool

Configuration Methods

src/tools/wasm/wrapper.rs

pub fn with_description(mut self, description: impl Into<String>) -> Self
pub fn with_schema(mut self, schema: serde_json::Value) -> Self
pub fn with_secrets_store(mut self, store: Arc<dyn SecretsStore + Send + Sync>) -> Self
pub fn with_oauth_refresh(mut self, config: OAuthRefreshConfig) -> Self

Optional configuration overrides.

Capabilities

Defines what host functions a WASM tool can access.

src/tools/wasm/capabilities.rs

pub struct Capabilities {
    pub http: Option<HttpCapability>,
    pub workspace: Option<WorkspaceCapability>,
    pub tool_invoke: Option<ToolInvokeCapability>,
    pub secrets: Option<SecretsCapability>,
}

Constructor

src/tools/wasm/capabilities.rs

pub fn none() -> Self

Creates a capabilities set with all features disabled (log and time are always available).

Configuration Methods

src/tools/wasm/capabilities.rs

pub fn with_http(mut self, http: HttpCapability) -> Self
pub fn with_workspace(mut self, workspace: WorkspaceCapability) -> Self
pub fn with_tool_invoke(mut self, tool_invoke: ToolInvokeCapability) -> Self
pub fn with_secrets(mut self, secrets: SecretsCapability) -> Self

HttpCapability

Allows HTTP requests to specific endpoints.

src/tools/wasm/capabilities.rs

pub struct HttpCapability {
    pub allowed_endpoints: Vec<EndpointPattern>,
    pub rate_limit: Option<RateLimitConfig>,
    pub credentials: HashMap<String, crate::secrets::CredentialMapping>,
}

Constructor

src/tools/wasm/capabilities.rs

pub fn new(allowed_endpoints: Vec<EndpointPattern>) -> Self

allowed_endpoints

Vec<EndpointPattern>

required

List of allowed URL patterns

EndpointPattern

Defines an allowed HTTP endpoint pattern.

src/tools/wasm/capabilities.rs

pub struct EndpointPattern {
    pub host: String,
    pub port: Option<u16>,
    pub path_prefix: Option<String>,
    pub allowed_methods: Vec<String>,
}

Constructors

src/tools/wasm/capabilities.rs

pub fn host(host: impl Into<String>) -> Self
pub fn localhost(port: u16) -> Self

pub fn with_port(mut self, port: u16) -> Self
pub fn with_path_prefix(mut self, prefix: impl Into<String>) -> Self
pub fn with_methods(mut self, methods: Vec<String>) -> Self

Example:

let pattern = EndpointPattern::host("api.openai.com")
    .with_path_prefix("/v1/")
    .with_methods(vec!["GET".into(), "POST".into()]);

WorkspaceCapability

Allows access to workspace files.

src/tools/wasm/capabilities.rs

pub struct WorkspaceCapability {
    pub reader: WorkspaceReader,
    pub allowed_paths: Option<Vec<String>>,
}

Constructor

src/tools/wasm/capabilities.rs

pub fn new(reader: WorkspaceReader) -> Self

reader

WorkspaceReader

required

Workspace reader for file access

Configuration

src/tools/wasm/capabilities.rs

pub fn with_allowed_paths(mut self, paths: Vec<String>) -> Self

Restricts access to specific paths only.

ResourceLimits

Defines execution resource limits.

src/tools/wasm/limits.rs

pub struct ResourceLimits {
    pub max_memory_bytes: usize,
    pub fuel_config: FuelConfig,
    pub max_execution_time: Duration,
}

max_memory_bytes

usize

default:"10MB"

Maximum memory the WASM instance can allocate

fuel_config

FuelConfig

Fuel-based CPU metering configuration

max_execution_time

Duration

default:"30s"

Maximum execution time before timeout

Defaults

src/tools/wasm/limits.rs

pub const DEFAULT_MEMORY_LIMIT: usize = 10 * 1024 * 1024; // 10 MB
pub const DEFAULT_FUEL_LIMIT: u64 = 200_000_000; // ~100ms on modern CPU
pub const DEFAULT_TIMEOUT: Duration = Duration::from_secs(30);

Storage

Persist WASM tools to the database.

WasmToolStore Trait

src/tools/wasm/storage.rs

#[async_trait]
pub trait WasmToolStore: Send + Sync {
    async fn store(&self, params: StoreToolParams) -> Result<StoredWasmTool, WasmStorageError>;
    async fn get(&self, user_id: &str, name: &str) -> Result<StoredWasmTool, WasmStorageError>;
    async fn get_with_binary(&self, user_id: &str, name: &str) -> Result<StoredWasmToolWithBinary, WasmStorageError>;
    async fn list(&self, user_id: &str) -> Result<Vec<StoredWasmTool>, WasmStorageError>;
    async fn delete(&self, user_id: &str, name: &str) -> Result<(), WasmStorageError>;
    async fn store_capabilities(&self, tool_id: Uuid, caps: StoredCapabilities) -> Result<(), WasmStorageError>;
    async fn get_capabilities(&self, tool_id: Uuid) -> Result<Option<StoredCapabilities>, WasmStorageError>;
}

StoreToolParams

src/tools/wasm/storage.rs

pub struct StoreToolParams {
    pub user_id: String,
    pub name: String,
    pub description: String,
    pub wasm_binary: Vec<u8>,
    pub parameters_schema: serde_json::Value,
    pub trust_level: TrustLevel,
    pub source: String,
}

Error Types

WasmError

src/tools/wasm/error.rs

pub enum WasmError {
    CompilationFailed(String),
    InstantiationFailed(String),
    ExecutionFailed(String),
    Trapped(TrapInfo),
    Timeout,
    FuelExhausted,
    InvalidComponent(String),
    InvalidParameters(String),
    CapabilityDenied(String),
}

TrapInfo

src/tools/wasm/error.rs

pub struct TrapInfo {
    pub code: TrapCode,
    pub message: String,
    pub backtrace: Option<String>,
}

Example: Register WASM Tool

use ironclaw::tools::wasm::{
    WasmToolRuntime, WasmRuntimeConfig, WasmToolWrapper,
    Capabilities, HttpCapability, EndpointPattern,
};
use std::sync::Arc;

// Create runtime
let runtime = Arc::new(WasmToolRuntime::new(WasmRuntimeConfig::default())?);

// Load WASM bytes
let wasm_bytes = std::fs::read("my_tool.wasm")?;

// Prepare the module
let prepared = runtime.prepare("my_tool", &wasm_bytes, None).await?;

// Configure capabilities
let capabilities = Capabilities::none()
    .with_http(HttpCapability::new(vec![
        EndpointPattern::host("api.example.com")
            .with_path_prefix("/v1/")
            .with_methods(vec!["GET".into(), "POST".into()]),
    ]));

// Create wrapper
let tool = WasmToolWrapper::new(runtime, prepared, capabilities)
    .with_description("My custom WASM tool");

// Register with tool registry
registry.register(Arc::new(tool)).await;

Example: Store and Load

use ironclaw::tools::wasm::{
    PostgresWasmToolStore, StoreToolParams, TrustLevel,
};

// Create store
let store = PostgresWasmToolStore::new(pool);

// Store tool
let tool = store.store(StoreToolParams {
    user_id: "user_123".into(),
    name: "my_tool".into(),
    description: "Does something useful".into(),
    wasm_binary: wasm_bytes,
    parameters_schema: schema,
    trust_level: TrustLevel::Trusted,
    source: "local".into(),
}).await?;

// Load and register
registry.register_wasm_from_storage(
    &store,
    &runtime,
    "user_123",
    "my_tool",
).await?;

Core Components

Tools

Overview

Architecture

Security Constraints

WasmToolRuntime

Constructor

prepare

WasmToolWrapper

Constructor

Configuration Methods

Capabilities

Constructor

Configuration Methods

HttpCapability

Constructor

EndpointPattern

Constructors

WorkspaceCapability

Constructor

Configuration

ResourceLimits

Defaults

Storage

WasmToolStore Trait

StoreToolParams

Error Types

WasmError

TrapInfo

Example: Register WASM Tool

Example: Store and Load

Build docs developers (and LLMs) love

Core Components

Tools

​Overview

​Architecture

​Security Constraints

​WasmToolRuntime

​Constructor

​prepare

​WasmToolWrapper

​Constructor

​Configuration Methods

​Capabilities

​Constructor

​Configuration Methods

​HttpCapability

​Constructor

​EndpointPattern

​Constructors

​WorkspaceCapability

​Constructor

​Configuration

​ResourceLimits

​Defaults

​Storage

​WasmToolStore Trait

​StoreToolParams

​Error Types

​WasmError

​TrapInfo

​Example: Register WASM Tool

​Example: Store and Load

Build docs developers (and LLMs) love

Overview

Architecture

Security Constraints

WasmToolRuntime

Constructor

prepare

WasmToolWrapper

Constructor

Configuration Methods

Capabilities

Constructor

Configuration Methods

HttpCapability

Constructor

EndpointPattern

Constructors

WorkspaceCapability

Constructor

Configuration

ResourceLimits

Defaults

Storage

WasmToolStore Trait

StoreToolParams

Error Types

WasmError

TrapInfo

Example: Register WASM Tool

Example: Store and Load