WASM Execution

The HCS-12 WASM execution system in the Standards SDK handles loading and executing WebAssembly modules for HashLinks actions.

WASM Interface

All actions must implement the WasmInterface with INFO, POST, and GET methods:

interface WasmInterface {
  // Returns module metadata in deterministic JSON format
  INFO(): string;

  // Executes actions that modify state or submit transactions
  POST(
    action: string,
    params: string,
    network: 'mainnet' | 'testnet',
    memo: string
  ): Promise<string>;

  // Retrieves information without modifying state
  GET(
    action: string,
    params: string,
    network: 'mainnet' | 'testnet'
  ): Promise<string>;
}

WASM Executor

The SDK provides a WasmExecutor for executing WASM modules:

import { WasmExecutor } from '@hashgraphonline/standards-sdk';

// Create WASM executor
const wasmExecutor = new WasmExecutor(logger, 'testnet');

// Execute an action
const result = await wasmExecutor.execute(actionRegistration, {
  method: 'POST',
  params: {
    action: 'transfer',
    amount: 100,
    to: '0.0.987654'
  }
});

JavaScript Wrapper Support

For wasm-bindgen generated modules, JavaScript wrappers are supported:

// Action registration with JavaScript wrapper
const actionRegistration: ActionRegistration = {
  p: 'hcs-12',
  op: 'register',
  t_id: '0.0.123456',        // WASM module topic ID
  js_t_id: '0.0.123457',     // JavaScript wrapper topic ID
  hash: 'e3b0c442...',       // INFO method result hash
  wasm_hash: 'a1b2c3d4...',  // WASM binary hash
  js_hash: 'f5e6d7c8...',    // JavaScript wrapper hash
  interface_version: '0.2.95' // wasm-bindgen version
};

// Execute with JavaScript wrapper
const result = await wasmExecutor.execute(actionRegistration, {
  method: 'POST',
  params: {
    action: 'transfer',
    amount: 100,
    to: '0.0.987654'
  }
});

Module Info Extraction

The SDK can extract module info from WASM binaries:

import { ActionBuilder, WasmValidator } from '@hashgraphonline/standards-sdk';

// Extract metadata from WASM data
const validator = new WasmValidator(logger);
const moduleInfo = await validator.extractMetadata(wasmData);

// Generate INFO hash
const infoHash = await new ActionBuilder(logger).generateInfoHash(moduleInfo);

// Generate WASM hash
const wasmHash = await new ActionBuilder(logger).generateWasmHash(wasmData);

WASM Loading

The executor handles WASM module loading from HCS-1 topics:

// Load WASM module from topic
const wasmResult = await hrlResolver.resolve(action.t_id, {
  network: 'testnet',
  returnRaw: true
});

// Load JavaScript wrapper from topic
const jsResult = await hrlResolver.resolve(action.js_t_id!, {
  network: 'testnet',
  returnRaw: false
});

Execution Context

Actions receive execution context with network and memo information:

interface WasmExecutionContext {
  method: 'INFO' | 'POST' | 'GET';
  params: {
    action: string;
    [key: string]: any;
  };
  state?: Record<string, any>;
}

Result Handling

Execution results are returned in a standardized format:

interface WasmExecutionResult {
  success: boolean;
  data?: any;
  error?: string;
  gasUsed?: number;
}

// Example successful result
const successResult: WasmExecutionResult = {
  success: true,
  data: {
    transactionId: '0.0.123456@1234567890.000000000',
    newValue: 42
  }
};

// Example error result
const errorResult: WasmExecutionResult = {
  success: false,
  error: 'Invalid parameter: amount must be positive'
};

Error Handling

The WASM executor provides comprehensive error handling:

try {
  const result = await wasmExecutor.execute(actionRegistration, context);
  
  if (result.success) {
    console.log('Execution successful:', result.data);
  } else {
    console.error('Execution failed:', result.error);
  }
} catch (error) {
  console.error('WASM execution error:', error.message);
}

Memory Management

The executor handles WASM memory management:

// Memory cleanup for cached instances
wasmExecutor.clearCache();

Validation

The executor validates action parameters and capabilities:

import { WasmValidator } from '@hashgraphonline/standards-sdk';

const validator = new WasmValidator(logger);
const report = await validator.validate(wasmData);
if (!report.isValid) {
  console.error(report.errors);
}

Performance Optimization

The executor includes performance optimizations:

// Concurrent execution
const results = await Promise.all([
  wasmExecutor.execute(action1, context1),
  wasmExecutor.execute(action2, context2),
  wasmExecutor.execute(action3, context3)
]);

// Resource cleanup
wasmExecutor.clearCache();

Security Features

The executor includes security features for safe execution:

import { WasmValidator } from '@hashgraphonline/standards-sdk';

const validator = new WasmValidator(logger);
const report = await validator.validate(wasmData);
console.log(report.isValid, report.errors, report.warnings);

Browser Support

The executor works in both Node.js and browser environments:

WasmExecutor is browser-oriented in the current SDK implementation. In Node.js/SSR contexts it returns an execution error rather than running the module.

Best Practices

1. Deterministic Execution: Ensure all actions are deterministic
2. Error Handling: Handle errors gracefully and provide meaningful error messages
3. Resource Management: Be mindful of resource usage and execution time
4. Security: Validate all inputs and sanitize outputs
5. Performance: Use caching for frequently executed actions
6. Validation: Validate parameters and capabilities before execution
7. Memory Management: Properly manage WASM memory and instances
8. Testing: Test actions with various input scenarios