Reading from Intelligent Contracts

Reading from Intelligent Contracts means querying contract state or executing view functions without modifying blockchain state. These read-only operations are free, require no fees, and provide immediate access to contract data.

Understanding View Operations

In GenLayer, functions marked with the @gl.public.view decorator are read-only operations that:

• Don't modify the contract's state
• Can be executed without requiring a transaction
• Return data immediately
• Don't consume gas
• Can be called by any account

Basic Contract Reading

Here's how to read from an Intelligent Contract:

import { simulator } from 'genlayer-js/chains';
import { createClient, createAccount } from 'genlayer-js';
 
const account = createAccount();
const client = createClient({
  chain: simulator,
  account: account,
});
 
const result = await client.readContract({
  address: contractAddress,
  functionName: 'get_complete_storage',
  args: [],
});

Parameters Explained

• address: The deployed contract's address on the GenLayer network
• functionName: The name of the view function you want to call
• args: An array of arguments that the function accepts (empty if none required)

Common View Operations

Intelligent Contracts typically include several types of view functions:

State Queries

// Reading a single value
const balance = await client.readContract({
  address: contractAddress,
  functionName: 'get_balance',
  args: [accountAddress],
});
 
// Reading multiple values
const userInfo = await client.readContract({
  address: contractAddress,
  functionName: 'get_user_info',
  args: [userId],
});

Computed Values

// Getting calculated results
const totalSupply = await client.readContract({
  address: contractAddress,
  functionName: 'calculate_total_supply',
  args: [],
});

Validation Checks

// Checking permissions
const hasAccess = await client.readContract({
  address: contractAddress,
  functionName: 'check_user_permission',
  args: [userId, 'ADMIN_ROLE'],
});

Error Handling

When reading from contracts, you should handle potential errors:

try {
  const result = await client.readContract({
    address: contractAddress,
    functionName: 'get_data',
    args: [],
  });
  console.log('Data retrieved:', result);
} catch (error) {
  if (error.message.includes('Contract not found')) {
    console.error('Invalid contract address');
  } else if (error.message.includes('Function not found')) {
    console.error('Invalid function name');
  } else {
    console.error('Error reading contract:', error);
  }
}

Best Practices

1. Batch Readings: When possible, use functions that return multiple values instead of making many separate calls.
2. Type Safety: Use TypeScript interfaces to ensure type safety when handling returned data.
3. Cache Shared Reads: Treat public RPC endpoints as shared infrastructure. Browser traffic can multiply gen_call requests quickly, so production DApps should avoid polling the chain independently from every tab or visitor.

Building Read-Heavy DApps

readContract calls are convenient for account pages, dashboards, and dispute views, but they still consume RPC capacity. If a frontend calls gen_call repeatedly from every browser session, the app can hit rate limits even though the operation is read-only and gasless.

For read-heavy DApps, use a layered pattern:

• On-chain source of truth: keep the Intelligent Contract as the authoritative state machine.
• Backend cache or sidecar: poll the contract at a controlled interval and serve many frontend users from the cached response.
• Batch view functions: expose view methods that return the full page state needed by the UI, instead of requiring many small reads.
• HTTP cache semantics: use ETag, Cache-Control, or stale-while-revalidate behavior so clients do not refetch unchanged data.
• Verify-on-chain fallback: keep a UI path that can re-read the contract directly for users who need to verify the cached value.

A minimal backend route can centralize reads like this:

let cachedPageState: unknown;
let cachedAt = 0;
const CACHE_TTL_MS = 12_000;
 
export async function getPageState() {
  const now = Date.now();
 
  if (cachedPageState && now - cachedAt < CACHE_TTL_MS) {
    return cachedPageState;
  }
 
  cachedPageState = await client.readContract({
    address: contractAddress,
    functionName: 'get_page_state',
    args: [],
  });
  cachedAt = now;
 
  return cachedPageState;
}

This does not replace on-chain verification. It reduces duplicate read load for normal browsing while preserving GenLayer as the source of truth.