context.client.readContract occasionally returns 0x

[donguks]

Version

latest

Current behavior

• When processing events in Ponder, a contract read function (readValue) is called using the event’s blockNumber to retrieve state at the time of the event.
• Occasionally, the readValue function unexpectedly returns 0x instead of the expected stored value.
• The issue seems to be more prevalent when using L2 networks (e.g., Op Stack).

Expected behavior

• The readValue function should return the correct stored value at the exact block number where the ValueUpdated event was emitted.
• The RPC provider should not return 0x unless the queried data is truly absent.
• If the event has been emitted and indexed, the corresponding state update should be immediately available for read operations without requiring retries.
• Ponder should ensure event processing does not occur before the L2 state update is fully committed.

Steps to reproduce

1. Set Up Ponder Configuration: Define the network and contract in ponder.config.ts:

import { createConfig } from "ponder";
import { http } from "viem";

import { ContractAbi } from "./abis/ContractAbi";

export default createConfig({
  networks: {
    l2Network: {
      chainId: 1234,
      transport: http(process.env.PONDER_RPC_URL_1234),
    },
  },
  contracts: {
    MyContract: {
      network: "l2Network",
      abi: ContractAbi,
      address: "0xYourContractAddress",
      startBlock: 1000000,
    },
  },
});

2. Implement Event Listener and Read Function: In src/index.ts, set up the event listener and call the read function

import { ponder } from "ponder:registry";

ponder.on("MyContract:ValueUpdated", async ({ event, context }) => {
  const { client } = context;
  const { MyContract } = context.contracts;

  try {
    // Call the read function at the block number where the event was emitted
    const value = await client.readContract({
      abi: MyContract.abi,
      address: MyContract.address,
      functionName: "readValue",
      args: [event.args.user],
    });

    console.log("Read value:", value);
  } catch (error) {
    console.error("Error reading contract:", error);
  }
});

3. Deploy and Test:

• Deploy the contract on the specified L2 network.
• Trigger the ValueUpdated event.
• Observe the output of the read function call.

Link to repository

No response

Anything else?

Possible Causes

1. L2 Network State Finality : The L2 network’s state may not be fully finalized at the time of the read operation, leading to temporary unavailability of the latest state.
2. RPC Provider Latency : Some RPC providers might lag behind in syncing L2 state, causing a delay in reflecting the most recent contract storage updates.
3. Event Processing Timing Issue in Ponder : Ponder might process events before the associated state updates are fully committed, leading to inconsistent read results.

Questions

• Is this a known issue with Ponder when interacting with L2 networks?
• Are there any recommended strategies to ensure that read operations retrieve the correct state immediately after event processing?
• Could this be related to how Ponder handles event processing and state synchronization on L2 networks?

[typedarray]

Hi, thanks for opening!

Questions:

1. What chain and RPC provider are you experiencing this with?
2. Does this only happen for requests in "realtime" / that are near the chain tip?

My gut says this has nothing to do with the chain being an L2, I think this problem can happen on any chain depending on the node software being used to serve the RPC request.

It's very difficult for the framework itself to know that a 0x response should be retried, because that's a totally valid response for an eth_call request. One possible fix here is to implement user-land retries - in your indexing function, if the response is 0x, wait ~1 second then try again, etc until you get the response you're looking for.

[donguks]

Hi, thanks for your reply!

• Network & RPC Providers: I’m experiencing this issue on Optimism Sepolia using Ankr and Alchemy as RPC providers.
• Occurrence: This mostly happens for requests in real-time, near the chain tip.

I understand that this might not be specifically related to the chain being an L2, but rather to the node software serving the RPC request. However, I’ve already implemented a retry mechanism where the request is retried 5 times with a 1-second delay between attempts, yet I still frequently get 0x responses.

Would you recommend any additional strategies to ensure reliable state reads in this scenario?