[Supanode](https://supanode.xyz/)[Learn](https://supanode.xyz/learn)Build an EVM head listener that survives gaps and reorgs

# Build an EVM head listener that survives gaps and reorgs

Key blocks by hash, verify parents and reconcile the range between notifications.

**On this page**[A notification stream is not a complete block archive](https://supanode.xyz/learn/newheads-reorg-duplicate-blocks#a-notification-stream-is-not-a-complete-block-archive)[Maintain a linked view](https://supanode.xyz/learn/newheads-reorg-duplicate-blocks#maintain-a-linked-view)[Recover after reconnect](https://supanode.xyz/learn/newheads-reorg-duplicate-blocks#recover-after-reconnect)[Separate inclusion from settlement](https://supanode.xyz/learn/newheads-reorg-duplicate-blocks#separate-inclusion-from-settlement)[Sources](https://supanode.xyz/learn/newheads-reorg-duplicate-blocks#sources)

## A notification stream is not a complete block archive

`newHeads` announces observed heads. A reconnection can miss blocks, and a reorganization can produce another block hash at a height you already stored. Deduplicating only by block number can hide replacements. Treat each notification as a prompt to reconcile your local chain view.

## Maintain a linked view

```
on_head(head):
    if head.parentHash != stored_tip.hash:
        reconcile_to_common_ancestor(head)
    fetch_missing_blocks(stored_tip.number + 1, head.number)
    store_block_by_hash(head)
    update_tip(head)
```

This pseudocode omits chain-specific finality policy. Store both the block number and hash, plus the parent hash. Preserve replaced records with a status instead of mixing their events into the canonical view.

## Recover after reconnect

1.  Open a new subscription and buffer arriving heads.
2.  Read the current tip through RPC.
3.  Fetch the missing numeric range and check parent continuity.
4.  Reconcile the overlap, then drain buffered notifications through the same deduplication path.

## Separate inclusion from settlement

A sequencer head on Robinhood Chain is an early view of L2 ordering. Settlement on Ethereum has additional stages. Use chain-specific finality documentation for financial acceptance rules, and monitor how far your collector lags the live head. A generic EVM subscription implementation can be reused, but assumptions about block pace, public mempools and finality cannot be copied unchanged from another chain.

## Sources

-   [Geth pub/sub behavior](https://geth.ethereum.org/docs/interacting-with-geth/rpc/pubsub)
-   [Robinhood finality](https://docs.robinhood.com/chain/transaction-finality/)

## Continue reading

[Robinhood RPC and WebSocket](https://supanode.xyz/blog/robinhood-chain-rpc-websocket)[Robinhood methods](https://supanode.xyz/docs/robinhood/rpc/whats-available)[Learn library](https://supanode.xyz/learn)

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Source: https://supanode.xyz/learn/newheads-reorg-duplicate-blocks