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Indexer Block Trigger

Workflows for processing new blocks and transactions using block-triggered webhooks from Alchemy Notify.

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Workflows for processing new blocks and transactions using block-triggered webhooks (from Alchemy Notify) and matching against watched addresses. These workflows demonstrate the block trigger pattern where the workflow reacts to incoming block data and extracts relevant transactions.

Directory Structure

building-blocks/indexer-block-trigger/
├── block-trigger-go/     (Go-based workflow)
│   └── workflow/
│       ├── main.go
│       ├── config.staging.json
│       ├── config.production.json
│       ├── workflow.yaml
│       └── README.md
├── block-trigger-ts/     (TypeScript-based workflow)
    └── workflow/
        ├── main.ts
        ├── package.json
        ├── config.staging.json (optional)
        ├── workflow.yaml
        └── README.md

Overview

These workflows demonstrate how to:

  • React to block events via HTTP webhook triggers (We use Alchemy Notify for this workflow)
  • Match transactions to a list of watched addresses
  • Process and return JSON-formatted block and transaction data
  • Implement the same logic in both Go and TypeScript

Both workflows process incoming block data and extract:

  • Block number, hash, timestamp
  • All transactions in the block
  • Transactions where the to address matches a watched address

Workflows

1 block-trigger-go (Go Implementation)

Language: Go

Features:

  • Uses http.Trigger from CRE Go SDK
  • Matches transactions to watched addresses from config
  • Returns formatted JSON summary of block and matched transactions

Running the workflow:

cd building-blocks/indexer-block-trigger/block-trigger-go
cre workflow simulate workflow --non-interactive --trigger-index 0 --http-payload test-block.json --target staging-settings
2 block-trigger-ts (TypeScript Implementation)

Language: TypeScript

Features:

  • Uses HTTP trigger from CRE TypeScript SDK
  • Matches transactions to watched addresses from config
  • Returns formatted JSON summary of block and matched transactions

Running the workflow:

cd building-blocks/indexer-block-trigger/block-trigger-ts/workflow
bun install
cre workflow simulate workflow --non-interactive --trigger-index 0 --http-payload test-block.json --target staging-settings

Setup and Testing

1 Prerequisites

For Go workflow:

  1. Install CRE CLI
  2. Login: cre login
  3. Install Go

For TypeScript workflow:

  1. Install CRE CLI
  2. Login: cre login
  3. Install Bun (or Node.js)
  4. Run bun install in the workflow directory
2 Running the Workflows

Go Workflow:

cd building-blocks/indexer-block-trigger/block-trigger-go
cre workflow simulate workflow --non-interactive --trigger-index 0 --http-payload test-block.json --target staging-settings

TypeScript Workflow:

cd building-blocks/indexer-block-trigger/block-trigger-ts
cre workflow simulate workflow --non-interactive --trigger-index 0 --http-payload test-block.json --target staging-settings
3 Example Output

Both workflows return JSON output like:

{
  "blockNumber": 12345678,
  "blockHash": "0xabc...",
  "timestamp": 1700000000,
  "totalLogs": 42,
  "uniqueTransactions": 10,
  "matchedTransactions": 2,
  "transactions": [
    {
      "hash": "0xdef...",
      "from": "0x...",
      "to": "0x73b668d8374ddb42c9e2f46fd5b754ac215495bc",
      "value": "1000000000000000000"
    }
  ]
}

Setting Up Alchemy Webhooks

1 Step-by-step Alchemy setup

To use Alchemy for block-triggered workflows, follow these steps:

  1. Sign up on Alchemy and navigate to their dashboard.
  2. Create a new app on the dashboard with your preferred network.
  3. Click on your app to open the app dashboard and scroll down to the services section.
  4. Click on the Webhooks service and in the pane that opens, click on Real-time Notifications, then click on Get Started.
  5. Choose webhook type Custom to listen for new blocks or events on every new block.
  6. In the custom webhook pane, add other details including webhook name, chain, network, query template, and webhook URL.
  7. Click on Create Webhook to save the webhook and test the webhook URL.

Tips:

  • Make sure your webhook URL is accessible and correctly configured to receive POST requests.
  • You may want to use a tool like Webhook.site for initial testing.
  • Double-check the network and chain settings to match your workflow requirements.
  • The query template should match the data you want to extract from each block/event.

Example Use Cases

1. Monitoring High-Value Addresses

Track transactions to specific addresses in real time:

{
  "watchedAddresses": ["0x...", "0x..."]
}

2. Contract Interaction Tracking

Detect when contracts of interest receive transactions:

{
  "watchedAddresses": ["0xContract1", "0xContract2"]
}

3. Block-Level Analytics

Summarize block activity and matched transactions for analytics dashboards.

Reference Documentation

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