Ethereum Watcher is a service built in Go to track transactions from subscribed addresses on the Ethereum network.
It provides an API for easy subscribing and transactions fetching.
Additionally, a webhook URL can be configured to receive live notifications about new transactions pertaining to the subscribed addresses.
The following environment variables can be configured:
ETH_SERVER_URL(optional): specifies which RPC node to connect to. Defaults tohttps://cloudflare-eth.com;WEBHOOK_URL(optional): when provided the service will make a post request to this URL informing about new transactions for one or more subscribed addresses;
Returns the latest block the service has ingested.
Subscribes {address} to the watcher service. Once subscribed, its transactions will be tracked and persisted in the service's storage.
Returns an array of all transactions sent to or received by {address} after the time of subscription.
Note: The API server is started by default on port 3000. The base URL for API calls is http://localhost:3000 when running locally.
Go 1.22(or higher) installed (this is essential for the API to function properly);
The service can be started with go run . on the root folder.
If you want to connect to an alternative RCP node (such as a testnet one) the environment variable can be set with export ETH_SERVER_URL=https://rpc.sepolia.org before running go run ..
In the same fashion, the webhook URL can be set with export WEBHOOK_URL=https://myserver/webhook.
The current implementation uses the eth_blockNumber method to fetch the latest block from the ledger. However, this method presented some lag in the tests conducted, taking a few seconds after the closing time of the latest block to return the updated value.
An alternative version calling eth_getBlockByNumber directly until the response is not empty is implemented on separate a branch performance-improvement. This approach presented a significant performance improvement (delays below 1s) over the current one, but it relies on RPC calls to error, which resulted in a different responses in the tests conducted (with https://rpc.sepolia.org and https://cloudflare-eth.com) depending on the RPC node. Although promising this approach requires further experimentation.
A third alternative was tested using eth_newBlockFilter and eth_getFilterChanges to get the latest block information. Although it presented great performance improvement (similar to the one described above), Cloudflare's Public RPC node doesn't support either of the methods as of now: see docs.
The webhook calls don't currently implement any retry logic, which should be done in future work.
An even more reliable approach would be to implement an event-based system such as Kafka as to guarantee delivery and minimize latency.