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Listen to Realtime Events

In this tutorial, we will build an indexer using the NEAR Indexer Framework. The indexer will listen realtime events from NEAR blockchain for FunctionCalls on a specific contract and log the details of each call.

The full source code for the indexer is available in the GitHub repository.

Initialization​

To run the NEAR Indexer connected to a network we need to have node configs and keys prepopulated. Navigate to the directory where you cloned the example and run the following command to initialize the configuration for the desired network:

  cargo run --release -- --home-dir ~/.near/localnet init

The above command should initialize necessary configs and keys to run localnet/testnet/mainnet in ~/.near/(localnet|testnet|mainnet).

The main configuration file for the node is config.json.

The above code will download the official genesis and config. The recommended config is accessible at:

This configuration is intended for RPC nodes. Any extra settings required for the indexer should be manually added to the configuration file config.json in your --home-dir (e.g. ~/.near/testnet/config.json).

Configs for the specified network are in the --home-dir provided folder. We need to ensure that NEAR Indexer follows all the necessary shards, so set "tracked_shards_config": "AllShards" parameters in ~/.near/testnet/config.json. Hint: See the Tweaks section below to learn more about further configuration options.

After that we can run NEAR Indexer.

  cargo run --release -- --home-dir ~/.near/localnet run

Custom Settings​

By default, nearcore is configured to do as little work as possible while still operating on an up-to-date state. Indexers may have different requirements, so there is no solution that would work for everyone, and thus we are going to provide you with the set of knobs you can tune for your requirements.

Shards/Accounts to Track​

As already has been mentioned above, the most common tweak you need to apply is listing all the shards you want to index data from; to do that, you should ensure that "tracked_shards_config" in the config.json lists all the shard UIDs:

...
"tracked_shards_config": {
       "Shards": [
              "s3.v3",
              "s4.v3"
       ]
},
...

Or, if you want to track specific accounts:

...
"tracked_shards_config": {
       "Accounts": [
              "account_a",
              "account_b"
       ]
},
...

Sync Mode​

You can choose Indexer Framework sync mode by setting what to stream:

  • LatestSynced - Real-time syncing, always taking the latest finalized block to stream
  • FromInterruption - Starts syncing from the block NEAR Indexer was interrupted last time
  • BlockHeight(u64) - Specific block height to start syncing from.

Historical Data​

Indexer Framework also exposes access to the internal APIs (see Indexer::client_actors method), so you can fetch data about any block, transaction, etc, yet by default, nearcore is configured to remove old data (garbage collection), so querying the data that was observed a few epochs before may return an error saying that the data is not found. If you only need blocks streaming, you don't need this tweak, but if you need access to the historical data right from your Indexer, consider updating "archive" setting in config.json to true:

...
"archive": true,
...

Parsing the Block Data​

From the block data, we can access the transactions, their receipts and actions. In this example, we will look for FunctionCall actions on a specific contract and log the details of each call.

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Happy coding! 🚀