how to detect a spl-token balance change?

Question

development environment : C#, Windows

Connecting to solana-mainnet web server using wss address.

        wss = new WebSocketSharp.WebSocket(this.Address);
        wss.SslConfiguration.EnabledSslProtocols = System.Security.Authentication.SslProtocols.Tls12;

        wss.OnMessage += (sender, e) =>
        {
            if (e.IsBinary)
            {
                HandleMessage(Opcode.Binary, e.RawData);
            }
            else if(e.IsText)
            {
                HandleMessage(Opcode.Text, e.RawData);
            }
        };
        wss.OnOpen += (sender, e) =>
        {
            HandleOpen();
        };
        wss.OnError += (sender, e) =>
        {
            HandleError(e.Exception);
        };
        wss.OnClose += (sender, e) =>
        {
            HandleClose(e.Code, e.Reason);
        };

OnMessage occurs when the solana balance changes. (At this time, I check solana balance.)

However, if there is a change in the spl-token balance, there is no event.

Therefore, I am periodically checking the spl-token.

This is very inefficient

how to detect spl-token balance change?

Best regards,

Answer 1

Solana JSON RPC API offers a way to subscribe to an account to receive notifications when the Lamports or data for a given account's public key changes.

https://docs.solana.com/developing/clients/jsonrpc-api#accountsubscribe

This includes any type of account, a token account is basically a data account initialized with a specific standard.

https://github.com/solana-labs/solana-program-library/blob/master/token/program/src/state.rs#L83

Here's an example of subscribing to CM78CPUeXjn8o3yroDHxUtKsZZgoy4GPkPPXfouKNH12. It doesn't matter what type of account it is.

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "accountSubscribe",
  "params": [
    "CM78CPUeXjn8o3yroDHxUtKsZZgoy4GPkPPXfouKNH12",
    {
      "encoding": "base64",
      "commitment": "finalized"
    }
  ]
}