[SOLVED] dynamic extend of subscribed topics of ethereum event log

dynamic extend of subscribed topics of ethereum event log

I am using go-ethereum for listening to events of a certian topic of a smart contract like this:

import "github.com/ethereum/go-ethereum/ethclient"                 
logs := make(chan types.Log)
client, _ := ethclient.Dial("wss://rinkeby.infura.io/ws/v3/{projectid}")          
var hashes []common.Hash
sub, _ := client.SubscribeFilterLogs(context.Background(), ethereum.FilterQuery{
        Addresses: []common.Address{contractAddress},
        Topics:    [][]common.Hash{hashes},
}, logs)

then I get the matching logs written into the variable logs.

Is there a way to extend the list of topics I subscribed too at runtime? I want to build a REST service which can get requests containing new topics to subscribe to.

Or do I need to start a new subscribtion then?

Solution

I've been testing this as I couldn't find a good answer.

You could create a some methods for subscription management, having a method for appending / removing hashes from your hashes array, which would also call the .Unsubscribe() method of your subscription, and then reinitialize with the new list. Could look something like this:

var hashes []common.Hash
var subscription ethereum.Subscription

func createSubscription(){
    if subscription != nil && len(hashes > 0){
        subscription.Unsubscribe()
        // your logic for creating a subscription
        // re-assign to subscription variable
    } else if len(hashes > 0) {
        // create subscription as normal, assign to subscription variable
    }
}

func appendHash(common.Hash hash){
    hashes = append(hashes, hash)
    createSubscription()
}