
# Event Indexers

If you come from Solidity, you’ll know that Solidity allows you to create indexed parameters in your contract events. The indexed parameters allow you to search for these events using the parameters as filters.

While StarkNet does not currently allow you to create indexed parameters by default in Cairo you can index your events using some available indexers such as **[Apibara](https://www.apibara.com/)** and **[StarkNet Indexer](https://github.com/olegabu/starknet-archive-docs#starknet-indexer)**.


## StarkNet Indexer

**StarkNet indexer** is a service created to listen to blockchain events and decode and persist the emitted data, making it available for analysis with SQL, GraphQL, and HTTP queries.

They’ve also created a **[GraphQL console](https://summary.dev/console/)** that enables developers to query blockchain data for events, transactions and their inputs, as well as to filter, aggregate, and sum up values easily.


## Apibara


**Apibara** is a framework and protocol that helps you build real-time, composable streams of Web3 and Web2 data. Apibara solves the challenge of streaming blockchain data: blocks are not immutable, and their data can be invalidated in response to a chain reorganization.

There’s an amazing template to help you get started indexing events [**here**](https://github.com/apibara/python-indexer-template) and a tutorial guide [**here**](https://www.apibara.com/docs/tutorials/indexing-starknet-nft-events).

Swagtimus.eth

What are Event Indexers in Cairo lang? What is a StarkNet indexer?
Can you explain more about how it work and is there any difference between StarkNet indexer and Solidity once?

Newton

What are Event Indexers in Cairo lang? What is a StarkNet indexer?

Hey there! 

I am using the Oz Nile framework for smart contract development on Starknet. More specifically, I am testing the proxy upgrade feature, but my tests fail with the error message TypeError: int() can't convert non-string with explicit base. This happens when nile.signer tries to sign a transaction. Here's the snippet in the stack trace below. 

```
def sign_transaction(self, sender, calls, nonce, max_fee):
        """Sign a transaction for an Account."""
        (call_array, calldata) = from_call_to_call_array(calls)
        message_hash = get_transaction_hash(
>           int(sender, 16), call_array, calldata, nonce, int(max_fee)
        )
```

Some relevant info:
cairo-lang==0.10.0
cairo-nile==0.8.2
openzeppelin-cairo-contracts==0.4.0b
pytest==7.1.2
python=3.9 

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Cairo/Nile: Testing the proxy upgrade feature, but my tests fail with the error message TypeError: int() can't convert non-string with explicit base.

Why will I use events in the Cairo language? Can I use it on a front-end client application side?

Why will I use events in Cairo language?

I’m signing a message using 
```
account.signMessage(data) 
```
and immediately verifying the signature with the same data and it’s returning false. I don’t see any issue open on this subject on starknet.js. Is this something you’ve already encountered by any chance?

here’s the code:

```python
const data = { types: proposeTypes, primaryType: 'Propose', domain, message };
const sig = await user.account.signMessage(data);
let res = await user.account.verifyMessage(data, sig); // returns `false`
```

I see that’s the expected way to use signMessage through the tests (https://github.com/0xs34n/starknet.js/blob/b20819424dea824c96ac31e0542733c84d87d441/__tests__/account.test.ts#L125-L126).

So I guess something’s going wrong when it comes to either hashing the data and signing it or hashing the data and verifying the signature?


btw: for those wondering: `verifyMessage` only works if the account is deployed: if you’re doing this with an account not deployed (basically just a keypair) then this won’t work :)

signing a message using account.signMessage(data) | starknet.js

Hi all, what are a few of the best apps to test on starknet?  thanks

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

What are a few of the best apps to test on starknet?

How would I go about passing a function as a parameter to a function. Ex map(function, array)


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/313)_

Cairo Passing Functions

Where can I learn more about starknet?

What is starknet all about people

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Where can I learn more about starknet?


I can often make a terminal recursive version of my functions with a little less elegant code. Should I do it because it could reduce the fees or should I keep the unoptimised version?


For example, here is an "unoptimised" function which sums elements of an array:



```
@view
func get_convoy_strength{syscall_ptr : felt*, pedersen_ptr : HashBuiltin*, range_check_ptr}(
    convoy_id : felt
) -> (strength : felt):
    alloc_locals
    let (convoyables_len : felt, convoyables : felt*) = get_convoyables(convoy_id)
    return _get_convoyables_strength(convoyables_len, convoyables)
end

```

and here is the tail call optimization:



```
func _get_convoyables_strength_tc{
    syscall_ptr : felt*, pedersen_ptr : HashBuiltin*, range_check_ptr
}(convoyables_len : felt, convoyables : felt*, sum : felt) -> (strength : felt):
    if convoyables_len == 0:
        return (sum)
    else:
        let convoyable_id = [convoyables]
        alloc_locals
        let (convoyable_strength) = _get_strength(convoyable_id)
        return _get_convoyables_strength_tc(
            convoyables_len - 1, convoyables + 1, sum + convoyable_strength
        )
    end
end

```

As you can see it's a little less friendly because it requires an additional argument (which will always be 0). On a normal computer this could be optimized to not fill the call stack but as FeedTheFed pointed out, the memory is immutable here so it doesn't seem to be useful. He did say, however, that it could be interesting for "not wasting memory cells for the intermediate return values". It would be very helpful to me to have a more detailed explanation as I'm not sure to understand.


Here is the cairo doc related to this: <https://www.cairo-lang.org/docs/how_cairo_works/functions.html?highlight=tail#tail-recursion>



ㅤ
_This question was originally posted on [Stack Overflow](https://stackoverflow.com/questions/72321871/when-to-use-tail-call-optimization-in-a-cairo-smartcontract)_

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What are Event Indexers in Cairo lang? What is a StarkNet indexer?

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