FallbackProvider - use custom method

[pkhien95]

Describe the Feature

FallbackProvider doesn't allow sending a request that has a custom method, ex: alchemy_getTokenBalances. We need a way to do that similar to the send function in JsonRpcProvider

Code Example

const provider = new FallbackProvider(...args)
const tokenBalances = await provider.send(`alchemy_getTokenBalances`)

// OR
const tokenBalances = await provider.getTokenBalances()

// OR allows sub-class to override _perform logic, 
// currently impossible due to error throw in #checkQuorum
class CustomFallbackProvider extends FallbackProvider {
  _translatePerform(
    provider: CustomJsonRpcProvider,
    req: CustomPerformActionRequest,
  ): Promise<any> {
    switch (req.method) {
      case 'getTokenBalances':
        return provider.getTokenBalances(req.address)
      //...
    }
    return super._translatePerform(provider, req)
  }
}

[ricmoo]

The FallbackProvider is meant to support any AbstractProvider, which may or may not use JSON-RPC, so a backend may not support JSON-RPC so there would be no way to pass that through.

That said, that method is only available on an Alchemy backend, so you can just use the AlchemyProvider directly, with its .send. Custom methods could also potentially be added to the AlchemyProvider.