Run the emulator from a snapshot of Testnet or Mainnet

[janezpodhostnik]

Issue To Be Solved

Some applications will want to build on top of other applications already deployed on Flow.
This is difficult, given currently there is no way to simulate live network contracts and their state besides manually deploying those contracts on the Emulator, and generating interactions to arrive at the desired starting state.

(Optional): Suggest A Solution

Ability to load a slice of time/block delineated protocol state (Testnet or Mainnet) into the Emulator using a cli command.

[turbolent]

I think what's required to make this work is an AN function to read individual register keys at a specific block height.

Then, the emulator's storage layer would transparently fetch the registers from another AN (e.g. testnet), and store the results locally. Basically, LedgerViewByHeight would return a delta view function which makes the request to the AN.

[10thfloor]

@turbolent sounds like this might take a while to implement? What about a set of scripts that automate deploying some of the contracts on the emulator, in the meantime?

[JeffreyDoyle]

During an internal sync on how to tackle this, two ideas emerged:

1. We could include a way for users to specify which contracts they want included when they boot up the emulator. These specified contracts could live in the flow.json file or in some other piece of configuration. We could also add other "core" contracts that aren't already included to be included by default.
2. We could allow the user to load a snapshot of the testnet/mainnet state to their local machine and have the emulator read and write from this snapshot. In this method, the user could have access to identical chain state as it existed when the snapshot was created. All of the contracts and accounts that existed at the time of this snapshot would be available to users of the emulator in this method.

[sideninja]

Closing in favour of buildathlon task.

[mwufi]

I'm curious... how does launching a development wallet help with this issue? I'm a bit new to Flow, so I don't get what scenarios having a FCL development wallet would help!