Add optional ibc entry point

[ethanfrey]

IBC-enabled contracts will have an extra entry point (like how migrate is optional) called ibc.

Related to #147

** This is a placeholder issue that needs some clarification before starting **

This entry point will accept a fixed set of life-cycle callbacks from the IBC module. The exact format of the message is still to be defined (we will spec before starting the issue), but the general entry point would look like:

pub fn ibc(
    deps: DepsMut,
    env: Env,
    msg: IbcMsg,
) -> Result<IbcResponse, ContractError> {
  // ...
}

pub enum IbcMsg {
  // TODO: @ethanfrey @alpe define this clearly  
}

pub struct IbcResponse {
  // Do we always return the same info for all callbacks, or will we need different responses for different inputs?
  // In such case, we should have different entry points for each different return value
}

This entry point should be exported through cosmwasm-vm and wasmvm into wasmd.

---

This ticket is broken down into multiple PRs:

• Definition of extry points for the contract (Add Ibc entry points for ibc-enabled contracts #711)
• Connecting and testing calls into the entry points (primarily packages/vm/src/calls.rs) (Add ibc stargate to vm #716)
• Testing calls for integration tests (packages/vm/src/testing/calls.rs) (Add ibc stargate to vm #716)
• Adding a development contract that uses the new entry points (Add Ibc sample contract #714)
• Adding integration tests to the development contract (Add Ibc sample contract #714)
• Exposing accessor on Instance to see if contract has ibc entry points (needed in wasmd for how to treat it) (Add Instance::has_ibc_entry_points #723)
• CHANGELOG entries for all the work (IBC Enhancements #728)

[webmaster128]

Exposing accessor on Instance to see if contract has ibc entry points (needed in wasmd for how to treat it)

Why is this needed? Can't we just try to call the function and fail if it doesn't (it's better to ask forgiveness than permission)?

[ethanfrey]

When we create a contract, if it supports IBC, we bind a port for it an allow others to connect.

It would be good to know if this contract will accept connections first, so we don't bind 100s of ports for contracts that will just refuse everything

[webmaster128]

When we create a contract, if it supports IBC, we bind a port for it an allow others to connect.

Okay, thanks. At which point does this happen exactly? Store code? Instantiate?

[ethanfrey]

This IBC port bind happens in instantiate.
The vm can pass the info in StoreCode and check in upon instantiation. Or it can pass the info on Instantiate.

I know the rust side of wasmvm gets a handle to the Instance. So if we expose this info on the instance, it should be possible to get it out.

We could return it on cache.save_wasm() during storage.
But simpler seems to be to expose the info on the Instance we use in do_init and return it (maybe via a *bool arg)

[webmaster128]

But simpler seems to be to expose the info on the Instance we use in do_init and return it (maybe via a *bool arg)

Yes, we can have a getter funtion on Instance that loops over the export functions and checks if all requirements are met. This is super fast, easy to implement, can be accessed at any time and does not require storing data.

[ethanfrey]

Sounds like you have a plan. If you could make a PR of that method, I'd appreciate it.

[webmaster128]

Sounds like you have a plan. If you could make a PR of that method, I'd appreciate it.

Good. This is a nobrainer (Monday).

[ethanfrey]

Okay, opening one last PR for the documentation / CHANGELOG items left to close this.
Please add items to #728 if you see minor enhancements needed

Will finish that up once CosmWasm/wasmvm#167 is finalized (and wasmd work can proceed).