Confusion regarding next sequence recv

[adizere]

Summary

A relayer operator reported this confusion:

what is the expected behaviour of the /ibc/core/channel/v1/channels/{channel_id}/ports/{port_id}/next_sequence endpoint? it seems to always return “next_sequence_receive”: “1" (https://rest-cosmoshub.ecostake.com/ibc/core/channel/v1/channels/channel-141/ports/transfer/next_sequence)

The answer, thanks for @crodriguezvega, was:

I see that this endpoint retrieves the next sequence recv and I think that value is set on RecvPacket only for ordered channels. So I guess it returns 1 because the transfer channel is unordered and the next sequence recv has never been incremented after being initialized to 1 either in ChanOpenInit (here) or ChanOpenTry (here).

Expected Behaviour

No confusion regarding this undocumented feature.

Possible suggestion for a fix:

Just an idea: could it be set to null for unordered channels to avoid the confusion?

Version

Steps to Reproduce

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For Admin Use

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[colin-axner]

Thanks for opening the issue @adizere! I agree with the suggested fix of using null as a return on unordered channels. In golang, I believe null would be 0. Might be best to just change the return value in the gRPC for now

[crodriguezvega]

Then the solution for now is to modify NextSequenceReceive by adding some code to retrieve the channel:

channel, found := q.GetChannel(ctx, req.PortId, req.ChannelId)
if !found {
  return nil, status.Error(
    codes.NotFound,
    sdkerrors.Wrapf(types.ErrChannelNotFound, "port-id: %s, channel-id %s", req.PortId, req.ChannelId).Error(),
  )
}

and then we declare and initialize to 0 the sequence and if the channel is ORDERED then we do the same thing that we're already doing to retrieve the sequence:

var sequence uint64 = 0 // return 0 for unordered channels
if channel.Ordering == types.ORDERED {
  sequence, found = q.GetNextSequenceRecv(ctx, req.PortId, req.ChannelId)
  if !found {
    return nil, status.Error(
      codes.NotFound,
      sdkerrors.Wrapf(types.ErrSequenceReceiveNotFound, "port-id: %s, channel-id %s", req.PortId, req.ChannelId).Error(),
    )
  }
}