Milestone 4: Co-op Channel Closes

[ekzyis]

Fuzz scenario

PostChannelReadySetup: We want to fuzz starting with shutdown followed by closing_complete and closing_sig, so we need to have an open, ready channel and option_simple_close must have been negotiated during init exchange. Therefore, the scenario setup would be a modified or extended version of PostInitSetup which includes option_simple_close, opening a channel and waiting for channel_ready:

  Smite                         Target
    |                              |
    |----------- init ------------>|
    |    *option_simple_close*     |
    |<---------- init -------------|
    |    *option_simple_close*     |
    |                              |
    |-------- open_channel ------->|
    |<------ accept_channel -------|
    |------- funding_created ----->|
    |<------ funding_signed -------|
    |                              |
    |  [tx broadcast+mine blocks]  |
    |                              |
    |------- channel_ready ------->|
    |<------ channel_ready --------|
    |                              |
    |---------- ping ------------->|
    |<--------- pong --------------|
    |                              |
    +---------- SNAPSHOT ----------+

During fuzzing, a mutual close is negotiated with a shutdown exchange. Since there are no pending HTLCs, an exchange of closing_complete and closing_sig should immediately follow:

  Smite                         Target
    +---------- SNAPSHOT ----------+
    |                              |
    |---------- shutdown --------->|
    |<--------- shutdown ----------|
    |                              |
    |------ closing_complete ----->|
    |<----- closing_complete ------|
    |                              |
    |--------- closing_sig ------->|
    |<-------- closing_sig --------|

Advanced scenarios could fuzz additional exchanges of closing_complete+closing_sig messages to bump fees etc.

What's needed?

Setup

• PostChannelReadySetup: see above

Messages

• init
• (ping, pong)
• open_channel
• accept_channel
• funding_created
• funding_signed
• channel_ready
• shutdown
• closing_complete (smite: add closing_complete codec #105)
• closing_sig (smite: add closing_sig codec #109)

Operations

For funding flow:

• BuildOpenChannel
• SendOpenChannel
• RecvAcceptChannel
• CreateFundingTransaction
• BuildFundingCreated (smite-ir: implement BuildFundingCreated and SendFundingCreated operation  #120)
• SendFundingCreated (smite-ir: implement BuildFundingCreated and SendFundingCreated operation  #120)
• RecvFundingSigned
• SendChannelReady
• RecvChannelReady

For closing flow:

• SendShutdown (smite-ir: add SendShutdown operation #162)
• RecvShutdown (smite-ir: add RecvShutdown operation #163)
• CreateClosingTransaction
• BuildClosingComplete
• SendClosingComplete
• RecvClosingSig
• BroadcastTransaction
• MineBlocks

Generator

• ChannelCloseGenerator:

emits instructions for channel close flow with:

• CreateClosingTransaction
• BuildClosingComplete
• SendClosingComplete
• RecvClosingSig

assumes option_simple_close was negotiated

References

• https://github.com/lightning/bolts/blob/master/02-peer-protocol.md#channel-close

[morehouse]

Sounds good. With @NishantBansal2003's work on the funding flow, we should soon have all the pieces we need to open channels. I think that's the only thing blocking this work now.

[ekzyis]

I updated the description now.

With @NishantBansal2003's work on the funding flow, we should soon have all the pieces we need to open channels

Yes, not much is needed anymore for PostChannelReadySetup. I will start with it in a draft PR, and review/push any code that's missing for it.