Fail create_channel early if peer is disconnected

[dunxen]

We need to ensure in the case where a peer is disconnected that we fail early when we invoke ChannelManager::create_channel for their_network_key.

The only thing we currently do is check if we know about the peer at all (they're in the per_peer_state):

rust-lightning/lightning/src/ln/channelmanager.rs

Line 2195 in e4c44f3

let peer_state_mutex = per_peer_state.get(&their_network_key)

We also need to check for .is_connected if we know about the peer.

See #2382 (comment)

[TheBlueMatt]

Bonus points if we instead address #2096 (ie don't fail but rebroadcast the open_channel message on reconnect, failing in a minute or two from a timeout instead).

[henghonglee]

@dunxen i can try this one

[dunxen]

@dunxen i can try this one

Great, thanks! Matt’s bonus points would be good to handle from his comment above alternatively :)

[nafisalawalidris]

To ensure robustness, I propose adding a check for peer disconnection within this function. Currently, we only verify if we know about the peer through the per_peer_state. However, it is crucial to also consider the peer's connection status by using .is_connected. This enhancement will enable us to fail early when attempting to invoke ChannelManager::create_channel for a disconnected peer. Here's the proposed code modification:

// Existing code
let peer_state_mutex = per_peer_state.get(&their_network_key)

// Proposed modification
if let Some(peer_state) = per_peer_state.get(&their_network_key) {
if peer_state.is_connected {
// Proceed with create_channel logic
} else {
// Handle the case where the peer is disconnected
// (e.g., return an error or take appropriate action)
}
}

By implementing this check, we can proactively address issues related to disconnected peers when using ChannelManager::create_channel.

[shaavan]

Hi! I couldn't help but notice the PR has been open for a little while. I've given it a shot at solving the issue. I would absolutely love to hear your thoughts on what I've come up with. Thanks a bunch! :)

[TheBlueMatt]

Oh, oops, dup of #2096.