Persisting ChannelManager and ChannelMonitors with Codable

[danielnordh]

My first attempt at persisting the channel manager and monitors was to try to convert it to Data:

let data = try! JSONEncoder().encode(self.channelManager)swift

But since ChannelManager does not conform to Codable, that doesn't work.

Any chance we could make that class (and ChannelMonitor) Codable?

[danielnordh]

OK, I figured it out somewhat.

For monitors, in persistNewChannel and updatePersistedChannel the LDK input types have .write() functions that return bytes that can be encoded in a ChannelMonitorData struct I defined that confirms to Codable.

let channelMonitorData = ChannelMonitorData(idBytes: channelId.write(), dataBytes: data.write())

public struct ChannelMonitorData: Codable {
    public var idBytes: [UInt8]
    public var dataBytes: [UInt8]

    public init(idBytes: [UInt8], dataBytes: [UInt8]) {
        self.idBytes = idBytes
        self.dataBytes = dataBytes
    }
}

And similar for the channel manager in persistManager, getting encodable data from the .write() function

let channelManagerData = channelManager.write()

[danielnordh]

Actually, it is still not clear to me what the serialized monitor data should be like when saved, to work when fed back to the channelMonitorsSerialized parameter of ChannelManagerConstructor()

It expects [[UInt8]], but each channel serialization seems to need idBytes and data, which each produces [UInt8]. Many channel monitors together should then result in [[[UInt8]]]. I'm confused.

[danielnordh]

So after asking in discord I found out that channelMonitorSerialized expects and array of the data only.

If anyone else is trying this here is what I ended up with. I save a custom class I created called ChannelState

// Saving
// Save everything together as ChannelState. Have getters for the required serialized data.
public struct ChannelMonitorData: Codable {
    public var idBytes: [UInt8]
    public var dataBytes: [UInt8]

    public init(idBytes: [UInt8], dataBytes: [UInt8]) {
        self.idBytes = idBytes
        self.dataBytes = dataBytes
    }
}

public class ChannelState: Codable {
    public var channelMonitors: [ChannelMonitorData]
    public var channelManager: [UInt8]

    public init(monitorsData: [ChannelMonitorData], managerData: [UInt8]) {
        self.channelMonitors = monitorsData
        self.channelManager = managerData
    }

    public func getSerializedMonitors() -> [[UInt8]] {
        var serializedMonitors: [[UInt8]] = []
        for monitorData in self.channelMonitors {
            serializedMonitors.append(monitorData.dataBytes)
        }
        return serializedMonitors
    }

    public func addChannelMonitor(channelMonitor: ChannelMonitorData) {
        self.channelMonitors.append(channelMonitor)
        do {
            try saveChannelState(channelState: self)
        } catch let error {
            debugPrint(error.localizedDescription)
        }
    }

    public func updateChannelMonitor(channelMonitor: ChannelMonitorData) {
        if let index = channelMonitors.firstIndex(where: {$0.idBytes == channelMonitor.idBytes}) {
            channelMonitors[index] = channelMonitor
            do {
                try saveChannelState(channelState: self)
            } catch let error {
                debugPrint(error.localizedDescription)
            }
        }
    }

    public func updateChannelManager(channelManager: ChannelManager) {
        self.channelManager = channelManager.write()
        do {
            try saveChannelState(channelState: self)
        } catch let error {
            debugPrint(error.localizedDescription)
        }
    }
}