lnp-core 0.9.2

// LNP/BP Core Library implementing LNPBP specifications & standards
// Written in 2020-2022 by
//     Dr. Maxim Orlovsky <orlovsky@pandoracore.com>
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to
// the public domain worldwide. This software is distributed without
// any warranty.
//
// You should have received a copy of the MIT License
// along with this software.
// If not, see <https://opensource.org/licenses/MIT>.

use bitcoin::util::psbt::raw::ProprietaryKey;
use bitcoin::{OutPoint, Transaction, TxOut, Txid};
use wallet::psbt::{Psbt, PsbtVersion};

pub const PSBT_LNP_PROPRIETARY_PREFIX: &[u8] = b"LNP";
pub const PSBT_OUT_LNP_CHANNEL_FUNDING: u8 = 0x01;

#[derive(
    Copy, Clone, Ord, PartialOrd, Eq, PartialEq, Hash, Debug, Display, Error
)]
#[display(doc_comments)]
pub enum Error {
    /// no funding output found in the funding transaction. The funding output
    /// must be marked with proprietary key having "LNP" prefix and 0x01
    /// subtype.
    NoFundingOutput,

    /// funding transaction does not contain output #{0} specified as a
    /// funding outpoint
    WrongOutput(u16),
}

/// Information about channel funding
#[derive(Getters, Clone, PartialEq, Eq, Debug, StrictEncode, StrictDecode)]
#[cfg_attr(
    feature = "serde",
    derive(Serialize, Deserialize),
    serde(crate = "serde_crate")
)]
pub struct Funding {
    /// PSBT containing full information about the funding of the channel in a
    /// structured way.
    ///
    /// Channel is always funded with a single input, that is why we need a
    /// single PSBT. If channel needs to receive more funds, it will require a
    /// new funding transaction to be created, spending previous funding
    /// transaction output.
    psbt: Psbt,

    // Cached information extracted from PSBT, which is the master data source
    #[getter(as_copy)]
    txid: Txid,

    #[getter(as_copy)]
    output: u16,

    #[getter(as_copy)]
    amount: u64,

    #[getter(as_copy)]
    signing_parties: u8,

    #[getter(as_copy)]
    signing_threshold: u8,
}

impl Funding {
    /// Constructs empty funding information. Can be used only during initial
    /// channel setup.
    #[inline]
    pub(super) fn new() -> Funding {
        let mut psbt = Psbt::with(
            Transaction {
                version: 2,
                lock_time: bitcoin::PackedLockTime(0),
                input: vec![],
                output: vec![TxOut {
                    value: 0,
                    script_pubkey: Default::default(),
                }],
            },
            PsbtVersion::V0,
        )
        .expect("dumb manual PSBT creation");
        psbt.outputs[0]
            .proprietary
            .insert(lnp_out_channel_funding_key(), vec![]);
        Funding::with(psbt).expect("dumb manual PSBT creation")
    }

    #[inline]
    pub fn with(psbt: Psbt) -> Result<Funding, Error> {
        psbt.extract_channel_funding()
    }

    #[inline]
    pub(super) fn preliminary(funding_amount: u64) -> Funding {
        let mut funding = Funding::new();
        funding.amount = funding_amount;
        funding
    }

    #[inline]
    pub fn outpoint(&self) -> OutPoint {
        OutPoint::new(self.txid, self.output as u32)
    }
}

fn lnp_out_channel_funding_key() -> ProprietaryKey {
    ProprietaryKey {
        prefix: PSBT_LNP_PROPRIETARY_PREFIX.to_vec(),
        subtype: PSBT_OUT_LNP_CHANNEL_FUNDING,
        key: vec![],
    }
}

pub trait PsbtLnpFunding {
    fn channel_funding_output(&self) -> Option<usize>;
    fn set_channel_funding_output(&mut self, vout: u16) -> Result<(), Error>;
    fn channel_funding_outpoint(&self) -> Result<OutPoint, Error>;
    fn extract_channel_funding(self) -> Result<Funding, Error>;
}

impl PsbtLnpFunding for Psbt {
    fn channel_funding_output(&self) -> Option<usize> {
        let funding_key = lnp_out_channel_funding_key();
        self.outputs
            .iter()
            .enumerate()
            .find(|(_, output)| output.proprietary.get(&funding_key).is_some())
            .map(|(index, _)| index)
    }

    fn set_channel_funding_output(&mut self, vout: u16) -> Result<(), Error> {
        self.outputs
            .get_mut(vout as usize)
            .map(|out| {
                out.proprietary
                    .insert(lnp_out_channel_funding_key(), vec![]);
            })
            .ok_or(Error::WrongOutput(vout))
    }

    fn channel_funding_outpoint(&self) -> Result<OutPoint, Error> {
        let vout = self
            .channel_funding_output()
            .ok_or(Error::NoFundingOutput)?;
        Ok(OutPoint::new(self.to_txid(), vout as u32))
    }

    fn extract_channel_funding(self) -> Result<Funding, Error> {
        let vout = self
            .channel_funding_output()
            .ok_or(Error::NoFundingOutput)?;
        let amount = self.outputs[vout].amount;
        let txid = self.to_txid();
        // TODO: Parse number of signing parties and signing threshold from
        //       witness script attached to the funding output
        Ok(Funding {
            psbt: self,
            txid,
            output: vout as u16,
            amount,
            signing_parties: 2,
            signing_threshold: 2,
        })
    }
}