serai/processor/src/coins/monero.rs

use std::sync::Arc;

use async_trait::async_trait;
use rand_core::{RngCore, CryptoRng};

use curve25519_dalek::{
  constants::ED25519_BASEPOINT_TABLE,
  scalar::Scalar,
  edwards::CompressedEdwardsY
};

use dalek_ff_group as dfg;
use frost::MultisigKeys;

use monero::{PublicKey, network::Network, util::address::Address};
use monero_serai::{
  frost::Ed25519,
  transaction::{Timelock, Transaction},
  rpc::Rpc,
  wallet::{SpendableOutput, SignableTransaction as MSignableTransaction}
};

use crate::{Transcript, Output as OutputTrait, CoinError, Coin, view_key};

#[derive(Clone)]
pub struct Output(SpendableOutput);
impl OutputTrait for Output {
  // While we could use (tx, o), using the key ensures we won't be susceptible to the burning bug.
  // While the Monero library offers a variant which allows senders to ensure their TXs have unique
  // output keys, Serai can still be targeted using the classic burning bug
  type Id = [u8; 32];

  fn id(&self) -> Self::Id {
    self.0.key.compress().to_bytes()
  }

  fn amount(&self) -> u64 {
    self.0.commitment.amount
  }

  fn serialize(&self) -> Vec<u8> {
    self.0.serialize()
  }

  fn deserialize<R: std::io::Read>(reader: &mut R) -> std::io::Result<Self> {
    SpendableOutput::deserialize(reader).map(|o| Output(o))
  }
}

impl From<SpendableOutput> for Output {
  fn from(output: SpendableOutput) -> Output {
    Output(output)
  }
}

pub struct SignableTransaction(
  Arc<MultisigKeys<Ed25519>>,
  Transcript,
  usize,
  MSignableTransaction
);

pub struct Monero {
  rpc: Rpc,
  view: Scalar,
  view_pub: CompressedEdwardsY
}

impl Monero {
  pub fn new(url: String) -> Monero {
    let view = view_key::<Monero>(0).0;
    Monero {
      rpc: Rpc::new(url),
      view,
      view_pub: (&view * &ED25519_BASEPOINT_TABLE).compress()
    }
  }
}

#[async_trait]
impl Coin for Monero {
  type Curve = Ed25519;

  type Output = Output;
  type Block = Vec<Transaction>;
  type SignableTransaction = SignableTransaction;

  type Address = Address;

  const ID: &'static [u8] = b"Monero";
  const CONFIRMATIONS: usize = 10;
  // Testnet TX bb4d188a4c571f2f0de70dca9d475abc19078c10ffa8def26dd4f63ce1bcfd79 uses 146 inputs
  // while using less than 100kb of space, albeit with just 2 outputs (though outputs share a BP)
  // The TX size limit is half the contextual median block weight, where said weight is >= 300,000
  // This means any TX which fits into 150kb will be accepted by Monero
  // 128, even with 16 outputs, should fit into 100kb. Further efficiency by 192 may be viable
  // TODO: Get hard numbers and tune
  const MAX_INPUTS: usize = 128;
  const MAX_OUTPUTS: usize = 16;

  async fn get_height(&self) -> Result<usize, CoinError> {
    self.rpc.get_height().await.map_err(|_| CoinError::ConnectionError)
  }

  async fn get_block(&self, height: usize) -> Result<Self::Block, CoinError> {
    self.rpc.get_block_transactions_possible(height).await.map_err(|_| CoinError::ConnectionError)
  }

  async fn get_outputs(&self, block: &Self::Block, key: dfg::EdwardsPoint) -> Vec<Self::Output> {
    block
      .iter()
      .flat_map(|tx| {
        let (outputs, timelock) = tx.scan(self.view, key.0);
        if timelock == Timelock::None {
          outputs
        } else {
          vec![]
        }
      })
      .map(Output::from)
      .collect()
  }

  async fn prepare_send(
    &self,
    keys: Arc<MultisigKeys<Ed25519>>,
    transcript: Transcript,
    height: usize,
    mut inputs: Vec<Output>,
    payments: &[(Address, u64)]
  ) -> Result<SignableTransaction, CoinError> {
    let spend = keys.group_key().0.compress();
    Ok(
      SignableTransaction(
        keys,
        transcript,
        height,
        MSignableTransaction::new(
          inputs.drain(..).map(|input| input.0).collect(),
          payments.to_vec(),
          Address::standard(
            Network::Mainnet,
            PublicKey { point: spend },
            PublicKey { point: self.view_pub }
          ),
          100000000
        ).map_err(|_| CoinError::ConnectionError)?
      )
    )
  }

  async fn attempt_send<R: RngCore + CryptoRng + std::marker::Send>(
    &self,
    rng: &mut R,
    transaction: SignableTransaction,
    included: &[u16]
  ) -> Result<(Vec<u8>, Vec<<Self::Output as OutputTrait>::Id>), CoinError> {
    let attempt = transaction.3.clone().multisig(
      rng,
      &self.rpc,
      (*transaction.0).clone(),
      transaction.1.clone(),
      transaction.2,
      included.to_vec()
    ).await.map_err(|_| CoinError::ConnectionError)?;

    /*
    let tx = None;
    self.rpc.publish_transaction(tx).await.map_err(|_| CoinError::ConnectionError)?;
    Ok(
      tx.hash().to_vec(),
      tx.outputs.iter().map(|output| output.key.compress().to_bytes().collect())
    )
    */
    Ok((vec![], vec![]))
  }
}