serai/processor/src/coin/monero.rs

use std::sync::Arc;

use async_trait::async_trait;

use curve25519_dalek::scalar::Scalar;

use dalek_ff_group as dfg;
use transcript::RecommendedTranscript;
use frost::{curve::Ed25519, FrostKeys};

use monero_serai::{
  transaction::Transaction,
  rpc::Rpc,
  wallet::{
    ViewPair,
    address::{Network, AddressType, Address},
    Fee, SpendableOutput, SignableTransaction as MSignableTransaction, TransactionMachine,
  },
};

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

#[derive(Clone, Debug)]
pub struct Output(SpendableOutput);
impl From<SpendableOutput> for Output {
  fn from(output: SpendableOutput) -> Output {
    Output(output)
  }
}

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(Output)
  }
}

#[derive(Debug)]
pub struct SignableTransaction(
  Arc<FrostKeys<Ed25519>>,
  RecommendedTranscript,
  usize,
  MSignableTransaction,
);

#[derive(Clone, Debug)]
pub struct Monero {
  pub(crate) rpc: Rpc,
  view: Scalar,
}

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

  fn view_pair(&self, spend: dfg::EdwardsPoint) -> ViewPair {
    ViewPair { spend: spend.0, view: self.view }
  }

  #[cfg(test)]
  fn empty_view_pair(&self) -> ViewPair {
    use group::Group;
    self.view_pair(dfg::EdwardsPoint::generator())
  }

  #[cfg(test)]
  fn empty_address(&self) -> Address {
    self.empty_view_pair().address(Network::Mainnet, AddressType::Standard, false)
  }
}

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

  type Fee = Fee;
  type Transaction = Transaction;
  type Block = Vec<Transaction>;

  type Output = Output;
  type SignableTransaction = SignableTransaction;
  type TransactionMachine = TransactionMachine;

  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;

  fn address(&self, key: dfg::EdwardsPoint) -> Self::Address {
    self.view_pair(key).address(Network::Mainnet, AddressType::Standard, true)
  }

  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| tx.scan(self.view_pair(key), true).not_locked())
      .map(Output::from)
      .collect()
  }

  async fn prepare_send(
    &self,
    keys: Arc<FrostKeys<Ed25519>>,
    transcript: RecommendedTranscript,
    height: usize,
    mut inputs: Vec<Output>,
    payments: &[(Address, u64)],
    fee: Fee,
  ) -> Result<SignableTransaction, CoinError> {
    let spend = keys.group_key();
    Ok(SignableTransaction(
      keys,
      transcript,
      height,
      MSignableTransaction::new(
        inputs.drain(..).map(|input| input.0).collect(),
        payments.to_vec(),
        Some(self.address(spend)),
        fee,
      )
      .map_err(|_| CoinError::ConnectionError)?,
    ))
  }

  async fn attempt_send(
    &self,
    transaction: SignableTransaction,
    included: &[u16],
  ) -> Result<Self::TransactionMachine, CoinError> {
    transaction
      .3
      .clone()
      .multisig(
        &self.rpc,
        (*transaction.0).clone(),
        transaction.1.clone(),
        transaction.2,
        included.to_vec(),
      )
      .await
      .map_err(|_| CoinError::ConnectionError)
  }

  async fn publish_transaction(
    &self,
    tx: &Self::Transaction,
  ) -> Result<(Vec<u8>, Vec<<Self::Output as OutputTrait>::Id>), CoinError> {
    self.rpc.publish_transaction(tx).await.map_err(|_| CoinError::ConnectionError)?;

    Ok((
      tx.hash().to_vec(),
      tx.prefix.outputs.iter().map(|output| output.key.compress().to_bytes()).collect(),
    ))
  }

  #[cfg(test)]
  async fn mine_block(&self) {
    #[derive(serde::Deserialize, Debug)]
    struct EmptyResponse {}
    let _: EmptyResponse = self
      .rpc
      .rpc_call(
        "json_rpc",
        Some(serde_json::json!({
          "method": "generateblocks",
          "params": {
            "wallet_address": self.empty_address().to_string(),
            "amount_of_blocks": 10
          },
        })),
      )
      .await
      .unwrap();
  }

  #[cfg(test)]
  async fn test_send(&self, address: Self::Address) {
    use rand::rngs::OsRng;

    let height = self.get_height().await.unwrap();

    self.mine_block().await;
    for _ in 0 .. 7 {
      self.mine_block().await;
    }

    let outputs = self
      .rpc
      .get_block_transactions_possible(height)
      .await
      .unwrap()
      .swap_remove(0)
      .scan(self.empty_view_pair(), false)
      .ignore_timelock();

    let amount = outputs[0].commitment.amount;
    let fee = 1000000000; // TODO
    let tx = MSignableTransaction::new(
      outputs,
      vec![(address, amount - fee)],
      Some(self.empty_address()),
      self.rpc.get_fee().await.unwrap(),
    )
    .unwrap()
    .sign(&mut OsRng, &self.rpc, &Scalar::one())
    .await
    .unwrap();
    self.rpc.publish_transaction(&tx).await.unwrap();
    self.mine_block().await;
  }
}