xmr-btc-swap/monero-wallet/src/lib.rs

use anyhow::{Context, Result};
use monero::consensus::encode::VarInt;
use monero::cryptonote::hash::Hashable;
use monero_rpc::monerod;
use monero_rpc::monerod::{GetBlockResponse, MonerodRpc as _};
use rand::Rng;

pub struct Wallet {
    client: monerod::Client,
}

impl Wallet {
    /// Chooses 10 random key offsets for use within a new confidential
    /// transactions.
    ///
    /// Choosing these offsets randomly is not ideal for privacy, instead they
    /// should be chosen in a way that mimics a real spending pattern as much as
    /// possible.
    pub async fn choose_ten_random_key_offsets(&self) -> Result<[VarInt; 10]> {
        let latest_block = self.client.get_block_count().await?;
        let latest_spendable_block = latest_block.count - 10;

        let block: GetBlockResponse = self.client.get_block(latest_spendable_block).await?;

        let tx_hash = block
            .blob
            .tx_hashes
            .first()
            .copied()
            .unwrap_or_else(|| block.blob.miner_tx.hash());

        let indices = self.client.get_o_indexes(tx_hash).await?;

        let last_index = indices
            .o_indexes
            .into_iter()
            .max()
            .context("Expected at least one output index")?;
        let oldest_index = last_index - (last_index / 100) * 40; // oldest index must be within last 40% TODO: CONFIRM THIS

        let mut rng = rand::thread_rng();

        Ok([
            VarInt(rng.gen_range(oldest_index, last_index)),
            VarInt(rng.gen_range(oldest_index, last_index)),
            VarInt(rng.gen_range(oldest_index, last_index)),
            VarInt(rng.gen_range(oldest_index, last_index)),
            VarInt(rng.gen_range(oldest_index, last_index)),
            VarInt(rng.gen_range(oldest_index, last_index)),
            VarInt(rng.gen_range(oldest_index, last_index)),
            VarInt(rng.gen_range(oldest_index, last_index)),
            VarInt(rng.gen_range(oldest_index, last_index)),
            VarInt(rng.gen_range(oldest_index, last_index)),
        ])
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use monero_harness::image::Monerod;
    use monero_rpc::monerod::{Client, GetOutputsOut};
    use testcontainers::clients::Cli;
    use testcontainers::Docker;

    #[tokio::test]
    async fn get_outs_for_key_offsets() {
        let cli = Cli::default();
        let container = cli.run(Monerod::default());
        let rpc_client = Client::localhost(container.get_host_port(18081).unwrap()).unwrap();
        rpc_client.generateblocks(150, "498AVruCDWgP9Az9LjMm89VWjrBrSZ2W2K3HFBiyzzrRjUJWUcCVxvY1iitfuKoek2FdX6MKGAD9Qb1G1P8QgR5jPmmt3Vj".to_owned()).await.unwrap();
        let wallet = Wallet {
            client: rpc_client.clone(),
        };

        let key_offsets = wallet.choose_ten_random_key_offsets().await.unwrap();
        let result = rpc_client
            .get_outs(
                key_offsets
                    .to_vec()
                    .into_iter()
                    .map(|varint| GetOutputsOut {
                        amount: 0,
                        index: varint.0,
                    })
                    .collect(),
            )
            .await
            .unwrap();

        assert_eq!(result.outs.len(), 10);
    }
}