serai/processor/src/main.rs

use std::{
  env,
  time::Duration,
  collections::{VecDeque, HashMap},
};

use zeroize::{Zeroize, Zeroizing};

use transcript::{Transcript, RecommendedTranscript};
use group::GroupEncoding;
use frost::{curve::Ciphersuite, ThresholdKeys};

use log::{info, warn, error};
use tokio::time::sleep;

use scale::Decode;

use serai_client::{
  primitives::{MAX_DATA_LEN, BlockHash},
  tokens::primitives::{OutInstruction, OutInstructionWithBalance},
  in_instructions::primitives::{
    Shorthand, RefundableInInstruction, InInstructionWithBalance, Batch,
  },
};

use messages::{SubstrateContext, CoordinatorMessage, ProcessorMessage};

mod plan;
pub use plan::*;

mod db;
pub use db::*;

mod coordinator;
pub use coordinator::*;

mod coins;
use coins::{OutputType, Output, PostFeeBranch, Block, Coin};
#[cfg(feature = "bitcoin")]
use coins::Bitcoin;
#[cfg(feature = "monero")]
use coins::Monero;

mod key_gen;
use key_gen::{KeyConfirmed, KeyGen};

mod signer;
use signer::{SignerEvent, Signer};

mod substrate_signer;
use substrate_signer::{SubstrateSignerEvent, SubstrateSigner};

mod scanner;
use scanner::{ScannerEvent, Scanner, ScannerHandle};

mod scheduler;
use scheduler::Scheduler;

#[cfg(test)]
mod tests;

// Generate a static additional key for a given chain in a globally consistent manner
// Doesn't consider the current group key to increase the simplicity of verifying Serai's status
// Takes an index, k, to support protocols which use multiple secondary keys
// Presumably a view key
pub(crate) fn additional_key<C: Coin>(k: u64) -> <C::Curve as Ciphersuite>::F {
  <C::Curve as Ciphersuite>::hash_to_F(
    b"Serai DEX Additional Key",
    &[C::ID.as_bytes(), &k.to_le_bytes()].concat(),
  )
}

async fn get_fee<C: Coin>(coin: &C, block_number: usize) -> C::Fee {
  loop {
    // TODO2: Use an fee representative of several blocks
    match coin.get_block(block_number).await {
      Ok(block) => {
        return block.median_fee();
      }
      Err(e) => {
        error!(
          "couldn't get block {block_number} in get_fee. {} {}",
          "this should only happen if the node is offline. error: ", e
        );
        // Since this block is considered finalized, we shouldn't be unable to get it unless the
        // node is offline, hence the long sleep
        sleep(Duration::from_secs(60)).await;
      }
    }
  }
}

async fn prepare_send<C: Coin>(
  coin: &C,
  keys: ThresholdKeys<C::Curve>,
  block_number: usize,
  fee: C::Fee,
  plan: Plan<C>,
) -> (Option<(C::SignableTransaction, C::Eventuality)>, Vec<PostFeeBranch>) {
  loop {
    match coin.prepare_send(keys.clone(), block_number, plan.clone(), fee).await {
      Ok(prepared) => {
        return prepared;
      }
      Err(e) => {
        error!("couldn't prepare a send for plan {}: {e}", hex::encode(plan.id()));
        // The processor is either trying to create an invalid TX (fatal) or the node went
        // offline
        // The former requires a patch, the latter is a connection issue
        // If the latter, this is an appropriate sleep. If the former, we should panic, yet
        // this won't flood the console ad infinitum
        sleep(Duration::from_secs(60)).await;
      }
    }
  }
}

// Items which are mutably borrowed by Tributary.
// Any exceptions to this have to be carefully monitored in order to ensure consistency isn't
// violated.
struct TributaryMutable<C: Coin, D: Db> {
  // The following are actually mutably borrowed by Substrate as well.
  // - Substrate triggers key gens, and determines which to use.
  // - SubstrateBlock events cause scheduling which causes signing.
  //
  // This is still considered Tributary-mutable as most mutation (preprocesses/shares) happens by
  // the Tributary.
  //
  // Creation of tasks is by Substrate, yet this is safe since the mutable borrow is transferred to
  // Tributary.
  //
  // Tributary stops mutating a key gen attempt before Substrate is made aware of it, ensuring
  // Tributary drops its mutable borrow before Substrate acquires it. Tributary will maintain a
  // mutable borrow on the *key gen task*, yet the finalization code can successfully run for any
  // attempt.
  //
  // The only other note is how the scanner may cause a signer task to be dropped, effectively
  // invalidating the Tributary's mutable borrow. The signer is coded to allow for attempted usage
  // of a dropped task.
  key_gen: KeyGen<C, D>,
  signers: HashMap<Vec<u8>, Signer<C, D>>,

  // This is also mutably borrowed by the Scanner.
  // The Scanner starts new sign tasks.
  // The Tributary mutates already-created signed tasks, potentially completing them.
  // Substrate may mark tasks as completed, invalidating any existing mutable borrows.
  // The safety of this follows as written above.

  // TODO: There should only be one SubstrateSigner at a time (see #277)
  substrate_signers: HashMap<Vec<u8>, SubstrateSigner<D>>,
}

// Items which are mutably borrowed by Substrate.
// Any exceptions to this have to be carefully monitored in order to ensure consistency isn't
// violated.
struct SubstrateMutable<C: Coin, D: Db> {
  // The scanner is expected to autonomously operate, scanning blocks as they appear.
  // When a block is sufficiently confirmed, the scanner mutates the signer to try and get a Batch
  // signed.
  // The scanner itself only mutates its list of finalized blocks and in-memory state though.
  // Disk mutations to the scan-state only happen when Substrate says to.

  // This can't be mutated as soon as a Batch is signed since the mutation which occurs then is
  // paired with the mutations caused by Burn events. Substrate's ordering determines if such a
  // pairing exists.
  scanner: ScannerHandle<C, D>,

  // Schedulers take in new outputs, from the scanner, and payments, from Burn events on Substrate.
  // These are paired when possible, in the name of efficiency. Accordingly, both mutations must
  // happen by Substrate.
  schedulers: HashMap<Vec<u8>, Scheduler<C>>,
}

async fn sign_plans<C: Coin, D: Db>(
  txn: &mut D::Transaction<'_>,
  coin: &C,
  substrate_mutable: &mut SubstrateMutable<C, D>,
  signers: &mut HashMap<Vec<u8>, Signer<C, D>>,
  context: SubstrateContext,
  plans: Vec<Plan<C>>,
) {
  let mut plans = VecDeque::from(plans);

  let mut block_hash = <C::Block as Block<C>>::Id::default();
  block_hash.as_mut().copy_from_slice(&context.coin_latest_finalized_block.0);
  let block_number = substrate_mutable
    .scanner
    .block_number(&block_hash)
    .await
    .expect("told to sign_plans on a context we're not synced to");

  let fee = get_fee(coin, block_number).await;

  while let Some(plan) = plans.pop_front() {
    let id = plan.id();
    info!("preparing plan {}: {:?}", hex::encode(id), plan);

    let key = plan.key.to_bytes();
    MainDb::<C, D>::save_signing(txn, key.as_ref(), block_number.try_into().unwrap(), &plan);
    let (tx, branches) =
      prepare_send(coin, signers.get_mut(key.as_ref()).unwrap().keys(), block_number, fee, plan)
        .await;

    for branch in branches {
      substrate_mutable
        .schedulers
        .get_mut(key.as_ref())
        .expect("didn't have a scheduler for a key we have a plan for")
        .created_output(branch.expected, branch.actual);
    }

    if let Some((tx, eventuality)) = tx {
      substrate_mutable.scanner.register_eventuality(block_number, id, eventuality.clone()).await;
      signers.get_mut(key.as_ref()).unwrap().sign_transaction(txn, id, tx, eventuality).await;
    }
  }
}

async fn handle_coordinator_msg<D: Db, C: Coin, Co: Coordinator>(
  txn: &mut D::Transaction<'_>,
  coin: &C,
  coordinator: &mut Co,
  tributary_mutable: &mut TributaryMutable<C, D>,
  substrate_mutable: &mut SubstrateMutable<C, D>,
  msg: &Message,
) {
  // If this message expects a higher block number than we have, halt until synced
  async fn wait<C: Coin, D: Db>(scanner: &ScannerHandle<C, D>, block_hash: &BlockHash) {
    let mut needed_hash = <C::Block as Block<C>>::Id::default();
    needed_hash.as_mut().copy_from_slice(&block_hash.0);

    let block_number;
    loop {
      // Ensure our scanner has scanned this block, which means our daemon has this block at
      // a sufficient depth
      let Some(block_number_inner) = scanner.block_number(&needed_hash).await else {
      warn!(
        "node is desynced. we haven't scanned {} which should happen after {} confirms",
        hex::encode(&needed_hash),
        C::CONFIRMATIONS,
      );
      sleep(Duration::from_secs(10)).await;
      continue;
    };
      block_number = block_number_inner;
      break;
    }

    // While the scanner has cemented this block, that doesn't mean it's been scanned for all
    // keys
    // ram_scanned will return the lowest scanned block number out of all keys
    while scanner.ram_scanned().await < block_number {
      sleep(Duration::from_secs(1)).await;
    }

    // TODO: Sanity check we got an AckBlock (or this is the AckBlock) for the block in
    // question

    /*
    let synced = |context: &SubstrateContext, key| -> Result<(), ()> {
      // Check that we've synced this block and can actually operate on it ourselves
      let latest = scanner.latest_scanned(key);
      if usize::try_from(context.coin_latest_block_number).unwrap() < latest {
        log::warn!(
          "coin node disconnected/desynced from rest of the network. \
          our block: {latest:?}, network's acknowledged: {}",
          context.coin_latest_block_number
        );
        Err(())?;
      }
      Ok(())
    };
    */
  }

  if let Some(required) = msg.msg.required_block() {
    // wait only reads from, it doesn't mutate, the scanner
    wait(&substrate_mutable.scanner, &required).await;
  }

  // TODO: Shouldn't we create a txn here and pass it around as needed?
  // The txn would ack this message ID. If we detect this mesage ID as handled in the DB,
  // we'd move on here. Only after committing the TX would we report it as acked.

  match msg.msg.clone() {
    CoordinatorMessage::KeyGen(msg) => {
      // TODO: This may be fired multiple times. What's our plan for that?
      coordinator
        .send(ProcessorMessage::KeyGen(tributary_mutable.key_gen.handle(txn, msg).await))
        .await;
    }

    CoordinatorMessage::Sign(msg) => {
      tributary_mutable.signers.get_mut(msg.key()).unwrap().handle(txn, msg).await;
    }

    CoordinatorMessage::Coordinator(msg) => {
      tributary_mutable.substrate_signers.get_mut(msg.key()).unwrap().handle(txn, msg).await;
    }

    CoordinatorMessage::Substrate(msg) => {
      match msg {
        messages::substrate::CoordinatorMessage::ConfirmKeyPair { context, id } => {
          // See TributaryMutable's struct definition for why this block is safe
          let KeyConfirmed { activation_block, substrate_keys, coin_keys } =
            tributary_mutable.key_gen.confirm(txn, context, id).await;
          tributary_mutable.substrate_signers.insert(
            substrate_keys.group_key().to_bytes().to_vec(),
            SubstrateSigner::new(substrate_keys),
          );

          let key = coin_keys.group_key();

          let mut activation_block_hash = <C::Block as Block<C>>::Id::default();
          activation_block_hash.as_mut().copy_from_slice(&activation_block.0);
          let activation_number = substrate_mutable
            .scanner
            .block_number(&activation_block_hash)
            .await
            .expect("KeyConfirmed from context we haven't synced");

          substrate_mutable.scanner.rotate_key(txn, activation_number, key).await;
          substrate_mutable
            .schedulers
            .insert(key.to_bytes().as_ref().to_vec(), Scheduler::<C>::new(key));

          tributary_mutable
            .signers
            .insert(key.to_bytes().as_ref().to_vec(), Signer::new(coin.clone(), coin_keys));
        }

        messages::substrate::CoordinatorMessage::SubstrateBlock {
          context,
          key: key_vec,
          burns,
        } => {
          let mut block_id = <C::Block as Block<C>>::Id::default();
          block_id.as_mut().copy_from_slice(&context.coin_latest_finalized_block.0);

          let key = <C::Curve as Ciphersuite>::read_G::<&[u8]>(&mut key_vec.as_ref()).unwrap();

          // We now have to acknowledge every block for this key up to the acknowledged block
          let (blocks, outputs) =
            substrate_mutable.scanner.ack_up_to_block(txn, key, block_id).await;
          // Since this block was acknowledged, we no longer have to sign the batch for it
          for block in blocks {
            for (_, signer) in tributary_mutable.substrate_signers.iter_mut() {
              signer.batch_signed(txn, block);
            }
          }

          let mut payments = vec![];
          for out in burns {
            let OutInstructionWithBalance {
              instruction: OutInstruction { address, data },
              balance,
            } = out;
            if let Ok(address) = C::Address::try_from(address.consume()) {
              payments.push(Payment {
                address,
                data: data.map(|data| data.consume()),
                amount: balance.amount.0,
              });
            }
          }

          let plans = substrate_mutable
            .schedulers
            .get_mut(&key_vec)
            .expect("key we don't have a scheduler for acknowledged a block")
            .schedule(outputs, payments);

          sign_plans(
            txn,
            coin,
            substrate_mutable,
            // See commentary in TributaryMutable for why this is safe
            &mut tributary_mutable.signers,
            context,
            plans,
          )
          .await;
        }
      }
    }
  }
}

async fn boot<C: Coin, D: Db>(
  raw_db: &mut D,
  coin: &C,
) -> (MainDb<C, D>, TributaryMutable<C, D>, SubstrateMutable<C, D>) {
  let mut entropy_transcript = {
    let entropy =
      Zeroizing::new(env::var("ENTROPY").expect("entropy wasn't provided as an env var"));
    if entropy.len() != 64 {
      panic!("entropy isn't the right length");
    }
    let bytes = Zeroizing::new(hex::decode(entropy).expect("entropy wasn't hex-formatted"));
    let mut entropy = Zeroizing::new([0; 32]);
    let entropy_mut: &mut [u8] = entropy.as_mut();
    entropy_mut.copy_from_slice(bytes.as_ref());

    let mut transcript = RecommendedTranscript::new(b"Serai Processor Entropy");
    transcript.append_message(b"entropy", entropy);
    transcript
  };

  // TODO: Save a hash of the entropy to the DB and make sure the entropy didn't change

  let mut entropy = |label| {
    let mut challenge = entropy_transcript.challenge(label);
    let mut res = Zeroizing::new([0; 32]);
    let res_mut: &mut [u8] = res.as_mut();
    res_mut.copy_from_slice(&challenge[.. 32]);
    challenge.zeroize();
    res
  };

  // We don't need to re-issue GenerateKey orders because the coordinator is expected to
  // schedule/notify us of new attempts
  let key_gen = KeyGen::<C, _>::new(raw_db.clone(), entropy(b"key-gen_entropy"));
  // The scanner has no long-standing orders to re-issue
  let (mut scanner, active_keys) = Scanner::new(coin.clone(), raw_db.clone());

  let schedulers = HashMap::<Vec<u8>, Scheduler<C>>::new();
  let mut substrate_signers = HashMap::new();
  let mut signers = HashMap::new();

  let main_db = MainDb::new(raw_db.clone());

  for key in &active_keys {
    // TODO: Load existing schedulers

    let (substrate_keys, coin_keys) = key_gen.keys(key);

    let substrate_key = substrate_keys.group_key();
    let substrate_signer = SubstrateSigner::new(substrate_keys);
    // We don't have to load any state for this since the Scanner will re-fire any events
    // necessary
    substrate_signers.insert(substrate_key.to_bytes().to_vec(), substrate_signer);

    let mut signer = Signer::new(coin.clone(), coin_keys);

    // Load any TXs being actively signed
    let key = key.to_bytes();
    for (block_number, plan) in main_db.signing(key.as_ref()) {
      let block_number = block_number.try_into().unwrap();

      let fee = get_fee(coin, block_number).await;

      let id = plan.id();
      info!("reloading plan {}: {:?}", hex::encode(id), plan);

      let (Some((tx, eventuality)), _) =
      prepare_send(coin, signer.keys(), block_number, fee, plan).await else {
        panic!("previously created transaction is no longer being created")
      };

      scanner.register_eventuality(block_number, id, eventuality.clone()).await;
      // TODO: Reconsider if the Signer should have the eventuality, or if just the coin/scanner
      // should
      let mut txn = raw_db.txn();
      signer.sign_transaction(&mut txn, id, tx, eventuality).await;
      // This should only have re-writes of existing data
      drop(txn);
    }

    signers.insert(key.as_ref().to_vec(), signer);
  }

  (
    main_db,
    TributaryMutable { key_gen, substrate_signers, signers },
    SubstrateMutable { scanner, schedulers },
  )
}

async fn run<C: Coin, D: Db, Co: Coordinator>(mut raw_db: D, coin: C, mut coordinator: Co) {
  // We currently expect a contextless bidirectional mapping between these two values
  // (which is that any value of A can be interpreted as B and vice versa)
  // While we can write a contextual mapping, we have yet to do so
  // This check ensures no coin which doesn't have a bidirectional mapping is defined
  assert_eq!(<C::Block as Block<C>>::Id::default().as_ref().len(), BlockHash([0u8; 32]).0.len());

  let (mut main_db, mut tributary_mutable, mut substrate_mutable) = boot(&mut raw_db, &coin).await;

  // We can't load this from the DB as we can't guarantee atomic increments with the ack function
  let mut last_coordinator_msg = None;

  loop {
    // Check if the signers have events
    // The signers will only have events after the following select executes, which will then
    // trigger the loop again, hence why having the code here with no timer is fine
    for (key, signer) in tributary_mutable.signers.iter_mut() {
      while let Some(msg) = signer.events.pop_front() {
        match msg {
          SignerEvent::ProcessorMessage(msg) => {
            coordinator.send(ProcessorMessage::Sign(msg)).await;
          }

          SignerEvent::SignedTransaction { id, tx } => {
            coordinator
              .send(ProcessorMessage::Sign(messages::sign::ProcessorMessage::Completed {
                key: key.clone(),
                id,
                tx: tx.as_ref().to_vec(),
              }))
              .await;

            let mut txn = raw_db.txn();
            // This does mutate the Scanner, yet the eventuality protocol is only run to mutate
            // the signer, which is Tributary mutable (and what's currently being mutated)
            substrate_mutable.scanner.drop_eventuality(id).await;
            main_db.finish_signing(&mut txn, key, id);
            txn.commit();

            // TODO
            // 1) We need to stop signing whenever a peer informs us or the chain has an
            //    eventuality
            // 2) If a peer informed us of an eventuality without an outbound payment, stop
            //    scanning the chain for it (or at least ack it's solely for sanity purposes?)
            // 3) When the chain has an eventuality, if it had an outbound payment, report it up to
            //    Substrate for logging purposes
          }
        }
      }
    }

    for (key, signer) in tributary_mutable.substrate_signers.iter_mut() {
      while let Some(msg) = signer.events.pop_front() {
        match msg {
          SubstrateSignerEvent::ProcessorMessage(msg) => {
            coordinator.send(ProcessorMessage::Coordinator(msg)).await;
          }
          SubstrateSignerEvent::SignedBatch(batch) => {
            coordinator
              .send(ProcessorMessage::Substrate(messages::substrate::ProcessorMessage::Update {
                key: key.clone(),
                batch,
              }))
              .await;
          }
        }
      }
    }

    tokio::select! {
      // This blocks the entire processor until it finishes handling this message
      // KeyGen specifically may take a notable amount of processing time
      // While that shouldn't be an issue in practice, as after processing an attempt it'll handle
      // the other messages in the queue, it may be beneficial to parallelize these
      // They could likely be parallelized by type (KeyGen, Sign, Substrate) without issue
      msg = coordinator.recv() => {
        assert_eq!(msg.id, (last_coordinator_msg.unwrap_or(msg.id - 1) + 1));
        last_coordinator_msg = Some(msg.id);

        // Only handle this if we haven't already
        if !main_db.handled_message(msg.id) {
          let mut txn = raw_db.txn();
          MainDb::<C, D>::handle_message(&mut txn, msg.id);

          // This is isolated to better think about how its ordered, or rather, about how the other
          // cases aren't ordered
          //
          // While the coordinator messages are ordered, they're not deterministically ordered
          // Tributary-caused messages are deterministically ordered, and Substrate-caused messages
          // are deterministically-ordered, yet they're both shoved into a singular queue
          // The order at which they're shoved in together isn't deterministic
          //
          // This is safe so long as Tributary and Substrate messages don't both expect mutable
          // references over the same data
          handle_coordinator_msg(
            &mut txn,
            &coin,
            &mut coordinator,
            &mut tributary_mutable,
            &mut substrate_mutable,
            &msg,
          ).await;

          txn.commit();
        }

        coordinator.ack(msg).await;
      },

      msg = substrate_mutable.scanner.events.recv() => {
        let mut txn = raw_db.txn();

        match msg.unwrap() {
          ScannerEvent::Block { key, block, batch, outputs } => {
            let key = key.to_bytes().as_ref().to_vec();

            let mut block_hash = [0; 32];
            block_hash.copy_from_slice(block.as_ref());

            let batch = Batch {
              network: C::NETWORK,
              id: batch,
              block: BlockHash(block_hash),
              instructions: outputs.iter().filter_map(|output| {
                // If these aren't externally received funds, don't handle it as an instruction
                if output.kind() != OutputType::External {
                  return None;
                }

                let mut data = output.data();
                let max_data_len = MAX_DATA_LEN.try_into().unwrap();
                if data.len() > max_data_len {
                  error!(
                    "data in output {} exceeded MAX_DATA_LEN ({MAX_DATA_LEN}): {}",
                    hex::encode(output.id()),
                    data.len(),
                  );
                  data = &data[.. max_data_len];
                }

                let shorthand = Shorthand::decode(&mut data).ok()?;
                let instruction = RefundableInInstruction::try_from(shorthand).ok()?;
                // TODO2: Set instruction.origin if not set (and handle refunds in general)
                Some(InInstructionWithBalance {
                  instruction: instruction.instruction,
                  balance: output.balance(),
                })
              }).collect()
            };

            // Start signing this batch
            tributary_mutable.substrate_signers.get_mut(&key).unwrap().sign(&mut txn, batch).await;
          },

          ScannerEvent::Completed(id, tx) => {
            // We don't know which signer had this plan, so inform all of them
            for (_, signer) in tributary_mutable.signers.iter_mut() {
              signer.eventuality_completion(&mut txn, id, &tx).await;
            }
          },
        }

        txn.commit();
      },
    }
  }
}

#[tokio::main]
async fn main() {
  let db = MemDb::new(); // TODO
  let coordinator = MemCoordinator::new(); // TODO
  let url = env::var("COIN_RPC").expect("coin rpc wasn't specified as an env var");
  match env::var("COIN").expect("coin wasn't specified as an env var").as_str() {
    #[cfg(feature = "bitcoin")]
    "bitcoin" => run(db, Bitcoin::new(url).await, coordinator).await,
    #[cfg(feature = "monero")]
    "monero" => run(db, Monero::new(url), coordinator).await,
    _ => panic!("unrecognized coin"),
  }
}