solana/src/bank.rs

//! The `bank` module tracks client balances and the progress of smart
//! contracts. It offers a high-level API that signs transactions
//! on behalf of the caller, and a low-level API for when they have
//! already been signed and verified.

extern crate libc;

use chrono::prelude::*;
use counter::Counter;
use entry::Entry;
use hash::Hash;
use itertools::Itertools;
use ledger::Block;
use mint::Mint;
use payment_plan::{Payment, PaymentPlan, Witness};
use signature::{KeyPair, PublicKey, Signature};
use std::collections::hash_map::Entry::Occupied;
use std::collections::{HashMap, HashSet, VecDeque};
use std::result;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::RwLock;
use std::time::Instant;
use streamer::WINDOW_SIZE;
use timing::duration_as_us;
use transaction::{Instruction, Plan, Transaction};

/// The number of most recent `last_id` values that the bank will track the signatures
/// of. Once the bank discards a `last_id`, it will reject any transactions that use
/// that `last_id` in a transaction. Lowering this value reduces memory consumption,
/// but requires clients to update its `last_id` more frequently. Raising the value
/// lengthens the time a client must wait to be certain a missing transaction will
/// not be processed by the network.
pub const MAX_ENTRY_IDS: usize = 1024 * 16;

pub const VERIFY_BLOCK_SIZE: usize = 16;

/// Reasons a transaction might be rejected.
#[derive(Debug, PartialEq, Eq)]
pub enum BankError {
    /// Attempt to debit from `PublicKey`, but no found no record of a prior credit.
    AccountNotFound(PublicKey),

    /// The requested debit from `PublicKey` has the potential to draw the balance
    /// below zero. This can occur when a debit and credit are processed in parallel.
    /// The bank may reject the debit or push it to a future entry.
    InsufficientFunds(PublicKey),

    /// The bank has seen `Signature` before. This can occur under normal operation
    /// when a UDP packet is duplicated, as a user error from a client not updating
    /// its `last_id`, or as a double-spend attack.
    DuplicateSignature(Signature),

    /// The bank has not seen the given `last_id` or the transaction is too old and
    /// the `last_id` has been discarded.
    LastIdNotFound(Hash),

    /// The transaction is invalid and has requested a debit or credit of negative
    /// tokens.
    NegativeTokens,

    /// Proof of History verification failed.
    LedgerVerificationFailed,
}

pub type Result<T> = result::Result<T, BankError>;

/// The state of all accounts and contracts after processing its entries.
pub struct Bank {
    /// A map of account public keys to the balance in that account.
    balances: RwLock<HashMap<PublicKey, i64>>,

    /// A map of smart contract transaction signatures to what remains of its payment
    /// plan. Each transaction that targets the plan should cause it to be reduced.
    /// Once it cannot be reduced, final payments are made and it is discarded.
    pending: RwLock<HashMap<Signature, Plan>>,

    /// A FIFO queue of `last_id` items, where each item is a set of signatures
    /// that have been processed using that `last_id`. Rejected `last_id`
    /// values are so old that the `last_id` has been pulled out of the queue.
    last_ids: RwLock<VecDeque<Hash>>,

    // Mapping of hashes to signature sets. The bank uses this data to
    /// reject transactions with signatures its seen before
    last_ids_sigs: RwLock<HashMap<Hash, HashSet<Signature>>>,

    /// The number of transactions the bank has processed without error since the
    /// start of the ledger.
    transaction_count: AtomicUsize,
}

impl Default for Bank {
    fn default() -> Self {
        Bank {
            balances: RwLock::new(HashMap::new()),
            pending: RwLock::new(HashMap::new()),
            last_ids: RwLock::new(VecDeque::new()),
            last_ids_sigs: RwLock::new(HashMap::new()),
            transaction_count: AtomicUsize::new(0),
        }
    }
}

impl Bank {
    /// Create an Bank using a deposit.
    pub fn new_from_deposit(deposit: &Payment) -> Self {
        let bank = Self::default();
        bank.apply_payment(deposit, &mut bank.balances.write().unwrap());
        bank
    }

    /// Create an Bank with only a Mint. Typically used by unit tests.
    pub fn new(mint: &Mint) -> Self {
        let deposit = Payment {
            to: mint.pubkey(),
            tokens: mint.tokens,
        };
        let bank = Self::new_from_deposit(&deposit);
        bank.register_entry_id(&mint.last_id());
        bank
    }

    /// Commit funds to the `payment.to` party.
    fn apply_payment(&self, payment: &Payment, balances: &mut HashMap<PublicKey, i64>) {
        *balances.entry(payment.to).or_insert(0) += payment.tokens;
    }

    /// Return the last entry ID registered.
    pub fn last_id(&self) -> Hash {
        let last_ids = self.last_ids.read().expect("'last_ids' read lock");
        let last_item = last_ids
            .iter()
            .last()
            .expect("get last item from 'last_ids' list");
        *last_item
    }

    /// Store the given signature. The bank will reject any transaction with the same signature.
    fn reserve_signature(signatures: &mut HashSet<Signature>, sig: &Signature) -> Result<()> {
        if let Some(sig) = signatures.get(sig) {
            return Err(BankError::DuplicateSignature(*sig));
        }
        signatures.insert(*sig);
        Ok(())
    }

    /// Forget the given `signature` because its transaction was rejected.
    fn forget_signature(signatures: &mut HashSet<Signature>, signature: &Signature) {
        signatures.remove(signature);
    }

    /// Forget the given `signature` with `last_id` because the transaction was rejected.
    fn forget_signature_with_last_id(&self, signature: &Signature, last_id: &Hash) {
        if let Some(entry) = self.last_ids_sigs
            .write()
            .expect("'last_ids' read lock in forget_signature_with_last_id")
            .get_mut(last_id)
        {
            Self::forget_signature(entry, signature);
        }
    }

    /// Forget all signatures. Useful for benchmarking.
    pub fn clear_signatures(&self) {
        for (_, sigs) in self.last_ids_sigs.write().unwrap().iter_mut() {
            sigs.clear();
        }
    }

    fn reserve_signature_with_last_id(&self, signature: &Signature, last_id: &Hash) -> Result<()> {
        if let Some(entry) = self.last_ids_sigs
            .write()
            .expect("'last_ids' read lock in reserve_signature_with_last_id")
            .get_mut(last_id)
        {
            return Self::reserve_signature(entry, signature);
        }
        Err(BankError::LastIdNotFound(*last_id))
    }

    /// Tell the bank which Entry IDs exist on the ledger. This function
    /// assumes subsequent calls correspond to later entries, and will boot
    /// the oldest ones once its internal cache is full. Once boot, the
    /// bank will reject transactions using that `last_id`.
    pub fn register_entry_id(&self, last_id: &Hash) {
        let mut last_ids = self.last_ids
            .write()
            .expect("'last_ids' write lock in register_entry_id");
        let mut last_ids_sigs = self.last_ids_sigs
            .write()
            .expect("last_ids_sigs write lock");
        if last_ids.len() >= MAX_ENTRY_IDS {
            let id = last_ids.pop_front().unwrap();
            last_ids_sigs.remove(&id);
        }
        last_ids_sigs.insert(*last_id, HashSet::new());
        last_ids.push_back(*last_id);
    }

    /// Deduct tokens from the 'from' address the account has sufficient
    /// funds and isn't a duplicate.
    fn apply_debits(&self, tx: &Transaction, bals: &mut HashMap<PublicKey, i64>) -> Result<()> {
        let mut purge = false;
        {
            let option = bals.get_mut(&tx.from);
            if option.is_none() {
                if let Instruction::NewVote(_) = &tx.instruction {
                    inc_new_counter!("bank-appy_debits-vote_account_not_found", 1);
                } else {
                    inc_new_counter!("bank-appy_debits-generic_account_not_found", 1);
                }
                return Err(BankError::AccountNotFound(tx.from));
            }
            let bal = option.unwrap();

            self.reserve_signature_with_last_id(&tx.sig, &tx.last_id)?;

            if let Instruction::NewContract(contract) = &tx.instruction {
                if contract.tokens < 0 {
                    return Err(BankError::NegativeTokens);
                }

                if *bal < contract.tokens {
                    self.forget_signature_with_last_id(&tx.sig, &tx.last_id);
                    return Err(BankError::InsufficientFunds(tx.from));
                } else if *bal == contract.tokens {
                    purge = true;
                } else {
                    *bal -= contract.tokens;
                }
            };
        }

        if purge {
            bals.remove(&tx.from);
        }

        Ok(())
    }

    /// Apply only a transaction's credits. Credits from multiple transactions
    /// may safely be applied in parallel.
    fn apply_credits(&self, tx: &Transaction, balances: &mut HashMap<PublicKey, i64>) {
        match &tx.instruction {
            Instruction::NewContract(contract) => {
                let plan = contract.plan.clone();
                if let Some(payment) = plan.final_payment() {
                    self.apply_payment(&payment, balances);
                } else {
                    let mut pending = self.pending
                        .write()
                        .expect("'pending' write lock in apply_credits");
                    pending.insert(tx.sig, plan);
                }
            }
            Instruction::ApplyTimestamp(dt) => {
                let _ = self.apply_timestamp(tx.from, *dt);
            }
            Instruction::ApplySignature(tx_sig) => {
                let _ = self.apply_signature(tx.from, *tx_sig);
            }
            Instruction::NewVote(_vote) => {
                info!("GOT VOTE!");
                // TODO: record the vote in the stake table...
            }
        }
    }

    /// Process a Transaction. If it contains a payment plan that requires a witness
    /// to progress, the payment plan will be stored in the bank.
    pub fn process_transaction(&self, tx: &Transaction) -> Result<()> {
        let bals = &mut self.balances.write().unwrap();
        self.apply_debits(tx, bals)?;
        self.apply_credits(tx, bals);
        self.transaction_count.fetch_add(1, Ordering::Relaxed);
        Ok(())
    }

    /// Process a batch of transactions.
    #[must_use]
    pub fn process_transactions(&self, txs: Vec<Transaction>) -> Vec<Result<Transaction>> {
        let bals = &mut self.balances.write().unwrap();
        debug!("processing Transactions {}", txs.len());
        let txs_len = txs.len();
        let now = Instant::now();
        let results: Vec<_> = txs.into_iter()
            .map(|tx| self.apply_debits(&tx, bals).map(|_| tx))
            .collect(); // Calling collect() here forces all debits to complete before moving on.

        let debits = now.elapsed();
        let now = Instant::now();

        let res: Vec<_> = results
            .into_iter()
            .map(|result| {
                result.map(|tx| {
                    self.apply_credits(&tx, bals);
                    tx
                })
            })
            .collect();

        debug!(
            "debits: {} us credits: {:?} us tx: {}",
            duration_as_us(&debits),
            duration_as_us(&now.elapsed()),
            txs_len
        );

        let mut tx_count = 0;
        for r in &res {
            if r.is_ok() {
                tx_count += 1;
            } else {
                info!("tx error: {:?}", r);
            }
        }
        self.transaction_count
            .fetch_add(tx_count, Ordering::Relaxed);
        res
    }

    fn process_entry(&self, entry: Entry) -> Result<()> {
        if !entry.transactions.is_empty() {
            for result in self.process_transactions(entry.transactions) {
                result?;
            }
        }
        if !entry.has_more {
            self.register_entry_id(&entry.id);
        }
        Ok(())
    }

    /// Process an ordered list of entries, populating a circular buffer "tail"
    ///   as we go.
    fn process_entries_tail(
        &self,
        entries: Vec<Entry>,
        tail: &mut Vec<Entry>,
        tail_idx: &mut usize,
    ) -> Result<u64> {
        let mut entry_count = 0;

        for entry in entries {
            if tail.len() > *tail_idx {
                tail[*tail_idx] = entry.clone();
            } else {
                tail.push(entry.clone());
            }
            *tail_idx = (*tail_idx + 1) % WINDOW_SIZE as usize;

            entry_count += 1;
            self.process_entry(entry)?;
        }

        Ok(entry_count)
    }

    /// Process an ordered list of entries.
    pub fn process_entries(&self, entries: Vec<Entry>) -> Result<u64> {
        let mut entry_count = 0;
        for entry in entries {
            entry_count += 1;
            self.process_entry(entry)?;
        }
        Ok(entry_count)
    }

    /// Append entry blocks to the ledger, verifying them along the way.
    fn process_blocks<I>(
        &self,
        entries: I,
        tail: &mut Vec<Entry>,
        tail_idx: &mut usize,
    ) -> Result<u64>
    where
        I: IntoIterator<Item = Entry>,
    {
        // Ledger verification needs to be parallelized, but we can't pull the whole
        // thing into memory. We therefore chunk it.
        let mut entry_count = 0;
        for block in &entries.into_iter().chunks(VERIFY_BLOCK_SIZE) {
            let block: Vec<_> = block.collect();
            if !block.verify(&self.last_id()) {
                return Err(BankError::LedgerVerificationFailed);
            }
            entry_count += self.process_entries_tail(block, tail, tail_idx)?;
        }
        Ok(entry_count)
    }

    /// Process a full ledger.
    pub fn process_ledger<I>(&self, entries: I) -> Result<(u64, Vec<Entry>)>
    where
        I: IntoIterator<Item = Entry>,
    {
        let mut entries = entries.into_iter();

        // The first item in the ledger is required to be an entry with zero num_hashes,
        // which implies its id can be used as the ledger's seed.
        let entry0 = entries.next().expect("invalid ledger: empty");

        // The second item in the ledger is a special transaction where the to and from
        // fields are the same. That entry should be treated as a deposit, not a
        // transfer to oneself.
        let entry1 = entries
            .next()
            .expect("invalid ledger: need at least 2 entries");
        {
            let tx = &entry1.transactions[0];
            let deposit = if let Instruction::NewContract(contract) = &tx.instruction {
                contract.plan.final_payment()
            } else {
                None
            }.expect("invalid ledger, needs to start with a contract");

            self.apply_payment(&deposit, &mut self.balances.write().unwrap());
        }
        self.register_entry_id(&entry0.id);
        self.register_entry_id(&entry1.id);

        let mut tail = Vec::with_capacity(WINDOW_SIZE as usize);
        tail.push(entry0);
        tail.push(entry1);
        let mut tail_idx = 2;
        let entry_count = 2 + self.process_blocks(entries, &mut tail, &mut tail_idx)?;

        // check f we need to rotate tail
        let tail = if tail.len() == WINDOW_SIZE as usize {
            rotate_vector(tail, tail_idx)
        } else {
            tail
        };

        Ok((entry_count, tail))
    }

    /// Process a Witness Signature. Any payment plans waiting on this signature
    /// will progress one step.
    fn apply_signature(&self, from: PublicKey, tx_sig: Signature) -> Result<()> {
        if let Occupied(mut e) = self.pending
            .write()
            .expect("write() in apply_signature")
            .entry(tx_sig)
        {
            e.get_mut().apply_witness(&Witness::Signature, &from);
            if let Some(payment) = e.get().final_payment() {
                self.apply_payment(&payment, &mut self.balances.write().unwrap());
                e.remove_entry();
            }
        };

        Ok(())
    }

    /// Process a Witness Timestamp. Any payment plans waiting on this timestamp
    /// will progress one step.
    fn apply_timestamp(&self, from: PublicKey, dt: DateTime<Utc>) -> Result<()> {
        // Check to see if any timelocked transactions can be completed.
        let mut completed = vec![];

        // Hold 'pending' write lock until the end of this function. Otherwise another thread can
        // double-spend if it enters before the modified plan is removed from 'pending'.
        let mut pending = self.pending
            .write()
            .expect("'pending' write lock in apply_timestamp");
        for (key, plan) in pending.iter_mut() {
            plan.apply_witness(&Witness::Timestamp(dt), &from);
            if let Some(payment) = plan.final_payment() {
                self.apply_payment(&payment, &mut self.balances.write().unwrap());
                completed.push(key.clone());
            }
        }

        for key in completed {
            pending.remove(&key);
        }

        Ok(())
    }

    /// Create, sign, and process a Transaction from `keypair` to `to` of
    /// `n` tokens where `last_id` is the last Entry ID observed by the client.
    pub fn transfer(
        &self,
        n: i64,
        keypair: &KeyPair,
        to: PublicKey,
        last_id: Hash,
    ) -> Result<Signature> {
        let tx = Transaction::new(keypair, to, n, last_id);
        let sig = tx.sig;
        self.process_transaction(&tx).map(|_| sig)
    }

    /// Create, sign, and process a postdated Transaction from `keypair`
    /// to `to` of `n` tokens on `dt` where `last_id` is the last Entry ID
    /// observed by the client.
    pub fn transfer_on_date(
        &self,
        n: i64,
        keypair: &KeyPair,
        to: PublicKey,
        dt: DateTime<Utc>,
        last_id: Hash,
    ) -> Result<Signature> {
        let tx = Transaction::new_on_date(keypair, to, dt, n, last_id);
        let sig = tx.sig;
        self.process_transaction(&tx).map(|_| sig)
    }

    pub fn get_balance(&self, pubkey: &PublicKey) -> i64 {
        let bals = self.balances
            .read()
            .expect("'balances' read lock in get_balance");
        bals.get(pubkey).cloned().unwrap_or(0)
    }

    pub fn transaction_count(&self) -> usize {
        self.transaction_count.load(Ordering::Relaxed)
    }

    pub fn has_signature(&self, signature: &Signature) -> bool {
        let last_ids_sigs = self.last_ids_sigs
            .read()
            .expect("'last_ids_sigs' read lock");
        for (_hash, signatures) in last_ids_sigs.iter() {
            if signatures.contains(signature) {
                return true;
            }
        }
        false
    }
}

fn rotate_vector<T: Clone>(v: Vec<T>, at: usize) -> Vec<T> {
    if at != 0 {
        let mut ret = Vec::with_capacity(v.len());
        ret.extend_from_slice(&v[at..]);
        ret.extend_from_slice(&v[0..at]);
        ret
    } else {
        v
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use bincode::serialize;
    use entry::next_entry;
    use entry::Entry;
    use entry_writer::{self, EntryWriter};
    use hash::hash;
    use signature::KeyPairUtil;
    use std::io::{BufReader, Cursor, Seek, SeekFrom};

    #[test]
    fn test_two_payments_to_one_party() {
        let mint = Mint::new(10_000);
        let pubkey = KeyPair::new().pubkey();
        let bank = Bank::new(&mint);
        assert_eq!(bank.last_id(), mint.last_id());

        bank.transfer(1_000, &mint.keypair(), pubkey, mint.last_id())
            .unwrap();
        assert_eq!(bank.get_balance(&pubkey), 1_000);

        bank.transfer(500, &mint.keypair(), pubkey, mint.last_id())
            .unwrap();
        assert_eq!(bank.get_balance(&pubkey), 1_500);
        assert_eq!(bank.transaction_count(), 2);
    }

    #[test]
    fn test_negative_tokens() {
        let mint = Mint::new(1);
        let pubkey = KeyPair::new().pubkey();
        let bank = Bank::new(&mint);
        assert_eq!(
            bank.transfer(-1, &mint.keypair(), pubkey, mint.last_id()),
            Err(BankError::NegativeTokens)
        );
        assert_eq!(bank.transaction_count(), 0);
    }

    #[test]
    fn test_account_not_found() {
        let mint = Mint::new(1);
        let bank = Bank::new(&mint);
        let keypair = KeyPair::new();
        assert_eq!(
            bank.transfer(1, &keypair, mint.pubkey(), mint.last_id()),
            Err(BankError::AccountNotFound(keypair.pubkey()))
        );
        assert_eq!(bank.transaction_count(), 0);
    }

    #[test]
    fn test_insufficient_funds() {
        let mint = Mint::new(11_000);
        let bank = Bank::new(&mint);
        let pubkey = KeyPair::new().pubkey();
        bank.transfer(1_000, &mint.keypair(), pubkey, mint.last_id())
            .unwrap();
        assert_eq!(bank.transaction_count(), 1);
        assert_eq!(
            bank.transfer(10_001, &mint.keypair(), pubkey, mint.last_id()),
            Err(BankError::InsufficientFunds(mint.pubkey()))
        );
        assert_eq!(bank.transaction_count(), 1);

        let mint_pubkey = mint.keypair().pubkey();
        assert_eq!(bank.get_balance(&mint_pubkey), 10_000);
        assert_eq!(bank.get_balance(&pubkey), 1_000);
    }

    #[test]
    fn test_transfer_to_newb() {
        let mint = Mint::new(10_000);
        let bank = Bank::new(&mint);
        let pubkey = KeyPair::new().pubkey();
        bank.transfer(500, &mint.keypair(), pubkey, mint.last_id())
            .unwrap();
        assert_eq!(bank.get_balance(&pubkey), 500);
    }

    #[test]
    fn test_transfer_on_date() {
        let mint = Mint::new(1);
        let bank = Bank::new(&mint);
        let pubkey = KeyPair::new().pubkey();
        let dt = Utc::now();
        bank.transfer_on_date(1, &mint.keypair(), pubkey, dt, mint.last_id())
            .unwrap();

        // Mint's balance will be zero because all funds are locked up.
        assert_eq!(bank.get_balance(&mint.pubkey()), 0);

        // tx count is 1, because debits were applied.
        assert_eq!(bank.transaction_count(), 1);

        // pubkey's balance will be None because the funds have not been
        // sent.
        assert_eq!(bank.get_balance(&pubkey), 0);

        // Now, acknowledge the time in the condition occurred and
        // that pubkey's funds are now available.
        bank.apply_timestamp(mint.pubkey(), dt).unwrap();
        assert_eq!(bank.get_balance(&pubkey), 1);

        // tx count is still 1, because we chose not to count timestamp transactions
        // tx count.
        assert_eq!(bank.transaction_count(), 1);

        bank.apply_timestamp(mint.pubkey(), dt).unwrap(); // <-- Attack! Attempt to process completed transaction.
        assert_ne!(bank.get_balance(&pubkey), 2);
    }

    #[test]
    fn test_cancel_transfer() {
        let mint = Mint::new(1);
        let bank = Bank::new(&mint);
        let pubkey = KeyPair::new().pubkey();
        let dt = Utc::now();
        let sig = bank.transfer_on_date(1, &mint.keypair(), pubkey, dt, mint.last_id())
            .unwrap();

        // Assert the debit counts as a transaction.
        assert_eq!(bank.transaction_count(), 1);

        // Mint's balance will be zero because all funds are locked up.
        assert_eq!(bank.get_balance(&mint.pubkey()), 0);

        // pubkey's balance will be None because the funds have not been
        // sent.
        assert_eq!(bank.get_balance(&pubkey), 0);

        // Now, cancel the trancaction. Mint gets her funds back, pubkey never sees them.
        bank.apply_signature(mint.pubkey(), sig).unwrap();
        assert_eq!(bank.get_balance(&mint.pubkey()), 1);
        assert_eq!(bank.get_balance(&pubkey), 0);

        // Assert cancel doesn't cause count to go backward.
        assert_eq!(bank.transaction_count(), 1);

        bank.apply_signature(mint.pubkey(), sig).unwrap(); // <-- Attack! Attempt to cancel completed transaction.
        assert_ne!(bank.get_balance(&mint.pubkey()), 2);
    }

    #[test]
    fn test_duplicate_transaction_signature() {
        let mint = Mint::new(1);
        let bank = Bank::new(&mint);
        let sig = Signature::default();
        assert!(
            bank.reserve_signature_with_last_id(&sig, &mint.last_id())
                .is_ok()
        );
        assert_eq!(
            bank.reserve_signature_with_last_id(&sig, &mint.last_id()),
            Err(BankError::DuplicateSignature(sig))
        );
    }

    #[test]
    fn test_forget_signature() {
        let mint = Mint::new(1);
        let bank = Bank::new(&mint);
        let sig = Signature::default();
        bank.reserve_signature_with_last_id(&sig, &mint.last_id())
            .unwrap();
        bank.forget_signature_with_last_id(&sig, &mint.last_id());
        assert!(
            bank.reserve_signature_with_last_id(&sig, &mint.last_id())
                .is_ok()
        );
    }

    #[test]
    fn test_has_signature() {
        let mint = Mint::new(1);
        let bank = Bank::new(&mint);
        let sig = Signature::default();
        bank.reserve_signature_with_last_id(&sig, &mint.last_id())
            .expect("reserve signature");
        assert!(bank.has_signature(&sig));
    }

    #[test]
    fn test_reject_old_last_id() {
        let mint = Mint::new(1);
        let bank = Bank::new(&mint);
        let sig = Signature::default();
        for i in 0..MAX_ENTRY_IDS {
            let last_id = hash(&serialize(&i).unwrap()); // Unique hash
            bank.register_entry_id(&last_id);
        }
        // Assert we're no longer able to use the oldest entry ID.
        assert_eq!(
            bank.reserve_signature_with_last_id(&sig, &mint.last_id()),
            Err(BankError::LastIdNotFound(mint.last_id()))
        );
    }

    #[test]
    fn test_debits_before_credits() {
        let mint = Mint::new(2);
        let bank = Bank::new(&mint);
        let keypair = KeyPair::new();
        let tx0 = Transaction::new(&mint.keypair(), keypair.pubkey(), 2, mint.last_id());
        let tx1 = Transaction::new(&keypair, mint.pubkey(), 1, mint.last_id());
        let txs = vec![tx0, tx1];
        let results = bank.process_transactions(txs);
        assert!(results[1].is_err());

        // Assert bad transactions aren't counted.
        assert_eq!(bank.transaction_count(), 1);
    }

    #[test]
    fn test_process_empty_entry_is_registered() {
        let mint = Mint::new(1);
        let bank = Bank::new(&mint);
        let keypair = KeyPair::new();
        let entry = next_entry(&mint.last_id(), 1, vec![]);
        let tx = Transaction::new(&mint.keypair(), keypair.pubkey(), 1, entry.id);

        // First, ensure the TX is rejected because of the unregistered last ID
        assert_eq!(
            bank.process_transaction(&tx),
            Err(BankError::LastIdNotFound(entry.id))
        );

        // Now ensure the TX is accepted despite pointing to the ID of an empty entry.
        bank.process_entries(vec![entry]).unwrap();
        assert!(bank.process_transaction(&tx).is_ok());
    }

    #[test]
    fn test_process_genesis() {
        let mint = Mint::new(1);
        let genesis = mint.create_entries();
        let bank = Bank::default();
        bank.process_ledger(genesis).unwrap();
        assert_eq!(bank.get_balance(&mint.pubkey()), 1);
    }

    fn create_sample_block(mint: &Mint, length: usize) -> impl Iterator<Item = Entry> {
        let mut entries = Vec::with_capacity(length);
        let mut hash = mint.last_id();
        let mut cur_hashes = 0;
        for _ in 0..length {
            let keypair = KeyPair::new();
            let tx = Transaction::new(&mint.keypair(), keypair.pubkey(), 1, hash);
            let entry = Entry::new_mut(&mut hash, &mut cur_hashes, vec![tx], false);
            entries.push(entry);
        }
        entries.into_iter()
    }
    fn create_sample_ledger(length: usize) -> (impl Iterator<Item = Entry>, PublicKey) {
        let mint = Mint::new(1 + length as i64);
        let genesis = mint.create_entries();
        let block = create_sample_block(&mint, length);
        (genesis.into_iter().chain(block), mint.pubkey())
    }

    #[test]
    fn test_process_ledger() {
        let (ledger, pubkey) = create_sample_ledger(1);
        let (ledger, dup) = ledger.tee();
        let bank = Bank::default();
        let (ledger_height, tail) = bank.process_ledger(ledger).unwrap();
        assert_eq!(bank.get_balance(&pubkey), 1);
        assert_eq!(ledger_height, 3);
        assert_eq!(tail.len(), 3);
        assert_eq!(tail, dup.collect_vec());
        let last_entry = &tail[tail.len() - 1];
        assert_eq!(bank.last_id(), last_entry.id);
    }

    #[test]
    fn test_process_ledger_around_window_size() {
        // TODO: put me back in when Criterion is up
        //        for _ in 0..10 {
        //            let (ledger, _) = create_sample_ledger(WINDOW_SIZE as usize);
        //            let bank = Bank::default();
        //            let (_, _) = bank.process_ledger(ledger).unwrap();
        //        }

        let window_size = WINDOW_SIZE as usize;
        for entry_count in window_size - 3..window_size + 2 {
            let (ledger, pubkey) = create_sample_ledger(entry_count);
            let bank = Bank::default();
            let (ledger_height, tail) = bank.process_ledger(ledger).unwrap();
            assert_eq!(bank.get_balance(&pubkey), 1);
            assert_eq!(ledger_height, entry_count as u64 + 2);
            assert!(tail.len() <= window_size);
            let last_entry = &tail[tail.len() - 1];
            assert_eq!(bank.last_id(), last_entry.id);
        }
    }

    // Write the given entries to a file and then return a file iterator to them.
    fn to_file_iter(entries: impl Iterator<Item = Entry>) -> impl Iterator<Item = Entry> {
        let mut file = Cursor::new(vec![]);
        EntryWriter::write_entries(&mut file, entries).unwrap();
        file.seek(SeekFrom::Start(0)).unwrap();

        let reader = BufReader::new(file);
        entry_writer::read_entries(reader).map(|x| x.unwrap())
    }

    #[test]
    fn test_process_ledger_from_file() {
        let (ledger, pubkey) = create_sample_ledger(1);
        let ledger = to_file_iter(ledger);

        let bank = Bank::default();
        bank.process_ledger(ledger).unwrap();
        assert_eq!(bank.get_balance(&pubkey), 1);
    }

    #[test]
    fn test_process_ledger_from_files() {
        let mint = Mint::new(2);
        let genesis = to_file_iter(mint.create_entries().into_iter());
        let block = to_file_iter(create_sample_block(&mint, 1));

        let bank = Bank::default();
        bank.process_ledger(genesis.chain(block)).unwrap();
        assert_eq!(bank.get_balance(&mint.pubkey()), 1);
    }

    #[test]
    fn test_rotate_vector() {
        let expect = vec![1, 2, 3, 4];

        assert_eq!(rotate_vector(vec![4, 1, 2, 3], 1), expect);
        assert_eq!(rotate_vector(vec![1, 2, 3, 4], 0), expect);
        assert_eq!(rotate_vector(vec![2, 3, 4, 1], 3), expect);
        assert_eq!(rotate_vector(vec![3, 4, 1, 2], 2), expect);
    }

}