Add DoS limits to tributary and require provided transactions be ordered

coordinator/tributary/src/provided.rs

@@ -1,33 +1,32 @@
-use std::collections::HashMap;
+use std::collections::VecDeque;
 
 use crate::{TransactionKind, Transaction};
 
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct ProvidedTransactions<T: Transaction> {
-  pub(crate) transactions: HashMap<[u8; 32], T>,
+  pub(crate) transactions: VecDeque<T>,
 }
 
 impl<T: Transaction> Default for ProvidedTransactions<T> {
   fn default() -> Self {
-    ProvidedTransactions { transactions: HashMap::new() }
+    ProvidedTransactions { transactions: VecDeque::new() }
   }
 }
 
 impl<T: Transaction> ProvidedTransactions<T> {
-  pub fn new() -> Self {
+  pub(crate) fn new() -> Self {
     ProvidedTransactions::default()
   }
 
   /// Provide a transaction for inclusion in a block.
-  pub fn provide(&mut self, tx: T) {
+  pub(crate) fn provide(&mut self, tx: T) {
+    // TODO: Make an error out of this
     assert_eq!(tx.kind(), TransactionKind::Provided, "provided a non-provided transaction");
-    self.transactions.insert(tx.hash(), tx);
+    self.transactions.push_back(tx);
   }
 
-  /// Withdraw a transaction, no longer proposing it or voting for its validity.
-  ///
-  /// Returns true if the transaction was withdrawn and false otherwise.
-  pub fn withdraw(&mut self, tx: [u8; 32]) -> bool {
-    self.transactions.remove(&tx).is_some()
+  /// Complete a provided transaction, no longer proposing it nor voting for its validity.
+  pub(crate) fn complete(&mut self, tx: [u8; 32]) {
+    assert_eq!(self.transactions.pop_front().unwrap().hash(), tx);
   }
 }