Faster tx known check (#1468)

* fast check for known tx when adding to pool

* rustfmt

pool/src/pool.rs

@@ -57,6 +57,11 @@ impl Pool {
 		}
 	}
 
+	/// Does the transaction pool contain an entry for the given transaction?
+	pub fn contains_tx(&self, tx: &Transaction) -> bool {
+		self.entries.iter().any(|x| x.tx.hash() == tx.hash())
+	}
+
 	/// Query the tx pool for all known txs based on kernel short_ids
 	/// from the provided compact_block.
 	/// Note: does not validate that we return the full set of required txs.

pool/src/transaction_pool.rs

@@ -101,6 +101,12 @@ impl TransactionPool {
 		stem: bool,
 		block_hash: &Hash,
 	) -> Result<(), PoolError> {
+		// Quick check to deal with common case of seeing the *same* tx
+		// broadcast from multiple peers simultaneously.
+		if !stem && self.txpool.contains_tx(&tx) {
+			return Err(PoolError::DuplicateTx);
+		}
+
 		// Do we have the capacity to accept this transaction?
 		self.is_acceptable(&tx)?;