frank/fast tx sender (#93)

* wip fast tx sender

* feat: fast tx sender

* fix: lazy load blockhash subscription

src/driftpy/tx/fast_tx_sender.py

@@ -0,0 +1,45 @@
+import asyncio
+
+from solders.hash import Hash
+
+from solana.rpc.async_api import AsyncClient
+from solana.rpc.types import TxOpts
+from solana.rpc.commitment import Commitment, Confirmed
+
+from driftpy.tx.standard_tx_sender import StandardTxSender
+
+
+class FastTxSender(StandardTxSender):
+    """
+    The FastTxSender will refresh the latest blockhash in the background to save an RPC when building transactions.
+    """
+
+    def __init__(
+        self,
+        connection: AsyncClient,
+        opts: TxOpts,
+        blockhash_refresh_interval_secs: int,
+        blockhash_commitment: Commitment = Confirmed,
+    ):
+        super().__init__(connection, opts, blockhash_commitment)
+        self.blockhash_refresh_interval = blockhash_refresh_interval_secs
+        self.recent_blockhash = None
+
+    async def subscribe_blockhash(self):
+        """
+        Must be called with asyncio.create_task to prevent blocking
+        """
+        while True:
+            try:
+                blockhash_info = await self.connection.get_latest_blockhash(
+                    self.blockhash_commitment
+                )
+                self.recent_blockhash = blockhash_info.value.blockhash
+            except Exception as e:
+                print(f"Error in subscribe_blockhash: {e}")
+            await asyncio.sleep(self.blockhash_refresh_interval)
+
+    async def fetch_latest_blockhash(self) -> Hash:
+        if self.recent_blockhash is None:
+            await self.subscribe_blockhash()
+        return self.recent_blockhash

src/driftpy/tx/standard_tx_sender.py

@@ -33,13 +33,16 @@ async def get_blockhash(self) -> Hash:
             await self.connection.get_latest_blockhash(self.blockhash_commitment)
         ).value.blockhash
 
+    async def fetch_latest_blockhash(self) -> Hash:
+        return await self.get_blockhash()
+
     async def get_legacy_tx(
         self,
         ixs: Sequence[Instruction],
         payer: Keypair,
         additional_signers: Optional[Sequence[Keypair]],
     ) -> Transaction:
-        latest_blockhash = await self.get_blockhash()
+        latest_blockhash = await self.fetch_latest_blockhash()
         tx = Transaction(
             instructions=ixs,
             recent_blockhash=latest_blockhash,
@@ -60,7 +63,7 @@ async def get_versioned_tx(
         lookup_tables: Sequence[AddressLookupTableAccount],
         additional_signers: Optional[Sequence[Keypair]],
     ) -> VersionedTransaction:
-        latest_blockhash = await self.get_blockhash()
+        latest_blockhash = await self.fetch_latest_blockhash()
         msg = MessageV0.try_compile(
             payer.pubkey(), ixs, lookup_tables, latest_blockhash
         )