feat: back off pending payment polling

tasks.py

@@ -34,7 +34,9 @@ from .paranoia import (
 )
 from .permission import nwc_permissions
 
-PAYMENT_STATUS_POLL_INTERVAL_SECONDS = 1.0
+PAYMENT_STATUS_POLL_INITIAL_INTERVAL_SECONDS = 1.0
+PAYMENT_STATUS_POLL_MAX_INTERVAL_SECONDS = 60.0
+PAYMENT_STATUS_POLL_BACKOFF_MULTIPLIER = 2.0
 
 
 async def _check(nwc: NWCKey | None, method: str) -> dict | None:
@@ -112,6 +114,7 @@ async def _process_invoice(
         True  # currently required by nip 47 specs, might change in future
     )
     payment_status: PaymentStatus | None = None
+    poll_interval = PAYMENT_STATUS_POLL_INITIAL_INTERVAL_SECONDS
     while wait_for_preimage:
         payment_status = await check_transaction_status(wallet_id, payment_hash)
         if payment_status.success:
@@ -124,7 +127,11 @@ async def _process_invoice(
                 },
                 "in_budget": in_budget,
             }
-        await asyncio.sleep(PAYMENT_STATUS_POLL_INTERVAL_SECONDS)
+        await asyncio.sleep(poll_interval)
+        poll_interval = min(
+            poll_interval * PAYMENT_STATUS_POLL_BACKOFF_MULTIPLIER,
+            PAYMENT_STATUS_POLL_MAX_INTERVAL_SECONDS,
+        )
     if not payment_status:
         raise Exception("Payment status not found")
     return {

tests/unit/test_tasks.py

@@ -32,29 +32,30 @@ async def test_process_invoice_returns_payment_failed_on_failed_status(monkeypat
 
 
 @pytest.mark.asyncio
-async def test_process_invoice_polls_pending_payment_at_sustainable_interval(
+async def test_process_invoice_backs_off_pending_payment_polling_to_configured_max(
     monkeypatch,
 ):
     async def fake_tracked_spend_nwc(*args, **kwargs):
         return True, "a" * 64
 
+    pending = SimpleNamespace(success=False, failed=False)
     statuses = iter(
-        [
-            SimpleNamespace(success=False, failed=False),
+        [pending] * 8
+        + [
             SimpleNamespace(
                 success=True,
                 failed=False,
                 preimage="b" * 64,
                 fee_msat=10,
                 paid=True,
-            ),
+            )
         ]
     )
 
     async def fake_check_transaction_status(wallet_id: str, payment_hash: str):
         return next(statuses)
 
-    sleep_calls = []
+    sleep_calls: list[float] = []
 
     async def fake_sleep(delay: float):
         sleep_calls.append(delay)
@@ -73,7 +74,7 @@ async def test_process_invoice_polls_pending_payment_at_sustainable_interval(
         description="test",
     )
 
-    assert sleep_calls == [tasks.PAYMENT_STATUS_POLL_INTERVAL_SECONDS]
+    assert sleep_calls == [1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 60.0, 60.0]
     assert result["preimage"] == "b" * 64
     assert result["fee_msats"] == 10
     assert result["paid"] is True