pytest: test for currencyrate median code when values are cached.
What the developer wrote
Authored by Rusty Russell
pytest: test for currencyrate median code when values are cached.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
What changed, and why it matters
This commit only adds a new automated test file for the currency rate feature. It does not change any production code, so it cannot introduce a security vulnerability by itself. The test is currently marked as expected to fail (xfail), meaning it documents a known behavior or bug in the median calculation when currency rates are cached.
No immediate security action required. Treat as a normal test-only commit. If the xfail test reflects a real bug, the currencyrate plugin's median/caching logic should be reviewed and fixed separately, after which the xfail marker can be removed.
Security signals we found
No strong security signals were identified.
Evidence from the diff
The diff adds tests/test_currencyrate.py content: a local Flask-based fake rate server with fast and slow endpoints, a pytest fixture, and an xfail test that checks the median of two cached currency sources is computed as the midpoint. No C/lightningd/plugin source is modified. The test is expected to fail, suggesting it reproduces a latent correctness issue in the currencyrate plugin’s median logic when cached values are present, but the patch itself is purely test code.
Changed components
tests/test_currencyrate.pyInspect captured patch +79 / −0
diff --git a/tests/test_currencyrate.py b/tests/test_currencyrate.py
index 66f704cb..2c28390f 100644
--- a/tests/test_currencyrate.py
+++ b/tests/test_currencyrate.py
@@ -1,7 +1,11 @@
import logging
import pytest
+import threading
+import time
from pyln.client import RpcError
from fixtures import * # noqa: F401,F403
+from flask import Flask, jsonify
+from werkzeug.serving import make_server
LOGGER = logging.getLogger(__name__)
@@ -194,3 +198,78 @@ def test_invalid_currency(node_factory):
l1.daemon.wait_for_log("failed to get `XXX` rate from coindesk")
l1.daemon.logsearch_start = needle
l1.daemon.wait_for_log("failed to get `XXX` rate from binance")
+
+
+class _ServerThread(threading.Thread):
+ def __init__(self, app):
+ super().__init__(daemon=True)
+ self._server = make_server("127.0.0.1", 0, app)
+ self.port = self._server.server_port
+
+ def run(self):
+ self._server.serve_forever()
+
+ def shutdown(self):
+ self._server.shutdown()
+
+
+@pytest.fixture
+def fake_rateserver():
+ app = Flask(__name__)
+
+ @app.get("/fast")
+ def fast():
+ # 1e11 / 100_000_000 = 1000 msat per USD
+ return jsonify({"price": 100_000_000})
+
+ @app.get("/slow")
+ def slow():
+ # Make this complete later, so it becomes latest_fresh_price().
+ time.sleep(1)
+ # 1e11 / 50_000_000 = 2000 msat per USD
+ return jsonify({"price": 50_000_000})
+
+ srv = _ServerThread(app)
+ srv.start()
+ try:
+ yield f"http://127.0.0.1:{srv.port}"
+ finally:
+ srv.shutdown()
+ srv.join()
+
+
+@pytest.mark.xfail(strict=True)
+def test_cached_median(node_factory, fake_rateserver):
+ """This should use the median of available sources"""
+ opts = {
+ "currencyrate-disable-source": [
+ "bitstamp",
+ "coinbase",
+ "coingecko",
+ "kraken",
+ "blockchain.info",
+ "coindesk",
+ "binance",
+ ],
+ "currencyrate-add-source": [
+ f"fast,{fake_rateserver}/fast,price",
+ f"slow,{fake_rateserver}/slow,price",
+ ],
+ }
+ l1 = node_factory.get_node(options=opts)
+
+ rates = l1.rpc.call("currencyrates", ["USD"])
+ LOGGER.info(rates)
+
+ assert "fast" in rates
+ assert "slow" in rates
+
+ assert rates["fast"] == 1000
+ assert rates["slow"] == 2000
+
+ # With two fresh cached rates, the correct median is midpoint(1000, 2000) = 1500.
+ # For 100 USD, that should be 150000 msat.
+ convert = l1.rpc.call("currencyconvert", [100, "USD"])
+ LOGGER.info(convert)
+
+ assert convert["msat"] == 150000
Why this scored 12/100
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