failure_onion: a test that only ensures lightningd doesn't crash.

tests/plugins/htlc_accepted-failonion.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python3
+"""A simply plugin that fails HTLCs with a meaningless onion.
+
+"""
+from pyln.client import Plugin
+
+
+plugin = Plugin()
+
+
+@plugin.hook("htlc_accepted")
+def on_htlc_accepted(htlc, onion, plugin, **kwargs):
+    print('returning failonion', plugin.failonion)
+    return {"result": "fail", "failure_onion": plugin.failonion}
+
+
+@plugin.method("setfailonion")
+def setfailonion(plugin, onion):
+    """Sets the failure_onion to return when receiving an incoming HTLC.
+    """
+    plugin.failonion = onion
+
+
+@plugin.init()
+def on_init(**kwargs):
+    plugin.failonion = None
+
+
+plugin.run()

tests/test_plugin.py

@@ -1928,3 +1928,14 @@ def test_htlc_accepted_hook_failcodes(node_factory):
         inv = l2.rpc.invoice(42, 'failcode{}'.format(failcode), '')['bolt11']
         with pytest.raises(RpcError, match=r'failcodename.: .{}.'.format(expected)):
             l1.rpc.pay(inv)
+
+
+def test_htlc_accepted_hook_failonion(node_factory):
+    plugin = os.path.join(os.path.dirname(__file__), 'plugins/htlc_accepted-failonion.py')
+    l1, l2 = node_factory.line_graph(2, opts=[{}, {'plugin': plugin}])
+
+    # an invalid onion
+    l2.rpc.setfailonion('0' * 292)
+    inv = l2.rpc.invoice(42, 'failonion000', '')['bolt11']
+    with pytest.raises(RpcError):
+        l1.rpc.pay(inv)