pytest: add spendable tests for askrene.

Make sure we're not exceeding the spendable amount of a local channel.

Signed-off-by: Rusty Russell <[email protected]>

tests/test_askrene.py

@@ -2,7 +2,7 @@
 from pyln.client import RpcError
 from utils import (
     only_one, first_scid, GenChannel, generate_gossip_store,
-    TEST_NETWORK
+    TEST_NETWORK, sync_blockheight, wait_for
 )
 import os
 import pytest
@@ -415,3 +415,76 @@ def test_getroutes_auto_localchans(node_factory):
                          paths=[[{'short_channel_id': scid12, 'amount_msat': 102010, 'delay': 99 + 6 + 6},
                                  {'short_channel_id': '0x1x0', 'amount_msat': 102010, 'delay': 99 + 6 + 6},
                                  {'short_channel_id': '1x2x1', 'amount_msat': 101000, 'delay': 99 + 6}]])
+
+
+def test_fees_dont_exceed_constraints(node_factory):
+    l1 = node_factory.get_node(start=False)
+
+    msat = 100000000
+    max_msat = int(msat * 0.45)
+    # 0 has to use two paths (1 and 2) to reach 3.  But we tell it 0->1 has limited capacity.
+    gsfile, nodemap = generate_gossip_store([GenChannel(0, 1, capacity_sats=msat // 1000, forward=GenChannel.Half(propfee=10000)),
+                                             GenChannel(0, 2, capacity_sats=msat // 1000, forward=GenChannel.Half(propfee=10000)),
+                                             GenChannel(1, 3, capacity_sats=msat // 1000, forward=GenChannel.Half(propfee=10000)),
+                                             GenChannel(2, 3, capacity_sats=msat // 1000, forward=GenChannel.Half(propfee=10000))])
+
+    # Set up l1 with this as the gossip_store
+    shutil.copy(gsfile.name, os.path.join(l1.daemon.lightning_dir, TEST_NETWORK, 'gossip_store'))
+    l1.start()
+
+    chan = only_one([c for c in l1.rpc.listchannels(source=nodemap[0])['channels'] if c['destination'] == nodemap[1]])
+    l1.rpc.askrene_inform_channel(layer='test_layers',
+                                  short_channel_id=chan['short_channel_id'],
+                                  direction=chan['direction'],
+                                  maximum_msat=max_msat)
+
+    routes = l1.rpc.getroutes(source=nodemap[0],
+                              destination=nodemap[3],
+                              amount_msat=msat,
+                              layers=['test_layers'],
+                              maxfee_msat=msat,
+                              final_cltv=99)['routes']
+    assert len(routes) == 2
+    for hop in routes[0]['path'] + routes[1]['path']:
+        if hop['short_channel_id'] == chan['short_channel_id']:
+            amount = hop['amount_msat']
+    assert amount <= max_msat
+
+
+def test_mpp_pay2(node_factory, bitcoind):
+    l1, l2, l3 = node_factory.get_nodes(3)
+    l1.fundwallet(10_000_000)
+    l2.fundwallet(10_000_000)
+    l1.rpc.connect(l2.info['id'], 'localhost', port=l2.port)
+    l2.rpc.connect(l3.info['id'], 'localhost', port=l3.port)
+
+    capacities = (100_000, 100_000, 200_000, 300_000, 400_000)
+    for capacity in capacities:
+        l1.rpc.fundchannel(l2.info["id"], capacity, mindepth=1)
+        l2.rpc.fundchannel(l3.info["id"], capacity, mindepth=1)
+
+        bitcoind.generate_block(1, wait_for_mempool=2)
+        sync_blockheight(bitcoind, [l1, l2])
+
+    bitcoind.generate_block(5)
+    wait_for(lambda: len(l1.rpc.listchannels()["channels"]) == 2 * 2 * len(capacities))
+
+    routes = l1.rpc.getroutes(
+        source=l1.info["id"],
+        destination=l3.info["id"],
+        amount_msat=800_000_000,
+        layers=["auto.localchans", "auto.sourcefree"],
+        maxfee_msat=50_000_000,
+        final_cltv=10,
+    )
+
+    # Don't exceed spendable_msat
+    maxes = {}
+    for chan in l1.rpc.listpeerchannels()['channels']:
+        maxes["{}/{}".format(chan['short_channel_id'], chan['direction'])] = chan['spendable_msat']
+
+    for r in routes['routes']:
+        for p in r['path']:
+            scidd = "{}/{}".format(p['short_channel_id'], p['direction'])
+            if scidd in maxes:
+                assert p['amount_msat'] <= maxes[scidd]