renepay: update the gossmap after addgossip

Whenever there is a payment failure that requires gossip update, for
example changing the fee rates of remote channels, we call addgossip.
For renepay to consider this changes in the coming payment attempts, it
must update gossmap.

plugins/renepay/pay.c

@@ -135,6 +135,16 @@ static struct command_result *addgossip_done(struct command *cmd,
 	 * happen later. */
 	pay_flow_finished_adding_gossip(adg->pf);
 
+	bool gossmap_changed = gossmap_refresh(pay_plugin->gossmap, NULL);
+
+	if (pay_plugin->gossmap == NULL)
+		plugin_err(pay_plugin->plugin, "Failed to refresh gossmap: %s",
+			   strerror(errno));
+
+	if (gossmap_changed)
+		uncertainty_network_update(pay_plugin->gossmap,
+					   pay_plugin->chan_extra_map);
+
 	return command_still_pending(cmd);
 }
 

tests/test_renepay.py

@@ -588,3 +588,39 @@ def test_previous_sendpays(node_factory, bitcoind):
     l1.rpc.call("renepay", {"invstring": invstr, "dev_use_shadow": False})
     invoice = only_one(l3.rpc.listinvoices("inv2")["invoices"])
     assert invoice["amount_received_msat"] == Millisatoshi("100000sat")
+
+
+def test_fees(node_factory):
+    """
+    Check that fees are correctly computed.
+    """
+    # made up some random fees for every node
+    opts = [
+        {"disable-mpp": None, "fee-base": 1000, "fee-per-satoshi": 100},
+        {"disable-mpp": None, "fee-base": 2222, "fee-per-satoshi": 203},
+        {"disable-mpp": None, "fee-base": 3333, "fee-per-satoshi": 300},
+        {"disable-mpp": None, "fee-base": 2012, "fee-per-satoshi": 200},
+        {"disable-mpp": None, "fee-base": 1010, "fee-per-satoshi": 100},
+        {"disable-mpp": None, "fee-base": 1050, "fee-per-satoshi": 100},
+    ]
+    nodes = node_factory.line_graph(len(opts), wait_for_announce=True, opts=opts)
+    source = nodes[0]
+    dest = nodes[-1]
+
+    # check that once gossip is in sync, fees are paid correctly
+    invstr = dest.rpc.invoice("100000sat", "inv1", "description")["bolt11"]
+    source.rpc.call("renepay", {"invstring": invstr})
+    invoice = only_one(dest.rpc.listinvoices("inv1")["invoices"])
+    assert invoice["amount_received_msat"] == Millisatoshi("100000sat")
+
+    # if we update fee policy but gossip is not updated ...
+    nodes[2].rpc.dev_suppress_gossip()
+    nodes[2].rpc.setchannel(nodes[3].info["id"], 4000, 300, enforcedelay=0)
+
+    nodes[3].rpc.dev_suppress_gossip()
+    nodes[3].rpc.setchannel(nodes[4].info["id"], 3000, 350, enforcedelay=0)
+
+    invstr = dest.rpc.invoice("150000sat", "inv2", "description")["bolt11"]
+    source.rpc.call("renepay", {"invstring": invstr})
+    invoice = only_one(dest.rpc.listinvoices("inv2")["invoices"])
+    assert invoice["amount_received_msat"] == Millisatoshi("150000sat")