Send onions along a fixed path

README.md

@@ -19,6 +19,7 @@ Community curated plugins for c-lightning.
 | [drain][drain]                     | Draining, filling and balancing channels with automatic chunks.                           |
 | [event-websocket][event-websocket] | Exposes notifications over a Websocket                                                    |
 | [feeadjuster][feeadjuster]         | Dynamic fees to keep your channels more balanced                                          |
+| [fixroute]                         | Compute a route that includes a number of specified waypoints                             |
 | [graphql][graphql]                 | Exposes the c-lightning API over [graphql][graphql-spec]                                  |
 | [invoice-queue][invoice-queue]     | Listen to lightning invoices from multiple nodes and send to a redis queue for processing |
 | [lightning-qt][lightning-qt]       | A bitcoin-qt-like GUI for lightningd                                                      |
@@ -168,6 +169,7 @@ Python plugins developers must ensure their plugin to work with all Python versi
 
 [esplora]: https://github.com/Blockstream/esplora
 [pers-chans]: https://github.com/lightningd/plugins/tree/master/persistent-channels
+[fixroute]: https://github.com/lightningd/plugins/tree/master/fixroute
 [probe]: https://github.com/lightningd/plugins/tree/master/probe
 [prometheus]: https://github.com/lightningd/plugins/tree/master/prometheus
 [summary]: https://github.com/lightningd/plugins/tree/master/summary

fixroute/README.md

@@ -0,0 +1,41 @@
+# Fixed Payment Route Plugin
+
+This plugin helps you to construct a route object (to be used with sendpay)
+which goes over a sequence of node ids. If all these nodeids are on a path of
+payment channels an onion following this path will be constructed. In the case
+of missing channels `lightning-cli getroute` is invoked to find partial
+routes.
+
+This plugin can be used to create circular onions or to send payments along
+specific paths if that is necessary (as long as the paths provide enough
+liquidity).
+
+I guess this plugin could also be used to simulate the behaviour of trampoline
+payments.
+
+And of course I imagine you the reader of this message will find even more
+creative ways of using it.
+
+
+> :warning: This plugin is still work in progress and may not work in all edge cases. :construction:
+
+## Command line options
+
+The plugin exposes no new command line options.
+
+## JSON-RPC methods
+
+The plugin also exposes the following methods:
+
+ - `getfixedroute`: constructs a route for an amount in `msat` and a list of
+   `nodeid`s over which the path should be constructed.
+
+ - `getfixedroute_purge`: As the plugin builds an index over the gossip store
+   on startup to know the channel metadata the index might be become outdated
+   and require a rebuild once in a while. This happens in particular if
+   `sendpay` can't forward onions because of wrong channel parameters.
+
+
+## Support: 
+If you like my work consider a donation at https://patreon.com/renepickhardt
+or https://tallyco.in/s/lnbook

fixroute/fixroute.py

@@ -0,0 +1,158 @@
+#!/usr/bin/env python3
+"""
+author: Rene Pickhardt (rene.m.pickhardt@ntnu.no)
+Date: 24.1.2020
+License: MIT
+
+This plugin helps you to construct a route object (to be used with `sendpay`)
+which goes over a sequence of node ids. If all these nodeids are on a path of
+payment channels an onion following this path will be constructed. In the case
+of missing channels `lightning-cli getroute` is invoked to find partial routes.
+
+This plugin can be used to create circular onions or to send payments along
+specific paths if that is necessary (as long as the paths provide enough
+liquidity).
+
+I guess this plugin could also be used to simulate the behaviour of trampoline
+payments.
+
+And of course I imagine you the reader of this message will find even more
+creative ways of using it.
+
+=== Support:
+
+If you like my work consider a donation at https://patreon.com/renepickhardt
+or https://tallyco.in/s/lnbook
+
+"""
+
+from pyln.client import Plugin
+from pyln.client import RpcError
+import itertools
+
+
+plugin = Plugin(autopatch=True)
+
+
+@plugin.method(
+    "getfixedroute",
+    long_desc="""
+Returns a route object to be used in send pay over a fixed set of nodes
+"""
+)
+def getfixedroute(plugin, amount, nodes):
+    """Construct a fixed route over a list of node ids.
+
+    If channels exist between consecutive nodes these channels will be used.
+    Otherwise `lightning-cli getroute` will be invoked to find partial routes.
+
+    """
+    delay = 9
+    fees = 0
+    result = []
+
+    def pairs(iterable):
+        x, y = itertools.tee(iterable)
+        next(y, None)
+        return zip(x, y)
+
+    for src, dest in reversed(list(pairs(nodes))):
+        amount = amount + fees
+        key = "{}:{}".format(src, dest)
+        if key not in plugin.channels:
+            try:
+                route = plugin.rpc.getroute(
+                    node_id=dest, msatoshi=amount, riskfactor=1, cltv=delay,
+                    fromid=src
+                )["route"]
+            except RpcError as exc:
+                raise ValueError((
+                    "could not compute route between waypoints {src} and "
+                    "{dest}: {e}"
+                ).format(src=src, dest=dest, e=exc))
+
+            for e in reversed(route):
+                result.append(e)
+
+            key = "{}:{}".format(src, route[0]["id"])
+            chan = plugin.channels[key]
+
+            base = chan["base_fee_millisatoshi"]
+            prop = chan["fee_per_millionth"]
+
+            fees = base + amount * prop / 10**6
+            delay = result[-1]["delay"] + chan["delay"]
+
+        else:
+            chan = plugin.channels[key]
+            # https://github.com/ElementsProject/lightning/blob/edbcb6/gossipd/routing.h#L253
+
+            direction = 0
+            # I guess the following reverses the definition with the DER
+            # encoding of channels for all my tests the results where the same
+            # as in getroute but I am not sure if this is actually
+            # correct. please can someone verify and remove this message:
+            # https://github.com/ElementsProject/lightning/blob/edbcb6/gossipd/routing.h#L56
+            if dest < src:
+                direction = 1
+
+            # https://github.com/ElementsProject/lightning/blob/edbcb6/gossipd/routing.c#L381
+            style = "legacy"
+
+            # https://github.com/ElementsProject/lightning/blob/edbcb6f/gossipd/routing.c#L2526
+            # and :
+            # https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
+            features = int(plugin.nodes[dest]["globalfeatures"], 16)
+            if features & 0x01 << 8 != 0 or features & 0x01 << 9 != 0:
+                style = "tlv"
+            entry = {
+                "id": dest,
+                "channel": chan["short_channel_id"],
+                "direction": direction,
+                "msatoshi": amount,
+                "amount_msat": "{}msat".format(amount),
+                "delay": delay,
+                "style": style
+            }
+            result.append(entry)
+
+            base = chan["base_fee_millisatoshi"]
+            prop = chan["fee_per_millionth"]
+
+            fees = base + amount * prop / 10**6
+            delay = delay + chan["delay"]
+
+        fees = int(fees)
+    result = list(reversed(result))
+
+    # id, chanel, direction, msatoshi, amount_msat, delay, style
+    return {"route": result}
+
+
+@plugin.method(
+    "getfixedroute_purge",
+    long_desc="purges the index of the gossip store"
+)
+def refresh_gossip_info(plugin):
+    """
+    purges the index gossip store.
+    """
+    channels = plugin.rpc.listchannels()["channels"]
+
+    for chan in channels:
+        key = "{}:{}".format(chan["source"], chan["destination"])
+        plugin.channels[key] = chan
+
+    for u in plugin.rpc.listnodes()["nodes"]:
+        plugin.nodes[u["nodeid"]] = u
+
+    return {"result": "successfully reindexed the gossip store."}
+
+
+@plugin.init()
+def init(options, configuration, plugin):
+    plugin.log("Plugin fixroute_pay registered")
+    refresh_gossip_info(plugin)
+
+
+plugin.run()

fixroute/requirements.txt

@@ -0,0 +1 @@
+pyln-client>=0.8

fixroute/test_fixroute.py

@@ -0,0 +1,31 @@
+import os
+from pyln.testing.fixtures import *  # noqa: F401,F403
+
+
+plugin_path = os.path.join(os.path.dirname(__file__), "fixroute.py")
+
+
+def test_fixroute_starts(node_factory):
+    l1 = node_factory.get_node(options={'plugin': plugin_path})
+
+    # Ensure the plugin is still running:
+    conf = l1.rpc.listconfigs()
+    expected = [{
+        'name': 'fixroute.py',
+        'path': plugin_path
+    }]
+    assert(conf['plugins'] == expected)
+
+
+def test_fixroute_dynamic_starts(node_factory):
+    l1 = node_factory.get_node()
+    l1.rpc.plugin_start(plugin_path)
+    l1.rpc.plugin_stop(plugin_path)
+    l1.rpc.plugin_start(plugin_path)
+    # Ensure the plugin is still running:
+    conf = l1.rpc.listconfigs()
+    expected = [{
+        'name': 'fixroute.py',
+        'path': plugin_path
+    }]
+    assert(conf['plugins'] == expected)