openingd: add openchannel hook.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

CHANGELOG.md

@@ -13,7 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - JSON API: `listpeers` status now shows how many confirmations until channel is open (#2405)
 - Config: Adds parameter `min-capacity-sat` to reject tiny channels.
 - JSON API: `listforwards` now includes the time an HTLC was received and when it was resolved. Both are expressed as UNIX timestamps to facilitate parsing (Issue [#2491](https://github.com/ElementsProject/lightning/issues/2491), PR [#2528](https://github.com/ElementsProject/lightning/pull/2528))
-- JSON API: new plugin `invoice_payment` hook for intercepting invoices before they're paid.
++- JSON API: new plugin hooks `invoice_payment` for intercepting invoices before they're paid, and `openchannel` for intercepting channel opens.
 - plugin: the `connected` hook can now send an `error_message` to the rejected peer.
 - Protocol: we now enforce `option_upfront_shutdown_script` if a peer negotiates it.
 - JSON API: `listforwards` now includes the local_failed forwards with failcode (Issue [#2435](https://github.com/ElementsProject/lightning/issues/2435), PR [#2524](https://github.com/ElementsProject/lightning/pull/2524))

doc/PLUGINS.md

@@ -314,6 +314,40 @@ It can return a non-zero `failure_code` field as defined for final
 nodes in [BOLT 4][bolt4-failure-codes], or otherwise an empty object
 to accept the payment.
 
+
+#### `openchannel`
+
+This hook is called whenever a remote peer tries to fund a channel to us,
+and it has passed basic sanity checks:
+
+```json
+{
+  "openchannel": {
+	"id": "03864ef025fde8fb587d989186ce6a4a186895ee44a926bfc370e2c366597a3f8f",
+	"funding_satoshis": "100000000msat",
+	"push_msat": "0msat",
+	"dust_limit_satoshis": "546000msat",
+	"max_htlc_value_in_flight_msat": "18446744073709551615msat",
+	"channel_reserve_satoshis": "1000000msat",
+	"htlc_minimum_msat": "0msat",
+	"feerate_per_kw": 7500,
+	"to_self_delay": 5,
+	"max_accepted_htlcs": 483,
+	"channel_flags": 1
+  }
+}
+```
+
+There may be additional fields, including `shutdown_scriptpubkey` and
+a hex-string.  You can see the definitions of these fields in [BOLT 2's description of the open_channel message][bolt2-open-channel].
+
+The returned result must contain a `result` member which is either
+the string `reject` or `continue`.  If `reject` and
+there's a member `error_message`, that member is sent to the peer
+before disconnection.
+
+
 [jsonrpc-spec]: https://www.jsonrpc.org/specification
 [jsonrpc-notification-spec]: https://www.jsonrpc.org/specification#notification
 [bolt4-failure-codes]: https://github.com/lightningnetwork/lightning-rfc/blob/master/04-onion-routing.md#failure-messages
+[bolt2-open-channel]: https://github.com/lightningnetwork/lightning-rfc/blob/master/02-peer-protocol.md#the-open_channel-message

lightningd/opening_control.c

@@ -25,6 +25,7 @@
 #include <lightningd/opening_control.h>
 #include <lightningd/peer_comms.h>
 #include <lightningd/peer_control.h>
+#include <lightningd/plugin_hook.h>
 #include <lightningd/subd.h>
 #include <openingd/gen_opening_wire.h>
 #include <wire/wire.h>
@@ -725,18 +726,144 @@ static void channel_config(struct lightningd *ld,
 	 ours->channel_reserve = AMOUNT_SAT(UINT64_MAX);
 }
 
+struct openchannel_hook_payload {
+	struct subd *openingd;
+	struct amount_sat funding_satoshis;
+	struct amount_msat push_msat;
+	struct amount_sat dust_limit_satoshis;
+	struct amount_msat max_htlc_value_in_flight_msat;
+	struct amount_sat channel_reserve_satoshis;
+	struct amount_msat htlc_minimum_msat;
+	u32 feerate_per_kw;
+	u16 to_self_delay;
+	u16 max_accepted_htlcs;
+	u8 channel_flags;
+	u8 *shutdown_scriptpubkey;
+};
+
+static void
+openchannel_hook_serialize(struct openchannel_hook_payload *payload,
+		       struct json_stream *stream)
+{
+	struct uncommitted_channel *uc = payload->openingd->channel;
+	json_object_start(stream, "openchannel");
+	json_add_node_id(stream, "id", &uc->peer->id);
+	json_add_amount_sat_only(stream, "funding_satoshis",
+				 payload->funding_satoshis);
+	json_add_amount_msat_only(stream, "push_msat", payload->push_msat);
+	json_add_amount_sat_only(stream, "dust_limit_satoshis",
+				 payload->dust_limit_satoshis);
+	json_add_amount_msat_only(stream, "max_htlc_value_in_flight_msat",
+				  payload->max_htlc_value_in_flight_msat);
+	json_add_amount_sat_only(stream, "channel_reserve_satoshis",
+				 payload->channel_reserve_satoshis);
+	json_add_amount_msat_only(stream, "htlc_minimum_msat",
+				  payload->htlc_minimum_msat);
+	json_add_num(stream, "feerate_per_kw", payload->feerate_per_kw);
+	json_add_num(stream, "to_self_delay", payload->to_self_delay);
+	json_add_num(stream, "max_accepted_htlcs", payload->max_accepted_htlcs);
+	json_add_num(stream, "channel_flags", payload->channel_flags);
+	if (tal_count(payload->shutdown_scriptpubkey) != 0)
+		json_add_hex(stream, "shutdown_scriptpubkey",
+			     payload->shutdown_scriptpubkey,
+			     tal_count(payload->shutdown_scriptpubkey));
+	json_object_end(stream); /* .openchannel */
+}
+
+/* openingd dies?  Remove openingd ptr from payload */
+static void openchannel_payload_remove_openingd(struct subd *openingd,
+					    struct openchannel_hook_payload *payload)
+{
+	assert(payload->openingd == openingd);
+	payload->openingd = NULL;
+}
+
+static void openchannel_hook_cb(struct openchannel_hook_payload *payload,
+			    const char *buffer,
+			    const jsmntok_t *toks)
+{
+	struct subd *openingd = payload->openingd;
+	const char *errmsg = NULL;
+
+	/* We want to free this, whatever happens. */
+	tal_steal(tmpctx, payload);
+
+	/* If openingd went away, don't send it anything! */
+	if (!openingd)
+		return;
+
+	tal_del_destructor2(openingd, openchannel_payload_remove_openingd, payload);
+
+	/* If we had a hook, check what it says */
+	if (buffer) {
+		const jsmntok_t *t = json_get_member(buffer, toks, "result");
+		if (!t)
+			fatal("Plugin returned an invalid response to the"
+			      " openchannel hook: %.*s",
+			      toks[0].end - toks[0].start,
+			      buffer + toks[0].start);
+
+		if (json_tok_streq(buffer, t, "reject")) {
+			t = json_get_member(buffer, toks, "error_message");
+			if (t)
+				errmsg = json_strdup(tmpctx, buffer, t);
+			else
+				errmsg = "";
+			log_debug(openingd->ld->log,
+				  "openchannel_hook_cb says '%s'",
+				  errmsg);
+		} else if (!json_tok_streq(buffer, t, "continue"))
+			fatal("Plugin returned an invalid result for the "
+			      "openchannel hook: %.*s",
+			      t->end - t->start, buffer + t->start);
+	}
+
+	subd_send_msg(openingd,
+		      take(towire_opening_got_offer_reply(NULL, errmsg)));
+}
+
+REGISTER_PLUGIN_HOOK(openchannel,
+		     openchannel_hook_cb,
+		     struct openchannel_hook_payload *,
+		     openchannel_hook_serialize,
+		     struct openchannel_hook_payload *);
+
 static void opening_got_offer(struct subd *openingd,
 			      const u8 *msg,
 			      struct uncommitted_channel *uc)
 {
-	const char *reason = NULL;
+	struct openchannel_hook_payload *payload;
 
 	/* Tell them they can't open, if we already have open channel. */
-	if (peer_active_channel(uc->peer))
-		reason = "Already have active channel";
-
+	if (peer_active_channel(uc->peer)) {
 		subd_send_msg(openingd,
-		      take(towire_opening_got_offer_reply(NULL, reason)));
+			      take(towire_opening_got_offer_reply(NULL,
+					  "Already have active channel")));
+		return;
+	}
+
+	payload = tal(openingd->ld, struct openchannel_hook_payload);
+	payload->openingd = openingd;
+	if (!fromwire_opening_got_offer(payload, msg,
+					&payload->funding_satoshis,
+					&payload->push_msat,
+					&payload->dust_limit_satoshis,
+					&payload->max_htlc_value_in_flight_msat,
+					&payload->channel_reserve_satoshis,
+					&payload->htlc_minimum_msat,
+					&payload->feerate_per_kw,
+					&payload->to_self_delay,
+					&payload->max_accepted_htlcs,
+					&payload->channel_flags,
+					&payload->shutdown_scriptpubkey)) {
+		log_broken(openingd->log, "Malformed opening_got_offer %s",
+			   tal_hex(tmpctx, msg));
+		tal_free(openingd);
+		return;
+	}
+
+	tal_add_destructor2(openingd, openchannel_payload_remove_openingd, payload);
+	plugin_hook_call_openchannel(openingd->ld, payload, payload);
 }
 
 static unsigned int openingd_msg(struct subd *openingd,

tests/plugins/reject_odd_funding_amounts.py

@@ -0,0 +1,24 @@
+#!/usr/bin/env python3
+"""Simple plugin to test the openchannel_hook.
+
+We just refuse to let them open channels with an odd amount of millisatoshis.
+"""
+
+from lightning import Plugin, Millisatoshi
+
+plugin = Plugin()
+
+
+@plugin.hook('openchannel')
+def on_openchannel(openchannel, plugin):
+    print("{} VARS".format(len(openchannel.keys())))
+    for k in sorted(openchannel.keys()):
+        print("{}={}".format(k, openchannel[k]))
+
+    if Millisatoshi(openchannel['funding_satoshis']).to_satoshi() % 2 == 1:
+        return {'result': 'reject', 'error_message': "I don't like odd amounts"}
+
+    return {'result': 'continue'}
+
+
+plugin.run()

tests/test_plugin.py

@@ -268,3 +268,44 @@ def test_invoice_payment_hook(node_factory):
     l2.daemon.wait_for_log('label=label2')
     l2.daemon.wait_for_log('msat=')
     l2.daemon.wait_for_log('preimage=' + '0' * 64)
+
+
+def test_openchannel_hook(node_factory, bitcoind):
+    """ l2 uses the reject_odd_funding_amounts plugin to reject some openings.
+    """
+    opts = [{}, {'plugin': 'tests/plugins/reject_odd_funding_amounts.py'}]
+    l1, l2 = node_factory.line_graph(2, fundchannel=False, opts=opts)
+
+    # Get some funds.
+    addr = l1.rpc.newaddr()['bech32']
+    bitcoind.rpc.sendtoaddress(addr, 10)
+    numfunds = len(l1.rpc.listfunds()['outputs'])
+    bitcoind.generate_block(1)
+    wait_for(lambda: len(l1.rpc.listfunds()['outputs']) > numfunds)
+
+    # Even amount: works.
+    l1.rpc.fundchannel(l2.info['id'], 100000)
+
+    # Make sure plugin got all the vars we expect
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py 11 VARS')
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py channel_flags=1')
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py channel_reserve_satoshis=1000000msat')
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py dust_limit_satoshis=546000msat')
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py feerate_per_kw=7500')
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py funding_satoshis=100000000msat')
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py htlc_minimum_msat=0msat')
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py id={}'.format(l1.info['id']))
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py max_accepted_htlcs=483')
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py max_htlc_value_in_flight_msat=18446744073709551615msat')
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py push_msat=0msat')
+    l2.daemon.wait_for_log('reject_odd_funding_amounts.py to_self_delay=5')
+
+    # Close it.
+    l1.rpc.close(l2.info['id'])
+    bitcoind.generate_block(1)
+    wait_for(lambda: [c['state'] for c in only_one(l1.rpc.listpeers(l2.info['id'])['peers'])['channels']] == ['ONCHAIN'])
+
+    # Odd amount: fails
+    l1.connect(l2)
+    with pytest.raises(RpcError, match=r"I don't like odd amounts"):
+        l1.rpc.fundchannel(l2.info['id'], 100001)