openingd/: Fail fundchannel_start if we already are, or will become…

…, the fundee.

Fixes: #4108

lightningd/opening_common.c

@@ -53,6 +53,8 @@ new_uncommitted_channel(struct peer *peer)
 	uc->peer->uncommitted_channel = uc;
 	tal_add_destructor(uc, destroy_uncommitted_channel);
 
+	uc->is_fundee = false;
+
 	return uc;
 }
 

lightningd/opening_common.h

@@ -42,6 +42,11 @@ struct uncommitted_channel {
 	/* Public key for funding tx. */
 	struct pubkey local_funding_pubkey;
 
+	/* If true, we are already in fundee-mode and any future
+	 * `fundchannel_start` on our end should fail.
+	 */
+	bool is_fundee;
+
 	/* These are *not* filled in by new_uncommitted_channel: */
 
 	/* Minimum funding depth (if opener == REMOTE). */

lightningd/opening_control.c

@@ -104,6 +104,11 @@ wallet_commit_channel(struct lightningd *ld,
 	bool option_static_remotekey;
 	bool option_anchor_outputs;
 
+	/* We cannot both be the fundee *and* have a `fundchannel_start`
+	 * command running!
+	 */
+	assert(!(uc->is_fundee && uc->fc));
+
 	/* Get a key to use for closing outputs from this tx */
 	final_key_idx = wallet_get_newindex(ld);
 	if (final_key_idx == -1) {
@@ -415,6 +420,17 @@ static void opening_funder_finished(struct subd *openingd, const u8 *resp,
 	tal_free(fc->uc);
 }
 
+static void
+opening_funder_failed_cancel_commands(struct uncommitted_channel *uc,
+				      const char *desc);
+static void opening_fundee_started(struct subd *openingd UNUSED,
+				   struct uncommitted_channel *uc)
+{
+	/* Cancel any pending funder-side commands: we are the fundee.  */
+	opening_funder_failed_cancel_commands(uc, "We are the fundee");
+	uc->is_fundee = true;
+}
+
 static void opening_fundee_finished(struct subd *openingd,
 				    const u8 *reply,
 				    const int *fds,
@@ -551,6 +567,17 @@ static void opening_funder_failed(struct subd *openingd, const u8 *msg,
 		return;
 	}
 
+	opening_funder_failed_cancel_commands(uc, desc);
+}
+
+static void
+opening_funder_failed_cancel_commands(struct uncommitted_channel *uc,
+				      const char *desc)
+{
+	/* If no funding command(s) pending, do nothing.  */
+	if (!uc->fc)
+		return;
+
 	/* Tell anyone who was trying to cancel */
 	for (size_t i = 0; i < tal_count(uc->fc->cancels); i++) {
 		struct json_stream *response;
@@ -565,7 +592,11 @@ static void opening_funder_failed(struct subd *openingd, const u8 *msg,
 		was_pending(command_fail(uc->fc->cmd, LIGHTNINGD, "%s", desc));
 
 	/* Clear uc->fc, so we can try again, and so we don't fail twice
-	 * if they close. */
+	 * if they close.
+	 * This code is also used in the case where we turn out to already
+	 * be the fundee, in which case we should not have any `fc` at all,
+	 * so we definitely should clear this.
+	 */
 	uc->fc = tal_free(uc->fc);
 }
 
@@ -797,6 +828,10 @@ static unsigned int openingd_msg(struct subd *openingd,
 		opening_funder_failed(openingd, msg, uc);
 		return 0;
 
+	case WIRE_OPENINGD_WILL_BE_FUNDEE:
+		opening_fundee_started(openingd, uc);
+		return 0;
+
 	case WIRE_OPENINGD_FUNDEE:
 		if (tal_count(fds) != 3)
 			return 3;
@@ -1086,6 +1121,10 @@ static struct command_result *json_fund_channel_start(struct command *cmd,
 		return command_fail(cmd, LIGHTNINGD, "Already funding channel");
 	}
 
+	if (peer->uncommitted_channel->is_fundee) {
+		return command_fail(cmd, LIGHTNINGD, "We are the fundee");
+	}
+
 	/* BOLT #2:
 	 *  - if both nodes advertised `option_support_large_channel`:
 	 *    - MAY set `funding_satoshis` greater than or equal to 2^24 satoshi.

openingd/openingd.c

@@ -974,6 +974,14 @@ static u8 *fundee_channel(struct state *state, const u8 *open_channel_msg)
 	if (!state->upfront_shutdown_script[LOCAL])
 		state->upfront_shutdown_script[LOCAL] = no_upfront_shutdown_script(state, state);
 
+	/* Just before we accept, we tell the master that we are now
+	 * going to be a fundee, so it should fail any pending
+	 * `fundchannel_start` on this peer, and fail all future ones
+	 * as well.
+	 */
+	msg = towire_openingd_will_be_fundee(NULL);
+	wire_sync_write(REQ_FD, take(msg));
+
 	/* OK, we accept! */
 	accept_tlvs = tlv_accept_channel_tlvs_new(tmpctx);
 	accept_tlvs->upfront_shutdown_script
@@ -1333,6 +1341,7 @@ static u8 *handle_master_in(struct state *state)
 	case WIRE_OPENINGD_INIT:
 	case WIRE_OPENINGD_FUNDER_REPLY:
 	case WIRE_OPENINGD_FUNDER_START_REPLY:
+	case WIRE_OPENINGD_WILL_BE_FUNDEE:
 	case WIRE_OPENINGD_FUNDEE:
 	case WIRE_OPENINGD_FUNDER_FAILED:
 	case WIRE_OPENINGD_GOT_OFFER:

openingd/openingd_wire.csv

@@ -104,6 +104,10 @@ msgtype,openingd_funder_cancel,6013
 msgtype,openingd_funder_failed,6004
 msgdata,openingd_funder_failed,reason,wirestring,
 
+# Openingd->master: we will enter into fundee route
+# and ignore all subsequent master->openingd messsages.
+msgtype,openingd_will_be_fundee,6023
+
 # Openingd->master: they offered channel.
 # This gives their txid and info, means we can send funding_signed: we're done.
 msgtype,openingd_fundee,6003

tests/test_connection.py

@@ -2653,7 +2653,6 @@ def test_connection_timeout(node_factory):
     l1.daemon.wait_for_log('conn timed out')
 
 
-@pytest.mark.xfail(strict=True)
 def test_fundchannel_start_alternate(node_factory, executor):
     ''' Test to see what happens if two nodes start channeling to
     each other alternately.