channeld: handle upgrade match.

We don't actually set desired_type yet, but this handles it.

Changelog-EXPERIMENTAL: Protocol: we can now upgrade old channels to `option_static_remotekey` from lightning/bolts#868
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

channeld/channeld.c

@@ -368,6 +368,50 @@ static bool handle_master_request_later(struct peer *peer, const u8 *msg)
 	}
 	return false;
 }
+
+static bool channel_type_eq(const struct channel_type *a,
+			    const struct channel_type *b)
+{
+	return featurebits_eq(a->features, b->features);
+}
+
+static bool match_type(const struct channel_type *desired,
+		       const struct channel_type *current,
+		       struct channel_type **upgradable)
+{
+	/* Missing fields are possible. */
+	if (!desired || !current)
+		return false;
+
+	if (channel_type_eq(desired, current))
+		return true;
+
+	for (size_t i = 0; i < tal_count(upgradable); i++) {
+		if (channel_type_eq(desired, upgradable[i]))
+			return true;
+	}
+
+	return false;
+}
+
+static void set_channel_type(struct channel *channel,
+			     const struct channel_type *type)
+{
+	const struct channel_type *cur = channel_type(tmpctx, channel);
+
+	if (channel_type_eq(cur, type))
+		return;
+
+	/* We only allow one upgrade at the moment, so that's it. */
+	assert(!channel->option_static_remotekey);
+	assert(feature_offered(type->features, OPT_STATIC_REMOTEKEY));
+
+	/* Do upgrade, tell master. */
+	channel->option_static_remotekey = true;
+	status_unusual("Upgraded channel to [%s]",
+		       fmt_featurebits(tmpctx, type->features));
+	wire_sync_write(MASTER_FD, take(towire_channeld_upgraded(NULL, true)));
+}
 #else /* !EXPERIMENTAL_FEATURES */
 static bool handle_master_request_later(struct peer *peer, const u8 *msg)
 {
@@ -2499,7 +2543,8 @@ static void peer_reconnect(struct peer *peer,
 				 &my_current_per_commitment_point, NULL);
 
 #if EXPERIMENTAL_FEATURES
-	send_tlvs = tlv_channel_reestablish_tlvs_new(tmpctx);
+	/* Subtle: we free tmpctx below as we loop, so tal off peer */
+	send_tlvs = tlv_channel_reestablish_tlvs_new(peer);
 	/* BOLT-upgrade_protocol #2:
 	 * A node sending `channel_reestablish`, if it supports upgrading channels:
 	 *   - MUST set `next_to_send` the commitment number of the next
@@ -2797,6 +2842,71 @@ static void peer_reconnect(struct peer *peer,
 			     fmt_featurebits(tmpctx,
 					     recv_tlvs->upgradable[i]->features));
 	}
+
+	/* BOLT-upgrade_protocol #2:
+	 *
+	 * A node receiving `channel_reestablish`:
+	 *  - if it has to retransmit `commitment_signed` or `revoke_and_ack`:
+	 *    - MUST consider the channel feature change failed.
+	 */
+	if (retransmit_commitment_signed || retransmit_revoke_and_ack) {
+		status_debug("No upgrade: we retransmitted");
+	/* BOLT-upgrade_protocol #2:
+	 *
+	 *  - if `next_to_send` is missing, or not equal to the
+	 *    `next_commitment_number` it sent:
+	 *    - MUST consider the channel feature change failed.
+	 */
+	} else if (!recv_tlvs->next_to_send) {
+		status_debug("No upgrade: no next_to_send received");
+	} else if (*recv_tlvs->next_to_send != peer->next_index[LOCAL]) {
+		status_debug("No upgrade: they're retransmitting");
+	/* BOLT-upgrade_protocol #2:
+	 *
+	 *  - if updates are pending on either sides' commitment transaction:
+	 *    - MUST consider the channel feature change failed.
+	 */
+		/* Note that we can have HTLCs we *want* to add or remove
+		 * but haven't yet: thats OK! */
+	} else if (pending_updates(peer->channel, LOCAL, true)
+		   || pending_updates(peer->channel, REMOTE, true)) {
+		status_debug("No upgrade: pending changes");
+	} else {
+		const struct tlv_channel_reestablish_tlvs *initr, *ninitr;
+		const struct channel_type *type;
+
+		if (peer->channel->opener == LOCAL) {
+			initr = send_tlvs;
+			ninitr = recv_tlvs;
+		} else {
+			initr = recv_tlvs;
+			ninitr = send_tlvs;
+		}
+
+		/* BOLT-upgrade_protocol #2:
+		 *
+		 * - if `desired_type` matches `current_type` or any
+		 *   `upgradable` `upgrades`:
+		 *   - MUST consider the channel type to be `desired_type`.
+		 * - otherwise:
+		 *   - MUST consider the channel feature change failed.
+		 *   - if there is a `current_type` field:
+		 *     - MUST consider the channel type to be `current_type`.
+		 */
+		/* Note: returns NULL on missing fields, aka NULL */
+		if (match_type(initr->desired_type,
+			       ninitr->current_type, ninitr->upgradable))
+			type = initr->desired_type;
+		else if (ninitr->current_type)
+			type = ninitr->current_type;
+		else
+			type = NULL;
+
+		if (type)
+			set_channel_type(peer->channel, type);
+	}
+	tal_free(send_tlvs);
+
 #endif /* EXPERIMENTAL_FEATURES */
 
 	/* Corner case: we didn't send shutdown before because update_add_htlc
@@ -3246,6 +3356,7 @@ static void req_in(struct peer *peer, const u8 *msg)
 	case WIRE_CHANNELD_DEV_MEMLEAK_REPLY:
 	case WIRE_CHANNELD_SEND_ERROR_REPLY:
 	case WIRE_CHANNELD_DEV_QUIESCE_REPLY:
+	case WIRE_CHANNELD_UPGRADED:
 		break;
 	}
 

channeld/channeld_wire.csv

@@ -221,3 +221,7 @@ msgtype,channeld_send_error_reply,1108
 # Ask channeld to quiesce.
 msgtype,channeld_dev_quiesce,1009
 msgtype,channeld_dev_quiesce_reply,1109
+
+# Tell master we're upgrading the commitment tx.
+msgtype,channeld_upgraded,1011
+msgdata,channeld_upgraded,option_static_remotekey,bool,

common/features.c

@@ -476,6 +476,20 @@ u8 *featurebits_or(const tal_t *ctx, const u8 *f1 TAKES, const u8 *f2 TAKES)
 	return result;
 }
 
+bool featurebits_eq(const u8 *f1, const u8 *f2)
+{
+	size_t len = tal_bytelen(f1);
+
+	if (tal_bytelen(f2) > len)
+		len = tal_bytelen(f2);
+
+	for (size_t i = 0; i < len * 8; i++) {
+		if (feature_is_set(f1, i) != feature_is_set(f2, i))
+			return false;
+	}
+	return true;
+}
+
 struct feature_set *fromwire_feature_set(const tal_t *ctx,
 					 const u8 **cursor, size_t *max)
 {

common/features.h

@@ -71,6 +71,10 @@ void set_feature_bit(u8 **ptr, u32 bit);
 /* Given two featurebit vectors, combine them by applying a logical OR. */
 u8 *featurebits_or(const tal_t *ctx, const u8 *f1 TAKES, const u8 *f2 TAKES);
 
+/* Are these two feature bitsets functionally equal (one may have
+ * trailing zeroes)? */
+bool featurebits_eq(const u8 *f1, const u8 *f2);
+
 /* Good for debugging: returns comma-separated string of bits. */
 const char *fmt_featurebits(const tal_t *ctx, const u8 *featurebits);
 

lightningd/channel_control.c

@@ -370,6 +370,29 @@ void forget_channel(struct channel *channel, const char *why)
 		forget(channel);
 }
 
+#if EXPERIMENTAL_FEATURES
+static void handle_channel_upgrade(struct channel *channel,
+				   const u8 *msg)
+{
+	bool option_static_remotekey;
+
+	if (!fromwire_channeld_upgraded(msg, &option_static_remotekey)) {
+		channel_internal_error(channel, "bad handle_channel_upgrade: %s",
+				       tal_hex(tmpctx, msg));
+		return;
+	}
+
+	channel->static_remotekey_start[LOCAL] = channel->next_index[LOCAL];
+	channel->static_remotekey_start[REMOTE] = channel->next_index[REMOTE];
+	log_debug(channel->log,
+		  "option_static_remotekey enabled at %"PRIu64"/%"PRIu64,
+		  channel->static_remotekey_start[LOCAL],
+		  channel->static_remotekey_start[REMOTE]);
+
+	wallet_channel_save(channel->peer->ld->wallet, channel);
+}
+#endif /* EXPERIMENTAL_FEATURES */
+
 static unsigned channel_msg(struct subd *sd, const u8 *msg, const int *fds)
 {
 	enum channeld_wire t = fromwire_peektype(msg);
@@ -405,6 +428,13 @@ static unsigned channel_msg(struct subd *sd, const u8 *msg, const int *fds)
 	case WIRE_CHANNELD_SEND_ERROR_REPLY:
 		handle_error_channel(sd->channel, msg);
 		break;
+#if EXPERIMENTAL_FEATURES
+	case WIRE_CHANNELD_UPGRADED:
+		handle_channel_upgrade(sd->channel, msg);
+		break;
+#else
+	case WIRE_CHANNELD_UPGRADED:
+#endif
 	/* And we never get these from channeld. */
 	case WIRE_CHANNELD_INIT:
 	case WIRE_CHANNELD_FUNDING_DEPTH: