lightningd/channel.c: add callbacks for when HTLCs fully committed/removed.

The three cases we care about only happen on specific transitions:
1. They can no longer spend our failed HTLC: we can fail the source now.
2. They are fully committed to their new HTLC htlc: we can forward now.
3. They can no longer timeout their fulfilled HTLC: the funds are ours.

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

lightningd/channel.c

@@ -619,11 +619,36 @@ static void htlc_incstate(struct channel *channel,
 	}
 }
 
+static void check_lockedin(const struct htlc *h,
+			   struct peer *peer,
+			   void (*oursfail)(struct peer *peer,
+					    const struct htlc *htlc),
+			   void (*theirslocked)(struct peer *peer,
+						const struct htlc *htlc),
+			   void (*theirsfulfilled)(struct peer *peer,
+						   const struct htlc *htlc))
+{
+	/* If it was fulfilled, we handled it immediately. */
+	if (h->state == RCVD_REMOVE_ACK_REVOCATION && !h->r)
+		oursfail(peer, h);
+	else if (h->state == RCVD_ADD_ACK_REVOCATION)
+		theirslocked(peer, h);
+	else if (h->state == RCVD_REMOVE_ACK_COMMIT && h->r)
+		theirsfulfilled(peer, h);
+}
+
 /* FIXME: Commit to storage when this happens. */
 static bool change_htlcs(struct channel *channel,
 			 enum side sidechanged,
 			 const enum htlc_state *htlc_states,
-			 size_t n_hstates)
+			 size_t n_hstates,
+			 struct peer *peer,
+			 void (*oursfail)(struct peer *peer,
+					  const struct htlc *htlc),
+			 void (*theirslocked)(struct peer *peer,
+					      const struct htlc *htlc),
+			 void (*theirsfulfilled)(struct peer *peer,
+						 const struct htlc *htlc))
 {
 	struct htlc_map_iter it;
 	struct htlc *h;
@@ -636,6 +661,10 @@ static bool change_htlcs(struct channel *channel,
 		for (i = 0; i < n_hstates; i++) {
 			if (h->state == htlc_states[i]) {
 				htlc_incstate(channel, h, sidechanged);
+				check_lockedin(h, peer,
+					       oursfail,
+					       theirslocked,
+					       theirsfulfilled);
 				changed = true;
 			}
 		}
@@ -651,10 +680,16 @@ bool channel_sent_commit(struct channel *channel)
 					   SENT_ADD_REVOCATION,
 					   SENT_REMOVE_HTLC };
 	status_trace("sent commit");
-	return change_htlcs(channel, REMOTE, states, ARRAY_SIZE(states));
+	return change_htlcs(channel, REMOTE, states, ARRAY_SIZE(states),
+			    NULL, NULL, NULL, NULL);
 }
 
-bool channel_rcvd_revoke_and_ack(struct channel *channel)
+bool channel_rcvd_revoke_and_ack(struct channel *channel,
+				 struct peer *peer,
+				 void (*oursfail)(struct peer *peer,
+						  const struct htlc *htlc),
+				 void (*theirslocked)(struct peer *peer,
+						      const struct htlc *htlc))
 {
 	const enum htlc_state states[] = { SENT_ADD_COMMIT,
 					   SENT_REMOVE_ACK_COMMIT,
@@ -662,11 +697,15 @@ bool channel_rcvd_revoke_and_ack(struct channel *channel)
 					   SENT_REMOVE_COMMIT };
 
 	status_trace("received revoke_and_ack");
-	return change_htlcs(channel, LOCAL, states, ARRAY_SIZE(states));
+	return change_htlcs(channel, LOCAL, states, ARRAY_SIZE(states),
+			    peer, oursfail, theirslocked, NULL);
 }
 
 /* FIXME: We can actually merge these two... */
-bool channel_rcvd_commit(struct channel *channel)
+bool channel_rcvd_commit(struct channel *channel,
+			 struct peer *peer,
+			 void (*theirsfulfilled)(struct peer *peer,
+						 const struct htlc *htlc))
 {
 	const enum htlc_state states[] = { RCVD_ADD_REVOCATION,
 					   RCVD_REMOVE_HTLC,
@@ -674,7 +713,8 @@ bool channel_rcvd_commit(struct channel *channel)
 					   RCVD_REMOVE_REVOCATION };
 
 	status_trace("received commit");
-	return change_htlcs(channel, LOCAL, states, ARRAY_SIZE(states));
+	return change_htlcs(channel, LOCAL, states, ARRAY_SIZE(states),
+			    peer, NULL, NULL, theirsfulfilled);
 }
 
 bool channel_sent_revoke_and_ack(struct channel *channel)
@@ -684,7 +724,8 @@ bool channel_sent_revoke_and_ack(struct channel *channel)
 					   RCVD_ADD_COMMIT,
 					   RCVD_REMOVE_ACK_COMMIT };
 	status_trace("sent revoke_and_ack");
-	return change_htlcs(channel, REMOTE, states, ARRAY_SIZE(states));
+	return change_htlcs(channel, REMOTE, states, ARRAY_SIZE(states),
+			    NULL, NULL, NULL, NULL);
 }
 
 static char *fmt_channel_view(const tal_t *ctx, const struct channel_view *view)

lightningd/channel.h

@@ -10,6 +10,7 @@
 #include <lightningd/derive_basepoints.h>
 #include <stdbool.h>
 
+struct peer;
 struct signature;
 
 /* View from each side */
@@ -330,18 +331,34 @@ bool channel_sent_commit(struct channel *channel);
 /**
  * channel_rcvd_revoke_and_ack: accept ack on remote committed changes.
  * @channel: the channel
+ * @peer: argument to pass through to @ourhtlcfail  & @theirhtlclocked
+ * @oursfail: callback for any unfilfilled htlcs which are now fully removed.
+ * @theirslocked: callback for any new htlcs which are now fully committed.
  *
  * This is where we commit to pending changes we've added; returns true if
- * anything changed. */
+ * anything changed.
-bool channel_rcvd_revoke_and_ack(struct channel *channel);
+ */
+bool channel_rcvd_revoke_and_ack(struct channel *channel,
+				 struct peer *peer,
+				 void (*oursfail)(struct peer *peer,
+						  const struct htlc *htlc),
+				 void (*theirslocked)(struct peer *peer,
+						      const struct htlc *htlc));
 
 /**
  * channel_rcvd_commit: commit all local outstanding changes.
  * @channel: the channel
+ * @peer: argument to pass through to @theirsfulfilled
+ * @theirsfulfilled: they are irrevocably committed to removal of htlc.
  *
  * This is where we commit to pending changes we've added; returns true if
- * anything changed. */
+ * anything changed.  @theirsfulfilled is called for any HTLC we fulfilled
-bool channel_rcvd_commit(struct channel *channel);
+ * which they are irrevocably committed to, and is in our current commitment.
+ */
+bool channel_rcvd_commit(struct channel *channel,
+			 struct peer *peer,
+			 void (*theirsfulfilled)(struct peer *peer,
+						 const struct htlc *htlc));
 
 /**
  * channel_sent_revoke_and_ack: sent ack on local committed changes.

lightningd/channel/channel.c

@@ -369,7 +369,8 @@ static void handle_peer_commit_sig(struct peer *peer, const u8 *msg)
 	const u8 **wscripts;
 	size_t i;
 
-	if (!channel_rcvd_commit(peer->channel)) {
+	/* FIXME: Handle theirsfulfilled! */
+	if (!channel_rcvd_commit(peer->channel, peer, NULL)) {
 		/* BOLT #2:
 		 *
 		 * A node MUST NOT send a `commitment_signed` message which

lightningd/test/run-channel.c

@@ -81,6 +81,10 @@ static u64 feerates[] = {
 	9651936
 };
 
+static void do_nothing(struct peer *peer, const struct htlc *htlc)
+{
+}
+
 /* BOLT #3:
  *
  *    htlc 0 direction: remote->local
@@ -150,11 +154,11 @@ static const struct htlc **include_htlcs(struct channel *channel, enum side side
 
 	/* Now make HTLCs fully committed. */
 	channel_sent_commit(channel);
-	channel_rcvd_revoke_and_ack(channel);
+	channel_rcvd_revoke_and_ack(channel, NULL, NULL, NULL);
-	channel_rcvd_commit(channel);
+	channel_rcvd_commit(channel, NULL, NULL);
 	channel_sent_revoke_and_ack(channel);
 	channel_sent_commit(channel);
-	channel_rcvd_revoke_and_ack(channel);
+	channel_rcvd_revoke_and_ack(channel, NULL, NULL, do_nothing);
 	return htlcs;
 }
 
@@ -236,27 +240,27 @@ static void send_and_fulfill_htlc(struct channel *channel,
 	if (sender == LOCAL) {
 		/* Step through a complete cycle. */
 		channel_sent_commit(channel);
-		channel_rcvd_revoke_and_ack(channel);
+		channel_rcvd_revoke_and_ack(channel, NULL, NULL, NULL);
-		channel_rcvd_commit(channel);
+		channel_rcvd_commit(channel, NULL, NULL);
 		channel_sent_revoke_and_ack(channel);
 		assert(channel_fulfill_htlc(channel, REMOTE, 1337, &r)
 		       == CHANNEL_ERR_REMOVE_OK);
-		channel_rcvd_commit(channel);
+		channel_rcvd_commit(channel, NULL, NULL);
 		channel_sent_revoke_and_ack(channel);
 		channel_sent_commit(channel);
-		channel_rcvd_revoke_and_ack(channel);
+		channel_rcvd_revoke_and_ack(channel, NULL, NULL, NULL);
 		assert(channel_get_htlc(channel, sender, 1337)->state
 		       == RCVD_REMOVE_ACK_REVOCATION);
 	} else {
-		channel_rcvd_commit(channel);
+		channel_rcvd_commit(channel, NULL, NULL);
 		channel_sent_revoke_and_ack(channel);
 		channel_sent_commit(channel);
-		channel_rcvd_revoke_and_ack(channel);
+		channel_rcvd_revoke_and_ack(channel, NULL, NULL, do_nothing);
 		assert(channel_fulfill_htlc(channel, LOCAL, 1337, &r)
 		       == CHANNEL_ERR_REMOVE_OK);
 		channel_sent_commit(channel);
-		channel_rcvd_revoke_and_ack(channel);
+		channel_rcvd_revoke_and_ack(channel, NULL, NULL, NULL);
-		channel_rcvd_commit(channel);
+		channel_rcvd_commit(channel, NULL, do_nothing);
 		channel_sent_revoke_and_ack(channel);
 		assert(channel_get_htlc(channel, sender, 1337)->state
 		       == SENT_REMOVE_ACK_REVOCATION);