funding: take into account HTLC add/remove.

Enhance funding_delta() to have an HTLC delta as well as an A->B delta.

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

funding.c

@@ -41,10 +41,12 @@ bool funding_delta(const OpenChannel *oa,
 		   const OpenChannel *ob,
 		   const OpenAnchor *anchor,
 		   int64_t delta_a,
+		   int64_t htlc,
 		   struct channel_oneside *a_side,
 		   struct channel_oneside *b_side)
 {
 	uint64_t a, b, a_fee, b_fee;
+	int64_t delta_b;
 	uint64_t fee;
 	bool got_fees;
 
@@ -57,20 +59,25 @@ bool funding_delta(const OpenChannel *oa,
 	if (is_funder(oa) == is_funder(ob))
 		return false;
 
+	/* B gets whatever A gives. */
+	delta_b = -delta_a;
+	/* A also pays for the htlc (if any). */
+	delta_a -= htlc;
+
 	/* Transferring more than we have? */
-	if (delta_a > 0 && delta_a > b)
+	if (delta_b < 0 && -delta_b > b)
 		return false;
 	if (delta_a < 0 && -delta_a > a)
 		return false;
 
 	/* Adjust amounts. */
 	a += delta_a;
-	b -= delta_a;
+	b += delta_b;
 
 	/* Take off fee from both parties if possible. */
 	if (is_funder(oa))
 		got_fees = subtract_fees(&a, &b, &a_fee, &b_fee,
-					 delta_a > 0, fee);
+					 delta_b < 0, fee);
 	else
 		got_fees = subtract_fees(&b, &a, &b_fee, &a_fee,
 					 delta_a < 0, fee);
@@ -106,7 +113,7 @@ struct channel_state *initial_funding(const tal_t *ctx,
 		invert_cstate(state);
 
 	/* This checks we only have 1 anchor, and is nice code reuse. */
-	if (!funding_delta(a, b, anchor, 0, &state->a, &state->b))
+	if (!funding_delta(a, b, anchor, 0, 0, &state->a, &state->b))
 		return tal_free(state);
 	return state;
 }

funding.h

@@ -35,6 +35,7 @@ struct channel_state *initial_funding(const tal_t *ctx,
  * @b: B's openchannel offer
  * @anchor: The anchor offer (A or B)
  * @delta_a: How much A changes (-ve => A pay B, +ve => B pays A)
+ * @htlc: How much A is putting into a HTLC (-ve if htlc is cancelled)
  * @a_side: channel a's state to update.
  * @b_side: channel b's state to update.
  */
@@ -42,6 +43,7 @@ bool funding_delta(const OpenChannel *a,
 		   const OpenChannel *b,
 		   const OpenAnchor *anchor,
 		   int64_t delta_a,
+		   int64_t htlc,
 		   struct channel_oneside *a_side,
 		   struct channel_oneside *b_side);
 

test-cli/gather_updates.c

@@ -92,7 +92,7 @@ struct channel_state *gather_updates(const tal_t *ctx,
 				get_rhash(pkt->update->revocation_hash,
 					  &old_our_rhash, our_rhash);
 			}
-			if (!funding_delta(o1, o2, oa, delta,
+			if (!funding_delta(o1, o2, oa, delta, 0,
 					   &cstate->a, &cstate->b))
 				errx(1, "Impossible funding update %lli %s",
 				     (long long)delta, *argv);