daemon/sphinx: support modern v0 hop payload.

This just means we put the outgoing_cltv_value where we used to put zeroes.
The old daemon simply ignores this, but the new one should check it as per
BOLT 4.

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

daemon/pay.c

@@ -340,11 +340,12 @@ static void json_sendpay(struct command *cmd,
 			/* What that hop will forward */
 			tal_resize(&hoppayloads, n_hops);
 			memset(&hoppayloads[n_hops-1], 0, sizeof(struct hoppayload));
-			if (!json_tok_u64(buffer, amttok, &hoppayloads[n_hops-1].amount)) {
+			if (!json_tok_u64(buffer, amttok, &hoppayloads[n_hops-1].amt_to_forward)) {
 				command_fail(cmd, "route %zu invalid msatoshi", n_hops);
 				return;
 			}
-			lastamount = hoppayloads[n_hops-1].amount;
+			/* FIXME: Populate outgoing_cltv_value */
+			lastamount = hoppayloads[n_hops-1].amt_to_forward;
 		}
 
 		tal_resize(&ids, n_hops+1);

daemon/peer.c

@@ -971,7 +971,7 @@ static void their_htlc_added(struct peer *peer, struct htlc *htlc,
 		goto free_packet;
 
 	case ONION_FORWARD:
-		route_htlc_onwards(peer, htlc, step->hoppayload->amount, step->next->nexthop,
+		route_htlc_onwards(peer, htlc, step->hoppayload->amt_to_forward, step->next->nexthop,
 				   serialize_onionpacket(step, step->next), only_dest);
 		goto free_packet;
 	default:

daemon/sphinx.c

@@ -110,8 +110,12 @@ static struct hoppayload *parse_hoppayload(const tal_t *ctx, u8 *src)
 	struct hoppayload *result = talz(ctx, struct hoppayload);
 
 	read_buffer(&result->realm, src, sizeof(result->realm), &p);
-	read_buffer(&result->amount, src, sizeof(result->amount), &p);
+	read_buffer(&result->amt_to_forward,
-	read_buffer(&result->remainder, src, sizeof(result->remainder), &p);
+		    src, sizeof(result->amt_to_forward), &p);
+	read_buffer(&result->outgoing_cltv_value,
+		    src, sizeof(result->outgoing_cltv_value), &p);
+	read_buffer(&result->unused_with_v0_version_on_header,
+		    src, sizeof(result->unused_with_v0_version_on_header), &p);
 	return result;
 }
 
@@ -120,8 +124,11 @@ static void serialize_hoppayload(u8 *dst, struct hoppayload *hp)
 	int p = 0;
 
 	write_buffer(dst, &hp->realm, sizeof(hp->realm), &p);
-	write_buffer(dst, &hp->amount, sizeof(hp->amount), &p);
+	write_buffer(dst, &hp->amt_to_forward, sizeof(hp->amt_to_forward), &p);
-	write_buffer(dst, &hp->remainder, sizeof(hp->remainder), &p);
+	write_buffer(dst, &hp->outgoing_cltv_value,
+		     sizeof(hp->outgoing_cltv_value), &p);
+	write_buffer(dst, &hp->unused_with_v0_version_on_header,
+		     sizeof(hp->unused_with_v0_version_on_header), &p);
 }
 
 

daemon/sphinx.h

@@ -35,10 +35,20 @@ enum route_next_case {
 	ONION_FORWARD = 1,
 };
 
+/* BOLT #4:
+ *
+ * The format of the per-hop-payload for a version 0 packet is as follows:
+```
++----------------+--------------------------+-------------------------------+--------------------------------------------+
+| realm (1 byte) | amt_to_forward (8 bytes) | outgoing_cltv_value (4 bytes) | unused_with_v0_version_on_header (7 bytes) |
++----------------+--------------------------+-------------------------------+--------------------------------------------+
+```
+*/
 struct hoppayload {
 	u8 realm;
-	u64 amount;
+	u64 amt_to_forward;
-	u8 remainder[11];
+	u32 outgoing_cltv_value;
+	u8 unused_with_v0_version_on_header[7];
 };
 
 struct route_step {