common/sphinx: add helper to prepend length to payload.

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

Author: rustyrussell

common/sphinx.c

@@ -112,6 +112,19 @@ void sphinx_add_hop(struct sphinx_path *path, const struct pubkey *pubkey,
 	tal_arr_expand(&path->hops, sp);
 }
 
+void sphinx_add_modern_hop(struct sphinx_path *path, const struct pubkey *pubkey,
+			   const u8 *payload TAKES)
+{
+	u8 *with_len = tal_arr(NULL, u8, 0);
+	size_t len = tal_bytelen(payload);
+	towire_bigsize(&with_len, len);
+	towire_u8_array(&with_len, payload, len);
+	if (taken(payload))
+		tal_free(payload);
+
+	sphinx_add_hop(path, pubkey, take(with_len));
+}
+
 /* Small helper to append data to a buffer and update the position
  * into the buffer
  */

common/sphinx.h

@@ -228,6 +228,13 @@ struct sphinx_path *sphinx_path_new_with_key(const tal_t *ctx,
 void sphinx_add_hop(struct sphinx_path *path, const struct pubkey *pubkey,
 		    const u8 *payload TAKES);
 
+/**
+ * Prepend length to payload and add: for onionmessage, any size is OK,
+ * for HTLC onions tal_bytelen(payload) must be > 1.
+ */
+void sphinx_add_modern_hop(struct sphinx_path *path, const struct pubkey *pubkey,
+			   const u8 *payload TAKES);
+
 /**
  * Compute the size of the serialized payloads.
  */

common/test/run-sphinx-xor_cipher_stream.c

@@ -110,6 +110,9 @@ void towire(u8 **pptr UNNEEDED, const void *data UNNEEDED, size_t len UNNEEDED)
 /* Generated stub for towire_amount_sat */
 void towire_amount_sat(u8 **pptr UNNEEDED, const struct amount_sat sat UNNEEDED)
 { fprintf(stderr, "towire_amount_sat called!\n"); abort(); }
+/* Generated stub for towire_bigsize */
+void towire_bigsize(u8 **pptr UNNEEDED, const bigsize_t val UNNEEDED)
+{ fprintf(stderr, "towire_bigsize called!\n"); abort(); }
 /* Generated stub for towire_bool */
 void towire_bool(u8 **pptr UNNEEDED, bool v UNNEEDED)
 { fprintf(stderr, "towire_bool called!\n"); abort(); }

lightningd/onion_message.c

@@ -423,14 +423,9 @@ static struct command_result *json_send_onion_message(struct command *cmd,
 	/* Create an onion which encodes this. */
 	populate_tlvs(hops, reply_path);
 	sphinx_path = sphinx_path_new(cmd, NULL);
-	for (size_t i = 0; i < tal_count(hops); i++) {
-		/* FIXME: Remove legacy, then length prefix can be removed! */
-		u8 *tlv_with_len = tal_arr(NULL, u8, 0);
-		towire_bigsize(&tlv_with_len, tal_bytelen(hops[i].rawtlv));
-		towire_u8_array(&tlv_with_len,
-				hops[i].rawtlv, tal_bytelen(hops[i].rawtlv));
-		sphinx_add_hop(sphinx_path, &hops[i].id, take(tlv_with_len));
-	}
+	for (size_t i = 0; i < tal_count(hops); i++)
+		sphinx_add_modern_hop(sphinx_path, &hops[i].id, hops[i].rawtlv);
+
 	/* BOLT-onion-message #4:
 	 * - SHOULD set `len` to 1366 or 32834.
 	 */