sphinx: Functions to enable RV mode and serialize compressed onions

We will later use these to generate RV compressed onions and to opt into the
rendezvous style generation.

common/sphinx.c

@@ -86,6 +86,19 @@ struct sphinx_path *sphinx_path_new_with_key(const tal_t *ctx,
 	return sp;
 }
 
+bool sphinx_path_set_rendezvous(struct sphinx_path *sp,
+				const struct node_id *rendezvous_id)
+{
+	if (rendezvous_id == NULL) {
+		sp->rendezvous_id = tal_free(sp->rendezvous_id);
+		return true;
+	} else {
+		sp->rendezvous_id = tal_free(sp->rendezvous_id);
+		sp->rendezvous_id = tal(sp, struct pubkey);
+		return pubkey_from_node_id(sp->rendezvous_id, rendezvous_id);
+	}
+}
+
 static size_t sphinx_hop_size(const struct sphinx_hop *hop)
 {
 	return tal_bytelen(hop->raw_payload) + HMAC_SIZE;
@@ -143,6 +156,30 @@ u8 *serialize_onionpacket(
 	return dst;
 }
 
+u8 *serialize_compressed_onion(const tal_t *ctx,
+			       const struct sphinx_path *sp,
+			       const struct onionpacket *packet)
+{
+	u8 *dst;
+	u8 der[PUBKEY_CMPR_LEN];
+	size_t payloads_size = sphinx_path_payloads_size(sp);
+	size_t max_prefill  = ROUTING_INFO_SIZE - payloads_size;
+	size_t rv_onion_size = TOTAL_PACKET_SIZE - max_prefill;
+	int p = 0;
+
+	assert(sp->rendezvous_id != NULL);
+
+	dst = tal_arr(ctx, u8, rv_onion_size);
+
+	pubkey_to_der(der, &packet->ephemeralkey);
+	write_buffer(dst, &packet->version, 1, &p);
+	write_buffer(dst, der, sizeof(der), &p);
+	write_buffer(dst, packet->routinginfo, ROUTING_INFO_SIZE - max_prefill, &p);
+	write_buffer(dst, packet->mac, sizeof(packet->mac), &p);
+	return dst;
+}
+
+
 enum onion_type parse_onionpacket(const u8 *src,
 				  const size_t srclen,
 				  struct onionpacket *dest)

common/sphinx.h

@@ -227,6 +227,25 @@ void sphinx_add_hop(struct sphinx_path *path, const struct pubkey *pubkey,
  */
 size_t sphinx_path_payloads_size(const struct sphinx_path *path);
 
+/**
+ * Compress a rendez-vous onion by removing the unused blinded middle
+ * part. This middle part can be regenerated by the node processing this
+ * onion.
+ */
+u8 *serialize_compressed_onion(const tal_t *ctx,
+			       const struct sphinx_path *sp,
+			       const struct onionpacket *packet);
+
+/**
+ * Set the rendez-vous node_id and make the onion generated from the
+ * sphinx_path compressible. To unset pass in a NULL rendezvous_id.
+ *
+ * Returns false if there was an error converting from the node_id to a public
+ * key.
+ */
+bool sphinx_path_set_rendezvous(struct sphinx_path *sp,
+				const struct node_id *rendezvous_id);
+
 #if DEVELOPER
 /* Override to force us to reject valid onion packets */
 extern bool dev_fail_process_onionpacket;

common/test/run-sphinx.c

@@ -45,6 +45,9 @@ size_t bigsize_get(const u8 *p UNNEEDED, size_t max UNNEEDED, bigsize_t *val UNN
 /* Generated stub for bigsize_put */
 size_t bigsize_put(u8 buf[BIGSIZE_MAX_LEN] UNNEEDED, bigsize_t v UNNEEDED)
 { fprintf(stderr, "bigsize_put called!\n"); abort(); }
+/* Generated stub for pubkey_from_node_id */
+bool pubkey_from_node_id(struct pubkey *key UNNEEDED, const struct node_id *id UNNEEDED)
+{ fprintf(stderr, "pubkey_from_node_id called!\n"); abort(); }
 /* AUTOGENERATED MOCKS END */
 
 extern secp256k1_context *secp256k1_ctx;