createonion to accept an optional custom onion_size

devtools/onion.c

@@ -130,7 +130,7 @@ static struct route_step *decode_with_privkey(const tal_t *ctx, const u8 *onion,
 	if (!hex_decode(hexprivkey, strlen(hexprivkey), &seckey, sizeof(seckey)))
 		errx(1, "Invalid private key hex '%s'", hexprivkey);
 
-	packet = parse_onionpacket(tmpctx, onion, TOTAL_PACKET_SIZE(ROUTING_INFO_SIZE), &why_bad);
+	packet = parse_onionpacket(tmpctx, onion, tal_bytelen(onion), &why_bad);
 
 	if (!packet)
 		errx(1, "Error parsing message: %s", onion_wire_name(why_bad));
@@ -147,7 +147,7 @@ static struct route_step *decode_with_privkey(const tal_t *ctx, const u8 *onion,
 static void do_decode(int argc, char **argv, const u8 *assocdata)
 {
 	const tal_t *ctx = talz(NULL, tal_t);
-	u8 serialized[TOTAL_PACKET_SIZE(ROUTING_INFO_SIZE)];
+	u8 *serialized;
 	struct route_step *step;
 
 	if (argc != 4)
@@ -161,7 +161,8 @@ static void do_decode(int argc, char **argv, const u8 *assocdata)
 	while (isspace(hextemp[hexlen-1]))
 		hexlen--;
 
-	if (!hex_decode(hextemp, hexlen, serialized, sizeof(serialized))) {
+	serialized = tal_hexdata(hextemp, hextemp, hexlen);
+	if (!serialized) {
 		errx(1, "Invalid onion hex '%s'", hextemp);
 	}
 

doc/lightning-createonion.7.md

@@ -4,7 +4,7 @@ lightning-createonion -- Low-level command to create a custom onion
 SYNOPSIS
 --------
 
-**createonion** *hops* *assocdata* \[*session_key*\]
+**createonion** *hops* *assocdata* \[*session_key*\] \[*onion_size*\]
 
 DESCRIPTION
 -----------
@@ -68,10 +68,10 @@ which the above *hops* parameter was generated:
 
  - Notice that the payload in the *hops* parameter is the hex-encoded version
    of the parameters in the `getroute` response.
- - The payloads are shifted left by one, i.e., payload 0 in `createonion`
-   corresponds to payload 1 from `getroute`.
+ - Except for the pubkey, the values are shifted left by one, i.e., the 1st
+   payload in `createonion` corresponds to the 2nd set of values from `getroute`.
  - The final payload is a copy of the last payload sans `channel`
- 
+
 These rules are directly derived from the onion construction. Please refer
 [BOLT 04][bolt04] for details and rationale.
 
@@ -85,6 +85,10 @@ should only be used for testing or if a specific shared secret is
 important. If not specified it will be securely generated internally, and the
 shared secrets will be returned.
 
+The optional *onion_size* parameter specifies a size different from the default
+payment onion (1300 bytes). May be used for custom protocols like trampoline
+routing.
+
 RETURN VALUE
 ------------
 
@@ -122,4 +126,3 @@ RESOURCES
 Main web site: <https://github.com/ElementsProject/lightning>
 
 [bolt04]: https://github.com/lightningnetwork/lightning-rfc/blob/master/04-onion-routing.md
-

lightningd/pay.c

@@ -1671,13 +1671,15 @@ static struct command_result *json_createonion(struct command *cmd,
 	struct secret *session_key, *shared_secrets;
 	struct sphinx_path *sp;
 	u8 *assocdata, *serialized;
+	u32 *packet_size;
 	struct onionpacket *packet;
 	struct sphinx_hop *hops;
 
 	if (!param(cmd, buffer, params,
 		   p_req("hops", param_hops_array, &hops),
 		   p_req("assocdata", param_bin_from_hex, &assocdata),
 		   p_opt("session_key", param_secret, &session_key),
+		   p_opt_def("onion_size", param_number, &packet_size, ROUTING_INFO_SIZE),
 		   NULL)) {
 		return command_param_failed();
 	}
@@ -1690,12 +1692,12 @@ static struct command_result *json_createonion(struct command *cmd,
 	for (size_t i=0; i<tal_count(hops); i++)
 		sphinx_add_hop(sp, &hops[i].pubkey, hops[i].raw_payload);
 
-	if (sphinx_path_payloads_size(sp) > ROUTING_INFO_SIZE)
+	if (sphinx_path_payloads_size(sp) > *packet_size)
 		return command_fail(
 		    cmd, JSONRPC2_INVALID_PARAMS,
 		    "Payloads exceed maximum onion packet size.");
 
-	packet = create_onionpacket(cmd, sp, ROUTING_INFO_SIZE, &shared_secrets);
+	packet = create_onionpacket(cmd, sp, *packet_size, &shared_secrets);
 	if (!packet)
 		return command_fail(cmd, LIGHTNINGD,
 				    "Could not create onion packet");

tests/test_pay.py

@@ -2816,7 +2816,8 @@ def test_partial_payment_htlc_loss(node_factory, bitcoind):
 def test_createonion_limits(node_factory):
     l1, = node_factory.get_nodes(1)
     hops = [{
-        "pubkey": "02eec7245d6b7d2ccb30380bfbe2a3648cd7a942653f5aa340edcea1f283686619",
+        # privkey: 41bfd2660762506c9933ade59f1debf7e6495b10c14a92dbcd2d623da2507d3d
+        "pubkey": "0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518",
         "payload": "00" * 228
     }, {
         "pubkey": "0324653eac434488002cc06bbfb7f10fe18991e35f9fe4302dbea6d2353dc0ab1c",
@@ -2840,6 +2841,20 @@ def test_createonion_limits(node_factory):
         hops[0]['payload'] += '01'
         l1.rpc.createonion(hops=hops, assocdata="BB" * 32)
 
+    # But with a larger onion, it will work!
+    oniontool = os.path.join(os.path.dirname(__file__), "..", "devtools", "onion")
+    onion = l1.rpc.createonion(hops=hops, assocdata="BB" * 32, onion_size=1301)['onion']
+
+    # Oniontool wants a filename :(
+    onionfile = os.path.join(l1.daemon.lightning_dir, 'onion')
+    with open(onionfile, "w") as f:
+        f.write(onion)
+
+    subprocess.check_output(
+        [oniontool, '--assoc-data', "BB" * 32,
+         'decode', onionfile, "41bfd2660762506c9933ade59f1debf7e6495b10c14a92dbcd2d623da2507d3d"]
+    )
+
 
 @pytest.mark.developer("needs use_shadow")
 def test_blockheight_disagreement(node_factory, bitcoind, executor):