pay: Allow `sendonion` callers to provide `shared_secrets`

This means that c-lightning can now internally decrypt an eventual error
message, and not force the caller to implement the decryption. The main
difficulty was that we now have a new state (channels and nodes not specified,
while shared_secrets are specified) which needed to be handled.

lightningd/pay.c

@@ -362,7 +362,24 @@ remote_routing_failure(const tal_t *ctx,
 
 	assert(route_nodes == NULL || origin_index < tal_count(route_nodes));
 
-	if (origin_index == tal_count(route_nodes) - 1) {
+	/* Either we have both channels and nodes, or neither */
+	assert((route_nodes == NULL) == (route_channels == NULL));
+
+	if (route_nodes == NULL) {
+		/* This means we have the `shared_secrets`, but cannot infer
+		 * the erring channel and node since we don't have them. This
+		 * can happen if the payment was initialized using `sendonion`
+		 * and the `shared_secrets` where specified. */
+		dir = 0;
+		erring_channel = NULL;
+		erring_node = NULL;
+
+		/* We don't know if there's another route, that'd depend on
+		 * where the failure occured and whether it was a node
+		 * failure. Let's assume it wasn't a terminal one, and have
+		 * the sendonion caller deal with the actual decision. */
+		*pay_errcode = PAY_TRY_OTHER_ROUTE;
+	} else if (origin_index == tal_count(route_nodes) - 1) {
 		/* If any channel is to blame, it's the last one. */
 		erring_channel = &route_channels[origin_index];
 		/* Single hop? */
@@ -484,7 +501,7 @@ void payment_failed(struct lightningd *ld, const struct htlc_out *hout,
 #else
 	assert(payment);
 #endif
-	assert((payment->path_secrets == NULL) == (payment->route_nodes == NULL));
+	assert((payment->route_channels == NULL) == (payment->route_nodes == NULL));
 
 	/* This gives more details than a generic failure message */
 	if (localfail) {
@@ -945,12 +962,16 @@ static struct command_result *json_sendonion(struct command *cmd,
 	struct lightningd *ld = cmd->ld;
 	struct wallet_payment *payment;
 	const char *label;
+	const jsmntok_t *secretstok, *cur;
+	struct secret *path_secrets;
+	size_t i;
 
 	if (!param(cmd, buffer, params,
 		   p_req("onion", param_bin_from_hex, &onion),
 		   p_req("first_hop", param_route_hop, &first_hop),
 		   p_req("payment_hash", param_sha256, &payment_hash),
 		   p_opt("label", param_escaped_string, &label),
+		   p_opt("shared_secrets", param_array, &secretstok),
 		   NULL))
 		return command_param_failed();
 
@@ -962,6 +983,20 @@ static struct command_result *json_sendonion(struct command *cmd,
 				    "with failcode=%d",
 				    failcode);
 
+	if (secretstok) {
+		path_secrets = tal_arr(cmd, struct secret, secretstok->size);
+		json_for_each_arr(i, cur, secretstok) {
+			if (!json_to_secret(buffer, cur, &path_secrets[i]))
+				return command_fail(
+				    cmd, JSONRPC2_INVALID_PARAMS,
+				    "shared_secret[%zu] isn't a valid "
+				    "hex-encoded 32 byte secret",
+				    i);
+		}
+	} else {
+		path_secrets = NULL;
+	}
+
 	/* FIXME if the user specified a short_channel_id, but no peer nodeid,
 	 * we need to resolve that first. */
 
@@ -996,10 +1031,10 @@ static struct command_result *json_sendonion(struct command *cmd,
 	 * externally, since we can't decrypt them.*/
 	payment->destination = NULL;
 	payment->payment_preimage = NULL;
-	payment->path_secrets = NULL;
 	payment->route_nodes = NULL;
 	payment->route_channels = NULL;
 	payment->bolt11 = NULL;
+	payment->path_secrets = tal_steal(payment, path_secrets);
 
 	if (label != NULL)
 		payment->label = tal_strdup(payment, label);

tests/test_pay.py

@@ -2543,3 +2543,21 @@ def test_sendonion_rpc(node_factory):
     pays = l1.rpc.listsendpays(payment_hash=payment_hash)['payments']
     assert(len(pays) == 1 and pays[0]['status'] == 'failed'
            and pays[0]['payment_hash'] == payment_hash)
+    assert('erroronion' in pays[0])
+
+    # Fail onion is msg + padding = 256 + 2*2 byte lengths + 32 byte HMAC
+    assert(len(pays[0]['erroronion']) == (256 + 32 + 2 + 2) * 2)
+
+    # Let's try that again, this time we give it the shared_secrets so it
+    # should be able to decode the error.
+    payment_hash = "01" * 32
+    onion = l1.rpc.createonion(hops=hops, assocdata=payment_hash)
+    l1.rpc.sendonion(onion=onion['onion'], first_hop=first_hop,
+                     payment_hash=payment_hash,
+                     shared_secrets=onion['shared_secrets'])
+
+    try:
+        l1.rpc.waitsendpay(payment_hash=payment_hash)
+    except RpcError as e:
+        assert(e.error['code'] == 202)
+        assert(e.error['message'] == "Malformed error reply")

wallet/wallet.c

@@ -2138,15 +2138,16 @@ void wallet_payment_store(struct wallet *wallet,
 	db_bind_amount_msat(stmt, 3, &payment->msatoshi);
 	db_bind_int(stmt, 4, payment->timestamp);
 
-	if (payment->route_nodes) {
-		assert(payment->path_secrets);
-		assert(payment->route_nodes);
-		assert(payment->route_channels);
+	if (payment->path_secrets != NULL)
 		db_bind_secret_arr(stmt, 5, payment->path_secrets);
+	else
+		db_bind_null(stmt, 5);
+
+	assert((payment->route_channels == NULL) == (payment->route_nodes == NULL));
+	if (payment->route_nodes) {
 		db_bind_node_id_arr(stmt, 6, payment->route_nodes);
 		db_bind_short_channel_id_arr(stmt, 7, payment->route_channels);
 	} else {
-		db_bind_null(stmt, 5);
 		db_bind_null(stmt, 6);
 		db_bind_null(stmt, 7);
 	}
@@ -2211,17 +2212,20 @@ static struct wallet_payment *wallet_stmt2payment(const tal_t *ctx,
 	} else
 		payment->payment_preimage = NULL;
 
-	/* Can be NULL for old db! */
-	if (!db_column_is_null(stmt, 7)) {
-		assert(!db_column_is_null(stmt, 8));
-		assert(!db_column_is_null(stmt, 9));
+	/* We either used `sendpay` or `sendonion` with the `shared_secrets`
+	 * argument. */
+	if (!db_column_is_null(stmt, 7))
 		payment->path_secrets = db_column_secret_arr(payment, stmt, 7);
+	else
+		payment->path_secrets = NULL;
 
+	/* Either none, or both are set */
+	assert(db_column_is_null(stmt, 8) == db_column_is_null(stmt, 9));
+	if (!db_column_is_null(stmt, 8)) {
 		payment->route_nodes = db_column_node_id_arr(payment, stmt, 8);
 		payment->route_channels =
 		    db_column_short_channel_id_arr(payment, stmt, 9);
 	} else {
-		payment->path_secrets = NULL;
 		payment->route_nodes = NULL;
 		payment->route_channels = NULL;
 	}