common/blindedpay: routines to construct a blinded payment.

Don't shoehorn it into onion_nonfinal_hop() and onion_final_hop(), but
provide an explicit routine "blinded_onion_hops" and an onion helper
"onion_blinded_hop()" for it to call.

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

common/Makefile

@@ -10,6 +10,7 @@ COMMON_SRC_NOGEN :=				\
 	common/billboard.c			\
 	common/bip32.c				\
 	common/blindedpath.c			\
+	common/blindedpay.c			\
 	common/blinding.c			\
 	common/blockheight_states.c		\
 	common/bolt11.c				\

common/blindedpay.c

@@ -0,0 +1,40 @@
+#include "config.h"
+#include <assert.h>
+#include <common/blindedpay.h>
+#include <common/bolt12.h>
+#include <common/onion.h>
+
+u8 **blinded_onion_hops(const tal_t *ctx,
+			struct amount_msat final_amount,
+			u32 final_cltv,
+			const struct blinded_path *path)
+{
+	u8 **onions = tal_arr(ctx, u8 *, tal_count(path->path));
+
+	assert(tal_count(onions) > 0);
+
+	for (size_t i = 0; i < tal_count(onions); i++) {
+		bool first = (i == 0);
+		bool final = (i == tal_count(onions) - 1);
+
+		/* BOLT-route-blinding #4:
+		 * - For every node inside a blinded route:
+		 *   - MUST include the `encrypted_data` provided by the
+		 *     recipient
+		 *   - For the first node in the blinded route:
+		 *     - MUST include the `blinding_point` provided by the
+		 *       recipient
+		 *   - If it is the final node:
+		 *     - MUST include `amt_to_forward` and `outgoing_cltv_value`.
+		 *   - Otherwise:
+		 *     - MUST NOT include `amt_to_forward` and
+		 *       `outgoing_cltv_value`.
+		 */
+		onions[i] = onion_blinded_hop(onions,
+					      final ? &final_amount : NULL,
+					      final ? &final_cltv : NULL,
+					      path->path[i]->encrypted_recipient_data,
+					      first ? &path->blinding : NULL);
+	}
+	return onions;
+}

common/blindedpay.h

@@ -0,0 +1,25 @@
+/* Code to create onion fragments to make payment down this struct blinded_path */
+#ifndef LIGHTNING_COMMON_BLINDEDPAY_H
+#define LIGHTNING_COMMON_BLINDEDPAY_H
+#include "config.h"
+#include <ccan/tal/tal.h>
+#include <common/amount.h>
+
+struct blinded_path;
+
+/**
+ * blinded_onion_hops - turn this path into a series of onion hops
+ * @ctx: context to allocate from
+ * @final_amount: amount we want to reach the end
+ * @final_cltv: cltv we want to at end
+ * @payinfo: fee and other restriction info
+ *
+ * This calls onion_nonfinal_hop and onion_final_hop to create onion
+ * blobs.
+ */
+u8 **blinded_onion_hops(const tal_t *ctx,
+			struct amount_msat final_amount,
+			u32 final_cltv,
+			const struct blinded_path *path);
+
+#endif /* LIGHTNING_COMMON_BLINDEDPAY_H */

common/onion.c

@@ -41,9 +41,7 @@ static u8 *make_tlv_hop(const tal_t *ctx,
 u8 *onion_nonfinal_hop(const tal_t *ctx,
 		       const struct short_channel_id *scid,
 		       struct amount_msat forward,
-		       u32 outgoing_cltv,
-		       const struct pubkey *blinding,
-		       const u8 *enctlv)
+		       u32 outgoing_cltv)
 {
 	struct tlv_tlv_payload *tlv = tlv_tlv_payload_new(tmpctx);
 
@@ -60,8 +58,6 @@ u8 *onion_nonfinal_hop(const tal_t *ctx,
 	tlv->amt_to_forward = &forward.millisatoshis; /* Raw: TLV convert */
 	tlv->outgoing_cltv_value = &outgoing_cltv;
 	tlv->short_channel_id = cast_const(struct short_channel_id *, scid);
-	tlv->blinding_point = cast_const(struct pubkey *, blinding);
-	tlv->encrypted_recipient_data = cast_const(u8 *, enctlv);
 	return make_tlv_hop(ctx, tlv);
 }
 
@@ -69,8 +65,6 @@ u8 *onion_final_hop(const tal_t *ctx,
 		    struct amount_msat forward,
 		    u32 outgoing_cltv,
 		    struct amount_msat total_msat,
-		    const struct pubkey *blinding,
-		    const u8 *enctlv,
 		    const struct secret *payment_secret,
 		    const u8 *payment_metadata)
 {
@@ -104,8 +98,26 @@ u8 *onion_final_hop(const tal_t *ctx,
 		tlv->payment_data = &tlv_pdata;
 	}
 	tlv->payment_metadata = cast_const(u8 *, payment_metadata);
-	tlv->blinding_point = cast_const(struct pubkey *, blinding);
+	return make_tlv_hop(ctx, tlv);
+}
+
+u8 *onion_blinded_hop(const tal_t *ctx,
+		      const struct amount_msat *amt_to_forward,
+		      const u32 *outgoing_cltv_value,
+		      const u8 *enctlv,
+		      const struct pubkey *blinding)
+{
+	struct tlv_tlv_payload *tlv = tlv_tlv_payload_new(tmpctx);
+
+	if (amt_to_forward) {
+		tlv->amt_to_forward
+			= cast_const(u64 *,
+				     &amt_to_forward->millisatoshis); /* Raw: TLV convert */
+	}
+	tlv->outgoing_cltv_value = cast_const(u32 *, outgoing_cltv_value);
 	tlv->encrypted_recipient_data = cast_const(u8 *, enctlv);
+	tlv->blinding_point = cast_const(struct pubkey *, blinding);
+
 	return make_tlv_hop(ctx, tlv);
 }
 

common/onion.h

@@ -26,20 +26,24 @@ struct onion_payload {
 u8 *onion_nonfinal_hop(const tal_t *ctx,
 		       const struct short_channel_id *scid,
 		       struct amount_msat forward,
-		       u32 outgoing_cltv,
-		       const struct pubkey *blinding,
-		       const u8 *enctlv);
+		       u32 outgoing_cltv);
 
 /* Note that this can fail if we supply payment_secret or payment_metadata and !use_tlv! */
 u8 *onion_final_hop(const tal_t *ctx,
 		    struct amount_msat forward,
 		    u32 outgoing_cltv,
 		    struct amount_msat total_msat,
-		    const struct pubkey *blinding,
-		    const u8 *enctlv,
 		    const struct secret *payment_secret,
 		    const u8 *payment_metadata);
 
+/* Blinding has more complex rules on what fields are encoded: this is the
+ * generic interface, as used by blindedpay.h */
+u8 *onion_blinded_hop(const tal_t *ctx,
+		      const struct amount_msat *amt_to_forward,
+		      const u32 *outgoing_cltv_value,
+		      const u8 *enctlv,
+		      const struct pubkey *blinding)
+	NON_NULL_ARGS(4);
 
 /**
  * onion_decode: decode payload from a decrypted onion.

common/route.c

@@ -102,10 +102,6 @@ static bool dijkstra_to_hops(struct route_hop **hops,
 	next = gossmap_nth_node(gossmap, c, !(*hops)[num_hops].direction);
 	gossmap_node_get_id(gossmap, next, &(*hops)[num_hops].node_id);
 
-	/* These are (ab)used by others. */
-	(*hops)[num_hops].blinding = NULL;
-	(*hops)[num_hops].enctlv = NULL;
-
 	if (!dijkstra_to_hops(hops, gossmap, dij, next, amount, cltv))
 		return false;
 

common/route.h

@@ -19,8 +19,6 @@ struct gossmap_node;
  * @node_id: the node_id of the destination of this hop.
  * @amount: amount to send through this hop.
  * @delay: total cltv delay at this hop.
- * @blinding: blinding key for this hop (if any)
- * @enctlv: encrypted TLV for this hop (if any)
  */
 struct route_hop {
 	struct short_channel_id scid;
@@ -28,8 +26,6 @@ struct route_hop {
 	struct node_id node_id;
 	struct amount_msat amount;
 	u32 delay;
-	struct pubkey *blinding;
-	u8 *enctlv;
 };
 
 /* Can c carry amount in dir? */

devtools/onion.c

@@ -79,15 +79,12 @@ static void do_generate(int argc, char **argv,
 				sphinx_add_hop_has_length(sp, &path[i],
 					       take(onion_final_hop(NULL,
 								    amt, i, amt,
-								    NULL, NULL,
 								    NULL, NULL)));
 			else
 				sphinx_add_hop_has_length(sp, &path[i],
 					       take(onion_nonfinal_hop(NULL,
 								       &scid,
-								       amt, i,
-								       NULL,
-								       NULL)));
+								       amt, i)));
 		}
 	}
 

lightningd/pay.c

@@ -1172,9 +1172,7 @@ send_payment(struct lightningd *ld,
 			       take(onion_nonfinal_hop(NULL,
 					&route[i + 1].scid,
 					route[i + 1].amount,
-					base_expiry + route[i + 1].delay,
-					route[i].blinding,
-					route[i].enctlv)));
+					base_expiry + route[i + 1].delay)));
 	}
 
 	/* And finally set the final hop to the special values in
@@ -1193,7 +1191,7 @@ send_payment(struct lightningd *ld,
 	onion = onion_final_hop(cmd,
 				route[i].amount,
 				base_expiry + route[i].delay,
-				total_msat, route[i].blinding, route[i].enctlv,
+				total_msat,
 				payment_secret, payment_metadata);
 	if (!onion) {
 		return command_fail(cmd, PAY_DESTINATION_PERM_FAIL,
@@ -1381,8 +1379,6 @@ static struct command_result *param_route_hops(struct command *cmd,
 		struct node_id *id;
 		struct short_channel_id *channel;
 		unsigned *delay, *direction;
-		struct pubkey *blinding;
-		u8 *enctlv;
 		int *ignored;
 
 		if (!param(cmd, buffer, t,
@@ -1394,8 +1390,6 @@ static struct command_result *param_route_hops(struct command *cmd,
 			   /* Allowed (getroute supplies it) but ignored */
 			   p_opt("direction", param_number, &direction),
 			   p_opt("style", param_route_hop_style, &ignored),
-			   p_opt("blinding", param_pubkey, &blinding),
-			   p_opt("encrypted_recipient_data", param_bin_from_hex, &enctlv),
 			   NULL))
 			return command_param_failed();
 
@@ -1403,8 +1397,6 @@ static struct command_result *param_route_hops(struct command *cmd,
 		(*hops)[i].node_id = *id;
 		(*hops)[i].delay = *delay;
 		(*hops)[i].scid = *channel;
-		(*hops)[i].blinding = blinding;
-		(*hops)[i].enctlv = enctlv;
 	}
 
 	return NULL;