common: update to latest route-blinding spec.

```
make check-source-bolt CHECK_BOLT_PREFIX="--prefix=BOLT-route-blinding" BOLTVERSION=guilt/offers
```

Other than textual changes, this does:

1. Ensures we put total_amount_msat in onion final hop (reported by @t-bast).
2. Require that they put total_amount_msat in onion final hop.
3. Return `invalid_onion_blinding` exactly as defined by the spec (i.e. less
   aggressive when we're the final hop) (also reported by @t-bast, but I already
   knew).

See: ElementsProject#5823
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-EXPERIMENTAL: `offers` breaking blinded payments change (total_amount_sat required, Eclair compat)

common/blindedpay.c

@@ -7,6 +7,7 @@
 u8 **blinded_onion_hops(const tal_t *ctx,
 			struct amount_msat final_amount,
 			u32 final_cltv,
+			struct amount_msat total_amount,
 			const struct blinded_path *path)
 {
 	u8 **onions = tal_arr(ctx, u8 *, tal_count(path->path));
@@ -25,12 +26,12 @@ u8 **blinded_onion_hops(const tal_t *ctx,
 		 *     - MUST include the `blinding_point` provided by the
 		 *       recipient in `current_blinding_point`
 		 *   - If it is the final node:
-		 *     - MUST include `amt_to_forward` and `outgoing_cltv_value`.
-		 *     - MUST include `total_amount_msat` when using `basic_mpp`.
+		 *     - MUST include `amt_to_forward`, `outgoing_cltv_value` and `total_amount_msat`.
 		 *   - MUST NOT include any other tlv field.
 		 */
 		onions[i] = onion_blinded_hop(onions,
 					      final ? &final_amount : NULL,
+					      final ? &total_amount : NULL,
 					      final ? &final_cltv : NULL,
 					      path->path[i]->encrypted_recipient_data,
 					      first ? &path->blinding : NULL);

common/blindedpay.h

@@ -12,6 +12,7 @@ struct blinded_path;
  * @ctx: context to allocate from
  * @final_amount: amount we want to reach the end
  * @final_cltv: cltv we want to at end
+ * @total_amount: amount of all parts together.
  * @payinfo: fee and other restriction info
  *
  * This calls onion_nonfinal_hop and onion_final_hop to create onion
@@ -20,6 +21,7 @@ struct blinded_path;
 u8 **blinded_onion_hops(const tal_t *ctx,
 			struct amount_msat final_amount,
 			u32 final_cltv,
+			struct amount_msat total_amount,
 			const struct blinded_path *path);
 
 #endif /* LIGHTNING_COMMON_BLINDEDPAY_H */

common/onion_decode.c

@@ -102,8 +102,8 @@ static bool handle_blinded_terminal(struct onion_payload *p,
 	}
 
 	/* BOLT-route-blinding #4:
-	 *   - MUST return an error if `amt_to_forward` or
-	 *     `outgoing_cltv_value` are not present.
+	 *   - MUST return an error if `amt_to_forward`, `outgoing_cltv_value`
+	 *     or `total_amount_msat` are not present.
 	 *   - MUST return an error if `amt_to_forward` is below what it expects
 	 *     for the payment.
 	 */
@@ -117,6 +117,11 @@ static bool handle_blinded_terminal(struct onion_payload *p,
 		return false;
 	}
 
+	if (!tlv->total_amount_msat) {
+		*failtlvtype = TLV_TLV_PAYLOAD_TOTAL_AMOUNT_MSAT;
+		return false;
+	}
+
 	p->amt_to_forward = amount_msat(*tlv->amt_to_forward);
 	p->outgoing_cltv = *tlv->outgoing_cltv_value;
 

common/onion_encode.c

@@ -103,6 +103,7 @@ u8 *onion_final_hop(const tal_t *ctx,
 
 u8 *onion_blinded_hop(const tal_t *ctx,
 		      const struct amount_msat *amt_to_forward,
+		      const struct amount_msat *total_amount_msat,
 		      const u32 *outgoing_cltv_value,
 		      const u8 *enctlv,
 		      const struct pubkey *blinding)
@@ -114,6 +115,11 @@ u8 *onion_blinded_hop(const tal_t *ctx,
 			= cast_const(u64 *,
 				     &amt_to_forward->millisatoshis); /* Raw: TLV convert */
 	}
+	if (total_amount_msat) {
+		tlv->total_amount_msat
+			= cast_const(u64 *,
+				     &total_amount_msat->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);

common/onion_encode.h

@@ -53,8 +53,9 @@ u8 *onion_final_hop(const tal_t *ctx,
  * generic interface, as used by blindedpay.h */
 u8 *onion_blinded_hop(const tal_t *ctx,
 		      const struct amount_msat *amt_to_forward,
+		      const struct amount_msat *total_amount_msat,
 		      const u32 *outgoing_cltv_value,
 		      const u8 *enctlv,
 		      const struct pubkey *blinding)
-	NON_NULL_ARGS(4);
+	NON_NULL_ARGS(5);
 #endif /* LIGHTNING_COMMON_ONION_ENCODE_H */

common/test/run-route_blinding_onion_test.c

@@ -106,7 +106,7 @@ int main(int argc, char *argv[])
 	}
 
 	/* FIXME: These amounts / scid should be in test vectors! */
-	onionhops = blinded_onion_hops(tmpctx, AMOUNT_MSAT(200), 700, bpath);
+	onionhops = blinded_onion_hops(tmpctx, AMOUNT_MSAT(200), 700, AMOUNT_MSAT(200), bpath);
 	assert(mk_short_channel_id(&initscid, 0, 0, 10));
 
 	/* Prepend Alice: poor thing doesn't speak blinding! */

lightningd/peer_htlcs.c

@@ -92,20 +92,33 @@ static bool htlc_out_update_state(struct channel *channel,
 	return true;
 }
 
+/* BOLT-route-blinding #4:
+ *   - if `blinding_point` is set in the incoming `update_add_htlc`:
+ *     - MUST return an `invalid_onion_blinding` error.
+ *   - if `current_blinding_point` is set in the onion payload and it is not the
+ *     final node:
+ *     - MUST return an `invalid_onion_blinding` error.
+ */
+static bool blind_error_return(const struct htlc_in *hin)
+{
+	if (hin->blinding)
+		return true;
+
+	if (hin->payload
+	    && hin->payload->blinding
+	    && !hin->payload->final)
+		return true;
+
+	return false;
+}
+
 static struct failed_htlc *mk_failed_htlc_badonion(const tal_t *ctx,
 						   const struct htlc_in *hin,
 						   enum onion_wire badonion)
 {
 	struct failed_htlc *f = tal(ctx, struct failed_htlc);
 
-	/* BOLT-route-blinding #4:
-	 * - If `blinding_point` is set in the incoming `update_add_htlc`:
-	 *    - MUST return `invalid_onion_blinding` for any local error or
-	 *      other downstream errors.
-	 */
-	/* FIXME: That's not enough!  Don't leak information about forward
-	 * failures either! */
-	if (hin->blinding || (hin->payload && hin->payload->blinding))
+	if (blind_error_return(hin))
 		badonion = WIRE_INVALID_ONION_BLINDING;
 
 	f->id = hin->key.id;
@@ -123,12 +136,7 @@ static struct failed_htlc *mk_failed_htlc(const tal_t *ctx,
 {
 	struct failed_htlc *f = tal(ctx, struct failed_htlc);
 
-	/* BOLT-route-blinding #4:
-	 * - If `blinding_point` is set in the incoming `update_add_htlc`:
-	 *    - MUST return `invalid_onion_blinding` for any local error or
-	 *      other downstream errors.
-	 */
-	if (hin->blinding) {
+	if (blind_error_return(hin)) {
 		return mk_failed_htlc_badonion(ctx, hin,
 					       WIRE_INVALID_ONION_BLINDING);
 	}

plugins/libplugin-pay.c

@@ -1671,7 +1671,8 @@ static void payment_add_blindedpath(const tal_t *ctx,
 {
 	/* It's a bit of a weird API for us, so we convert it back to
 	 * the struct tlv_tlv_payload */
-	u8 **tlvs = blinded_onion_hops(tmpctx, final_amt, final_cltv, bpath);
+	u8 **tlvs = blinded_onion_hops(tmpctx, final_amt, final_cltv,
+				       final_amt, bpath);
 
 	for (size_t i = 0; i < tal_count(tlvs); i++) {
 		const u8 *cursor = tlvs[i];

plugins/test/run-route-overlong.c

@@ -12,6 +12,7 @@
 u8 **blinded_onion_hops(const tal_t *ctx UNNEEDED,
 			struct amount_msat final_amount UNNEEDED,
 			u32 final_cltv UNNEEDED,
+			struct amount_msat total_amount UNNEEDED,
 			const struct blinded_path *path UNNEEDED)
 { fprintf(stderr, "blinded_onion_hops called!\n"); abort(); }
 /* Generated stub for command_finished */