bolt11: reorder invoice production to match test vectors.

After this, we can exactly reproduce the vectors (in DEVELOPER mode).

1. Move payment_metadata position to match test vector.
2. Create flag to suppress `c` field production.
3. Some vectors put secret before payment_hash, hack that in.

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

common/bolt11.c

@@ -11,6 +11,25 @@
 #include <inttypes.h>
 #include <lightningd/lightningd.h>
 
+#if DEVELOPER
+bool dev_bolt11_no_c_generation;
+
+/* For test vectors, older ones put p before s. */
+static bool modern_order(const struct bolt11 *b11)
+{
+	if (!b11->description)
+		return true;
+	if (streq(b11->description,
+		  "Blockstream Store: 88.85 USD for Blockstream Ledger Nano S x 1, \"Back In My Day\" Sticker x 2, \"I Got Lightning Working\" Sticker x 2 and 1 more items"))
+		return false;
+	if (streq(b11->description, "coffee beans"))
+		return false;
+	if (streq(b11->description, "payment metadata inside"))
+		return false;
+	return true;
+}
+#endif
+
 struct multiplier {
 	const char letter;
 	/* We can't represent p postfix to msat, so we multiply this by 10 */
@@ -996,6 +1015,8 @@ static void encode_x(u5 **data, u64 expiry)
 
 static void encode_c(u5 **data, u16 min_final_cltv_expiry)
 {
+	if (IFDEV(dev_bolt11_no_c_generation, false))
+		return;
 	push_varlen_field(data, 'c', min_final_cltv_expiry);
 }
 
@@ -1154,6 +1175,13 @@ char *bolt11_encode_(const tal_t *ctx,
 	 */
 	push_varlen_uint(&data, b11->timestamp, 35);
 
+	/* This is a hack to match the test vectors, *some* of which
+	 * order differently! */
+	if (IFDEV(modern_order(b11), true)) {
+		if (b11->payment_secret)
+			encode_s(&data, b11->payment_secret);
+	}
+
 	/* BOLT #11:
 	 *
 	 * if a writer offers more than one of any field type,
@@ -1174,23 +1202,25 @@ char *bolt11_encode_(const tal_t *ctx,
 	else if (b11->description)
 		encode_d(&data, b11->description);
 
+	if (b11->metadata)
+		encode_m(&data, b11->metadata);
+
 	if (n_field)
 		encode_n(&data, &b11->receiver_id);
 
+	if (IFDEV(!modern_order(b11), false)) {
+		if (b11->payment_secret)
+			encode_s(&data, b11->payment_secret);
+	}
+
 	if (b11->expiry != DEFAULT_X)
 		encode_x(&data, b11->expiry);
 
-	if (b11->metadata)
-		encode_m(&data, b11->metadata);
-
 	/* BOLT #11:
 	 *   - MUST include one `c` field (`min_final_cltv_expiry`).
 	 */
 	encode_c(&data, b11->min_final_cltv_expiry);
 
-	if (b11->payment_secret)
-		encode_s(&data, b11->payment_secret);
-
 	for (size_t i = 0; i < tal_count(b11->fallbacks); i++)
 		encode_f(&data, b11->fallbacks[i]);
 

common/bolt11.h

@@ -125,4 +125,9 @@ char *bolt11_encode_(const tal_t *ctx,
 				secp256k1_ecdsa_recoverable_signature *rsig), \
 		       (arg))
 
+#if DEVELOPER
+/* Flag for tests to suppress `min_final_cltv_expiry` field generation, to match test vectors */
+extern bool dev_bolt11_no_c_generation;
+#endif
+
 #endif /* LIGHTNING_COMMON_BOLT11_H */

common/test/run-bolt11.c

@@ -49,7 +49,6 @@ static void test_b11(const char *b11str,
 {
 	struct bolt11 *b11;
 	char *fail;
-	char *reproduce;
 	struct bolt11_field *b11_extra, *expect_extra;
 
 	b11 = bolt11_decode(tmpctx, b11str, NULL, hashed_desc,
@@ -115,20 +114,22 @@ static void test_b11(const char *b11str,
 	assert(!expect_extra);
 
 	/* FIXME: Spec changed to require c fields, but test vectors don't! */
-	if (b11->min_final_cltv_expiry == 18)
-		return;
+
+#if DEVELOPER
+	char *reproduce;
+
+	dev_bolt11_no_c_generation = (b11->min_final_cltv_expiry == 18);
 
 	/* Also blockstream store example signature doesn't match? */
 	/* Re-encode to check */
 	reproduce = bolt11_encode(tmpctx, b11, false, test_sign, NULL);
-#if 0
 	for (size_t i = 0; i < strlen(reproduce); i++) {
 		if (reproduce[i] != b11str[i]
 		    && reproduce[i] != tolower(b11str[i]))
 			abort();
 	}
-#endif
 	assert(strlen(reproduce) == strlen(b11str));
+#endif
 }
 
 int main(int argc, char *argv[])
@@ -478,8 +479,13 @@ int main(int argc, char *argv[])
 	set_feature_bit(&b11->features, 100);
 	badstr = bolt11_encode(tmpctx, b11, false, test_sign, NULL);
 
-	/* FIXME: above has missing c field! */
-	assert(streq(badstr, "lnbc25m1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5vdhkven9v5sxyetpdeescqpjsp5zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zygs9q4psqqqqqqqqqqqqqqqqsgqjckhuumq7mk7pdua9s6umdg34sjhlju9qgcvclxl35guw3dhhyrrtnmudz3kspyqk6k6r7thyzyrleq9s9lmgh59zlc49mc3nd7ngecqllqtym"));
+	/* Needs DEVELOPER to munge this into BOLT example order! */
+#if DEVELOPER
+	assert(streq(badstr, "lnbc25m1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5vdhkven9v5sxyetpdeessp5zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zygs9q4psqqqqqqqqqqqqqqqqsgqtqyx5vggfcsll4wu246hz02kp85x4katwsk9639we5n5yngc3yhqkm35jnjw4len8vrnqnf5ejh0mzj9n3vz2px97evektfm2l6wqccp3y7372"));
+#else
+	assert(streq(badstr, "lnbc25m1pvjluezsp5zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zygspp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5vdhkven9v5sxyetpdeescqpj9q4psqqqqqqqqqqqqqqqqsgqf0nf0agw8xncpemlreh8wl0z5exhz3pky094lu7pf62nvcxq2vljzhhw69xfdftrgm0jklut3h25nlsfw5prz4c0pjy46xyer0k85hqpnathfq"));
+#endif
+
 	/* Empty set of allowed bits, ensures this fails! */
 	fset = tal(tmpctx, struct feature_set);
 	fset->bits[BOLT11_FEATURE] = tal_arr(fset, u8, 0);