fuzz-tests: Make `fuzz-bolt12-offer-decode` roundrip

diff --git a/tests/fuzz/fuzz-bolt12-offer-decode.c b/tests/fuzz/fuzz-bolt12-offer-decode.c
index d062b95a..4ab229c6 100644
--- a/tests/fuzz/fuzz-bolt12-offer-decode.c
+++ b/tests/fuzz/fuzz-bolt12-offer-decode.c
@@ -1,4 +1,6 @@
 #include "config.h"
+#include <assert.h>
+#include <ccan/mem/mem.h>
 #include <common/bolt12.h>
 #include <common/utils.h>
 #include <stddef.h>
@@ -7,12 +9,163 @@
 
 const char *bech32_hrp = "lno";
 
+static bool sciddir_or_pubkey_eq(const struct sciddir_or_pubkey *a,
+				 const struct sciddir_or_pubkey *b)
+{
+	if (a->is_pubkey != b->is_pubkey)
+		return false;
+	if (a->is_pubkey)
+		return pubkey_eq(&a->pubkey, &b->pubkey);
+	else
+		return short_channel_id_dir_eq(&a->scidd, &b->scidd);
+}
+
+static bool recurrence_eq(const struct recurrence *a, const struct recurrence *b)
+{
+	return a->time_unit == b->time_unit && a->period == b->period;
+}
+
+static bool recurrence_paywindow_eq(const struct recurrence_paywindow *a,
+                                    const struct recurrence_paywindow *b)
+{
+	return a->seconds_before == b->seconds_before && a->seconds_after == b->seconds_after;
+}
+
+static bool recurrence_base_eq(const struct recurrence_base *a,
+                               const struct recurrence_base *b)
+{
+	return a->basetime == b->basetime && a->proportional_amount == b->proportional_amount;
+}
+
+static bool blinded_path_eq(const struct blinded_path *a,
+                            const struct blinded_path *b)
+{
+	if (!sciddir_or_pubkey_eq(&a->first_node_id, &b->first_node_id))
+		return false;
+	if (!pubkey_eq(&a->first_path_key, &b->first_path_key))
+		return false;
+	if (tal_count(a->path) != tal_count(b->path))
+		return false;
+	for (size_t i = 0; i < tal_count(a->path); i++) {
+		const struct blinded_path_hop *h1 = a->path[i];
+		const struct blinded_path_hop *h2 = b->path[i];
+		if (h1 == h2)
+			continue;
+		if (!h1 || !h2)
+			return false;
+		if (!pubkey_eq(&h1->blinded_node_id, &h2->blinded_node_id))
+			return false;
+		if (tal_bytelen(h1->encrypted_recipient_data) !=
+			tal_bytelen(h2->encrypted_recipient_data))
+			return false;
+		if (memcmp(h1->encrypted_recipient_data, h2->encrypted_recipient_data,
+				tal_bytelen(h1->encrypted_recipient_data)) != 0)
+			return false;
+	}
+	return true;
+}
+
+static bool tlv_offer_eq(const struct tlv_offer *a, const struct tlv_offer *b)
+{
+
+#define PTR_EQ(field, eqfn)							\
+do {										\
+	if (a->field != b->field) {						\
+		if (!a->field || !b->field)					\
+			return false;						\
+		if (!eqfn(a->field, b->field))					\
+			return false;						\
+        }									\
+} while (0)
+
+#define MEM_EQ(field)								\
+do {										\
+	if (a->field != b->field) {						\
+		if (!a->field || !b->field)					\
+			return false;						\
+		if (tal_bytelen(a->field) != tal_bytelen(b->field))		\
+			return false;						\
+		if (memcmp(a->field, b->field, tal_bytelen(a->field)) != 0)	\
+			return false;						\
+        }									\
+} while (0)
+
+#define VAL_EQ(field)								\
+do {										\
+	if (a->field != b->field) {						\
+		if (!a->field || !b->field)					\
+			return false;						\
+		if (*a->field != *b->field)					\
+			return false;						\
+	}									\
+} while (0)
+
+#define ARR_EQ(field, eqfn)							\
+do {										\
+	if (a->field != b->field) {						\
+		if (!a->field || !b->field)					\
+			return false;						\
+		if (tal_count(a->field) != tal_count(b->field))			\
+			return false;						\
+		for (size_t i = 0; i < tal_count(a->field); i++) {		\
+			if (!eqfn(&a->field[i], &b->field[i]))			\
+				return false;					\
+		}								\
+        }									\
+} while (0)
+
+#define PTR_ARR_EQ(field, eqfn)							\
+do {										\
+	if (a->field != b->field) {						\
+		if (!a->field || !b->field)					\
+			return false;						\
+		if (tal_count(a->field) != tal_count(b->field))			\
+			return false;						\
+		for (size_t i = 0; i < tal_count(a->field); i++) {		\
+			if (!eqfn(a->field[i], b->field[i]))			\
+				return false;					\
+		}								\
+	}									\
+} while (0)
+
+	ARR_EQ(offer_chains, bitcoin_blkid_eq);
+	MEM_EQ(offer_metadata);
+	MEM_EQ(offer_currency);
+	VAL_EQ(offer_amount);
+	MEM_EQ(offer_description);
+	MEM_EQ(offer_features);
+	VAL_EQ(offer_absolute_expiry);
+	PTR_ARR_EQ(offer_paths, blinded_path_eq);
+	MEM_EQ(offer_issuer);
+	VAL_EQ(offer_quantity_max);
+	PTR_EQ(offer_issuer_id, pubkey_eq);
+	PTR_EQ(offer_recurrence_compulsory, recurrence_eq);
+	PTR_EQ(offer_recurrence_optional, recurrence_eq);
+	PTR_EQ(offer_recurrence_base, recurrence_base_eq);
+	PTR_EQ(offer_recurrence_paywindow, recurrence_paywindow_eq);
+	VAL_EQ(offer_recurrence_limit);
+
+	return true;
+}
+
 void run(const u8 *data, size_t size)
 {
-	char *fail;
+	struct tlv_offer *offer, *decoded_offer;
+	char *fail = NULL, *encoded_offer;
+
+	offer = offer_decode(tmpctx, (const char *)data, size,
+			/*feature_set=*/NULL, /*must_be_chain=*/NULL, &fail);
+	if (!offer)
+		goto cleanup;
+
+	encoded_offer = offer_encode(tmpctx, offer);
 
-	offer_decode(tmpctx, (const char *)data, size, /*feature_set=*/NULL,
-		     /*must_be_chain=*/NULL, &fail);
+	decoded_offer = offer_decode(tmpctx, encoded_offer, strlen(encoded_offer),
+					NULL, NULL, &fail);
+	assert(!fail);
+	assert(decoded_offer);
+	assert(tlv_offer_eq(offer, decoded_offer));
 
+cleanup:
 	clean_tmpctx();
 }