Detect if transaction is elements when possible

Do not allow WALLY_TX_FLAG_USE_ELEMENTS bit to be set for
wally_tx_to_* as is it already possible to determine if the
transaction is elements.

Author: LeoComandini

src/ctest/test_elements_tx.c

@@ -43,10 +43,10 @@ static bool tx_roundtrip(const char *tx_hex, const char *sighash_hex)
     size_t i;
     size_t is_elements;
     int ret;
-    const uint32_t flags = WALLY_TX_FLAG_USE_WITNESS | WALLY_TX_FLAG_USE_ELEMENTS;
+    const uint32_t flags = WALLY_TX_FLAG_USE_WITNESS;
 
     /* Unserialize and serialize the tx and verify they match */
-    ret = wally_tx_from_hex(tx_hex, flags, &tx);
+    ret = wally_tx_from_hex(tx_hex, flags | WALLY_TX_FLAG_USE_ELEMENTS, &tx);
     check_ret(ret);
 
     ret = wally_tx_to_hex(tx, flags, &new_hex);
@@ -170,12 +170,12 @@ static bool tx_coinbase(const char *tx_hex)
 {
     struct wally_tx *tx;
     char *new_hex;
-    const uint32_t flags = WALLY_TX_FLAG_USE_WITNESS | WALLY_TX_FLAG_USE_ELEMENTS;
+    const uint32_t flags = WALLY_TX_FLAG_USE_WITNESS;
     size_t is_elements, is_coinbase;
     int ret;
 
     /* Unserialize and serialize the tx and verify they match */
-    ret = wally_tx_from_hex(tx_hex, flags, &tx);
+    ret = wally_tx_from_hex(tx_hex, flags | WALLY_TX_FLAG_USE_ELEMENTS, &tx);
     check_ret(ret);
 
     ret = wally_tx_to_hex(tx, flags, &new_hex);
@@ -207,12 +207,12 @@ static bool tx_pegin(const char *tx_hex, const char **tx_pegin_wit_hex, size_t n
     struct wally_tx_witness_stack *pegin_wit;
     struct wally_tx_witness_item *item;
     char *new_hex;
-    const uint32_t flags = WALLY_TX_FLAG_USE_WITNESS | WALLY_TX_FLAG_USE_ELEMENTS;
+    const uint32_t flags = WALLY_TX_FLAG_USE_WITNESS;
     size_t is_elements, is_pegin, siz, i;
     int ret;
 
     /* Unserialize and serialize the tx and verify they match */
-    ret = wally_tx_from_hex(tx_hex, flags, &tx);
+    ret = wally_tx_from_hex(tx_hex, flags | WALLY_TX_FLAG_USE_ELEMENTS, &tx);
     check_ret(ret);
 
     ret = wally_tx_to_hex(tx, flags, &new_hex);

src/swig_python/contrib/elements_tx.py

@@ -82,7 +82,13 @@ def test_tx(self):
         tx_add_elements_raw_output(tx, script, None, ct_value, None, None, None, 0)
         size = tx_get_length(tx, 0)
         vsize = tx_vsize_from_weight(tx_get_weight(tx))
-        tx_hex = tx_to_hex(tx, WALLY_TX_FLAG_USE_WITNESS|WALLY_TX_FLAG_USE_ELEMENTS)
+        tx_hex = tx_to_hex(tx, WALLY_TX_FLAG_USE_WITNESS)
+        tx_bytes = tx_to_bytes(tx, WALLY_TX_FLAG_USE_WITNESS)
+        self.assertEqual(tx_hex, hex_from_bytes(tx_bytes))
+        with self.assertRaises(ValueError):
+            tx_to_hex(tx, WALLY_TX_FLAG_USE_ELEMENTS)
+        with self.assertRaises(ValueError):
+            tx_to_bytes(tx, WALLY_TX_FLAG_USE_ELEMENTS)
 
     def test_coinbase(self):
         txhash, seq, script = bytearray(b'\x00'*32), 0xffffffff, b'0000'

src/test/test_transaction.py

@@ -37,6 +37,7 @@ def test_serialization(self):
         for args in [
             (TX_FAKE_HEX[:9]+utf8('0')+TX_FAKE_HEX[92:], 0, pointer(wally_tx())), # No inputs
             (TX_FAKE_HEX[:93]+utf8('0')+TX_FAKE_HEX[112:], 0, pointer(wally_tx())), # No outputs
+            (TX_FAKE_HEX, 2, pointer(wally_tx())), # Elements flag must not be set for serialization
         ]:
             self.assertEqual(WALLY_OK, wally_tx_from_hex(*args))
             self.assertEqual(WALLY_EINVAL, wally_tx_to_hex(args[2][0], 0)[0])

src/transaction.c

@@ -2146,8 +2146,13 @@ int wally_tx_to_bytes(const struct wally_tx *tx, uint32_t flags,
                       unsigned char *bytes_out, size_t len,
                       size_t *written)
 {
-    return tx_to_bytes(tx, NULL, flags & ~WALLY_TX_FLAG_USE_ELEMENTS, bytes_out, len, written,
-                       flags & WALLY_TX_FLAG_USE_ELEMENTS);
+    size_t is_elements = 0;
+
+#ifdef BUILD_ELEMENTS
+    if (wally_tx_is_elements(tx, &is_elements) != WALLY_OK)
+        return WALLY_EINVAL;
+#endif
+    return tx_to_bytes(tx, NULL, flags, bytes_out, len, written, is_elements);
 }
 
 static int tx_to_hex(const struct wally_tx *tx, uint32_t flags,
@@ -2182,8 +2187,13 @@ static int tx_to_hex(const struct wally_tx *tx, uint32_t flags,
 int wally_tx_to_hex(const struct wally_tx *tx, uint32_t flags,
                     char **output)
 {
-    return tx_to_hex(tx, flags & ~WALLY_TX_FLAG_USE_ELEMENTS, output,
-                     flags & WALLY_TX_FLAG_USE_ELEMENTS);
+    size_t is_elements = 0;
+
+#ifdef BUILD_ELEMENTS
+    if (wally_tx_is_elements(tx, &is_elements) != WALLY_OK)
+        return WALLY_EINVAL;
+#endif
+    return tx_to_hex(tx, flags, output, is_elements);
 }
 
 static int analyze_tx(const unsigned char *bytes, size_t bytes_len,