Add Zcash Sapling support (#624)

electrumx/lib/tx.py

@@ -320,26 +320,47 @@ class TxJoinSplit(namedtuple("Tx", "version inputs outputs locktime")):
 class DeserializerZcash(DeserializerEquihash):
     def read_tx(self):
         header = self._read_le_uint32()
-        overwinterd = ((header >> 31) == 1)
-        if overwinterd:
+        overwintered = ((header >> 31) == 1)
+        if overwintered:
             version = header & 0x7fffffff
-            self._read_le_uint32()  # versionGroupId
+            self.cursor += 4  # versionGroupId
         else:
             version = header
+
+        is_overwinter_v3 = version == 3
+        is_sapling_v4 = version == 4
+
         base_tx = TxJoinSplit(
             version,
             self._read_inputs(),    # inputs
             self._read_outputs(),   # outputs
             self._read_le_uint32()  # locktime
         )
-        if base_tx.version >= 3:
-            self._read_le_uint32()  # expiryHeight
+
+        if is_overwinter_v3 or is_sapling_v4:
+            self.cursor += 4  # expiryHeight
+
+        has_shielded = False
+        if is_sapling_v4:
+            self.cursor += 8  # valueBalance
+            shielded_spend_size = self._read_varint()
+            self.cursor += shielded_spend_size * 384  # vShieldedSpend
+            shielded_output_size = self._read_varint()
+            self.cursor += shielded_output_size * 948  # vShieldedOutput
+            has_shielded = shielded_spend_size > 0 or shielded_output_size > 0
+
         if base_tx.version >= 2:
             joinsplit_size = self._read_varint()
             if joinsplit_size > 0:
-                self.cursor += joinsplit_size * 1802  # JSDescription
+                joinsplit_desc_len = 1506 + (192 if is_sapling_v4 else 296)
+                # JSDescription
+                self.cursor += joinsplit_size * joinsplit_desc_len
                 self.cursor += 32  # joinSplitPubKey
                 self.cursor += 64  # joinSplitSig
+
+        if is_sapling_v4 and has_shielded:
+            self.cursor += 64  # bindingSig
+
         return base_tx