Fix of TODO regarding explicitly having to add the 00 byte for non segwit inputs in segwit transactions

bitcoinutils/transactions.py

@@ -310,7 +310,7 @@ def from_raw(txoutputrawhex: Union[str, bytes], cursor: int = 0, has_segwit: boo
             txoutputraw = txoutputrawhex
         else:
             raise TypeError("Input must be a hexadecimal string or bytes")
-        
+
 
         # Unpack the amount of the TxOutput directly in bytes
         amount_format = "<Q"  # Little-endian unsigned long long (8 bytes)
@@ -493,6 +493,8 @@ class Transaction:
         Calculates the tx segwit size
     copy()
         creates a copy of the object (classmethod)
+    set_witness(txin_index, witness)
+        sets the witness for a particular input index
     get_transaction_digest(txin_index, script, sighash)
         returns the transaction input's digest that is to be signed according
     get_transaction_segwit_digest(txin_index, script, amount, sighash)
@@ -552,7 +554,7 @@ def from_raw(rawtxhex: Union[str, bytes]):
             rawtx = rawtxhex
         else:
             raise TypeError("Input must be a hexadecimal string or bytes")
-        
+
 
         # Read version (4 bytes)
         version = rawtx[0:4]
@@ -639,6 +641,26 @@ def copy(cls, tx: "Transaction") -> "Transaction":
         wits = [TxWitnessInput.copy(witness) for witness in tx.witnesses]
         return cls(ins, outs, tx.locktime, tx.version, tx.has_segwit, wits)
 
+    # this sets empty witness slots (if necessary)
+    # makes length of witness equal to the number of inputs, to prevent expliclty defining empty witness inputs
+    # for non segwit inputs
+    def set_witness(self, txin_index: int, witness: TxWitnessInput):
+        """Safely set a witness at the specified index"""
+        if not self.has_segwit:
+            raise RuntimeError(
+                "Transaction should be segwit in order to set segwit slots"
+            )
+        witness_len = len(self.witnesses)
+        input_len = len(self.inputs)
+        if witness_len < input_len:
+            # append empty witness inputs if input_len>witness_len
+            for _ in range(input_len - witness_len):
+                self.witnesses.append(TxWitnessInput([]))
+
+        if txin_index < 0 or txin_index >= len(self.inputs):
+            raise IndexError("txin_index out of range")
+        self.witnesses[txin_index] = witness
+
     def get_transaction_digest(
         self, txin_index: int, script: Script, sighash: int = SIGHASH_ALL
     ):

examples/spend_multi_input_p2tr_and_p2pkh.py

@@ -84,12 +84,10 @@ def main():
     sig2 = priv2.sign_input(tx, 1, utxos_script_pubkeys[1])
     sig3 = priv3.sign_taproot_input(tx, 2, utxos_script_pubkeys, amounts)
 
-    tx.witnesses.append(TxWitnessInput([sig1]))
+    #set witness sets the witness at a particular input index
+    tx.set_witness(0, TxWitnessInput([sig1]))
     txin2.script_sig = Script([sig2, pub2.to_hex()])
-    # the second input is not segwit but we still need to add an empty
-    # witness input script
-    tx.witnesses.append(TxWitnessInput([]))
-    tx.witnesses.append(TxWitnessInput([sig3]))
+    tx.set_witness(2, TxWitnessInput([sig3]))
 
     # print raw signed transaction ready to be broadcasted
     print("\nRaw signed transaction:\n" + tx.serialize())

run_all_examples.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-for fil in ./examples/*.py; do 
+for fil in ./examples/*.py; do
   python $fil;
   sleep 2;
 done