Add more details to the message of expection when UTxO selectors fail

Author: cffls

pycardano/txbuilder.py

@@ -608,10 +608,12 @@ def build(self, change_address: Optional[Address] = None) -> TransactionBody:
         # When there are positive coin or native asset quantity in unfulfilled Value
         if Value() < unfulfilled_amount:
             additional_utxo_pool = []
+            additional_amount = Value()
             for address in self.input_addresses:
                 for utxo in self.context.utxos(str(address)):
                     if utxo not in selected_utxos and utxo not in self.excluded_inputs:
                         additional_utxo_pool.append(utxo)
+                        additional_amount += utxo.output.amount
 
             for i, selector in enumerate(self.utxo_selectors):
                 try:
@@ -631,7 +633,28 @@ def build(self, change_address: Optional[Address] = None) -> TransactionBody:
                         logger.info(e)
                         logger.info(f"{selector} failed. Trying next selector.")
                     else:
-                        raise UTxOSelectionException("All UTxO selectors failed.")
+                        trimmed_additional_amount = Value(
+                            additional_amount.coin,
+                            additional_amount.multi_asset.filter(
+                                lambda p, n, v: p in requested_amount.multi_asset
+                                and n in requested_amount.multi_asset[p]
+                            ),
+                        )
+                        diff = (
+                            requested_amount
+                            - trimmed_selected_amount
+                            - trimmed_additional_amount
+                        )
+                        diff.multi_asset = diff.multi_asset.filter(
+                            lambda p, n, v: v > 0
+                        )
+                        raise UTxOSelectionException(
+                            f"All UTxO selectors failed.\n"
+                            f"Requested output:\n {requested_amount} \n"
+                            f"Pre-selected inputs:\n {selected_amount} \n"
+                            f"Additional UTxO pool:\n {additional_utxo_pool} \n"
+                            f"Unfulfilled amount:\n {diff}"
+                        )
 
         selected_utxos.sort(
             key=lambda utxo: (str(utxo.input.transaction_id), utxo.input.index)

test/pycardano/test_coinselection.py

@@ -9,7 +9,6 @@
     InputUTxODepletedException,
     InsufficientUTxOBalanceException,
     MaxInputCountExceededException,
-    UTxOSelectionException,
 )
 from pycardano.transaction import TransactionInput, TransactionOutput, UTxO, Value
 

test/pycardano/test_txbuilder.py

@@ -12,6 +12,7 @@
 from pycardano.exception import (
     InsufficientUTxOBalanceException,
     InvalidTransactionException,
+    UTxOSelectionException,
 )
 from pycardano.hash import SCRIPT_HASH_SIZE, ScriptHash
 from pycardano.key import VerificationKey
@@ -141,6 +142,27 @@ def test_tx_builder_multi_asset(chain_context):
     assert expected == tx_body.to_primitive()
 
 
+def test_tx_builder_raises_utxo_selection(chain_context):
+    tx_builder = TransactionBuilder(chain_context)
+    sender = "addr_test1vrm9x2zsux7va6w892g38tvchnzahvcd9tykqf3ygnmwtaqyfg52x"
+    sender_address = Address.from_primitive(sender)
+
+    # Add sender address as input
+    tx_builder.add_input_address(sender).add_output(
+        TransactionOutput.from_primitive([sender, 1000000000])
+    ).add_output(
+        TransactionOutput.from_primitive(
+            [sender, [2000000, {b"1" * 28: {b"NewToken": 1}}]]
+        )
+    )
+
+    with pytest.raises(UTxOSelectionException) as e:
+        tx_body = tx_builder.build(change_address=sender_address)
+    assert "Unfulfilled amount:" in e.value.args[0]
+    assert "'coin': 991000000" in e.value.args[0]
+    assert "{AssetName(b'NewToken'): 1}" in e.value.args[0]
+
+
 def test_tx_too_big_exception(chain_context):
     tx_builder = TransactionBuilder(chain_context)
     sender = "addr_test1vrm9x2zsux7va6w892g38tvchnzahvcd9tykqf3ygnmwtaqyfg52x"