Add support for partially signed tx, closes #38

tx_builder.go

@@ -15,6 +15,8 @@ type TxBuilder struct {
 	pkeys    []crypto.PrvKey
 
 	changeReceiver *Address
+
+	additionalWitnesses uint
 }
 
 // NewTxBuilder returns a new instance of TxBuilder.
@@ -48,6 +50,12 @@ func (tb *TxBuilder) SetFee(fee Coin) {
 	tb.tx.Body.Fee = fee
 }
 
+// SetAdditionalWitnesses sets future witnesses for a partially signed transction.
+// This is useful to compute the real length and so fee in advance
+func (tb *TxBuilder) SetAdditionalWitnesses(witnesses uint) {
+	tb.additionalWitnesses = witnesses
+}
+
 // AddAuxiliaryData adds auxiliary data to the transaction.
 func (tb *TxBuilder) AddAuxiliaryData(data *AuxiliaryData) {
 	tb.tx.AuxiliaryData = data
@@ -141,7 +149,24 @@ func (tb *TxBuilder) MinCoinsForTxOut(txOut *TxOutput) Coin {
 
 // calculateMinFee computes the minimal fee required for the transaction.
 func (tb *TxBuilder) calculateMinFee() Coin {
+	if tb.additionalWitnesses > 0 {
+		// we can asssume the list of VKeyWitnessSet is not a nil value, as `build()` method is always allocating a slice
+		additionalVKeyWitnessSet := make([]VKeyWitness, tb.additionalWitnesses)
+		for i := uint(0); i < tb.additionalWitnesses; i++ {
+			additionalVKeyWitnessSet[i] = VKeyWitness{
+				VKey:      crypto.PubKey(make([]byte, 32)),
+				Signature: make([]byte, 64),
+			}
+		}
+		tb.tx.WitnessSet.VKeyWitnessSet = append(tb.tx.WitnessSet.VKeyWitnessSet, additionalVKeyWitnessSet...)
+	}
+
 	txBytes := tb.tx.Bytes()
+
+	if tb.additionalWitnesses > 0 {
+		tb.tx.WitnessSet.VKeyWitnessSet = tb.tx.WitnessSet.VKeyWitnessSet[:len(tb.tx.WitnessSet.VKeyWitnessSet)-int(tb.additionalWitnesses)]
+	}
+
 	txLength := uint64(len(txBytes))
 	return tb.protocol.MinFeeA*Coin(txLength) + tb.protocol.MinFeeB
 }
@@ -208,7 +233,7 @@ func (tb *TxBuilder) addChangeIfNeeded(inputAmount, outputAmount *Value) error {
 
 	if inputOutputCmp := inputAmount.Cmp(outputAmount); inputOutputCmp == -1 || inputOutputCmp == 2 {
 		return fmt.Errorf(
-			"insuficient input in transaction, got %v want atleast %v",
+			"insufficient input in transaction, got %v want atleast %v",
 			inputAmount,
 			outputAmount,
 		)

tx_builder_test.go

@@ -593,3 +593,157 @@ func TestAddChangeIfNeeded(t *testing.T) {
 		})
 	}
 }
+
+func TestCalculateMinFee(t *testing.T) {
+	key := crypto.NewXPrvKeyFromEntropy([]byte("receiver address"), "foo")
+	payment, err := NewKeyCredential(key.PubKey())
+	if err != nil {
+		t.Fatal(err)
+	}
+	receiver, err := NewEnterpriseAddress(Testnet, payment)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	type fields struct {
+		tx       Tx
+		protocol *ProtocolParams
+		inputs   []*TxInput
+		outputs  []*TxOutput
+		certs    []Certificate
+		// ttl uint64
+		// fee uint64
+	}
+
+	testcases := []struct {
+		name                string
+		fields              fields
+		expectedFee         Coin
+		additionalWitnesses uint
+	}{
+		{
+			name: "input == output + fee",
+			fields: fields{
+				protocol: alonzoProtocol,
+				inputs: []*TxInput{
+					{
+						TxHash: make([]byte, 32),
+						Index:  uint64(0),
+						Amount: NewValue(20000000),
+					},
+				},
+				outputs: []*TxOutput{
+					{
+						Address: receiver,
+						Amount:  NewValue(18831991),
+					},
+				},
+			},
+			expectedFee: Coin(165413), //Coin(168009),
+		},
+		{
+			name: "with only change address",
+			fields: fields{
+				protocol: alonzoProtocol,
+				inputs: []*TxInput{
+					{
+						TxHash: make([]byte, 32),
+						Index:  uint64(0),
+						Amount: NewValue(20000000),
+					},
+				},
+			},
+			expectedFee: Coin(163785), // cardano-cli would propose Coin(165149) as fee for a tx with only change address and no output,
+		},
+		{
+			name: "input == output + fee (two additional witness)",
+			fields: fields{
+				protocol: alonzoProtocol,
+				inputs: []*TxInput{
+					{
+						TxHash: make([]byte, 32),
+						Index:  uint64(0),
+						Amount: NewValue(20000000),
+					},
+				},
+				outputs: []*TxOutput{
+					{
+						Address: receiver,
+						// Amount:  NewValue(19823103),
+						Amount: NewValue(1982310),
+					},
+				},
+			},
+			expectedFee:         Coin(174301), //Coin(176897),
+			additionalWitnesses: 2,
+		},
+		{
+			name: "input == output + fee, one delegation certificate, implies one additional witness",
+			fields: fields{
+				protocol: alonzoProtocol,
+				inputs: []*TxInput{
+					{
+						TxHash: make([]byte, 32),
+						Index:  uint64(0),
+						Amount: NewValue(20000000),
+					},
+				},
+				outputs: []*TxOutput{
+					{
+						Address: receiver,
+						Amount:  NewValue(19827547),
+					},
+				},
+				certs: []Certificate{
+					func() Certificate {
+						c, _ := NewStakeDelegationCertificate(crypto.PubKey(make([]byte, 32)), Hash28(make([]byte, 28)))
+						return c
+					}(),
+				},
+			},
+			expectedFee:         Coin(172453),
+			additionalWitnesses: 1,
+		},
+	}
+
+	for _, tc := range testcases {
+		t.Run(tc.name, func(t *testing.T) {
+			key := crypto.NewXPrvKeyFromEntropy([]byte("change address"), "foo")
+			payment, err := NewKeyCredential(key.PubKey())
+			if err != nil {
+				t.Fatal(err)
+			}
+			changeAddr, err := NewEnterpriseAddress(Testnet, payment)
+			if err != nil {
+				t.Fatal(err)
+			}
+			txBuilder := NewTxBuilder(alonzoProtocol)
+			txBuilder.AddInputs(tc.fields.inputs...)
+			txBuilder.AddOutputs(tc.fields.outputs...)
+			for _, cert := range tc.fields.certs {
+				txBuilder.AddCertificate(cert)
+			}
+			txBuilder.AddChangeIfNeeded(changeAddr)
+			txBuilder.SetAdditionalWitnesses(tc.additionalWitnesses)
+			txBuilder.Sign(key.PrvKey())
+			tx, err := txBuilder.Build()
+			if err != nil {
+				t.Fatal(err)
+			}
+			var totalIn Coin
+			for _, input := range tx.Body.Inputs {
+				totalIn += input.Amount.Coin
+			}
+			var totalOut Coin
+			for _, output := range tx.Body.Outputs {
+				totalOut += output.Amount.Coin
+			}
+			if got, want := tx.Body.Fee+totalOut, totalIn; got != want {
+				t.Errorf("invalid fee+totalOut: got %v want %v", got, want)
+			}
+			if got, want := tx.Body.Fee, tc.expectedFee; got != want {
+				t.Errorf("calculated fee is not the expected one: got %v want %v", got, want)
+			}
+		})
+	}
+}