Add helper for signing transactions

blockchain/test_utils.go

@@ -49,12 +49,8 @@ func newTxBody() TxBody {
 func newTransaction() *Transaction {
 	sender := newWallet()
 	tbody := newTxBody()
-	digest := HashSum(tbody)
-	sig, _ := sender.Sign(digest, crand.Reader)
-	return &Transaction{
-		TxBody: tbody,
-		Sig:    sig,
-	}
+	t, _ := tbody.Signed(sender, crand.Reader)
+	return t
 }
 
 func newBlockHeader() BlockHeader {

blockchain/transaction.go

@@ -1,6 +1,9 @@
 package blockchain
 
-import "encoding/binary"
+import (
+	"encoding/binary"
+	"io"
+)
 
 const (
 	// TxHashPointerLen is the length in bytes of a hash pointer.
@@ -60,6 +63,13 @@ func (tb TxBody) Marshal() []byte {
 	return buf
 }
 
+// Signed returns a signed Transaction from a TxBody
+func (tb TxBody) Signed(w Wallet, r io.Reader) (*Transaction, error) {
+	digest := HashSum(tb)
+	sig, err := w.Sign(digest, r)
+	return &Transaction{tb, sig}, err
+}
+
 // Transaction contains a TxBody and a signature verifying it
 type Transaction struct {
 	TxBody