Enhancement: Tx Unlocker (#67)

* added generic tx unlocker interface

* made unlocker a general signature script unlocker

* fixed linter

* Unlocker.Unlock return the data used to build the unlocking script

* reverted back to the unlocker just returning an error

* fix doc string comment

* change switch statement to if/else

* fixed test names and doc comments

bscript/script.go

@@ -26,6 +26,8 @@ const (
 	ScriptTypePubKey      = "pubkey"
 	ScriptTypePubKeyHash  = "pubkeyhash"
 	ScriptTypeNonStandard = "nonstandard"
+	ScriptTypeEmpty       = "empty"
+	ScriptTypeSecureHash  = "securehash"
 	ScriptTypeMultiSig    = "multisig"
 	ScriptTypeNullData    = "nulldata"
 )
@@ -349,7 +351,7 @@ func (s *Script) PublicKeyHash() ([]byte, error) {
 // ScriptType returns the type of script this is as a string.
 func (s *Script) ScriptType() string {
 	if len(*s) == 0 {
-		return ScriptTypeNonStandard
+		return ScriptTypeEmpty
 	}
 	if s.IsP2PKH() {
 		return ScriptTypePubKeyHash

examples/create_tx/create_tx.go

@@ -22,7 +22,7 @@ func main() {
 
 	decodedWif, _ := wif.DecodeWIF("KznvCNc6Yf4iztSThoMH6oHWzH9EgjfodKxmeuUGPq5DEX5maspS")
 
-	if err := tx.SignAll(context.Background(), &bt.LocalSignerGetter{PrivateKey: decodedWif.PrivKey}); err != nil {
+	if err := tx.UnlockAll(context.Background(), &bt.LocalUnlockerGetter{PrivateKey: decodedWif.PrivKey}); err != nil {
 		log.Fatal(err.Error())
 	}
 	log.Printf("tx: %s\n", tx)

examples/create_tx_with_opreturn/create_tx_with_opreturn.go

@@ -24,7 +24,7 @@ func main() {
 
 	decodedWif, _ := wif.DecodeWIF("L3VJH2hcRGYYG6YrbWGmsxQC1zyYixA82YjgEyrEUWDs4ALgk8Vu")
 
-	err := tx.SignAll(context.Background(), &bt.LocalSignerGetter{PrivateKey: decodedWif.PrivKey})
+	err := tx.UnlockAll(context.Background(), &bt.LocalUnlockerGetter{PrivateKey: decodedWif.PrivKey})
 	if err != nil {
 		log.Fatal(err.Error())
 	}

localunlocker.go

@@ -0,0 +1,60 @@
+package bt
+
+import (
+	"context"
+	"errors"
+
+	"github.com/libsv/go-bk/bec"
+	"github.com/libsv/go-bt/v2/bscript"
+	"github.com/libsv/go-bt/v2/sighash"
+)
+
+// LocalUnlockerGetter implements the UnlockerGetter interface. It unlocks a Tx locally,
+// using a bec PrivateKey.
+type LocalUnlockerGetter struct {
+	PrivateKey *bec.PrivateKey
+}
+
+// Unlocker builds a new *bt.LocalUnlocker with the same private key
+// as the calling *bt.LocalUnlockerGetter.
+func (lg *LocalUnlockerGetter) Unlocker(ctx context.Context, lockingScript *bscript.Script) (Unlocker, error) {
+	return &LocalUnlocker{PrivateKey: lg.PrivateKey}, nil
+}
+
+// LocalUnlocker implements the unlocker interface. It is used to unlock a tx locally using a
+// bec Private Key.
+type LocalUnlocker struct {
+	PrivateKey *bec.PrivateKey
+}
+
+// Unlock a transaction at a given input using the PrivateKey passed in through the LocalUnlocker
+// struct.
+// Unlock generates, applies, and returns an ECDSA signature for the provided hash digest using the private key
+// as well as the public key corresponding to the private key used. The produced
+// signature is deterministic (same message and same key yield the same signature) and
+// canonical in accordance with RFC6979 and BIP0062.
+func (lu *LocalUnlocker) Unlock(ctx context.Context, tx *Tx, idx uint32, shf sighash.Flag) error {
+	if shf == 0 {
+		shf = sighash.AllForkID
+	}
+
+	sh, err := tx.CalcInputSignatureHash(idx, shf)
+	if err != nil {
+		return err
+	}
+
+	sig, err := lu.PrivateKey.Sign(sh)
+	if err != nil {
+		return err
+	}
+
+	pubKey := lu.PrivateKey.PubKey().SerialiseCompressed()
+	signature := sig.Serialise()
+
+	switch tx.Inputs[idx].PreviousTxScript.ScriptType() {
+	case bscript.ScriptTypePubKeyHash:
+		return tx.ApplyP2PKHUnlockingScript(idx, pubKey, signature, shf)
+	}
+
+	return errors.New("currently only p2pkh supported")
+}