watchtower/multi: move MockSigner+MockPeer to wtmock

watchtower/wtmock/signer.go

@@ -0,0 +1,81 @@
+package wtmock
+
+import (
+	"sync"
+
+	"github.com/btcsuite/btcd/btcec"
+	"github.com/btcsuite/btcd/txscript"
+	"github.com/btcsuite/btcd/wire"
+	"github.com/lightningnetwork/lnd/input"
+	"github.com/lightningnetwork/lnd/keychain"
+)
+
+// MockSigner is an input.Signer that allows one to add arbitrary private keys
+// and sign messages by passing the assigned keychain.KeyLocator.
+type MockSigner struct {
+	mu sync.Mutex
+
+	index uint32
+	keys  map[keychain.KeyLocator]*btcec.PrivateKey
+}
+
+// NewMockSigner returns a fresh MockSigner.
+func NewMockSigner() *MockSigner {
+	return &MockSigner{
+		keys: make(map[keychain.KeyLocator]*btcec.PrivateKey),
+	}
+}
+
+// SignOutputRaw signs an input on the passed transaction using the input index
+// in the sign descriptor. The returned signature is the raw DER-encoded
+// signature without the signhash flag.
+func (s *MockSigner) SignOutputRaw(tx *wire.MsgTx,
+	signDesc *input.SignDescriptor) ([]byte, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	witnessScript := signDesc.WitnessScript
+	amt := signDesc.Output.Value
+
+	privKey, ok := s.keys[signDesc.KeyDesc.KeyLocator]
+	if !ok {
+		panic("cannot sign w/ unknown key")
+	}
+
+	sig, err := txscript.RawTxInWitnessSignature(
+		tx, signDesc.SigHashes, signDesc.InputIndex, amt,
+		witnessScript, signDesc.HashType, privKey,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return sig[:len(sig)-1], nil
+}
+
+// ComputeInputScript is not implemented.
+func (s *MockSigner) ComputeInputScript(tx *wire.MsgTx,
+	signDesc *input.SignDescriptor) (*input.Script, error) {
+	panic("not implemented")
+}
+
+// AddPrivKey records the passed privKey in the MockSigner's registry of keys it
+// can sign with in the future. A unique key locator is returned, allowing the
+// caller to sign with this key when presented via an input.SignDescriptor.
+func (s *MockSigner) AddPrivKey(privKey *btcec.PrivateKey) keychain.KeyLocator {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	keyLoc := keychain.KeyLocator{
+		Index: s.index,
+	}
+	s.index++
+
+	s.keys[keyLoc] = privKey
+
+	return keyLoc
+}
+
+// Compile-time constraint ensuring the MockSigner implements the input.Signer
+// interface.
+var _ input.Signer = (*MockSigner)(nil)