wallet: truncate file when writing

If wallet size decreases, we need to remove trailing garbage if it
exists. This can happen when removing account or reading pretty-printed
wallet. It doesn't affect our CLI (we decode only file prefix), but
it is nice to always have a valid JSON file.

Signed-off-by: Evgeniy Stratonikov <evgeniy@nspcc.ru>

cli/wallet_test.go

@@ -19,6 +19,38 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestWalletAccountRemove(t *testing.T) {
+	tmpDir, err := ioutil.TempDir("", "neogo.test.walletinit")
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		os.RemoveAll(tmpDir)
+	})
+
+	e := newExecutor(t, false)
+
+	walletPath := path.Join(tmpDir, "wallet.json")
+	e.In.WriteString("acc1\r")
+	e.In.WriteString("pass\r")
+	e.In.WriteString("pass\r")
+	e.Run(t, "neo-go", "wallet", "init", "--wallet", walletPath, "--account")
+
+	e.In.WriteString("acc2\r")
+	e.In.WriteString("pass\r")
+	e.In.WriteString("pass\r")
+	e.Run(t, "neo-go", "wallet", "create", "--wallet", walletPath)
+
+	w, err := wallet.NewWalletFromFile(walletPath)
+	require.NoError(t, err)
+
+	addr := w.Accounts[0].Address
+	e.Run(t, "neo-go", "wallet", "remove", "--wallet", walletPath,
+		"--address", addr, "--force")
+
+	rawWallet, err := ioutil.ReadFile(walletPath)
+	require.NoError(t, err)
+	require.NoError(t, json.Unmarshal(rawWallet, new(wallet.Wallet)))
+}
+
 func TestWalletInit(t *testing.T) {
 	tmpDir, err := ioutil.TempDir("", "neogo.test.walletinit")
 	require.NoError(t, err)

pkg/wallet/wallet.go

@@ -167,7 +167,16 @@ func (w *Wallet) writeRaw(data []byte) error {
 	}
 
 	_, err := w.rw.Write(data)
+	if err != nil {
 		return err
+	}
+
+	if f, ok := w.rw.(*os.File); ok {
+		if err := f.Truncate(int64(len(data))); err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 func (w *Wallet) rewind() error {