cli: add --out flag to the wallet transfer command

When transferring assets from multisig accounts,
it is useful to export tx into a file, so that
other participants can sign it too.

cli/wallet/wallet.go

@@ -3,8 +3,10 @@ package wallet
 import (
 	"bufio"
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"strings"
 	"syscall"
@@ -15,6 +17,7 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/encoding/address"
 	"github.com/nspcc-dev/neo-go/pkg/rpc/client"
 	"github.com/nspcc-dev/neo-go/pkg/rpc/request"
+	context2 "github.com/nspcc-dev/neo-go/pkg/smartcontract/context"
 	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/nspcc-dev/neo-go/pkg/wallet"
 	"github.com/urfave/cli"
@@ -47,6 +50,10 @@ var (
 		Name:  "timeout, t",
 		Usage: "Timeout for the operation",
 	}
+	outFlag = cli.StringFlag{
+		Name:  "out",
+		Usage: "file to put JSON transaction to",
+	}
 )
 
 // NewCommands returns 'wallet' command.
@@ -144,12 +151,13 @@ func NewCommands() []cli.Command {
 				Name:  "transfer",
 				Usage: "transfer NEO/GAS",
 				UsageText: "transfer --path <path> --from <addr> --to <addr>" +
-					" --amount <amount> --asset [NEO|GAS|<hex-id>]",
+					" --amount <amount> --asset [NEO|GAS|<hex-id>] [--out <path>]",
 				Action: transferAsset,
 				Flags: []cli.Flag{
 					walletPathFlag,
 					rpcFlag,
 					timeoutFlag,
+					outFlag,
 					cli.StringFlag{
 						Name:  "from",
 						Usage: "Address to send an asset from",
@@ -431,10 +439,24 @@ func transferAsset(ctx *cli.Context) error {
 		Position:   1,
 	})
 
+	if outFile := ctx.String("out"); outFile != "" {
+		priv := acc.PrivateKey()
+		pub := priv.PublicKey()
+		sign := priv.Sign(tx.GetSignedPart())
+		c := context2.NewParameterContext("Neo.Core.ContractTransaction", tx)
+		if err := c.AddSignature(acc.Contract, pub, sign); err != nil {
+			return cli.NewExitError(fmt.Errorf("can't add signature: %v", err), 1)
+		} else if data, err := json.Marshal(c); err != nil {
+			return cli.NewExitError(fmt.Errorf("can't marshal tx to JSON: %v", err), 1)
+		} else if err := ioutil.WriteFile(outFile, data, 0644); err != nil {
+			return cli.NewExitError(fmt.Errorf("can't write tx to file: %v", err), 1)
+		}
+	} else {
 		_ = acc.SignTx(tx)
 		if err := c.SendRawTransaction(tx); err != nil {
 			return cli.NewExitError(err, 1)
 		}
+	}
 
 	fmt.Println(tx.Hash().StringLE())
 	return nil