cli: hardcode NEO and GAS token info

Don't make extra network queries for already known contracts.

cli/wallet/nep5.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io/ioutil"
+	"strings"
 
 	"github.com/nspcc-dev/neo-go/cli/flags"
 	"github.com/nspcc-dev/neo-go/cli/options"
@@ -16,6 +17,11 @@ import (
 	"github.com/urfave/cli"
 )
 
+var (
+	neoToken = wallet.NewToken(client.NeoContractHash, "NEO", "neo", 0)
+	gasToken = wallet.NewToken(client.GasContractHash, "GAS", "gas", 8)
+)
+
 func newNEP5Commands() []cli.Command {
 	balanceFlags := []cli.Flag{
 		walletPathFlag,
@@ -163,6 +169,12 @@ func getNEP5Balance(ctx *cli.Context) error {
 }
 
 func getMatchingToken(w *wallet.Wallet, name string) (*wallet.Token, error) {
+	switch strings.ToLower(name) {
+	case "neo":
+		return neoToken, nil
+	case "gas":
+		return gasToken, nil
+	}
 	return getMatchingTokenAux(func(i int) *wallet.Token {
 		return w.Extra.Tokens[i]
 	}, len(w.Extra.Tokens), name)

pkg/rpc/client/nep5.go

@@ -16,6 +16,13 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/wallet"
 )
 
+var (
+	// NeoContractHash is a hash of the NEO native contract.
+	NeoContractHash, _ = util.Uint160DecodeStringBE("3b7d3711c6f0ccf9b1dca903d1bfa1d896f1238c")
+	// GasContractHash is a hash of the GAS native contract.
+	GasContractHash, _ = util.Uint160DecodeStringBE("897720d8cd76f4f00abfa37c0edd889c208fde9b")
+)
+
 // NEP5Decimals invokes `decimals` NEP5 method on a specified contract.
 func (c *Client) NEP5Decimals(tokenHash util.Uint160) (int64, error) {
 	result, err := c.InvokeFunction(tokenHash.StringLE(), "decimals", []smartcontract.Parameter{}, nil)