go-ethereum/signer/core/signed_data.go

// Copyright 2018 The go-ethereum Authors
// This file is part of go-ethereum.
//
// go-ethereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// go-ethereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
//
package core

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"math/big"
	"mime"
	"reflect"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"unicode"

	"github.com/ethereum/go-ethereum/accounts"
	"github.com/ethereum/go-ethereum/accounts/abi"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/crypto/sha3"
	"github.com/ethereum/go-ethereum/rlp"
)

type SigFormat struct {
	Mime        string
	ByteVersion byte
}

var (
	TextValidator = SigFormat{
		"text/validator",
		0x00,
	}
	DataTyped = SigFormat{
		"data/typed",
		0x01,
	}
	ApplicationClique = SigFormat{
		"application/clique",
		0x02,
	}
	TextPlain = SigFormat{
		"text/plain",
		0x45,
	}
)

type ValidatorData struct {
	Address common.Address
	Message hexutil.Bytes
}

type TypedData struct {
	Types       Types            `json:"types"`
	PrimaryType string           `json:"primaryType"`
	Domain      TypedDataDomain  `json:"domain"`
	Message     TypedDataMessage `json:"message"`
}

type Type []map[string]string

type Types map[string]Type

type TypePriority struct {
	Type  string
	Value uint
}

type TypedDataMessage = map[string]interface{}

type TypedDataDomain struct {
	Name              string   `json:"name"`
	Version           string   `json:"version"`
	ChainId           *big.Int `json:"chainId"`
	VerifyingContract string   `json:"verifyingContract"`
	Salt              string   `json:"salt"`
}

var typedDataRegexp = regexp.MustCompile(`^((address|bool|bytes|string)|((bytes)([1-9]|[1-2][0-9]|3[0-2]))|((int|uint)(8|16|32|64|128|256)))(\[])?$`)

// Sign receives a request and produces a signature

// Note, the produced signature conforms to the secp256k1 curve R, S and V values,
// where the V value will be 27 or 28 for legacy reasons.
func (api *SignerAPI) Sign(ctx context.Context, addr common.MixedcaseAddress, req *SignDataRequest) (hexutil.Bytes, error) {
	req.Address = addr
	req.Meta = MetadataFromContext(ctx)

	// We make the request prior to looking up if we actually have the account, to prevent
	// account-enumeration via the API
	res, err := api.UI.ApproveSignData(req)
	if err != nil {
		return nil, err
	}
	if !res.Approved {
		return nil, ErrRequestDenied
	}
	// Look up the wallet containing the requested signer
	account := accounts.Account{Address: addr.Address()}
	wallet, err := api.am.Find(account)
	if err != nil {
		return nil, err
	}
	// Sign the data with the wallet
	signature, err := wallet.SignHashWithPassphrase(account, res.Password, req.Hash)
	if err != nil {
		return nil, err
	}
	signature[64] += 27 // Transform V from 0/1 to 27/28 according to the yellow paper
	return signature, nil
}

// SignData signs the hash of the provided data, but does so differently
// depending on the content-type specified.
//
// Different types of validation occur.
func (api *SignerAPI) SignData(ctx context.Context, contentType string, addr common.MixedcaseAddress, data interface{}) (hexutil.Bytes, error) {
	var req, err = api.determineSignatureFormat(contentType, addr, data)
	if err != nil {
		return nil, err
	}

	signature, err := api.Sign(ctx, addr, req)
	if err != nil {
		api.UI.ShowError(err.Error())
		return nil, err
	}

	return signature, nil
}

// Determines which signature method should be used based upon the mime type
// In the cases where it matters ensure that the charset is handled. The charset
// resides in the 'params' returned as the second returnvalue from mime.ParseMediaType
// charset, ok := params["charset"]
// As it is now, we accept any charset and just treat it as 'raw'.
func (api *SignerAPI) determineSignatureFormat(contentType string, addr common.MixedcaseAddress, data interface{}) (*SignDataRequest, error) {
	var req *SignDataRequest
	mediaType, _, err := mime.ParseMediaType(contentType)
	if err != nil {
		return nil, err
	}

	switch mediaType {
	case TextValidator.Mime:
		// Data with an intended validator
		validatorData, err := UnmarshalValidatorData(data)
		if err != nil {
			return nil, err
		}
		sighash, msg := SignTextValidator(validatorData)
		message := []*NameValueType{
			{
				Name:  "message",
				Typ:   "text",
				Value: msg,
			},
		}
		req = &SignDataRequest{ContentType: mediaType, Rawdata: validatorData, Message: message, Hash: sighash}
	case ApplicationClique.Mime:
		// Clique is the Ethereum PoA standard
		cliqueData, err := hexutil.Decode(data.(string))
		if err != nil {
			return nil, err
		}
		header := &types.Header{}
		if err := rlp.DecodeBytes(cliqueData, header); err != nil {
			return nil, err
		}
		sighash, err := SignCliqueHeader(header)
		if err != nil {
			return nil, err
		}
		message := []*NameValueType{
			{
				Name:  "Clique block",
				Typ:   "clique",
				Value: fmt.Sprintf("clique block %d [0x%x]", header.Number, header.Hash()),
			},
		}
		req = &SignDataRequest{ContentType: mediaType, Rawdata: cliqueData, Message: message, Hash: sighash}
	case TextPlain.Mime:
		// Calculates an Ethereum ECDSA signature for:
		// hash = keccak256("\x19${byteVersion}Ethereum Signed Message:\n${message length}${message}")
		plainData, err := hexutil.Decode(data.(string))
		if err != nil {
			return nil, err
		}
		sighash, msg := SignTextPlain(plainData)
		message := []*NameValueType{
			{
				Name:  "message",
				Typ:   "text/plain",
				Value: msg,
			},
		}

		req = &SignDataRequest{ContentType: mediaType, Rawdata: plainData, Message: message, Hash: sighash}
	default:
		return nil, fmt.Errorf("content type '%s' not implemented for signing", contentType)
	}
	return req, nil

}

// SignTextWithValidator signs the given message which can be further recovered
// with the given validator.
// hash = keccak256("\x19\x00"${address}${data}).
func SignTextValidator(validatorData ValidatorData) (hexutil.Bytes, string) {
	msg := fmt.Sprintf("\x19\x00%s%s", string(validatorData.Address.Bytes()), string(validatorData.Message))
	fmt.Printf("SignTextValidator:%s\n", msg)
	return crypto.Keccak256([]byte(msg)), msg
}

// SignCliqueHeader returns the hash which is used as input for the proof-of-authority
// signing. It is the hash of the entire header apart from the 65 byte signature
// contained at the end of the extra data.
//
// The method requires the extra data to be at least 65 bytes -- the original implementation
// in clique.go panics if this is the case, thus it's been reimplemented here to avoid the panic
// and simply return an error instead
func SignCliqueHeader(header *types.Header) (hexutil.Bytes, error) {
	hash := common.Hash{}
	if len(header.Extra) < 65 {
		return hash.Bytes(), fmt.Errorf("clique header extradata too short, %d < 65", len(header.Extra))
	}
	hasher := sha3.NewKeccak256()
	rlp.Encode(hasher, []interface{}{
		header.ParentHash,
		header.UncleHash,
		header.Coinbase,
		header.Root,
		header.TxHash,
		header.ReceiptHash,
		header.Bloom,
		header.Difficulty,
		header.Number,
		header.GasLimit,
		header.GasUsed,
		header.Time,
		header.Extra[:len(header.Extra)-65],
		header.MixDigest,
		header.Nonce,
	})
	hasher.Sum(hash[:0])
	return hash.Bytes(), nil
}

// SignTextPlain is a helper function that calculates a hash for the given message that can be
// safely used to calculate a signature from. This gives context to the signed message and prevents
// signing of transactions.
// hash = keccak256("\x19$Ethereum Signed Message:\n"${message length}${message}).
func SignTextPlain(data hexutil.Bytes) (hexutil.Bytes, string) {
	// The letter `E` is \x45 in hex, retrofitting
	// https://github.com/ethereum/go-ethereum/pull/2940/commits
	msg := fmt.Sprintf("\x19Ethereum Signed Message:\n%d%s", len(data), string(data))
	return crypto.Keccak256([]byte(msg)), msg
}

// SignTypedData signs EIP-712 conformant typed data
// hash = keccak256("\x19${byteVersion}${domainSeparator}${hashStruct(message)}")
func (api *SignerAPI) SignTypedData(ctx context.Context, addr common.MixedcaseAddress, typedData TypedData) (hexutil.Bytes, error) {
	if err := typedData.Validate(); err != nil {
		return nil, err
	}
	domainSeparator, err := typedData.HashStruct("EIP712Domain", typedData.Domain.Map())
	if err != nil {
		return nil, err
	}
	typedDataHash, err := typedData.HashStruct(typedData.PrimaryType, typedData.Message)
	if err != nil {
		return nil, err
	}
	sighash := crypto.Keccak256([]byte(fmt.Sprintf("\x19\x01%s%s", string(domainSeparator), string(typedDataHash))))
	//output := typedData.PrettyPrint()
	message := typedData.Format()
	req := &SignDataRequest{ContentType: DataTyped.Mime, Rawdata: typedData.Map(), Message: message, Hash: sighash}
	signature, err := api.Sign(ctx, addr, req)
	if err != nil {
		api.UI.ShowError(err.Error())
		return nil, err
	}
	return signature, nil
}

// HashStruct generates a keccak256 hash of the encoding of the provided data
func (typedData *TypedData) HashStruct(primaryType string, data TypedDataMessage) (hexutil.Bytes, error) {
	encodedData, err := typedData.EncodeData(primaryType, data, 1)
	if err != nil {
		return nil, err
	}
	return crypto.Keccak256(encodedData), nil
}

// Dependencies returns an array of custom types ordered by their hierarchical reference tree
func (typedData *TypedData) Dependencies(primaryType string, found []string) []string {
	includes := func(arr []string, str string) bool {
		for _, obj := range arr {
			if obj == str {
				return true
			}
		}
		return false
	}

	if includes(found, primaryType) {
		return found
	}
	if typedData.Types[primaryType] == nil {
		return found
	}
	found = append(found, primaryType)
	for _, field := range typedData.Types[primaryType] {
		for _, dep := range typedData.Dependencies(field["type"], found) {
			if !includes(found, dep) {
				found = append(found, dep)
			}
		}
	}
	return found
}

// EncodeType generates the following encoding:
// `name ‖ "(" ‖ member₁ ‖ "," ‖ member₂ ‖ "," ‖ … ‖ memberₙ ")"`
//
// each member is written as `type ‖ " " ‖ name` encodings cascade down and are sorted by name
func (typedData *TypedData) EncodeType(primaryType string) hexutil.Bytes {
	// Get dependencies primary first, then alphabetical
	deps := typedData.Dependencies(primaryType, []string{})
	slicedDeps := deps[1:]
	sort.Strings(slicedDeps)
	deps = append([]string{primaryType}, slicedDeps...)

	// Format as a string with fields
	var buffer bytes.Buffer
	for _, dep := range deps {
		buffer.WriteString(dep)
		buffer.WriteString("(")
		for _, obj := range typedData.Types[dep] {
			buffer.WriteString(obj["type"])
			buffer.WriteString(" ")
			buffer.WriteString(obj["name"])
			buffer.WriteString(",")
		}
		buffer.Truncate(buffer.Len() - 1)
		buffer.WriteString(")")
	}
	return buffer.Bytes()
}

func (typedData *TypedData) TypeHash(primaryType string) hexutil.Bytes {
	return crypto.Keccak256(typedData.EncodeType(primaryType))
}

// EncodeData generates the following encoding:
// `enc(value₁) ‖ enc(value₂) ‖ … ‖ enc(valueₙ)`
//
// each encoded member is 32-byte long
func (typedData *TypedData) EncodeData(primaryType string, data map[string]interface{}, depth int) (hexutil.Bytes, error) {
	buffer := bytes.Buffer{}

	// Verify extra data
	if len(typedData.Types[primaryType]) < len(data) {
		return nil, errors.New("there is extra data provided in the message")
	}

	// Add typehash
	buffer.Write(typedData.TypeHash(primaryType))

	// Add field contents. Structs and arrays have special handlers.
	for _, field := range typedData.Types[primaryType] {
		encType := field["type"]
		encValue := data[field["name"]]
		if encType[len(encType)-1:] == "]" {
			arrayValue, ok := encValue.([]interface{})
			if !ok {
				return nil, dataMismatchError(encType, encValue)
			}

			arrayBuffer := bytes.Buffer{}
			parsedType := strings.Split(encType, "[")[0]
			for _, item := range arrayValue {
				if typedData.Types[parsedType] != nil {
					mapValue, ok := item.(map[string]interface{})
					if !ok {
						return nil, dataMismatchError(parsedType, item)
					}
					encodedData, err := typedData.EncodeData(parsedType, mapValue, depth+1)
					if err != nil {
						return nil, err
					}
					arrayBuffer.Write(encodedData)
				} else {
					encValue, err := typedData.EncodePrimitiveValue(encType, encValue, depth)
					if err != nil {
						return nil, err
					}
					bytesValue, err := bytesValueOf(encValue)
					if err != nil {
						return nil, err
					}
					arrayBuffer.Write(bytesValue)
				}
			}

			buffer.Write(crypto.Keccak256(arrayBuffer.Bytes()))
		} else if typedData.Types[field["type"]] != nil {
			mapValue, ok := encValue.(map[string]interface{})
			if !ok {
				return nil, dataMismatchError(encType, encValue)
			}

			encodedData, err := typedData.EncodeData(field["type"], mapValue, depth+1)
			if err != nil {
				return nil, err
			}

			buffer.Write(crypto.Keccak256(encodedData))
		} else {
			primitiveEncValue, err := typedData.EncodePrimitiveValue(encType, encValue, depth)
			if err != nil {
				return nil, err
			}
			bytesValue, err := bytesValueOf(primitiveEncValue)
			if err != nil {
				return nil, err
			}
			buffer.Write(bytesValue)
		}
	}
	return buffer.Bytes(), nil
}

// EncodePrimitiveValue deals with the primitive values found
// while searching through the typed data
func (typedData *TypedData) EncodePrimitiveValue(encType string, encValue interface{}, depth int) (interface{}, error) {
	var primitiveEncValue interface{}

	switch encType {
	case "address":
		bytesValue := hexutil.Bytes{}
		for i := 0; i < 12; i++ {
			bytesValue = append(bytesValue, 0)
		}
		stringValue, ok := encValue.(string)
		if !ok || !common.IsHexAddress(stringValue) {
			return nil, dataMismatchError(encType, encValue)
		}
		addressValue := common.HexToAddress(stringValue)
		for _, _byte := range addressValue {
			bytesValue = append(bytesValue, _byte)
		}
		primitiveEncValue = bytesValue
	case "bool":
		var int64Val int64
		boolValue, ok := encValue.(bool)
		if !ok {
			return nil, dataMismatchError(encType, encValue)
		}
		if boolValue {
			int64Val = 1
		}
		primitiveEncValue = abi.U256(big.NewInt(int64Val))
	case "bytes", "string":
		bytesValue, err := bytesValueOf(encValue)
		if err != nil {
			return nil, dataMismatchError(encType, encValue)
		}
		primitiveEncValue = crypto.Keccak256(bytesValue)
	default:
		if strings.HasPrefix(encType, "bytes") {
			sizeStr := strings.TrimPrefix(encType, "bytes")
			size, _ := strconv.Atoi(sizeStr)
			bytesValue := hexutil.Bytes{}
			for i := 0; i < 32-size; i++ {
				bytesValue = append(bytesValue, 0)
			}
			if _, ok := encValue.(hexutil.Bytes); !ok {
				return nil, dataMismatchError(encType, encValue)
			}
			bytesValue = append(bytesValue, encValue.(hexutil.Bytes)...)
			primitiveEncValue = bytesValue
		} else if strings.HasPrefix(encType, "uint") || strings.HasPrefix(encType, "int") {
			bigIntValue, ok := encValue.(*big.Int)
			if !ok {
				return nil, dataMismatchError(encType, encValue)
			}
			primitiveEncValue = abi.U256(bigIntValue)
		} else {
			return nil, fmt.Errorf("unrecognized type '%s'", encType)
		}
	}
	return primitiveEncValue, nil
}

// dataMismatchError generates an error for a mismatch between
// the provided type and data
func dataMismatchError(encType string, encValue interface{}) error {
	return fmt.Errorf("provided data '%v' doesn't match type '%s'", encValue, encType)
}

// bytesValuesOf returns the bytes value of the given interface
func bytesValueOf(_interface interface{}) (hexutil.Bytes, error) {
	bytesValue, ok := _interface.(hexutil.Bytes)
	if ok {
		return bytesValue, nil
	}

	switch reflect.TypeOf(_interface) {
	case reflect.TypeOf(hexutil.Bytes{}):
		return _interface.(hexutil.Bytes), nil
	case reflect.TypeOf([]byte{}):
		return hexutil.Bytes(_interface.([]byte)), nil
	case reflect.TypeOf([]uint8{}):
		return _interface.([]uint8), nil
	case reflect.TypeOf(string("")):
		return hexutil.Bytes(_interface.(string)), nil
	default:
		break
	}

	return nil, fmt.Errorf("unrecognized type '%T'", _interface)
}

// EcRecover recovers the address associated with the given sig.
// Only compatible with `text/plain`
func (api *SignerAPI) EcRecover(ctx context.Context, data hexutil.Bytes, sig hexutil.Bytes) (common.Address, error) {
	// Returns the address for the Account that was used to create the signature.
	//
	// Note, this function is compatible with eth_sign and personal_sign. As such it recovers
	// the address of:
	// hash = keccak256("\x19${byteVersion}Ethereum Signed Message:\n${message length}${message}")
	// addr = ecrecover(hash, signature)
	//
	// Note, the signature must conform to the secp256k1 curve R, S and V values, where
	// the V value must be be 27 or 28 for legacy reasons.
	//
	// https://github.com/ethereum/go-ethereum/wiki/Management-APIs#personal_ecRecover
	if len(sig) != 65 {
		return common.Address{}, fmt.Errorf("signature must be 65 bytes long")
	}
	if sig[64] != 27 && sig[64] != 28 {
		return common.Address{}, fmt.Errorf("invalid Ethereum signature (V is not 27 or 28)")
	}
	sig[64] -= 27 // Transform yellow paper V from 27/28 to 0/1
	hash, _ := SignTextPlain(data)
	rpk, err := crypto.SigToPub(hash, sig)
	if err != nil {
		return common.Address{}, err
	}
	return crypto.PubkeyToAddress(*rpk), nil
}

// UnmarshalValidatorData converts the bytes input to typed data
func UnmarshalValidatorData(data interface{}) (ValidatorData, error) {
	raw := data.(map[string]interface{})

	addr, ok := raw["address"].(string)
	if !ok {
		return ValidatorData{}, errors.New("validator address is not sent as a string")
	}
	addrBytes, err := hexutil.Decode(addr)
	if err != nil {
		return ValidatorData{}, err
	}
	if !ok || len(addrBytes) == 0 {
		return ValidatorData{}, errors.New("validator address is undefined")
	}

	message, ok := raw["message"].(string)
	if !ok {
		return ValidatorData{}, errors.New("message is not sent as a string")
	}
	messageBytes, err := hexutil.Decode(message)
	if err != nil {
		return ValidatorData{}, err
	}
	if !ok || len(messageBytes) == 0 {
		return ValidatorData{}, errors.New("message is undefined")
	}

	return ValidatorData{
		Address: common.BytesToAddress(addrBytes),
		Message: messageBytes,
	}, nil
}

// Validate make sure the types are sound
func (typedData *TypedData) Validate() error {
	if err := typedData.Types.Validate(); err != nil {
		return err
	}
	if err := typedData.Domain.Validate(); err != nil {
		return err
	}
	return nil
}

// Map generates a map version of the typed data
func (typedData *TypedData) Map() map[string]interface{} {
	dataMap := map[string]interface{}{
		"types":       typedData.Types,
		"domain":      typedData.Domain.Map(),
		"primaryType": typedData.PrimaryType,
		"message":     typedData.Message,
	}
	return dataMap
}

// PrettyPrint generates a nice output to help the users
// of clef present data in their apps
func (typedData *TypedData) PrettyPrint() string {
	output := bytes.Buffer{}
	formatted := typedData.Format()
	for _, item := range formatted {
		output.WriteString(fmt.Sprintf("%v\n", item.Pprint(0)))
	}
	return output.String()
}

// Format returns a representation of d, which can be easily displayed by a user-interface
// without in-depth knowledge about 712 rules
func (typedData *TypedData) Format() []*NameValueType {
	var nvts []*NameValueType
	nvts = append(nvts, &NameValueType{
		Name:  "EIP712Domain",
		Value: typedData.formatData("EIP712Domain", typedData.Domain.Map()),
		Typ:   "domain",
	})
	nvts = append(nvts, &NameValueType{
		Name:  typedData.PrimaryType,
		Value: typedData.formatData(typedData.PrimaryType, typedData.Message),
		Typ:   "primary type",
	})
	return nvts
}

func (typedData *TypedData) formatData(primaryType string, data map[string]interface{}) []*NameValueType {
	var output []*NameValueType

	// Add field contents. Structs and arrays have special handlers.
	for _, field := range typedData.Types[primaryType] {
		encType := field["type"]
		encName := field["name"]
		encValue := data[encName]
		item := &NameValueType{
			Name: encName,
			Typ:  encType,
		}
		if encType[len(encType)-1:] == "]" {
			arrayValue, _ := encValue.([]interface{})
			parsedType := strings.Split(encType, "[")[0]
			for _, v := range arrayValue {
				if typedData.Types[parsedType] != nil {
					mapValue, _ := v.(map[string]interface{})
					mapOutput := typedData.formatData(parsedType, mapValue)
					item.Value = mapOutput
				} else {
					primitiveOutput := formatPrimitiveValue(encType, encValue)
					item.Value = primitiveOutput
				}
			}
		} else if typedData.Types[field["type"]] != nil {
			mapValue, _ := encValue.(map[string]interface{})
			mapOutput := typedData.formatData(field["type"], mapValue)
			item.Value = mapOutput
		} else {
			primitiveOutput := formatPrimitiveValue(encType, encValue)
			item.Value = primitiveOutput
		}
		output = append(output, item)
	}
	return output
}

func formatPrimitiveValue(encType string, encValue interface{}) string {
	switch encType {
	case "address":
		stringValue, _ := encValue.(string)
		return common.HexToAddress(stringValue).String()
	case "bool":
		boolValue, _ := encValue.(bool)
		return fmt.Sprintf("%t", boolValue)
	case "bytes", "string":
		return fmt.Sprintf("%s", encValue)
	}
	if strings.HasPrefix(encType, "bytes") {
		return fmt.Sprintf("%s", encValue)
	} else if strings.HasPrefix(encType, "uint") || strings.HasPrefix(encType, "int") {
		bigIntValue, _ := encValue.(*big.Int)
		return fmt.Sprintf("%d (0x%x)", bigIntValue, bigIntValue)
	}
	return "NA"
}

// NameValueType is a very simple struct with Name, Value and Type. It's meant for simple
// json structures used to communicate signing-info about typed data with the UI
type NameValueType struct {
	Name  string      `json:"name"`
	Value interface{} `json:"value"`
	Typ   string      `json:"type"`
}

// Pprint returns a pretty-printed version of nvt
func (nvt *NameValueType) Pprint(depth int) string {
	output := bytes.Buffer{}
	output.WriteString(strings.Repeat("\u00a0", depth*2))
	output.WriteString(fmt.Sprintf("%s [%s]: ", nvt.Name, nvt.Typ))
	if nvts, ok := nvt.Value.([]*NameValueType); ok {
		output.WriteString("\n")
		for _, next := range nvts {
			sublevel := next.Pprint(depth + 1)
			output.WriteString(sublevel)
		}
	} else {
		output.WriteString(fmt.Sprintf("%s\n", nvt.Value))
	}
	return output.String()
}

// Validate checks if the types object is conformant to the specs
func (types *Types) Validate() error {
	for typeKey, typeArr := range *types {
		for _, typeObj := range typeArr {
			typeVal := typeObj["type"]
			if typeKey == typeVal {
				return fmt.Errorf("type '%s' cannot reference itself", typeVal)
			}
			firstChar := []rune(typeVal)[0]
			if unicode.IsUpper(firstChar) {
				if (*types)[typeVal] == nil {
					return fmt.Errorf("referenced type '%s' is undefined", typeVal)
				}
			} else {
				if !typedDataRegexp.MatchString(typeVal) {
					if (*types)[typeVal] != nil {
						return fmt.Errorf("referenced type '%s' must be capitalized", typeVal)
					} else {
						return fmt.Errorf("unknown atomic type '%s'", typeVal)
					}
				}
			}
		}
	}
	return nil
}

// Validate checks if the given domain is valid, i.e. contains at least
// the minimum viable keys and values
func (domain *TypedDataDomain) Validate() error {
	if domain.ChainId == big.NewInt(0) {
		return errors.New("chainId must be specified according to EIP-155")
	}

	if len(domain.Name) == 0 && len(domain.Version) == 0 && len(domain.VerifyingContract) == 0 && len(domain.Salt) == 0 {
		return errors.New("domain is undefined")
	}

	return nil
}

// Map is a helper function to generate a map version of the domain
func (domain *TypedDataDomain) Map() map[string]interface{} {
	dataMap := map[string]interface{}{
		"chainId": domain.ChainId,
	}

	if len(domain.Name) > 0 {
		dataMap["name"] = domain.Name
	}

	if len(domain.Version) > 0 {
		dataMap["version"] = domain.Version
	}

	if len(domain.VerifyingContract) > 0 {
		dataMap["verifyingContract"] = domain.VerifyingContract
	}

	if len(domain.Salt) > 0 {
		dataMap["salt"] = domain.Salt
	}
	return dataMap
}