json.go

// Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package util

import (
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"reflect"
	"strconv"
)

var bytesT = reflect.TypeOf(Bytes(nil))

// Bytes marshals/unmarshals as a JSON string with 0x prefix.
// The empty slice marshals as "0x".
type Bytes []byte

// MarshalText implements encoding.TextMarshaler.
func (b Bytes) MarshalText() ([]byte, error) {
	result := make([]byte, len(b)*2+2)
	copy(result, `0x`)
	hex.Encode(result[2:], b)
	return result, nil
}

// UnmarshalJSON implements json.Unmarshaler.
func (b *Bytes) UnmarshalJSON(input []byte) error {
	if !isString(input) {
		return errNonString(bytesT)
	}
	return wrapTypeError(b.UnmarshalText(input[1:len(input)-1]), bytesT)
}

// UnmarshalText implements encoding.TextUnmarshaler.
func (b *Bytes) UnmarshalText(input []byte) error {
	raw, err := checkText(input, true)
	if err != nil {
		return err
	}
	dec := make([]byte, len(raw)/2)
	if _, err = hex.Decode(dec, raw); err != nil {
		err = mapError(err)
	} else {
		*b = dec
	}
	return err
}

// String returns the hex encoding of b.
func (b Bytes) String() string {
	return Encode(b)
}

// UnmarshalFixedJSON decodes the input as a string with 0x prefix. The length of out
// determines the required input length. This function is commonly used to implement the
// UnmarshalJSON method for fixed-size types.
func UnmarshalFixedJSON(typ reflect.Type, input, out []byte) error {
	if !isString(input) {
		return errNonString(typ)
	}
	return wrapTypeError(UnmarshalFixedText(typ.String(), input[1:len(input)-1], out), typ)
}

// UnmarshalFixedText decodes the input as a string with 0x prefix. The length of out
// determines the required input length. This function is commonly used to implement the
// UnmarshalText method for fixed-size types.
func UnmarshalFixedText(typename string, input, out []byte) error {
	raw, err := checkText(input, true)
	if err != nil {
		return err
	}
	if len(raw)/2 != len(out) {
		return fmt.Errorf("hex string has length %d, want %d for %s", len(raw), len(out)*2, typename)
	}
	// Pre-verify syntax before modifying out.
	for _, b := range raw {
		if decodeNibble(b) == badNibble {
			return ErrSyntax
		}
	}
	hex.Decode(out, raw)
	return nil
}

func isString(input []byte) bool {
	return len(input) >= 2 && input[0] == '"' && input[len(input)-1] == '"'
}

func bytesHave0xPrefix(input []byte) bool {
	return len(input) >= 2 && input[0] == '0' && (input[1] == 'x' || input[1] == 'X')
}

func checkText(input []byte, wantPrefix bool) ([]byte, error) {
	if len(input) == 0 {
		return nil, nil // empty strings are allowed
	}
	if bytesHave0xPrefix(input) {
		input = input[2:]
	} else if wantPrefix {
		return nil, ErrMissingPrefix
	}
	if len(input)%2 != 0 {
		return nil, ErrOddLength
	}
	return input, nil
}

func wrapTypeError(err error, typ reflect.Type) error {
	switch {
	case errors.Is(err, ErrSyntax):
		return &json.UnmarshalTypeError{Value: err.Error(), Type: typ}
	case errors.Is(err, ErrMissingPrefix):
		return &json.UnmarshalTypeError{Value: err.Error(), Type: typ}
	case errors.Is(err, ErrOddLength):
		return &json.UnmarshalTypeError{Value: err.Error(), Type: typ}
	case errors.Is(err, ErrUint64Range):
		return &json.UnmarshalTypeError{Value: err.Error(), Type: typ}
	default:
		return err
	}
}

func errNonString(typ reflect.Type) error {
	return &json.UnmarshalTypeError{Value: "non-string", Type: typ}
}

const badNibble = ^uint64(0)

func decodeNibble(in byte) uint64 {
	switch {
	case in >= '0' && in <= '9':
		return uint64(in - '0')
	case in >= 'A' && in <= 'F':
		return uint64(in - 'A' + 10)
	case in >= 'a' && in <= 'f':
		return uint64(in - 'a' + 10)
	default:
		return badNibble
	}
}

func mapError(err error) error {
	var numErr *strconv.NumError
	if errors.As(err, &numErr) {
		switch numErr.Err {
		case strconv.ErrRange:
			return ErrUint64Range
		case strconv.ErrSyntax:
			return ErrSyntax
		}
	}
	var syntaxErr hex.InvalidByteError
	if errors.As(err, &syntaxErr) {
		return ErrSyntax
	}
	if errors.Is(err, hex.ErrLength) {
		return ErrOddLength
	}
	return err
}

func Base64Encode(src []byte) []byte {
	n := base64.StdEncoding.EncodedLen(len(src))
	dst := make([]byte, n)
	base64.StdEncoding.Encode(dst, src)
	return dst
}

func Base64Decode(dst, src []byte) error {
	n, err := base64.StdEncoding.Decode(dst, src)
	if err != nil {
		return err
	}
	if n != len(dst) {
		return fmt.Errorf("incomplete decoding: %d != %d", n, len(src))
	}
	return err
}