marshal.go

// Copyright (c) 2012 The gocql Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package gocql

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"math"
	"math/big"
	"net"
	"reflect"
	"strconv"
	"strings"
	"time"

	"gopkg.in/inf.v0"
)

var (
	bigOne = big.NewInt(1)
)

var (
	ErrorUDTUnavailable = errors.New("UDT are not available on protocols less than 3, please update config")
)

// Marshaler is the interface implemented by objects that can marshal
// themselves into values understood by Cassandra.
type Marshaler interface {
	MarshalCQL(info TypeInfo) ([]byte, error)
}

// Unmarshaler is the interface implemented by objects that can unmarshal
// a Cassandra specific description of themselves.
type Unmarshaler interface {
	UnmarshalCQL(info TypeInfo, data []byte) error
}

// Marshal returns the CQL encoding of the value for the Cassandra
// internal type described by the info parameter.
func Marshal(info TypeInfo, value interface{}) ([]byte, error) {
	if info.Version() < protoVersion1 {
		panic("protocol version not set")
	}

	if valueRef := reflect.ValueOf(value); valueRef.Kind() == reflect.Ptr {
		if valueRef.IsNil() {
			return nil, nil
		} else if v, ok := value.(Marshaler); ok {
			return v.MarshalCQL(info)
		} else {
			return Marshal(info, valueRef.Elem().Interface())
		}
	}

	if v, ok := value.(Marshaler); ok {
		return v.MarshalCQL(info)
	}

	switch info.Type() {
	case TypeVarchar, TypeAscii, TypeBlob, TypeText:
		return marshalVarchar(info, value)
	case TypeBoolean:
		return marshalBool(info, value)
	case TypeInt:
		return marshalInt(info, value)
	case TypeBigInt, TypeCounter:
		return marshalBigInt(info, value)
	case TypeFloat:
		return marshalFloat(info, value)
	case TypeDouble:
		return marshalDouble(info, value)
	case TypeDecimal:
		return marshalDecimal(info, value)
	case TypeTimestamp:
		return marshalTimestamp(info, value)
	case TypeList, TypeSet:
		return marshalList(info, value)
	case TypeMap:
		return marshalMap(info, value)
	case TypeUUID, TypeTimeUUID:
		return marshalUUID(info, value)
	case TypeVarint:
		return marshalVarint(info, value)
	case TypeInet:
		return marshalInet(info, value)
	case TypeTuple:
		return marshalTuple(info, value)
	case TypeUDT:
		return marshalUDT(info, value)
	}

	// detect protocol 2 UDT
	if strings.HasPrefix(info.Custom(), "org.apache.cassandra.db.marshal.UserType") && info.Version() < 3 {
		return nil, ErrorUDTUnavailable
	}

	// TODO(tux21b): add the remaining types
	return nil, fmt.Errorf("can not marshal %T into %s", value, info)
}

// Unmarshal parses the CQL encoded data based on the info parameter that
// describes the Cassandra internal data type and stores the result in the
// value pointed by value.
func Unmarshal(info TypeInfo, data []byte, value interface{}) error {
	if v, ok := value.(Unmarshaler); ok {
		return v.UnmarshalCQL(info, data)
	}
	if isNullableValue(value) {
		return unmarshalNullable(info, data, value)
	}

	switch info.Type() {
	case TypeVarchar, TypeAscii, TypeBlob, TypeText:
		return unmarshalVarchar(info, data, value)
	case TypeBoolean:
		return unmarshalBool(info, data, value)
	case TypeInt:
		return unmarshalInt(info, data, value)
	case TypeBigInt, TypeCounter:
		return unmarshalBigInt(info, data, value)
	case TypeVarint:
		return unmarshalVarint(info, data, value)
	case TypeFloat:
		return unmarshalFloat(info, data, value)
	case TypeDouble:
		return unmarshalDouble(info, data, value)
	case TypeDecimal:
		return unmarshalDecimal(info, data, value)
	case TypeTimestamp:
		return unmarshalTimestamp(info, data, value)
	case TypeList, TypeSet:
		return unmarshalList(info, data, value)
	case TypeMap:
		return unmarshalMap(info, data, value)
	case TypeTimeUUID:
		return unmarshalTimeUUID(info, data, value)
	case TypeUUID:
		return unmarshalUUID(info, data, value)
	case TypeInet:
		return unmarshalInet(info, data, value)
	case TypeTuple:
		return unmarshalTuple(info, data, value)
	case TypeUDT:
		return unmarshalUDT(info, data, value)
	}

	// detect protocol 2 UDT
	if strings.HasPrefix(info.Custom(), "org.apache.cassandra.db.marshal.UserType") && info.Version() < 3 {
		return ErrorUDTUnavailable
	}

	// TODO(tux21b): add the remaining types
	return fmt.Errorf("can not unmarshal %s into %T", info, value)
}

func isNullableValue(value interface{}) bool {
	v := reflect.ValueOf(value)
	return v.Kind() == reflect.Ptr && v.Type().Elem().Kind() == reflect.Ptr
}

func isNullData(info TypeInfo, data []byte) bool {
	return len(data) == 0
}

func unmarshalNullable(info TypeInfo, data []byte, value interface{}) error {
	valueRef := reflect.ValueOf(value)

	if isNullData(info, data) {
		nilValue := reflect.Zero(valueRef.Type().Elem())
		valueRef.Elem().Set(nilValue)
		return nil
	}

	newValue := reflect.New(valueRef.Type().Elem().Elem())
	valueRef.Elem().Set(newValue)
	return Unmarshal(info, data, newValue.Interface())
}

func marshalVarchar(info TypeInfo, value interface{}) ([]byte, error) {
	switch v := value.(type) {
	case Marshaler:
		return v.MarshalCQL(info)
	case string:
		return []byte(v), nil
	case []byte:
		return v, nil
	}

	if value == nil {
		return nil, nil
	}

	rv := reflect.ValueOf(value)
	t := rv.Type()
	k := t.Kind()
	switch {
	case k == reflect.String:
		return []byte(rv.String()), nil
	case k == reflect.Slice && t.Elem().Kind() == reflect.Uint8:
		return rv.Bytes(), nil
	}
	return nil, marshalErrorf("can not marshal %T into %s", value, info)
}

func unmarshalVarchar(info TypeInfo, data []byte, value interface{}) error {
	switch v := value.(type) {
	case Unmarshaler:
		return v.UnmarshalCQL(info, data)
	case *string:
		*v = string(data)
		return nil
	case *[]byte:
		var dataCopy []byte
		if data != nil {
			dataCopy = make([]byte, len(data))
			copy(dataCopy, data)
		}
		*v = dataCopy
		return nil
	}
	rv := reflect.ValueOf(value)
	if rv.Kind() != reflect.Ptr {
		return unmarshalErrorf("can not unmarshal into non-pointer %T", value)
	}
	rv = rv.Elem()
	t := rv.Type()
	k := t.Kind()
	switch {
	case k == reflect.String:
		rv.SetString(string(data))
		return nil
	case k == reflect.Slice && t.Elem().Kind() == reflect.Uint8:
		var dataCopy []byte
		if data != nil {
			dataCopy = make([]byte, len(data))
			copy(dataCopy, data)
		}
		rv.SetBytes(dataCopy)
		return nil
	}
	return unmarshalErrorf("can not unmarshal %s into %T", info, value)
}

func marshalInt(info TypeInfo, value interface{}) ([]byte, error) {
	switch v := value.(type) {
	case Marshaler:
		return v.MarshalCQL(info)
	case int:
		if v > math.MaxInt32 || v < math.MinInt32 {
			return nil, marshalErrorf("marshal int: value %d out of range", v)
		}
		return encInt(int32(v)), nil
	case uint:
		if v > math.MaxInt32 {
			return nil, marshalErrorf("marshal int: value %d out of range", v)
		}
		return encInt(int32(v)), nil
	case int64:
		if v > math.MaxInt32 || v < math.MinInt32 {
			return nil, marshalErrorf("marshal int: value %d out of range", v)
		}
		return encInt(int32(v)), nil
	case uint64:
		if v > math.MaxInt32 {
			return nil, marshalErrorf("marshal int: value %d out of range", v)
		}
		return encInt(int32(v)), nil
	case int32:
		return encInt(v), nil
	case uint32:
		if v > math.MaxInt32 {
			return nil, marshalErrorf("marshal int: value %d out of range", v)
		}
		return encInt(int32(v)), nil
	case int16:
		return encInt(int32(v)), nil
	case uint16:
		return encInt(int32(v)), nil
	case int8:
		return encInt(int32(v)), nil
	case uint8:
		return encInt(int32(v)), nil
	case string:
		i, err := strconv.ParseInt(value.(string), 10, 32)
		if err != nil {
			return nil, marshalErrorf("can not marshal string to int: %s", err)
		}
		return encInt(int32(i)), nil
	}

	if value == nil {
		return nil, nil
	}

	switch rv := reflect.ValueOf(value); rv.Type().Kind() {
	case reflect.Int, reflect.Int64, reflect.Int32, reflect.Int16, reflect.Int8:
		v := rv.Int()
		if v > math.MaxInt32 || v < math.MinInt32 {
			return nil, marshalErrorf("marshal int: value %d out of range", v)
		}
		return encInt(int32(v)), nil
	case reflect.Uint, reflect.Uint64, reflect.Uint32, reflect.Uint16, reflect.Uint8:
		v := rv.Uint()
		if v > math.MaxInt32 {
			return nil, marshalErrorf("marshal int: value %d out of range", v)
		}
		return encInt(int32(v)), nil
	default:
		if rv.IsNil() {
			return nil, nil
		}
	}

	return nil, marshalErrorf("can not marshal %T into %s", value, info)
}

func encInt(x int32) []byte {
	return []byte{byte(x >> 24), byte(x >> 16), byte(x >> 8), byte(x)}
}

func decInt(x []byte) int32 {
	if len(x) != 4 {
		return 0
	}
	return int32(x[0])<<24 | int32(x[1])<<16 | int32(x[2])<<8 | int32(x[3])
}

func marshalBigInt(info TypeInfo, value interface{}) ([]byte, error) {
	switch v := value.(type) {
	case Marshaler:
		return v.MarshalCQL(info)
	case int:
		return encBigInt(int64(v)), nil
	case uint:
		if uint64(v) > math.MaxInt64 {
			return nil, marshalErrorf("marshal bigint: value %d out of range", v)
		}
		return encBigInt(int64(v)), nil
	case int64:
		return encBigInt(v), nil
	case uint64:
		if v > math.MaxInt64 {
			return nil, marshalErrorf("marshal bigint: value %d out of range", v)
		}
		return encBigInt(int64(v)), nil
	case int32:
		return encBigInt(int64(v)), nil
	case uint32:
		return encBigInt(int64(v)), nil
	case int16:
		return encBigInt(int64(v)), nil
	case uint16:
		return encBigInt(int64(v)), nil
	case int8:
		return encBigInt(int64(v)), nil
	case uint8:
		return encBigInt(int64(v)), nil
	case big.Int:
		return encBigInt2C(&v), nil
	case string:
		i, err := strconv.ParseInt(value.(string), 10, 64)
		if err != nil {
			return nil, marshalErrorf("can not marshal string to bigint: %s", err)
		}
		return encBigInt(i), nil
	}

	if value == nil {
		return nil, nil
	}

	rv := reflect.ValueOf(value)
	switch rv.Type().Kind() {
	case reflect.Int, reflect.Int64, reflect.Int32, reflect.Int16, reflect.Int8:
		v := rv.Int()
		return encBigInt(v), nil
	case reflect.Uint, reflect.Uint64, reflect.Uint32, reflect.Uint16, reflect.Uint8:
		v := rv.Uint()
		if v > math.MaxInt64 {
			return nil, marshalErrorf("marshal bigint: value %d out of range", v)
		}
		return encBigInt(int64(v)), nil
	}
	return nil, marshalErrorf("can not marshal %T into %s", value, info)
}

func encBigInt(x int64) []byte {
	return []byte{byte(x >> 56), byte(x >> 48), byte(x >> 40), byte(x >> 32),
		byte(x >> 24), byte(x >> 16), byte(x >> 8), byte(x)}
}

func bytesToInt64(data []byte) (ret int64) {
	for i := range data {
		ret |= int64(data[i]) << (8 * uint(len(data)-i-1))
	}
	return ret
}

func unmarshalBigInt(info TypeInfo, data []byte, value interface{}) error {
	return unmarshalIntlike(info, decBigInt(data), data, value)
}

func unmarshalInt(info TypeInfo, data []byte, value interface{}) error {
	return unmarshalIntlike(info, int64(decInt(data)), data, value)
}

func unmarshalVarint(info TypeInfo, data []byte, value interface{}) error {
	switch value.(type) {
	case *big.Int:
		return unmarshalIntlike(info, 0, data, value)
	}

	if len(data) > 8 {
		return unmarshalErrorf("unmarshal int: varint value %v out of range for %T (use big.Int)", data, value)
	}

	int64Val := bytesToInt64(data)
	if len(data) < 8 && data[0]&0x80 > 0 {
		int64Val -= (1 << uint(len(data)*8))
	}
	return unmarshalIntlike(info, int64Val, data, value)
}

func marshalVarint(info TypeInfo, value interface{}) ([]byte, error) {
	var (
		retBytes []byte
		err      error
	)

	switch v := value.(type) {
	case uint64:
		if v > uint64(math.MaxInt64) {
			retBytes = make([]byte, 9)
			binary.BigEndian.PutUint64(retBytes[1:], v)
		} else {
			retBytes = make([]byte, 8)
			binary.BigEndian.PutUint64(retBytes, v)
		}
	default:
		retBytes, err = marshalBigInt(info, value)
	}

	if err == nil {
		// trim down to most significant byte
		i := 0
		for ; i < len(retBytes)-1; i++ {
			b0 := retBytes[i]
			if b0 != 0 && b0 != 0xFF {
				break
			}

			b1 := retBytes[i+1]
			if b0 == 0 && b1 != 0 {
				if b1&0x80 == 0 {
					i++
				}
				break
			}

			if b0 == 0xFF && b1 != 0xFF {
				if b1&0x80 > 0 {
					i++
				}
				break
			}
		}
		retBytes = retBytes[i:]
	}

	return retBytes, err
}

func unmarshalIntlike(info TypeInfo, int64Val int64, data []byte, value interface{}) error {
	switch v := value.(type) {
	case *int:
		if ^uint(0) == math.MaxUint32 && (int64Val < math.MinInt32 || int64Val > math.MaxInt32) {
			return unmarshalErrorf("unmarshal int: value %d out of range for %T", int64Val, *v)
		}
		*v = int(int64Val)
		return nil
	case *uint:
		if int64Val < 0 || (^uint(0) == math.MaxUint32 && int64Val > math.MaxUint32) {
			return unmarshalErrorf("unmarshal int: value %d out of range for %T", int64Val, *v)
		}
		*v = uint(int64Val)
		return nil
	case *int64:
		*v = int64Val
		return nil
	case *uint64:
		if int64Val < 0 {
			return unmarshalErrorf("unmarshal int: value %d out of range for %T", int64Val, *v)
		}
		*v = uint64(int64Val)
		return nil
	case *int32:
		if int64Val < math.MinInt32 || int64Val > math.MaxInt32 {
			return unmarshalErrorf("unmarshal int: value %d out of range for %T", int64Val, *v)
		}
		*v = int32(int64Val)
		return nil
	case *uint32:
		if int64Val < 0 || int64Val > math.MaxUint32 {
			return unmarshalErrorf("unmarshal int: value %d out of range for %T", int64Val, *v)
		}
		*v = uint32(int64Val)
		return nil
	case *int16:
		if int64Val < math.MinInt16 || int64Val > math.MaxInt16 {
			return unmarshalErrorf("unmarshal int: value %d out of range for %T", int64Val, *v)
		}
		*v = int16(int64Val)
		return nil
	case *uint16:
		if int64Val < 0 || int64Val > math.MaxUint16 {
			return unmarshalErrorf("unmarshal int: value %d out of range for %T", int64Val, *v)
		}
		*v = uint16(int64Val)
		return nil
	case *int8:
		if int64Val < math.MinInt8 || int64Val > math.MaxInt8 {
			return unmarshalErrorf("unmarshal int: value %d out of range for %T", int64Val, *v)
		}
		*v = int8(int64Val)
		return nil
	case *uint8:
		if int64Val < 0 || int64Val > math.MaxUint8 {
			return unmarshalErrorf("unmarshal int: value %d out of range for %T", int64Val, *v)
		}
		*v = uint8(int64Val)
		return nil
	case *big.Int:
		decBigInt2C(data, v)
		return nil
	case *string:
		*v = strconv.FormatInt(int64Val, 10)
		return nil
	}

	rv := reflect.ValueOf(value)
	if rv.Kind() != reflect.Ptr {
		return unmarshalErrorf("can not unmarshal into non-pointer %T", value)
	}
	rv = rv.Elem()

	switch rv.Type().Kind() {
	case reflect.Int:
		if ^uint(0) == math.MaxUint32 && (int64Val < math.MinInt32 || int64Val > math.MaxInt32) {
			return unmarshalErrorf("unmarshal int: value %d out of range", int64Val)
		}
		rv.SetInt(int64Val)
		return nil
	case reflect.Int64:
		rv.SetInt(int64Val)
		return nil
	case reflect.Int32:
		if int64Val < math.MinInt32 || int64Val > math.MaxInt32 {
			return unmarshalErrorf("unmarshal int: value %d out of range", int64Val)
		}
		rv.SetInt(int64Val)
		return nil
	case reflect.Int16:
		if int64Val < math.MinInt16 || int64Val > math.MaxInt16 {
			return unmarshalErrorf("unmarshal int: value %d out of range", int64Val)
		}
		rv.SetInt(int64Val)
		return nil
	case reflect.Int8:
		if int64Val < math.MinInt8 || int64Val > math.MaxInt8 {
			return unmarshalErrorf("unmarshal int: value %d out of range", int64Val)
		}
		rv.SetInt(int64Val)
		return nil
	case reflect.Uint:
		if int64Val < 0 || (^uint(0) == math.MaxUint32 && int64Val > math.MaxUint32) {
			return unmarshalErrorf("unmarshal int: value %d out of range", int64Val)
		}
		rv.SetUint(uint64(int64Val))
		return nil
	case reflect.Uint64:
		if int64Val < 0 {
			return unmarshalErrorf("unmarshal int: value %d out of range", int64Val)
		}
		rv.SetUint(uint64(int64Val))
		return nil
	case reflect.Uint32:
		if int64Val < 0 || int64Val > math.MaxUint32 {
			return unmarshalErrorf("unmarshal int: value %d out of range", int64Val)
		}
		rv.SetUint(uint64(int64Val))
		return nil
	case reflect.Uint16:
		if int64Val < 0 || int64Val > math.MaxUint16 {
			return unmarshalErrorf("unmarshal int: value %d out of range", int64Val)
		}
		rv.SetUint(uint64(int64Val))
		return nil
	case reflect.Uint8:
		if int64Val < 0 || int64Val > math.MaxUint8 {
			return unmarshalErrorf("unmarshal int: value %d out of range", int64Val)
		}
		rv.SetUint(uint64(int64Val))
		return nil
	}
	return unmarshalErrorf("can not unmarshal %s into %T", info, value)
}

func decBigInt(data []byte) int64 {
	if len(data) != 8 {
		return 0
	}
	return int64(data[0])<<56 | int64(data[1])<<48 |
		int64(data[2])<<40 | int64(data[3])<<32 |
		int64(data[4])<<24 | int64(data[5])<<16 |
		int64(data[6])<<8 | int64(data[7])
}

func marshalBool(info TypeInfo, value interface{}) ([]byte, error) {
	switch v := value.(type) {
	case Marshaler:
		return v.MarshalCQL(info)
	case bool:
		return encBool(v), nil
	}

	if value == nil {
		return nil, nil
	}

	rv := reflect.ValueOf(value)
	switch rv.Type().Kind() {
	case reflect.Bool:
		return encBool(rv.Bool()), nil
	}
	return nil, marshalErrorf("can not marshal %T into %s", value, info)
}

func encBool(v bool) []byte {
	if v {
		return []byte{1}
	}
	return []byte{0}
}

func unmarshalBool(info TypeInfo, data []byte, value interface{}) error {
	switch v := value.(type) {
	case Unmarshaler:
		return v.UnmarshalCQL(info, data)
	case *bool:
		*v = decBool(data)
		return nil
	}
	rv := reflect.ValueOf(value)
	if rv.Kind() != reflect.Ptr {
		return unmarshalErrorf("can not unmarshal into non-pointer %T", value)
	}
	rv = rv.Elem()
	switch rv.Type().Kind() {
	case reflect.Bool:
		rv.SetBool(decBool(data))
		return nil
	}
	return unmarshalErrorf("can not unmarshal %s into %T", info, value)
}

func decBool(v []byte) bool {
	if len(v) == 0 {
		return false
	}
	return v[0] != 0
}

func marshalFloat(info TypeInfo, value interface{}) ([]byte, error) {
	switch v := value.(type) {
	case Marshaler:
		return v.MarshalCQL(info)
	case float32:
		return encInt(int32(math.Float32bits(v))), nil
	}

	if value == nil {
		return nil, nil
	}

	rv := reflect.ValueOf(value)
	switch rv.Type().Kind() {
	case reflect.Float32:
		return encInt(int32(math.Float32bits(float32(rv.Float())))), nil
	}
	return nil, marshalErrorf("can not marshal %T into %s", value, info)
}

func unmarshalFloat(info TypeInfo, data []byte, value interface{}) error {
	switch v := value.(type) {
	case Unmarshaler:
		return v.UnmarshalCQL(info, data)
	case *float32:
		*v = math.Float32frombits(uint32(decInt(data)))
		return nil
	}
	rv := reflect.ValueOf(value)
	if rv.Kind() != reflect.Ptr {
		return unmarshalErrorf("can not unmarshal into non-pointer %T", value)
	}
	rv = rv.Elem()
	switch rv.Type().Kind() {
	case reflect.Float32:
		rv.SetFloat(float64(math.Float32frombits(uint32(decInt(data)))))
		return nil
	}
	return unmarshalErrorf("can not unmarshal %s into %T", info, value)
}

func marshalDouble(info TypeInfo, value interface{}) ([]byte, error) {
	switch v := value.(type) {
	case Marshaler:
		return v.MarshalCQL(info)
	case float64:
		return encBigInt(int64(math.Float64bits(v))), nil
	}
	if value == nil {
		return nil, nil
	}
	rv := reflect.ValueOf(value)
	switch rv.Type().Kind() {
	case reflect.Float64:
		return encBigInt(int64(math.Float64bits(rv.Float()))), nil
	}
	return nil, marshalErrorf("can not marshal %T into %s", value, info)
}

func unmarshalDouble(info TypeInfo, data []byte, value interface{}) error {
	switch v := value.(type) {
	case Unmarshaler:
		return v.UnmarshalCQL(info, data)
	case *float64:
		*v = math.Float64frombits(uint64(decBigInt(data)))
		return nil
	}
	rv := reflect.ValueOf(value)
	if rv.Kind() != reflect.Ptr {
		return unmarshalErrorf("can not unmarshal into non-pointer %T", value)
	}
	rv = rv.Elem()
	switch rv.Type().Kind() {
	case reflect.Float64:
		rv.SetFloat(math.Float64frombits(uint64(decBigInt(data))))
		return nil
	}
	return unmarshalErrorf("can not unmarshal %s into %T", info, value)
}

func marshalDecimal(info TypeInfo, value interface{}) ([]byte, error) {
	if value == nil {
		return nil, nil
	}

	switch v := value.(type) {
	case Marshaler:
		return v.MarshalCQL(info)
	case inf.Dec:
		unscaled := encBigInt2C(v.UnscaledBig())
		if unscaled == nil {
			return nil, marshalErrorf("can not marshal %T into %s", value, info)
		}

		buf := make([]byte, 4+len(unscaled))
		copy(buf[0:4], encInt(int32(v.Scale())))
		copy(buf[4:], unscaled)
		return buf, nil
	}
	return nil, marshalErrorf("can not marshal %T into %s", value, info)
}

func unmarshalDecimal(info TypeInfo, data []byte, value interface{}) error {
	switch v := value.(type) {
	case Unmarshaler:
		return v.UnmarshalCQL(info, data)
	case *inf.Dec:
		scale := decInt(data[0:4])
		unscaled := decBigInt2C(data[4:], nil)
		*v = *inf.NewDecBig(unscaled, inf.Scale(scale))
		return nil
	}
	return unmarshalErrorf("can not unmarshal %s into %T", info, value)
}

// decBigInt2C sets the value of n to the big-endian two's complement
// value stored in the given data. If data[0]&80 != 0, the number
// is negative. If data is empty, the result will be 0.
func decBigInt2C(data []byte, n *big.Int) *big.Int {
	if n == nil {
		n = new(big.Int)
	}
	n.SetBytes(data)
	if len(data) > 0 && data[0]&0x80 > 0 {
		n.Sub(n, new(big.Int).Lsh(bigOne, uint(len(data))*8))
	}
	return n
}

// encBigInt2C returns the big-endian two's complement
// form of n.
func encBigInt2C(n *big.Int) []byte {
	switch n.Sign() {
	case 0:
		return []byte{0}
	case 1:
		b := n.Bytes()
		if b[0]&0x80 > 0 {
			b = append([]byte{0}, b...)
		}
		return b
	case -1:
		length := uint(n.BitLen()/8+1) * 8
		b := new(big.Int).Add(n, new(big.Int).Lsh(bigOne, length)).Bytes()
		// When the most significant bit is on a byte
		// boundary, we can get some extra significant
		// bits, so strip them off when that happens.
		if len(b) >= 2 && b[0] == 0xff && b[1]&0x80 != 0 {
			b = b[1:]
		}
		return b
	}
	return nil
}

func marshalTimestamp(info TypeInfo, value interface{}) ([]byte, error) {
	switch v := value.(type) {
	case Marshaler:
		return v.MarshalCQL(info)
	case int64:
		return encBigInt(v), nil
	case time.Time:
		if v.IsZero() {
			return []byte{}, nil
		}
		x := int64(v.UTC().Unix()*1e3) + int64(v.UTC().Nanosecond()/1e6)
		return encBigInt(x), nil
	}

	if value == nil {
		return nil, nil
	}

	rv := reflect.ValueOf(value)
	switch rv.Type().Kind() {
	case reflect.Int64:
		return encBigInt(rv.Int()), nil
	}
	return nil, marshalErrorf("can not marshal %T into %s", value, info)
}

func unmarshalTimestamp(info TypeInfo, data []byte, value interface{}) error {
	switch v := value.(type) {
	case Unmarshaler:
		return v.UnmarshalCQL(info, data)
	case *int64:
		*v = decBigInt(data)
		return nil
	case *time.Time:
		if len(data) == 0 {
			return nil
		}
		x := decBigInt(data)
		sec := x / 1000
		nsec := (x - sec*1000) * 1000000
		*v = time.Unix(sec, nsec).In(time.UTC)
		return nil
	}
	rv := reflect.ValueOf(value)
	if rv.Kind() != reflect.Ptr {
		return unmarshalErrorf("can not unmarshal into non-pointer %T", value)
	}
	rv = rv.Elem()
	switch rv.Type().Kind() {
	case reflect.Int64:
		rv.SetInt(decBigInt(data))
		return nil
	}
	return unmarshalErrorf("can not unmarshal %s into %T", info, value)
}

func writeCollectionSize(info CollectionType, n int, buf *bytes.Buffer) error {
	if info.proto > protoVersion2 {
		if n > math.MaxInt32 {
			return marshalErrorf("marshal: collection too large")
		}

		buf.WriteByte(byte(n >> 24))
		buf.WriteByte(byte(n >> 16))
		buf.WriteByte(byte(n >> 8))
		buf.WriteByte(byte(n))
	} else {
		if n > math.MaxUint16 {
			return marshalErrorf("marshal: collection too large")
		}

		buf.WriteByte(byte(n >> 8))
		buf.WriteByte(byte(n))
	}

	return nil
}

func marshalList(info TypeInfo, value interface{}) ([]byte, error) {
	listInfo, ok := info.(CollectionType)
	if !ok {
		return nil, marshalErrorf("marshal: can not marshal non collection type into list")
	}

	rv := reflect.ValueOf(value)
	t := rv.Type()
	k := t.Kind()
	switch k {
	case reflect.Slice, reflect.Array:
		buf := &bytes.Buffer{}
		n := rv.Len()

		if err := writeCollectionSize(listInfo, n, buf); err != nil {
			return nil, err
		}

		for i := 0; i < n; i++ {
			item, err := Marshal(listInfo.Elem, rv.Index(i).Interface())
			if err != nil {
				return nil, err
			}
			if err := writeCollectionSize(listInfo, len(item), buf); err != nil {
				return nil, err
			}
			buf.Write(item)
		}
		return buf.Bytes(), nil
	case reflect.Map:
		elem := t.Elem()
		if elem.Kind() == reflect.Struct && elem.NumField() == 0 {
			rkeys := rv.MapKeys()
			keys := make([]interface{}, len(rkeys))
			for i := 0; i < len(keys); i++ {
				keys[i] = rkeys[i].Interface()
			}
			return marshalList(listInfo, keys)
		}
	}
	return nil, marshalErrorf("can not marshal %T into %s", value, info)
}

func readCollectionSize(info CollectionType, data []byte) (size, read int) {
	if info.proto > protoVersion2 {
		size = int(data[0])<<24 | int(data[1])<<16 | int(data[2])<<8 | int(data[3])
		read = 4
	} else {
		size = int(data[0])<<8 | int(data[1])
		read = 2
	}
	return
}

func unmarshalList(info TypeInfo, data []byte, value interface{}) error {
	listInfo, ok := info.(CollectionType)
	if !ok {
		return unmarshalErrorf("unmarshal: can not unmarshal none collection type into list")
	}

	rv := reflect.ValueOf(value)
	if rv.Kind() != reflect.Ptr {
		return unmarshalErrorf("can not unmarshal into non-pointer %T", value)
	}
	rv = rv.Elem()
	t := rv.Type()
	k := t.Kind()

	switch k {
	case reflect.Slice, reflect.Array:
		if data == nil {
			if k == reflect.Array {
				return unmarshalErrorf("unmarshal list: can not store nil in array value")
			}
			rv.Set(reflect.Zero(t))
			return nil
		}
		if len(data) < 2 {
			return unmarshalErrorf("unmarshal list: unexpected eof")
		}
		n, p := readCollectionSize(listInfo, data)
		data = data[p:]
		if k == reflect.Array {
			if rv.Len() != n {
				return unmarshalErrorf("unmarshal list: array with wrong size")
			}
		} else {
			rv.Set(reflect.MakeSlice(t, n, n))
		}
		for i := 0; i < n; i++ {
			if len(data) < 2 {
				return unmarshalErrorf("unmarshal list: unexpected eof")
			}
			m, p := readCollectionSize(listInfo, data)
			data = data[p:]
			if err := Unmarshal(listInfo.Elem, data[:m], rv.Index(i).Addr().Interface()); err != nil {
				return err
			}
			data = data[m:]
		}
		return nil
	}
	return unmarshalErrorf("can not unmarshal %s into %T", info, value)
}

func marshalMap(info TypeInfo, value interface{}) ([]byte, error) {
	mapInfo, ok := info.(CollectionType)
	if !ok {
		return nil, marshalErrorf("marshal: can not marshal none collection type into map")
	}

	rv := reflect.ValueOf(value)
	t := rv.Type()
	if t.Kind() != reflect.Map {
		return nil, marshalErrorf("can not marshal %T into %s", value, info)
	}

	buf := &bytes.Buffer{}
	n := rv.Len()

	if err := writeCollectionSize(mapInfo, n, buf); err != nil {
		return nil, err
	}

	keys := rv.MapKeys()
	for _, key := range keys {
		item, err := Marshal(mapInfo.Key, key.Interface())
		if err != nil {
			return nil, err
		}
		if err := writeCollectionSize(mapInfo, len(item), buf); err != nil {
			return nil, err
		}
		buf.Write(item)

		item, err = Marshal(mapInfo.Elem, rv.MapIndex(key).Interface())
		if err != nil {
			return nil, err
		}
		if err := writeCollectionSize(mapInfo, len(item), buf); err != nil {
			return nil, err
		}
		buf.Write(item)
	}
	return buf.Bytes(), nil
}

func unmarshalMap(info TypeInfo, data []byte, value interface{}) error {
	mapInfo, ok := info.(CollectionType)
	if !ok {
		return unmarshalErrorf("unmarshal: can not unmarshal none collection type into map")
	}

	rv := reflect.ValueOf(value)
	if rv.Kind() != reflect.Ptr {
		return unmarshalErrorf("can not unmarshal into non-pointer %T", value)
	}
	rv = rv.Elem()
	t := rv.Type()
	if t.Kind() != reflect.Map {
		return unmarshalErrorf("can not unmarshal %s into %T", info, value)
	}
	if data == nil {
		rv.Set(reflect.Zero(t))
		return nil
	}
	rv.Set(reflect.MakeMap(t))
	if len(data) < 2 {
		return unmarshalErrorf("unmarshal map: unexpected eof")
	}
	n, p := readCollectionSize(mapInfo, data)
	data = data[p:]
	for i := 0; i < n; i++ {
		if len(data) < 2 {
			return unmarshalErrorf("unmarshal list: unexpected eof")
		}
		m, p := readCollectionSize(mapInfo, data)
		data = data[p:]
		key := reflect.New(t.Key())
		if err := Unmarshal(mapInfo.Key, data[:m], key.Interface()); err != nil {
			return err
		}
		data = data[m:]

		m, p = readCollectionSize(mapInfo, data)
		data = data[p:]
		val := reflect.New(t.Elem())
		if err := Unmarshal(mapInfo.Elem, data[:m], val.Interface()); err != nil {
			return err
		}
		data = data[m:]

		rv.SetMapIndex(key.Elem(), val.Elem())
	}
	return nil
}

func marshalUUID(info TypeInfo, value interface{}) ([]byte, error) {
	switch val := value.(type) {
	case UUID:
		return val.Bytes(), nil
	case []byte:
		if len(val) == 16 {
			return val, nil
		}
	case string:
		b, err := ParseUUID(val)
		if err != nil {
			return nil, err
		}
		return b[:], nil
	}

	if value == nil {
		return nil, nil
	}

	return nil, marshalErrorf("can not marshal %T into %s", value, info)
}

func unmarshalUUID(info TypeInfo, data []byte, value interface{}) error {
	if data == nil || len(data) == 0 {
		switch v := value.(type) {
		case *string:
			*v = ""
		case *[]byte:
			*v = nil
		case *UUID:
			*v = UUID{}
		default:
			return unmarshalErrorf("can not unmarshal X %s into %T", info, value)
		}

		return nil
	}

	u, err := UUIDFromBytes(data)
	if err != nil {
		return unmarshalErrorf("Unable to parse UUID: %s", err)
	}

	switch v := value.(type) {
	case *string:
		*v = u.String()
		return nil
	case *[]byte:
		*v = u[:]
		return nil
	case *UUID:
		*v = u
		return nil
	}
	return unmarshalErrorf("can not unmarshal X %s into %T", info, value)
}

func unmarshalTimeUUID(info TypeInfo, data []byte, value interface{}) error {
	switch v := value.(type) {
	case Unmarshaler:
		return v.UnmarshalCQL(info, data)
	case *time.Time:
		id, err := UUIDFromBytes(data)
		if err != nil {
			return err
		} else if id.Version() != 1 {
			return unmarshalErrorf("invalid timeuuid")
		}
		*v = id.Time()
		return nil
	default:
		return unmarshalUUID(info, data, value)
	}
}

func marshalInet(info TypeInfo, value interface{}) ([]byte, error) {
	// we return either the 4 or 16 byte representation of an
	// ip address here otherwise the db value will be prefixed
	// with the remaining byte values e.g. ::ffff:127.0.0.1 and not 127.0.0.1
	switch val := value.(type) {
	case net.IP:
		t := val.To4()
		if t == nil {
			return val.To16(), nil
		}
		return t, nil
	case string:
		b := net.ParseIP(val)
		if b != nil {
			t := b.To4()
			if t == nil {
				return b.To16(), nil
			}
			return t, nil
		}
		return nil, marshalErrorf("cannot marshal. invalid ip string %s", val)
	}

	if value == nil {
		return nil, nil
	}

	return nil, marshalErrorf("cannot marshal %T into %s", value, info)
}

func unmarshalInet(info TypeInfo, data []byte, value interface{}) error {
	switch v := value.(type) {
	case Unmarshaler:
		return v.UnmarshalCQL(info, data)
	case *net.IP:
		ip := net.IP(data)
		if v4 := ip.To4(); v4 != nil {
			*v = v4
			return nil
		}
		*v = ip
		return nil
	case *string:
		if len(data) == 0 {
			*v = ""
			return nil
		}
		ip := net.IP(data)
		if v4 := ip.To4(); v4 != nil {
			*v = v4.String()
			return nil
		}
		*v = ip.String()
		return nil
	}
	return unmarshalErrorf("cannot unmarshal %s into %T", info, value)
}

func marshalTuple(info TypeInfo, value interface{}) ([]byte, error) {
	tuple := info.(TupleTypeInfo)
	switch v := value.(type) {
	case []interface{}:
		var buf []byte

		if len(v) != len(tuple.Elems) {
			return nil, unmarshalErrorf("cannont marshal tuple: wrong number of elements")
		}

		for i, elem := range v {
			data, err := Marshal(tuple.Elems[i], elem)
			if err != nil {
				return nil, err
			}

			n := len(data)
			buf = appendInt(buf, int32(n))
			buf = append(buf, data...)
		}

		return buf, nil
	}

	return nil, unmarshalErrorf("cannot marshal %T into %s", value, tuple)
}

// currently only support unmarshal into a list of values, this makes it possible
// to support tuples without changing the query API. In the future this can be extend
// to allow unmarshalling into custom tuple types.
func unmarshalTuple(info TypeInfo, data []byte, value interface{}) error {
	if v, ok := value.(Unmarshaler); ok {
		return v.UnmarshalCQL(info, data)
	}

	tuple := info.(TupleTypeInfo)
	switch v := value.(type) {
	case []interface{}:
		for i, elem := range tuple.Elems {
			// each element inside data is a [bytes]
			size := readInt(data)
			data = data[4:]

			err := Unmarshal(elem, data[:size], v[i])
			if err != nil {
				return err
			}
			data = data[size:]
		}

		return nil
	}

	return unmarshalErrorf("cannot unmarshal %s into %T", info, value)
}

// UDTMarshaler is an interface which should be implemented by users wishing to
// handle encoding UDT types to sent to Cassandra. Note: due to current implentations
// methods defined for this interface must be value receivers not pointer receivers.
type UDTMarshaler interface {
	// MarshalUDT will be called for each field in the the UDT returned by Cassandra,
	// the implementor should marshal the type to return by for example calling
	// Marshal.
	MarshalUDT(name string, info TypeInfo) ([]byte, error)
}

// UDTUnmarshaler should be implemented by users wanting to implement custom
// UDT unmarshaling.
type UDTUnmarshaler interface {
	// UnmarshalUDT will be called for each field in the UDT return by Cassandra,
	// the implementor should unmarshal the data into the value of their chosing,
	// for example by calling Unmarshal.
	UnmarshalUDT(name string, info TypeInfo, data []byte) error
}

func marshalUDT(info TypeInfo, value interface{}) ([]byte, error) {
	udt := info.(UDTTypeInfo)

	switch v := value.(type) {
	case Marshaler:
		return v.MarshalCQL(info)
	case UDTMarshaler:
		var buf []byte
		for _, e := range udt.Elements {
			data, err := v.MarshalUDT(e.Name, e.Type)
			if err != nil {
				return nil, err
			}

			if data == nil && typeCanBeNull(e.Type) {
				buf = appendInt(buf, -1)
			} else {
				buf = appendInt(buf, int32(len(data)))
				buf = append(buf, data...)
			}
		}

		return buf, nil
	case map[string]interface{}:
		var buf []byte
		for _, e := range udt.Elements {
			val, ok := v[e.Name]
			if !ok {
				return nil, marshalErrorf("missing UDT field in map: %s", e.Name)
			}

			data, err := Marshal(e.Type, val)
			if err != nil {
				return nil, err
			}

			if data == nil && typeCanBeNull(e.Type) {
				buf = appendInt(buf, -1)
			} else {
				buf = appendInt(buf, int32(len(data)))
				buf = append(buf, data...)
			}
		}

		return buf, nil
	}

	k := reflect.ValueOf(value)
	if k.Kind() == reflect.Ptr {
		if k.IsNil() {
			return nil, marshalErrorf("cannot marshal %T into %s", value, info)
		}
		k = k.Elem()
	}

	if k.Kind() != reflect.Struct || !k.IsValid() {
		return nil, marshalErrorf("cannot marshal %T into %s", value, info)
	}

	fields := make(map[string]reflect.Value)
	t := reflect.TypeOf(value)
	for i := 0; i < t.NumField(); i++ {
		sf := t.Field(i)

		if tag := sf.Tag.Get("cql"); tag != "" {
			fields[tag] = k.Field(i)
		}
	}

	var buf []byte
	for _, e := range udt.Elements {
		f, ok := fields[e.Name]
		if !ok {
			f = k.FieldByName(e.Name)
		}

		if !f.IsValid() {
			if _, ok := e.Type.(CollectionType); ok {
				f = reflect.Zero(goType(e.Type))
			} else {
				buf = appendInt(buf, -1)
				continue
			}
		} else if f.Kind() == reflect.Ptr {
			if f.IsNil() {
				buf = appendInt(buf, -1)
				continue
			} else {
				f = f.Elem()
			}
		}

		data, err := Marshal(e.Type, f.Interface())
		if err != nil {
			return nil, err
		}

		if data == nil && typeCanBeNull(e.Type) {
			buf = appendInt(buf, -1)
		} else {
			buf = appendInt(buf, int32(len(data)))
			buf = append(buf, data...)
		}
	}

	return buf, nil

}

func unmarshalUDT(info TypeInfo, data []byte, value interface{}) error {
	switch v := value.(type) {
	case Unmarshaler:
		return v.UnmarshalCQL(info, data)
	case UDTUnmarshaler:
		udt := info.(UDTTypeInfo)

		for _, e := range udt.Elements {
			size := readInt(data[:4])
			data = data[4:]

			var err error
			if size < 0 {
				err = v.UnmarshalUDT(e.Name, e.Type, nil)
			} else {
				err = v.UnmarshalUDT(e.Name, e.Type, data[:size])
				data = data[size:]
			}

			if err != nil {
				return err
			}
		}

		return nil
	case *map[string]interface{}:
		udt := info.(UDTTypeInfo)

		rv := reflect.ValueOf(value)
		if rv.Kind() != reflect.Ptr {
			return unmarshalErrorf("can not unmarshal into non-pointer %T", value)
		}

		rv = rv.Elem()
		t := rv.Type()
		if t.Kind() != reflect.Map {
			return unmarshalErrorf("can not unmarshal %s into %T", info, value)
		} else if data == nil {
			rv.Set(reflect.Zero(t))
			return nil
		}

		rv.Set(reflect.MakeMap(t))
		m := *v

		for _, e := range udt.Elements {
			size := readInt(data[:4])
			data = data[4:]

			val := reflect.New(goType(e.Type))

			var err error
			if size < 0 {
				err = Unmarshal(e.Type, nil, val.Interface())
			} else {
				err = Unmarshal(e.Type, data[:size], val.Interface())
				data = data[size:]
			}

			if err != nil {
				return err
			}

			m[e.Name] = val.Elem().Interface()
		}

		return nil
	}

	k := reflect.ValueOf(value).Elem()
	if k.Kind() != reflect.Struct || !k.IsValid() {
		return unmarshalErrorf("cannot unmarshal %s into %T", info, value)
	}

	fields := make(map[string]reflect.Value)
	t := k.Type()
	for i := 0; i < t.NumField(); i++ {
		sf := t.Field(i)

		if tag := sf.Tag.Get("cql"); tag != "" {
			fields[tag] = k.Field(i)
		}
	}

	if len(data) == 0 {
		if k.CanSet() {
			k.Set(reflect.Zero(k.Type()))
		}

		return nil
	}

	udt := info.(UDTTypeInfo)
	for _, e := range udt.Elements {
		size := readInt(data[:4])
		data = data[4:]

		var err error
		if size >= 0 {
			f, ok := fields[e.Name]
			if !ok {
				f = k.FieldByName(e.Name)
			}

			if !f.IsValid() || !f.CanAddr() {
				return unmarshalErrorf("cannot unmarshal %s into %T", info, value)
			}

			fk := f.Addr().Interface()
			if err := Unmarshal(e.Type, data[:size], fk); err != nil {
				return err
			}
			data = data[size:]
		}

		if err != nil {
			return err
		}
	}

	return nil
}

// TypeInfo describes a Cassandra specific data type.
type TypeInfo interface {
	Type() Type
	Version() byte
	Custom() string

	// New creates a pointer to an empty version of whatever type
	// is referenced by the TypeInfo receiver
	New() interface{}
}

type NativeType struct {
	proto  byte
	typ    Type
	custom string // only used for TypeCustom
}

func (t NativeType) New() interface{} {
	return reflect.New(goType(t)).Interface()
}

func (s NativeType) Type() Type {
	return s.typ
}

func (s NativeType) Version() byte {
	return s.proto
}

func (s NativeType) Custom() string {
	return s.custom
}

func (s NativeType) String() string {
	switch s.typ {
	case TypeCustom:
		return fmt.Sprintf("%s(%s)", s.typ, s.custom)
	default:
		return s.typ.String()
	}
}

type CollectionType struct {
	NativeType
	Key  TypeInfo // only used for TypeMap
	Elem TypeInfo // only used for TypeMap, TypeList and TypeSet
}

func (t CollectionType) New() interface{} {
	return reflect.New(goType(t)).Interface()
}

func (c CollectionType) String() string {
	switch c.typ {
	case TypeMap:
		return fmt.Sprintf("%s(%s, %s)", c.typ, c.Key, c.Elem)
	case TypeList, TypeSet:
		return fmt.Sprintf("%s(%s)", c.typ, c.Elem)
	case TypeCustom:
		return fmt.Sprintf("%s(%s)", c.typ, c.custom)
	default:
		return c.typ.String()
	}
}

type TupleTypeInfo struct {
	NativeType
	Elems []TypeInfo
}

type UDTField struct {
	Name string
	Type TypeInfo
}

type UDTTypeInfo struct {
	NativeType
	KeySpace string
	Name     string
	Elements []UDTField
}

func (u UDTTypeInfo) String() string {
	buf := &bytes.Buffer{}

	fmt.Fprintf(buf, "%s.%s{", u.KeySpace, u.Name)
	first := true
	for _, e := range u.Elements {
		if !first {
			fmt.Fprint(buf, ",")
		} else {
			first = false
		}

		fmt.Fprintf(buf, "%s=%v", e.Name, e.Type)
	}
	fmt.Fprint(buf, "}")

	return buf.String()
}

// String returns a human readable name for the Cassandra datatype
// described by t.
// Type is the identifier of a Cassandra internal datatype.
type Type int

const (
	TypeCustom    Type = 0x0000
	TypeAscii     Type = 0x0001
	TypeBigInt    Type = 0x0002
	TypeBlob      Type = 0x0003
	TypeBoolean   Type = 0x0004
	TypeCounter   Type = 0x0005
	TypeDecimal   Type = 0x0006
	TypeDouble    Type = 0x0007
	TypeFloat     Type = 0x0008
	TypeInt       Type = 0x0009
	TypeText      Type = 0x000A
	TypeTimestamp Type = 0x000B
	TypeUUID      Type = 0x000C
	TypeVarchar   Type = 0x000D
	TypeVarint    Type = 0x000E
	TypeTimeUUID  Type = 0x000F
	TypeInet      Type = 0x0010
	TypeList      Type = 0x0020
	TypeMap       Type = 0x0021
	TypeSet       Type = 0x0022
	TypeUDT       Type = 0x0030
	TypeTuple     Type = 0x0031
)

// String returns the name of the identifier.
func (t Type) String() string {
	switch t {
	case TypeCustom:
		return "custom"
	case TypeAscii:
		return "ascii"
	case TypeBigInt:
		return "bigint"
	case TypeBlob:
		return "blob"
	case TypeBoolean:
		return "boolean"
	case TypeCounter:
		return "counter"
	case TypeDecimal:
		return "decimal"
	case TypeDouble:
		return "double"
	case TypeFloat:
		return "float"
	case TypeInt:
		return "int"
	case TypeText:
		return "text"
	case TypeTimestamp:
		return "timestamp"
	case TypeUUID:
		return "uuid"
	case TypeVarchar:
		return "varchar"
	case TypeTimeUUID:
		return "timeuuid"
	case TypeInet:
		return "inet"
	case TypeList:
		return "list"
	case TypeMap:
		return "map"
	case TypeSet:
		return "set"
	case TypeVarint:
		return "varint"
	case TypeTuple:
		return "tuple"
	default:
		return fmt.Sprintf("unknown_type_%d", t)
	}
}

type MarshalError string

func (m MarshalError) Error() string {
	return string(m)
}

func marshalErrorf(format string, args ...interface{}) MarshalError {
	return MarshalError(fmt.Sprintf(format, args...))
}

type UnmarshalError string

func (m UnmarshalError) Error() string {
	return string(m)
}

func unmarshalErrorf(format string, args ...interface{}) UnmarshalError {
	return UnmarshalError(fmt.Sprintf(format, args...))
}