unsigned64.go

/*
Copyright 2023 Alexander Bartolomey (github@alexanderbartolomey.de)

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package ipfix

import (
	"encoding/binary"
	"encoding/json"
	"fmt"
	"io"
)

type Unsigned64 struct {
	value uint64

	reducedLength bool
	length        uint16
}

func NewUnsigned64() DataType {
	return &Unsigned64{}
}

func (t *Unsigned64) String() string {
	return fmt.Sprintf("%v", uint64(t.value))
}

func (*Unsigned64) Type() string {
	return "unsigned64"
}

func (t *Unsigned64) Value() interface{} {
	return t.value
}

func (t *Unsigned64) SetValue(v any) DataType {
	switch ty := v.(type) {
	case float64:
		t.value = uint64(ty)
	case int:
		t.value = uint64(ty)
	default:
		panic(fmt.Errorf("%T cannot be asserted to %T", v, t.value))
	}
	return t
}

func (t *Unsigned64) Length() uint16 {
	if t.length > 0 {
		return t.length
	}
	return t.DefaultLength()
}

func (*Unsigned64) DefaultLength() uint16 {
	return 8
}

func (t *Unsigned64) Clone() DataType {
	return &Unsigned64{
		value: t.value,
	}
}

func (t *Unsigned64) WithLength(length uint16) DataTypeConstructor {
	if length > 0 && length < t.DefaultLength() {
		return func() DataType {
			return &Unsigned64{
				reducedLength: true,
				length:        length,
			}
		}
	}
	return NewUnsigned64
}

func (t *Unsigned64) SetLength(length uint16) DataType {
	// only valid lengths for unsigned64 are reduced-length encodings
	if length > 0 && length < t.DefaultLength() {
		t.length = length
		t.reducedLength = true
	} else {
		t.length = t.DefaultLength()
	}
	return t
}

func (t *Unsigned64) IsReducedLength() bool {
	return t.reducedLength
}

func (t *Unsigned64) Decode(in io.Reader) (n int, err error) {
	// allocate a buffer of the (possibly reduced) length of the data type
	b := make([]byte, t.Length())
	n, err = in.Read(b)
	if err != nil {
		return n, fmt.Errorf("failed to read data in %T, %w", t, err)
	}
	if !t.reducedLength {
		// fast-track
		t.value = binary.BigEndian.Uint64(b)
		return
	}
	// because reduced-length encoding still preserves BigEndian, we pad the
	// internal uint64
	offset := t.DefaultLength() - t.Length()
	c := make([]byte, t.DefaultLength())
	// abusing golangs initialization of values with 0 here
	for i := uint16(0); i < t.length; i++ {
		c[i+offset] = b[i]
	}
	t.value = binary.BigEndian.Uint64(c)
	return
}

func (t *Unsigned64) Encode(w io.Writer) (int, error) {
	b := make([]byte, t.Length())
	if !t.reducedLength {
		// fast-track
		binary.BigEndian.PutUint64(b, t.value)
		return w.Write(b)
	}
	offset := t.DefaultLength() - t.Length()
	c := make([]byte, t.DefaultLength())
	binary.BigEndian.PutUint64(c, t.value)

	for i := uint16(0); i < t.length; i++ {
		b[i] = c[i+offset]
	}
	return w.Write(b)
}

func (t *Unsigned64) MarshalJSON() ([]byte, error) {
	return json.Marshal(t.value)
}

func (t *Unsigned64) UnmarshalJSON(in []byte) error {
	return json.Unmarshal(in, &t.value)
}

var _ DataTypeConstructor = NewUnsigned64
var _ DataType = &Unsigned64{}