varfield.go

/*
 * File: varfield.go
 * Project: mrsign
 * Created Date: Tuesday, October 19th 2021, 12:16:54 pm
 * Authors: Marcello Russo, Fabio Zito
 * -----
 * Last Modified:
 * Modified By:
 * -----
 * MIT License
 *
 * Copyright (c) 2021 MR&&Z
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is furnished to do
 * so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 * -----
 * HISTORY:
 * Date      	By	Comments
 * ----------	---	----------------------------------------------------------
 */

package main

import (
	"errors"
)

type VarField struct {
	Len    uint16
	MaxLen uint16
	Offset uint32
}

func (f VarField) ReadFrom(buffer []byte) ([]byte,
	error) {
	if len(buffer) < int(f.Offset+uint32(f.Len)) {
		return nil, errors.New("error reading data, VarField extends beyond buffer")
	}
	return buffer[f.Offset : f.Offset+uint32(f.Len)], nil
}

func (f VarField) ReadStringFrom(buffer []byte) (string, error) {
	d, err := f.ReadFrom(buffer)
	if err != nil {
		return "", err
	}
	return string(d), err
}

func NewVarField(ptr *int, fieldSize int) VarField {
	f := VarField{
		Len:    uint16(fieldSize),
		MaxLen: uint16(fieldSize),
		Offset: uint32(*ptr),
	}
	*ptr += fieldSize
	return f
}