github.com/iDigitalFlame/xmt@v0.5.1/device/id.go

// Copyright (C) 2020 - 2023 iDigitalFlame
//
// This program 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
// any later version.
//
// This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
//

package device

import (
	"io"
	"os"

	"github.com/iDigitalFlame/xmt/data"
	"github.com/iDigitalFlame/xmt/util"
)

const (
	// IDSize is the amount of bytes used to store the Host ID and
	// SessionID values. The ID is the (HostID + SessionID).
	IDSize = 32
	// MachineIDSize is the amount of bytes that is used as the Host
	// specific ID value that does not change when on the same host.
	MachineIDSize = 28
)

// ID is an alias for a byte array that represents a 32 byte client
// identification number. This is used for tracking and detection purposes.
//
// The first byte and the machine ID byte should NEVER be zero, otherwise it
// signals an invalid ID value or missing a random identifier.
type ID [IDSize]byte

// Empty returns true if this ID is considered empty.
func (i ID) Empty() bool {
	return i[0] == 0
}

// Hash returns the 32bit hash sum of this ID value. The hash mechanism used is
// similar to the hash/fnv mechanism.
func (i ID) Hash() uint32 {
	h := uint32(2166136261)
	for x := range i {
		h *= 16777619
		h ^= uint32(i[x])
	}
	return h
}

// Full returns the full string representation of this ID instance.
func (i ID) Full() string {
	return i.string(0, IDSize)
}

// String returns a representation of this ID instance.
func (i ID) String() string {
	if i[MachineIDSize] == 0 {
		return i.string(0, MachineIDSize)
	}
	return i.string(MachineIDSize, IDSize)
}

// Seed will set the random portion of the ID value to the specified byte array
// value.
func (i *ID) Seed(b []byte) {
	if len(b) == 0 {
		return
	}
	copy(i[MachineIDSize:], b)
}

// Signature returns the signature portion of the ID value. This value is
// constant and unique for each device.
func (i ID) Signature() string {
	if i[MachineIDSize] == 0 {
		return i.string(0, MachineIDSize)
	}
	return i.string(0, MachineIDSize)
}

// Load will attempt to load the Session UUID from the specified file. This
// function will return an error if the file cannot be read or not found.
func (i *ID) Load(s string) error {
	// 0 - READONLY
	r, err := os.OpenFile(s, 0, 0)
	if err != nil {
		return err
	}
	err = i.Read(r)
	if r.Close(); err != nil {
		return err
	}
	return nil
}

// Save will attempt to save the Session UUID to the specified file. This
// function will return an error if the file cannot be written to or created.
func (i ID) Save(s string) error {
	// 0x242 - CREATE | TRUNCATE | RDWR
	w, err := os.OpenFile(s, 0x242, 0644)
	if err != nil {
		return err
	}
	_, err = w.Write(i[:])
	if w.Close(); err != nil {
		return err
	}
	return nil
}

// Read will attempt to read up to 'IDSize' bytes from the reader into this ID.
func (i *ID) Read(r io.Reader) error {
	if n, err := io.ReadFull(r, i[:]); n != IDSize || i[0] == 0 {
		// NOTE(dij): This line causes empty ID values to be considered read
		//            errors. Technically this is incorrect, but we should never
		//            be using empty ID values to communicate so it's sorta ok.
		if err != nil {
			return err
		}
		return io.ErrUnexpectedEOF
	}
	return nil
}

// Write will attempt to write the ID bytes into the supplied writer.
func (i ID) Write(w io.Writer) error {
	n, err := w.Write(i[:])
	if err == nil && n != IDSize {
		return io.ErrShortWrite
	}
	return err
}
func (i ID) string(start, end int) string {
	var (
		b [64]byte
		n int
	)
	for x := start; x < end; x++ {
		b[n] = util.HexTable[i[x]>>4]
		b[n+1] = util.HexTable[i[x]&0x0F]
		n += 2
	}
	return string(b[:n])
}

// MarshalStream transform this struct into a binary format and writes to the
// supplied data.Writer.
func (i ID) MarshalStream(w data.Writer) error {
	_, err := w.Write(i[:])
	return err
}

// UnmarshalStream transforms this struct from a binary format that is read from
// the supplied data.Reader.
func (i *ID) UnmarshalStream(r data.Reader) error {
	return i.Read(r)
}