diskii/disk/marshal.go
2021-07-10 21:09:57 -04:00

136 lines
4.2 KiB
Go

// Copyright © 2016 Zellyn Hunter <zellyn@gmail.com>
// marshal.go contains helpers for marshaling sector structs to/from
// disk and block structs to/from devices.
package disk
import "fmt"
// BlockDevice is the interface used to read and write devices by
// logical block number.
// SectorSource is the interface for types that can marshal to sectors.
type SectorSource interface {
// ToSector marshals the sector struct to exactly 256 bytes.
ToSector() ([]byte, error)
// GetTrack returns the track that a sector struct was loaded from.
GetTrack() byte
// GetSector returns the sector that a sector struct was loaded from.
GetSector() byte
}
// SectorSink is the interface for types that can unmarshal from sectors.
type SectorSink interface {
// FromSector unmarshals the sector struct from bytes. Input is
// expected to be exactly 256 bytes.
FromSector(data []byte) error
// SetTrack sets the track that a sector struct was loaded from.
SetTrack(track byte)
// SetSector sets the sector that a sector struct was loaded from.
SetSector(sector byte)
}
// UnmarshalLogicalSector reads a sector from a disk image, and unmarshals it
// into a SectorSink, setting its track and sector.
func UnmarshalLogicalSector(diskbytes []byte, ss SectorSink, track, sector byte) error {
bytes, err := ReadSector(diskbytes, track, sector)
if err != nil {
return err
}
if err := ss.FromSector(bytes); err != nil {
return err
}
ss.SetTrack(track)
ss.SetSector(sector)
return nil
}
// ReadSector just reads 256 bytes from the given track and sector.
func ReadSector(diskbytes []byte, track, sector byte) ([]byte, error) {
start := int(track)*FloppyTrackBytes + int(sector)*256
end := start + 256
if len(diskbytes) < end {
return nil, fmt.Errorf("cannot read track %d/sector %d (bytes %d-%d) from disk of length %d", track, sector, start, end, len(diskbytes))
}
bytes := make([]byte, 256)
copy(bytes, diskbytes[start:end])
return bytes, nil
}
// MarshalLogicalSector marshals a SectorSource to its track/sector on a disk
// image.
func MarshalLogicalSector(diskbytes []byte, ss SectorSource) error {
track := ss.GetTrack()
sector := ss.GetSector()
bytes, err := ss.ToSector()
if err != nil {
return err
}
return WriteSector(diskbytes, track, sector, bytes)
}
// WriteSector writes 256 bytes to the given track and sector.
func WriteSector(diskbytes []byte, track, sector byte, data []byte) error {
if len(data) != 256 {
return fmt.Errorf("call to writeSector with len(data)==%d; want 256", len(data))
}
start := int(track)*FloppyTrackBytes + int(sector)*256
end := start + 256
if len(diskbytes) < end {
return fmt.Errorf("cannot write track %d/sector %d (bytes %d-%d) to disk of length %d", track, sector, start, end, len(diskbytes))
}
copy(diskbytes[start:end], data)
return nil
}
// BlockSource is the interface for types that can marshal to blocks.
type BlockSource interface {
// ToBlock marshals the block struct to exactly 512 bytes.
ToBlock() (Block, error)
// GetBlock returns the index that a block struct was loaded from.
GetBlock() uint16
}
// BlockSink is the interface for types that can unmarshal from blocks.
type BlockSink interface {
// FromBlock unmarshals the block struct from a Block. Input is
// expected to be exactly 512 bytes.
FromBlock(block Block) error
// SetBlock sets the index that a block struct was loaded from.
SetBlock(index uint16)
}
// UnmarshalBlock reads a block from a block device, and unmarshals it into a
// BlockSink, setting its index.
func UnmarshalBlock(diskbytes []byte, bs BlockSink, index uint16) error {
start := int(index) * 512
end := start + 512
if len(diskbytes) < end {
return fmt.Errorf("device too small to read block %d", index)
}
var block Block
copy(block[:], diskbytes[start:end])
if err := bs.FromBlock(block); err != nil {
return err
}
bs.SetBlock(index)
return nil
}
// MarshalBlock marshals a BlockSource to its block on a block device.
func MarshalBlock(diskbytes []byte, bs BlockSource) error {
index := bs.GetBlock()
block, err := bs.ToBlock()
if err != nil {
return err
}
start := int(index) * 512
end := start + 512
if len(diskbytes) < end {
return fmt.Errorf("device too small to write block %d", index)
}
copy(diskbytes[start:end], block[:])
return nil
}