squashfs - compressor.go

  package squashfs
  
  import (
  	"compress/zlib"
  	"fmt"
  	"io"
  	"math/bits"
  
  	"vimagination.zapto.org/byteio"
  )
  
  type Compressor uint16
  
  const (
  	CompressorGZIP Compressor = 1
  	CompressorLZMA Compressor = 2
  	CompressorLZO  Compressor = 3
  	CompressorXZ   Compressor = 4
  	CompressorLZ4  Compressor = 5
  	CompressorZSTD Compressor = 6
  )
  
  func (c Compressor) String() string {
  	switch c {
  	case CompressorGZIP:
  		return "gzip"
  	case CompressorLZMA:
  		return "lzma"
  	case CompressorLZO:
  		return "lzo"
  	case CompressorXZ:
  		return "xz"
  	case CompressorLZ4:
  		return "lz4"
  	case CompressorZSTD:
  		return "zstd"
  	}
  
  	return "unknown"
  }
  
  func (c Compressor) decompress(r io.Reader) (io.Reader, error) {
  	switch c {
  	case CompressorGZIP:
  		return zlib.NewReader(r)
  	default:
  		return nil, fmt.Errorf("%s: %w", c, ErrUnsupportedCompressor)
  	}
  }
  
  type CompressorOptions interface {
  	makeWriter(io.Writer) (io.WriteCloser, error)
  	asCompressor() Compressor
  	isDefault() bool
  	writeTo(*byteio.StickyLittleEndianWriter)
  }
  
  func (c Compressor) parseOptions(hasOptionsFlag bool, ler *byteio.StickyLittleEndianReader) (CompressorOptions, error) {
  	switch c {
  	case CompressorGZIP:
  		if hasOptionsFlag {
  			return parseGZipOptions(ler)
  		} else {
  			return defaultGzipOptions(), nil
  		}
  	case CompressorLZMA:
  		return nil, ErrNoCompressorOptions
  	case CompressorLZO:
  		if hasOptionsFlag {
  			return parseLZOOptions(ler)
  		} else {
  			return defaultLZOOptions(), nil
  		}
  	case CompressorXZ:
  		if hasOptionsFlag {
  			return parseXZOptions(ler)
  		} else {
  			return defaultXZOptions(), nil
  		}
  	case CompressorLZ4:
  		return parseLZ4Options(ler)
  	case CompressorZSTD:
  		if hasOptionsFlag {
  			return parseZStdOptions(ler)
  		} else {
  			return defaultZStdOptions(), nil
  		}
  	}
  
  	return nil, ErrInvalidCompressor
  }
  
  type GZipOptions struct {
  	CompressionLevel uint32
  	WindowSize       uint16
  	Strategies       uint16
  }
  
  const (
  	minimumWindowSize = 8
  	maximumWindowSize = 15
  )
  
  func parseGZipOptions(ler *byteio.StickyLittleEndianReader) (*GZipOptions, error) {
  	compressionlevel := ler.ReadUint32()
  	if compressionlevel == 0 || compressionlevel > zlib.BestCompression {
  		return nil, ErrInvalidCompressionLevel
  	}
  
  	windowsize := ler.ReadUint16()
  	if windowsize < minimumWindowSize || windowsize > maximumWindowSize {
  		return nil, ErrInvalidWindowSize
  	}
  
  	const maxStrategy = 21
  
  	strategies := ler.ReadUint16()
  	if strategies > maxStrategy {
  		return nil, ErrInvalidCompressionStrategies
  	}
  
  	return &GZipOptions{
  		CompressionLevel: compressionlevel,
  		WindowSize:       windowsize,
  		Strategies:       strategies,
  	}, nil
  }
  
  func defaultGzipOptions() *GZipOptions {
  	return &GZipOptions{
  		CompressionLevel: zlib.BestCompression,
  		WindowSize:       maximumWindowSize,
  	}
  }
  
  func (g *GZipOptions) makeWriter(w io.Writer) (io.WriteCloser, error) {
  	return zlib.NewWriterLevel(w, int(g.CompressionLevel))
  }
  
  func (GZipOptions) asCompressor() Compressor {
  	return CompressorGZIP
  }
  
  func (g *GZipOptions) isDefault() bool {
  	return g.CompressionLevel == zlib.BestCompression && g.WindowSize == maximumWindowSize
  }
  
  func (g *GZipOptions) writeTo(w *byteio.StickyLittleEndianWriter) {
  	w.WriteUint32(g.CompressionLevel)
  	w.WriteUint16(g.WindowSize)
  	w.WriteUint16(g.Strategies)
  }
  
  type LZOOptions struct {
  	Algorithm        uint32
  	CompressionLevel uint32
  }
  
  func parseLZOOptions(ler *byteio.StickyLittleEndianReader) (*LZOOptions, error) {
  	const maxAlgorithm = 4
  
  	algorithm := ler.ReadUint32()
  	if algorithm > maxAlgorithm {
  		return nil, ErrInvalidCompressionAlgorithm
  	}
  
  	compressionlevel := ler.ReadUint32()
  	if compressionlevel > zlib.BestCompression || algorithm != 4 && compressionlevel != 0 {
  		return nil, ErrInvalidCompressionLevel
  	}
  
  	return &LZOOptions{
  		Algorithm:        algorithm,
  		CompressionLevel: compressionlevel,
  	}, nil
  }
  
  const (
  	lzoDefaultAlgorithm        = 4
  	lzoDefaultCompressionLevel = 8
  )
  
  func defaultLZOOptions() *LZOOptions {
  	return &LZOOptions{
  		Algorithm:        lzoDefaultAlgorithm,
  		CompressionLevel: lzoDefaultCompressionLevel,
  	}
  }
  
  func (l *LZOOptions) isDefault() bool {
  	return l.CompressionLevel == lzoDefaultCompressionLevel && l.Algorithm == lzoDefaultAlgorithm
  }
  
  func (LZOOptions) makeWriter(w io.Writer) (io.WriteCloser, error) {
  	return nil, ErrUnsupportedCompressor
  }
  
  func (LZOOptions) asCompressor() Compressor {
  	return CompressorLZO
  }
  
  func (l *LZOOptions) writeTo(w *byteio.StickyLittleEndianWriter) {
  	w.WriteUint32(l.Algorithm)
  	w.WriteUint32(l.CompressionLevel)
  }
  
  type XZOptions struct {
  	DictionarySize uint32
  	Filters        uint32
  }
  
  const maxDictionarySize = 8192
  
  func parseXZOptions(ler *byteio.StickyLittleEndianReader) (*XZOptions, error) {
  	dictionarysize := ler.ReadUint32()
  	if lead, trail := bits.LeadingZeros32(dictionarysize), bits.TrailingZeros32(dictionarysize); dictionarysize < maxDictionarySize || 32-trail-lead > 2 {
  		return nil, ErrInvalidDictionarySize
  	}
  
  	const maxFilters = 63
  
  	filters := ler.ReadUint32()
  	if filters > maxFilters {
  		return nil, ErrInvalidFilters
  	}
  
  	return &XZOptions{
  		DictionarySize: dictionarysize,
  		Filters:        filters,
  	}, nil
  }
  
  func defaultXZOptions() *XZOptions {
  	return &XZOptions{
  		DictionarySize: maxDictionarySize,
  	}
  }
  
  func (XZOptions) makeWriter(w io.Writer) (io.WriteCloser, error) {
  	return nil, ErrUnsupportedCompressor
  }
  
  func (XZOptions) asCompressor() Compressor {
  	return CompressorXZ
  }
  
  func (x *XZOptions) isDefault() bool {
  	return x.DictionarySize == maxDictionarySize && x.Filters == 0
  }
  
  func (x *XZOptions) writeTo(w *byteio.StickyLittleEndianWriter) {
  	w.WriteUint32(x.DictionarySize)
  	w.WriteUint32(x.Filters)
  }
  
  type LZ4Options struct {
  	Version uint32
  	Flags   uint32
  }
  
  func parseLZ4Options(ler *byteio.StickyLittleEndianReader) (*LZ4Options, error) {
  	if ler.ReadUint32() != 1 {
  		return nil, ErrInvalidCompressorVersion
  	}
  
  	flags := ler.ReadUint32()
  	if flags > 1 {
  		return nil, ErrInvalidCompressorFlags
  	}
  
  	return &LZ4Options{
  		Version: 1,
  		Flags:   flags,
  	}, nil
  }
  
  func (LZ4Options) makeWriter(w io.Writer) (io.WriteCloser, error) {
  	return nil, ErrUnsupportedCompressor
  }
  
  func (LZ4Options) asCompressor() Compressor {
  	return CompressorLZ4
  }
  
  func (LZ4Options) isDefault() bool {
  	return false
  }
  
  func (l *LZ4Options) writeTo(w *byteio.StickyLittleEndianWriter) {
  	w.WriteUint32(l.Version)
  	w.WriteUint32(l.Flags)
  }
  
  type ZStdOptions struct {
  	CompressionLevel uint32
  }
  
  func parseZStdOptions(ler *byteio.StickyLittleEndianReader) (*ZStdOptions, error) {
  	const maxZStdCompressionLevel = 22
  
  	compressionlevel := ler.ReadUint32()
  	if compressionlevel == 0 || compressionlevel > maxZStdCompressionLevel {
  		return nil, ErrInvalidCompressionLevel
  	}
  
  	return &ZStdOptions{
  		CompressionLevel: compressionlevel,
  	}, nil
  }
  
  func defaultZStdOptions() *ZStdOptions {
  	return &ZStdOptions{
  		CompressionLevel: zlib.BestCompression,
  	}
  }
  
  func (ZStdOptions) makeWriter(w io.Writer) (io.WriteCloser, error) {
  	return nil, ErrUnsupportedCompressor
  }
  
  func (ZStdOptions) asCompressor() Compressor {
  	return CompressorZSTD
  }
  
  func (z *ZStdOptions) isDefault() bool {
  	return z.CompressionLevel == zlib.BestCompression
  }
  
  func (z *ZStdOptions) writeTo(w *byteio.StickyLittleEndianWriter) {
  	w.WriteUint32(z.CompressionLevel)
  }