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|
package lz4
import (
"encoding/binary"
"fmt"
"io"
)
// ReaderLegacy implements the LZ4Demo frame decoder.
// The Header is set after the first call to Read().
type ReaderLegacy struct {
Header
// Handler called when a block has been successfully read.
// It provides the number of bytes read.
OnBlockDone func(size int)
lastBlock bool
buf [8]byte // Scrap buffer.
pos int64 // Current position in src.
src io.Reader // Source.
zdata []byte // Compressed data.
data []byte // Uncompressed data.
idx int // Index of unread bytes into data.
skip int64 // Bytes to skip before next read.
dpos int64 // Position in dest
}
// NewReaderLegacy returns a new LZ4Demo frame decoder.
// No access to the underlying io.Reader is performed.
func NewReaderLegacy(src io.Reader) *ReaderLegacy {
r := &ReaderLegacy{src: src}
return r
}
// readHeader checks the frame magic number and parses the frame descriptoz.
// Skippable frames are supported even as a first frame although the LZ4
// specifications recommends skippable frames not to be used as first frames.
func (z *ReaderLegacy) readLegacyHeader() error {
z.lastBlock = false
magic, err := z.readUint32()
if err != nil {
z.pos += 4
if err == io.ErrUnexpectedEOF {
return io.EOF
}
return err
}
if magic != frameMagicLegacy {
return ErrInvalid
}
z.pos += 4
// Legacy has fixed 8MB blocksizes
// https://github.com/lz4/lz4/blob/dev/doc/lz4_Frame_format.md#legacy-frame
bSize := blockSize4M * 2
// Allocate the compressed/uncompressed buffers.
// The compressed buffer cannot exceed the uncompressed one.
if n := 2 * bSize; cap(z.zdata) < n {
z.zdata = make([]byte, n, n)
}
if debugFlag {
debug("header block max size size=%d", bSize)
}
z.zdata = z.zdata[:bSize]
z.data = z.zdata[:cap(z.zdata)][bSize:]
z.idx = len(z.data)
z.Header.done = true
if debugFlag {
debug("header read: %v", z.Header)
}
return nil
}
// Read decompresses data from the underlying source into the supplied buffer.
//
// Since there can be multiple streams concatenated, Header values may
// change between calls to Read(). If that is the case, no data is actually read from
// the underlying io.Reader, to allow for potential input buffer resizing.
func (z *ReaderLegacy) Read(buf []byte) (int, error) {
if debugFlag {
debug("Read buf len=%d", len(buf))
}
if !z.Header.done {
if err := z.readLegacyHeader(); err != nil {
return 0, err
}
if debugFlag {
debug("header read OK compressed buffer %d / %d uncompressed buffer %d : %d index=%d",
len(z.zdata), cap(z.zdata), len(z.data), cap(z.data), z.idx)
}
}
if len(buf) == 0 {
return 0, nil
}
if z.idx == len(z.data) {
// No data ready for reading, process the next block.
if debugFlag {
debug(" reading block from writer %d %d", z.idx, blockSize4M*2)
}
// Reset uncompressed buffer
z.data = z.zdata[:cap(z.zdata)][len(z.zdata):]
bLen, err := z.readUint32()
if err != nil {
return 0, err
}
if debugFlag {
debug(" bLen %d (0x%x) offset = %d (0x%x)", bLen, bLen, z.pos, z.pos)
}
z.pos += 4
// Legacy blocks are always compressed, even when detrimental
if debugFlag {
debug(" compressed block size %d", bLen)
}
if int(bLen) > cap(z.data) {
return 0, fmt.Errorf("lz4: invalid block size: %d", bLen)
}
zdata := z.zdata[:bLen]
if _, err := io.ReadFull(z.src, zdata); err != nil {
return 0, err
}
z.pos += int64(bLen)
n, err := UncompressBlock(zdata, z.data)
if err != nil {
return 0, err
}
z.data = z.data[:n]
if z.OnBlockDone != nil {
z.OnBlockDone(n)
}
z.idx = 0
// Legacy blocks are fixed to 8MB, if we read a decompressed block smaller than this
// it means we've reached the end...
if n < blockSize4M*2 {
z.lastBlock = true
}
}
if z.skip > int64(len(z.data[z.idx:])) {
z.skip -= int64(len(z.data[z.idx:]))
z.dpos += int64(len(z.data[z.idx:]))
z.idx = len(z.data)
return 0, nil
}
z.idx += int(z.skip)
z.dpos += z.skip
z.skip = 0
n := copy(buf, z.data[z.idx:])
z.idx += n
z.dpos += int64(n)
if debugFlag {
debug("%v] copied %d bytes to input (%d:%d)", z.lastBlock, n, z.idx, len(z.data))
}
if z.lastBlock && len(z.data) == z.idx {
return n, io.EOF
}
return n, nil
}
// Seek implements io.Seeker, but supports seeking forward from the current
// position only. Any other seek will return an error. Allows skipping output
// bytes which aren't needed, which in some scenarios is faster than reading
// and discarding them.
// Note this may cause future calls to Read() to read 0 bytes if all of the
// data they would have returned is skipped.
func (z *ReaderLegacy) Seek(offset int64, whence int) (int64, error) {
if offset < 0 || whence != io.SeekCurrent {
return z.dpos + z.skip, ErrUnsupportedSeek
}
z.skip += offset
return z.dpos + z.skip, nil
}
// Reset discards the Reader's state and makes it equivalent to the
// result of its original state from NewReader, but reading from r instead.
// This permits reusing a Reader rather than allocating a new one.
func (z *ReaderLegacy) Reset(r io.Reader) {
z.Header = Header{}
z.pos = 0
z.src = r
z.zdata = z.zdata[:0]
z.data = z.data[:0]
z.idx = 0
}
// readUint32 reads an uint32 into the supplied buffer.
// The idea is to make use of the already allocated buffers avoiding additional allocations.
func (z *ReaderLegacy) readUint32() (uint32, error) {
buf := z.buf[:4]
_, err := io.ReadFull(z.src, buf)
x := binary.LittleEndian.Uint32(buf)
return x, err
}
|
