func (w *Writer) writeBlock(buf *util.Buffer, compression opt.Compression) (bh blockHandle, err error) {
// Compress the buffer if necessary.
var b []byte
if compression == opt.SnappyCompression {
// Allocate scratch enough for compression and block trailer.
if n := snappy.MaxEncodedLen(buf.Len()) + blockTrailerLen; len(w.compressionScratch) < n {
w.compressionScratch = make([]byte, n)
}
compressed := snappy.Encode(w.compressionScratch, buf.Bytes())
n := len(compressed)
b = compressed[:n+blockTrailerLen]
b[n] = blockTypeSnappyCompression
} else {
tmp := buf.Alloc(blockTrailerLen)
tmp[0] = blockTypeNoCompression
b = buf.Bytes()
}
// Calculate the checksum.
n := len(b) - 4
checksum := util.NewCRC(b[:n]).Value()
binary.LittleEndian.PutUint32(b[n:], checksum)
// Write the buffer to the file.
_, err = w.writer.Write(b)
if err != nil {
return
}
bh = blockHandle{w.offset, uint64(len(b) - blockTrailerLen)}
w.offset += uint64(len(b))
return
}
// fillHeader fills in the header for the pending chunk.
func (w *Writer) fillHeader(last bool) {
if w.i+headerSize > w.j || w.j > blockSize {
panic("leveldb/journal: bad writer state")
}
if last {
if w.first {
w.buf[w.i+6] = fullChunkType
} else {
w.buf[w.i+6] = lastChunkType
}
} else {
if w.first {
w.buf[w.i+6] = firstChunkType
} else {
w.buf[w.i+6] = middleChunkType
}
}
binary.LittleEndian.PutUint32(w.buf[w.i+0:w.i+4], util.NewCRC(w.buf[w.i+6:w.j]).Value())
binary.LittleEndian.PutUint16(w.buf[w.i+4:w.i+6], uint16(w.j-w.i-headerSize))
}
func (r *Reader) readRawBlock(bh blockHandle, verifyChecksum bool) ([]byte, error) {
data := r.bpool.Get(int(bh.length + blockTrailerLen))
if _, err := r.reader.ReadAt(data, int64(bh.offset)); err != nil && err != io.EOF {
return nil, err
}
if verifyChecksum {
n := bh.length + 1
checksum0 := binary.LittleEndian.Uint32(data[n:])
checksum1 := util.NewCRC(data[:n]).Value()
if checksum0 != checksum1 {
r.bpool.Put(data)
return nil, r.newErrCorruptedBH(bh, fmt.Sprintf("checksum mismatch, want=%#x got=%#x", checksum0, checksum1))
}
}
switch data[bh.length] {
case blockTypeNoCompression:
data = data[:bh.length]
case blockTypeSnappyCompression:
decLen, err := snappy.DecodedLen(data[:bh.length])
if err != nil {
return nil, r.newErrCorruptedBH(bh, err.Error())
}
decData := r.bpool.Get(decLen)
decData, err = snappy.Decode(decData, data[:bh.length])
r.bpool.Put(data)
if err != nil {
r.bpool.Put(decData)
return nil, r.newErrCorruptedBH(bh, err.Error())
}
data = decData
default:
r.bpool.Put(data)
return nil, r.newErrCorruptedBH(bh, fmt.Sprintf("unknown compression type %#x", data[bh.length]))
}
return data, nil
}
// nextChunk sets r.buf[r.i:r.j] to hold the next chunk's payload, reading the
// next block into the buffer if necessary.
func (r *Reader) nextChunk(first bool) error {
for {
if r.j+headerSize <= r.n {
checksum := binary.LittleEndian.Uint32(r.buf[r.j+0 : r.j+4])
length := binary.LittleEndian.Uint16(r.buf[r.j+4 : r.j+6])
chunkType := r.buf[r.j+6]
if checksum == 0 && length == 0 && chunkType == 0 {
// Drop entire block.
m := r.n - r.j
r.i = r.n
r.j = r.n
return r.corrupt(m, "zero header", false)
} else {
m := r.n - r.j
r.i = r.j + headerSize
r.j = r.j + headerSize + int(length)
if r.j > r.n {
// Drop entire block.
r.i = r.n
r.j = r.n
return r.corrupt(m, "chunk length overflows block", false)
} else if r.checksum && checksum != util.NewCRC(r.buf[r.i-1:r.j]).Value() {
// Drop entire block.
r.i = r.n
r.j = r.n
return r.corrupt(m, "checksum mismatch", false)
}
}
if first && chunkType != fullChunkType && chunkType != firstChunkType {
m := r.j - r.i
r.i = r.j
// Report the error, but skip it.
return r.corrupt(m+headerSize, "orphan chunk", true)
}
r.last = chunkType == fullChunkType || chunkType == lastChunkType
return nil
}
// The last block.
if r.n < blockSize && r.n > 0 {
if !first {
return r.corrupt(0, "missing chunk part", false)
}
r.err = io.EOF
return r.err
}
// Read block.
n, err := io.ReadFull(r.r, r.buf[:])
if err != nil && err != io.EOF && err != io.ErrUnexpectedEOF {
return err
}
if n == 0 {
if !first {
return r.corrupt(0, "missing chunk part", false)
}
r.err = io.EOF
return r.err
}
r.i, r.j, r.n = 0, 0, n
}
}