513 lines
14 KiB
Go
513 lines
14 KiB
Go
package unsnap
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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"io"
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"io/ioutil"
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"os"
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"hash/crc32"
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snappy "github.com/golang/snappy"
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// The C library can be used, but this makes the binary dependent
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// lots of extraneous c-libraries; it is no longer stand-alone. Yuck.
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//
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// Therefore we comment out the "dgryski/go-csnappy" path and use the
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// "github.com/golang/snappy/snappy" above instead. If you are
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// performance limited and can deal with distributing more libraries,
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// then this is easy to swap.
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//
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// If you swap, note that some of the tests won't pass
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// because snappy-go produces slightly different (but still
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// conformant) encodings on some data. Here are bindings
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// to the C-snappy:
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// snappy "github.com/dgryski/go-csnappy"
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)
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// SnappyFile: create a drop-in-replacement/wrapper for an *os.File that handles doing the unsnappification online as more is read from it
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type SnappyFile struct {
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Fname string
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Reader io.Reader
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Writer io.Writer
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// allow clients to substitute us for an os.File and just switch
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// off compression if they don't want it.
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SnappyEncodeDecodeOff bool // if true, we bypass straight to Filep
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EncBuf FixedSizeRingBuf // holds any extra that isn't yet returned, encoded
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DecBuf FixedSizeRingBuf // holds any extra that isn't yet returned, decoded
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// for writing to stream-framed snappy
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HeaderChunkWritten bool
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// Sanity check: we can only read, or only write, to one SnappyFile.
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// EncBuf and DecBuf are used differently in each mode. Verify
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// that we are consistent with this flag.
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Writing bool
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}
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var total int
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// for debugging, show state of buffers
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func (f *SnappyFile) Dump() {
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fmt.Printf("EncBuf has length %d and contents:\n%s\n", len(f.EncBuf.Bytes()), string(f.EncBuf.Bytes()))
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fmt.Printf("DecBuf has length %d and contents:\n%s\n", len(f.DecBuf.Bytes()), string(f.DecBuf.Bytes()))
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}
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func (f *SnappyFile) Read(p []byte) (n int, err error) {
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if f.SnappyEncodeDecodeOff {
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return f.Reader.Read(p)
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}
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if f.Writing {
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panic("Reading on a write-only SnappyFile")
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}
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// before we unencrypt more, try to drain the DecBuf first
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n, _ = f.DecBuf.Read(p)
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if n > 0 {
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total += n
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return n, nil
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}
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//nEncRead, nDecAdded, err := UnsnapOneFrame(f.Filep, &f.EncBuf, &f.DecBuf, f.Fname)
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_, _, err = UnsnapOneFrame(f.Reader, &f.EncBuf, &f.DecBuf, f.Fname)
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if err != nil && err != io.EOF {
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panic(err)
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}
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n, _ = f.DecBuf.Read(p)
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if n > 0 {
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total += n
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return n, nil
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}
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if f.DecBuf.Readable == 0 {
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if f.DecBuf.Readable == 0 && f.EncBuf.Readable == 0 {
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// only now (when EncBuf is empty) can we give io.EOF.
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// Any earlier, and we leave stuff un-decoded!
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return 0, io.EOF
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}
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}
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return 0, nil
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}
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func Open(name string) (file *SnappyFile, err error) {
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fp, err := os.Open(name)
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if err != nil {
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return nil, err
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}
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// encoding in snappy can apparently go beyond the original size, so
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// we make our buffers big enough, 2*max snappy chunk => 2 * CHUNK_MAX(65536)
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snap := NewReader(fp)
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snap.Fname = name
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return snap, nil
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}
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func NewReader(r io.Reader) *SnappyFile {
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return &SnappyFile{
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Reader: r,
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EncBuf: *NewFixedSizeRingBuf(CHUNK_MAX * 2), // buffer of snappy encoded bytes
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DecBuf: *NewFixedSizeRingBuf(CHUNK_MAX * 2), // buffer of snapppy decoded bytes
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Writing: false,
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}
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}
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func NewWriter(w io.Writer) *SnappyFile {
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return &SnappyFile{
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Writer: w,
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EncBuf: *NewFixedSizeRingBuf(65536), // on writing: temp for testing compression
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DecBuf: *NewFixedSizeRingBuf(65536 * 2), // on writing: final buffer of snappy framed and encoded bytes
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Writing: true,
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}
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}
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func Create(name string) (file *SnappyFile, err error) {
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fp, err := os.Create(name)
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if err != nil {
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return nil, err
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}
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snap := NewWriter(fp)
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snap.Fname = name
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return snap, nil
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}
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func (f *SnappyFile) Close() error {
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if f.Writing {
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wc, ok := f.Writer.(io.WriteCloser)
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if ok {
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return wc.Close()
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}
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return nil
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}
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rc, ok := f.Reader.(io.ReadCloser)
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if ok {
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return rc.Close()
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}
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return nil
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}
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func (f *SnappyFile) Sync() error {
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file, ok := f.Writer.(*os.File)
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if ok {
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return file.Sync()
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}
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return nil
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}
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// for an increment of a frame at a time:
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// read from r into encBuf (encBuf is still encoded, thus the name), and write unsnappified frames into outDecodedBuf
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// the returned n: number of bytes read from the encrypted encBuf
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func UnsnapOneFrame(r io.Reader, encBuf *FixedSizeRingBuf, outDecodedBuf *FixedSizeRingBuf, fname string) (nEnc int64, nDec int64, err error) {
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// b, err := ioutil.ReadAll(r)
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// if err != nil {
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// panic(err)
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// }
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nEnc = 0
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nDec = 0
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// read up to 65536 bytes from r into encBuf, at least a snappy frame
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nread, err := io.CopyN(encBuf, r, 65536) // returns nwrotebytes, err
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nEnc += nread
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if err != nil {
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if err == io.EOF {
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if nread == 0 {
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if encBuf.Readable == 0 {
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return nEnc, nDec, io.EOF
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}
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// else we have bytes in encBuf, so decode them!
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err = nil
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} else {
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// continue below, processing the nread bytes
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err = nil
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}
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} else {
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panic(err)
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}
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}
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// flag for printing chunk size alignment messages
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verbose := false
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const snappyStreamHeaderSz = 10
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const headerSz = 4
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const crc32Sz = 4
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// the magic 18 bytes accounts for the snappy streaming header and the first chunks size and checksum
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// http://code.google.com/p/snappy/source/browse/trunk/framing_format.txt
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chunk := (*encBuf).Bytes()
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// however we exit, advance as
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// defer func() { (*encBuf).Next(N) }()
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// 65536 is the max size of a snappy framed chunk. See
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// http://code.google.com/p/snappy/source/browse/trunk/framing_format.txt:91
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// buf := make([]byte, 65536)
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// fmt.Printf("read from file, b is len:%d with value: %#v\n", len(b), b)
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// fmt.Printf("read from file, bcut is len:%d with value: %#v\n", len(bcut), bcut)
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//fmt.Printf("raw bytes of chunksz are: %v\n", b[11:14])
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fourbytes := make([]byte, 4)
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chunkCount := 0
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for nDec < 65536 {
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if len(chunk) == 0 {
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break
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}
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chunkCount++
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fourbytes[3] = 0
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copy(fourbytes, chunk[1:4])
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chunksz := binary.LittleEndian.Uint32(fourbytes)
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chunk_type := chunk[0]
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switch true {
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case chunk_type == 0xff:
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{ // stream identifier
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streamHeader := chunk[:snappyStreamHeaderSz]
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if 0 != bytes.Compare(streamHeader, []byte{0xff, 0x06, 0x00, 0x00, 0x73, 0x4e, 0x61, 0x50, 0x70, 0x59}) {
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panic("file had chunk starting with 0xff but then no magic snappy streaming protocol bytes, aborting.")
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} else {
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//fmt.Printf("got streaming snappy magic header just fine.\n")
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}
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chunk = chunk[snappyStreamHeaderSz:]
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(*encBuf).Advance(snappyStreamHeaderSz)
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nEnc += snappyStreamHeaderSz
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continue
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}
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case chunk_type == 0x00:
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{ // compressed data
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if verbose {
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fmt.Fprintf(os.Stderr, "chunksz is %d while total bytes avail are: %d\n", int(chunksz), len(chunk)-4)
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}
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crc := binary.LittleEndian.Uint32(chunk[headerSz:(headerSz + crc32Sz)])
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section := chunk[(headerSz + crc32Sz):(headerSz + chunksz)]
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dec, ok := snappy.Decode(nil, section)
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if ok != nil {
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// we've probably truncated a snappy frame at this point
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// ok=snappy: corrupt input
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// len(dec) == 0
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//
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panic(fmt.Sprintf("could not decode snappy stream: '%s' and len dec=%d and ok=%v\n", fname, len(dec), ok))
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// get back to caller with what we've got so far
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return nEnc, nDec, nil
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}
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// fmt.Printf("ok, b is %#v , %#v\n", ok, dec)
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// spit out decoded text
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// n, err := w.Write(dec)
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//fmt.Printf("len(dec) = %d, outDecodedBuf.Readable=%d\n", len(dec), outDecodedBuf.Readable)
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bnb := bytes.NewBuffer(dec)
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n, err := io.Copy(outDecodedBuf, bnb)
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if err != nil {
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//fmt.Printf("got n=%d, err= %s ; when trying to io.Copy(outDecodedBuf: N=%d, Readable=%d)\n", n, err, outDecodedBuf.N, outDecodedBuf.Readable)
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panic(err)
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}
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if n != int64(len(dec)) {
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panic("could not write all bytes to outDecodedBuf")
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}
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nDec += n
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// verify the crc32 rotated checksum
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m32 := masked_crc32c(dec)
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if m32 != crc {
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panic(fmt.Sprintf("crc32 masked failiure. expected: %v but got: %v", crc, m32))
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} else {
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//fmt.Printf("\nchecksums match: %v == %v\n", crc, m32)
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}
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// move to next header
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inc := (headerSz + int(chunksz))
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chunk = chunk[inc:]
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(*encBuf).Advance(inc)
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nEnc += int64(inc)
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continue
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}
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case chunk_type == 0x01:
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{ // uncompressed data
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//n, err := w.Write(chunk[(headerSz+crc32Sz):(headerSz + int(chunksz))])
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n, err := io.Copy(outDecodedBuf, bytes.NewBuffer(chunk[(headerSz+crc32Sz):(headerSz+int(chunksz))]))
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if verbose {
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//fmt.Printf("debug: n=%d err=%v chunksz=%d outDecodedBuf='%v'\n", n, err, chunksz, outDecodedBuf)
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}
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if err != nil {
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panic(err)
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}
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if n != int64(chunksz-crc32Sz) {
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panic("could not write all bytes to stdout")
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}
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nDec += n
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inc := (headerSz + int(chunksz))
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chunk = chunk[inc:]
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(*encBuf).Advance(inc)
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nEnc += int64(inc)
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continue
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}
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case chunk_type == 0xfe:
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fallthrough // padding, just skip it
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case chunk_type >= 0x80 && chunk_type <= 0xfd:
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{ // Reserved skippable chunks
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//fmt.Printf("\nin reserved skippable chunks, at nEnc=%v\n", nEnc)
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inc := (headerSz + int(chunksz))
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chunk = chunk[inc:]
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nEnc += int64(inc)
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(*encBuf).Advance(inc)
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continue
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}
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default:
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panic(fmt.Sprintf("unrecognized/unsupported chunk type %#v", chunk_type))
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}
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} // end for{}
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return nEnc, nDec, err
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//return int64(N), nil
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}
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// for whole file at once:
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//
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// receive on stdin a stream of bytes in the snappy-streaming framed
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// format, defined here: http://code.google.com/p/snappy/source/browse/trunk/framing_format.txt
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// Grab each frame, run it through the snappy decoder, and spit out
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// each frame all joined back-to-back on stdout.
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//
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func Unsnappy(r io.Reader, w io.Writer) (err error) {
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b, err := ioutil.ReadAll(r)
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if err != nil {
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panic(err)
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}
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// flag for printing chunk size alignment messages
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verbose := false
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const snappyStreamHeaderSz = 10
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const headerSz = 4
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const crc32Sz = 4
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// the magic 18 bytes accounts for the snappy streaming header and the first chunks size and checksum
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// http://code.google.com/p/snappy/source/browse/trunk/framing_format.txt
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chunk := b[:]
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// 65536 is the max size of a snappy framed chunk. See
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// http://code.google.com/p/snappy/source/browse/trunk/framing_format.txt:91
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//buf := make([]byte, 65536)
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// fmt.Printf("read from file, b is len:%d with value: %#v\n", len(b), b)
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// fmt.Printf("read from file, bcut is len:%d with value: %#v\n", len(bcut), bcut)
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//fmt.Printf("raw bytes of chunksz are: %v\n", b[11:14])
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fourbytes := make([]byte, 4)
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chunkCount := 0
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for {
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if len(chunk) == 0 {
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break
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}
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chunkCount++
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fourbytes[3] = 0
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copy(fourbytes, chunk[1:4])
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chunksz := binary.LittleEndian.Uint32(fourbytes)
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chunk_type := chunk[0]
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switch true {
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case chunk_type == 0xff:
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{ // stream identifier
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streamHeader := chunk[:snappyStreamHeaderSz]
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if 0 != bytes.Compare(streamHeader, []byte{0xff, 0x06, 0x00, 0x00, 0x73, 0x4e, 0x61, 0x50, 0x70, 0x59}) {
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panic("file had chunk starting with 0xff but then no magic snappy streaming protocol bytes, aborting.")
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} else {
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//fmt.Printf("got streaming snappy magic header just fine.\n")
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}
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chunk = chunk[snappyStreamHeaderSz:]
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continue
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}
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case chunk_type == 0x00:
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{ // compressed data
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if verbose {
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fmt.Fprintf(os.Stderr, "chunksz is %d while total bytes avail are: %d\n", int(chunksz), len(chunk)-4)
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}
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//crc := binary.LittleEndian.Uint32(chunk[headerSz:(headerSz + crc32Sz)])
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section := chunk[(headerSz + crc32Sz):(headerSz + chunksz)]
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dec, ok := snappy.Decode(nil, section)
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if ok != nil {
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panic("could not decode snappy stream")
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}
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// fmt.Printf("ok, b is %#v , %#v\n", ok, dec)
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// spit out decoded text
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n, err := w.Write(dec)
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if err != nil {
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panic(err)
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}
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if n != len(dec) {
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panic("could not write all bytes to stdout")
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}
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// TODO: verify the crc32 rotated checksum?
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// move to next header
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chunk = chunk[(headerSz + int(chunksz)):]
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continue
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}
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case chunk_type == 0x01:
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{ // uncompressed data
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//crc := binary.LittleEndian.Uint32(chunk[headerSz:(headerSz + crc32Sz)])
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section := chunk[(headerSz + crc32Sz):(headerSz + chunksz)]
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n, err := w.Write(section)
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if err != nil {
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panic(err)
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}
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if n != int(chunksz-crc32Sz) {
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panic("could not write all bytes to stdout")
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}
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chunk = chunk[(headerSz + int(chunksz)):]
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continue
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}
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case chunk_type == 0xfe:
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fallthrough // padding, just skip it
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case chunk_type >= 0x80 && chunk_type <= 0xfd:
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{ // Reserved skippable chunks
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chunk = chunk[(headerSz + int(chunksz)):]
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continue
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}
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default:
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panic(fmt.Sprintf("unrecognized/unsupported chunk type %#v", chunk_type))
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}
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} // end for{}
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return nil
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}
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// 0xff 0x06 0x00 0x00 sNaPpY
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var SnappyStreamHeaderMagic = []byte{0xff, 0x06, 0x00, 0x00, 0x73, 0x4e, 0x61, 0x50, 0x70, 0x59}
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const CHUNK_MAX = 65536
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const _STREAM_TO_STREAM_BLOCK_SIZE = CHUNK_MAX
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const _STREAM_IDENTIFIER = `sNaPpY`
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const _COMPRESSED_CHUNK = 0x00
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const _UNCOMPRESSED_CHUNK = 0x01
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const _IDENTIFIER_CHUNK = 0xff
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const _RESERVED_UNSKIPPABLE0 = 0x02 // chunk ranges are [inclusive, exclusive)
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const _RESERVED_UNSKIPPABLE1 = 0x80
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const _RESERVED_SKIPPABLE0 = 0x80
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const _RESERVED_SKIPPABLE1 = 0xff
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// the minimum percent of bytes compression must save to be enabled in automatic
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// mode
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const _COMPRESSION_THRESHOLD = .125
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var crctab *crc32.Table
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func init() {
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crctab = crc32.MakeTable(crc32.Castagnoli) // this is correct table, matches the crc32c.c code used by python
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}
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func masked_crc32c(data []byte) uint32 {
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// see the framing format specification, http://code.google.com/p/snappy/source/browse/trunk/framing_format.txt
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var crc uint32 = crc32.Checksum(data, crctab)
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return (uint32((crc>>15)|(crc<<17)) + 0xa282ead8)
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}
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func ReadSnappyStreamCompressedFile(filename string) ([]byte, error) {
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snappyFile, err := Open(filename)
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if err != nil {
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return []byte{}, err
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}
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var bb bytes.Buffer
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_, err = bb.ReadFrom(snappyFile)
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|
if err == io.EOF {
|
|
err = nil
|
|
}
|
|
if err != nil {
|
|
panic(err)
|
|
}
|
|
|
|
return bb.Bytes(), err
|
|
}
|