forgejo-federation/vendor/github.com/glycerine/go-unsnap-stream/unsnap.go
2018-05-19 20:49:46 +08:00

513 lines
14 KiB
Go

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