--- /dev/null
+// Copyright 2011 The Snappy-Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package snappy
+
+import (
+ "encoding/binary"
+ "errors"
+ "io"
+)
+
+var (
+ // ErrCorrupt reports that the input is invalid.
+ ErrCorrupt = errors.New("snappy: corrupt input")
+ // ErrTooLarge reports that the uncompressed length is too large.
+ ErrTooLarge = errors.New("snappy: decoded block is too large")
+ // ErrUnsupported reports that the input isn't supported.
+ ErrUnsupported = errors.New("snappy: unsupported input")
+
+ errUnsupportedLiteralLength = errors.New("snappy: unsupported literal length")
+)
+
+// DecodedLen returns the length of the decoded block.
+func DecodedLen(src []byte) (int, error) {
+ v, _, err := decodedLen(src)
+ return v, err
+}
+
+// decodedLen returns the length of the decoded block and the number of bytes
+// that the length header occupied.
+func decodedLen(src []byte) (blockLen, headerLen int, err error) {
+ v, n := binary.Uvarint(src)
+ if n <= 0 || v > 0xffffffff {
+ return 0, 0, ErrCorrupt
+ }
+
+ const wordSize = 32 << (^uint(0) >> 32 & 1)
+ if wordSize == 32 && v > 0x7fffffff {
+ return 0, 0, ErrTooLarge
+ }
+ return int(v), n, nil
+}
+
+const (
+ decodeErrCodeCorrupt = 1
+ decodeErrCodeUnsupportedLiteralLength = 2
+)
+
+// Decode returns the decoded form of src. The returned slice may be a sub-
+// slice of dst if dst was large enough to hold the entire decoded block.
+// Otherwise, a newly allocated slice will be returned.
+//
+// The dst and src must not overlap. It is valid to pass a nil dst.
+func Decode(dst, src []byte) ([]byte, error) {
+ dLen, s, err := decodedLen(src)
+ if err != nil {
+ return nil, err
+ }
+ if dLen <= len(dst) {
+ dst = dst[:dLen]
+ } else {
+ dst = make([]byte, dLen)
+ }
+ switch decode(dst, src[s:]) {
+ case 0:
+ return dst, nil
+ case decodeErrCodeUnsupportedLiteralLength:
+ return nil, errUnsupportedLiteralLength
+ }
+ return nil, ErrCorrupt
+}
+
+// NewReader returns a new Reader that decompresses from r, using the framing
+// format described at
+// https://github.com/google/snappy/blob/master/framing_format.txt
+func NewReader(r io.Reader) *Reader {
+ return &Reader{
+ r: r,
+ decoded: make([]byte, maxBlockSize),
+ buf: make([]byte, maxEncodedLenOfMaxBlockSize+checksumSize),
+ }
+}
+
+// Reader is an io.Reader that can read Snappy-compressed bytes.
+type Reader struct {
+ r io.Reader
+ err error
+ decoded []byte
+ buf []byte
+ // decoded[i:j] contains decoded bytes that have not yet been passed on.
+ i, j int
+ readHeader bool
+}
+
+// Reset discards any buffered data, resets all state, and switches the Snappy
+// reader to read from r. This permits reusing a Reader rather than allocating
+// a new one.
+func (r *Reader) Reset(reader io.Reader) {
+ r.r = reader
+ r.err = nil
+ r.i = 0
+ r.j = 0
+ r.readHeader = false
+}
+
+func (r *Reader) readFull(p []byte, allowEOF bool) (ok bool) {
+ if _, r.err = io.ReadFull(r.r, p); r.err != nil {
+ if r.err == io.ErrUnexpectedEOF || (r.err == io.EOF && !allowEOF) {
+ r.err = ErrCorrupt
+ }
+ return false
+ }
+ return true
+}
+
+// Read satisfies the io.Reader interface.
+func (r *Reader) Read(p []byte) (int, error) {
+ if r.err != nil {
+ return 0, r.err
+ }
+ for {
+ if r.i < r.j {
+ n := copy(p, r.decoded[r.i:r.j])
+ r.i += n
+ return n, nil
+ }
+ if !r.readFull(r.buf[:4], true) {
+ return 0, r.err
+ }
+ chunkType := r.buf[0]
+ if !r.readHeader {
+ if chunkType != chunkTypeStreamIdentifier {
+ r.err = ErrCorrupt
+ return 0, r.err
+ }
+ r.readHeader = true
+ }
+ chunkLen := int(r.buf[1]) | int(r.buf[2])<<8 | int(r.buf[3])<<16
+ if chunkLen > len(r.buf) {
+ r.err = ErrUnsupported
+ return 0, r.err
+ }
+
+ // The chunk types are specified at
+ // https://github.com/google/snappy/blob/master/framing_format.txt
+ switch chunkType {
+ case chunkTypeCompressedData:
+ // Section 4.2. Compressed data (chunk type 0x00).
+ if chunkLen < checksumSize {
+ r.err = ErrCorrupt
+ return 0, r.err
+ }
+ buf := r.buf[:chunkLen]
+ if !r.readFull(buf, false) {
+ return 0, r.err
+ }
+ checksum := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
+ buf = buf[checksumSize:]
+
+ n, err := DecodedLen(buf)
+ if err != nil {
+ r.err = err
+ return 0, r.err
+ }
+ if n > len(r.decoded) {
+ r.err = ErrCorrupt
+ return 0, r.err
+ }
+ if _, err := Decode(r.decoded, buf); err != nil {
+ r.err = err
+ return 0, r.err
+ }
+ if crc(r.decoded[:n]) != checksum {
+ r.err = ErrCorrupt
+ return 0, r.err
+ }
+ r.i, r.j = 0, n
+ continue
+
+ case chunkTypeUncompressedData:
+ // Section 4.3. Uncompressed data (chunk type 0x01).
+ if chunkLen < checksumSize {
+ r.err = ErrCorrupt
+ return 0, r.err
+ }
+ buf := r.buf[:checksumSize]
+ if !r.readFull(buf, false) {
+ return 0, r.err
+ }
+ checksum := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
+ // Read directly into r.decoded instead of via r.buf.
+ n := chunkLen - checksumSize
+ if n > len(r.decoded) {
+ r.err = ErrCorrupt
+ return 0, r.err
+ }
+ if !r.readFull(r.decoded[:n], false) {
+ return 0, r.err
+ }
+ if crc(r.decoded[:n]) != checksum {
+ r.err = ErrCorrupt
+ return 0, r.err
+ }
+ r.i, r.j = 0, n
+ continue
+
+ case chunkTypeStreamIdentifier:
+ // Section 4.1. Stream identifier (chunk type 0xff).
+ if chunkLen != len(magicBody) {
+ r.err = ErrCorrupt
+ return 0, r.err
+ }
+ if !r.readFull(r.buf[:len(magicBody)], false) {
+ return 0, r.err
+ }
+ for i := 0; i < len(magicBody); i++ {
+ if r.buf[i] != magicBody[i] {
+ r.err = ErrCorrupt
+ return 0, r.err
+ }
+ }
+ continue
+ }
+
+ if chunkType <= 0x7f {
+ // Section 4.5. Reserved unskippable chunks (chunk types 0x02-0x7f).
+ r.err = ErrUnsupported
+ return 0, r.err
+ }
+ // Section 4.4 Padding (chunk type 0xfe).
+ // Section 4.6. Reserved skippable chunks (chunk types 0x80-0xfd).
+ if !r.readFull(r.buf[:chunkLen], false) {
+ return 0, r.err
+ }
+ }
+}
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