add other session providers (#5963)

vendor/github.com/siddontang/go-snappy/snappy/decode.go

@@ -0,0 +1,124 @@
+// 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"
+)
+
+// ErrCorrupt reports that the input is invalid.
+var ErrCorrupt = errors.New("snappy: corrupt input")
+
+// 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 {
+		return 0, 0, ErrCorrupt
+	}
+	if uint64(int(v)) != v {
+		return 0, 0, errors.New("snappy: decoded block is too large")
+	}
+	return int(v), n, nil
+}
+
+// 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.
+// 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 len(dst) < dLen {
+		dst = make([]byte, dLen)
+	}
+
+	var d, offset, length int
+	for s < len(src) {
+		switch src[s] & 0x03 {
+		case tagLiteral:
+			x := uint(src[s] >> 2)
+			switch {
+			case x < 60:
+				s += 1
+			case x == 60:
+				s += 2
+				if s > len(src) {
+					return nil, ErrCorrupt
+				}
+				x = uint(src[s-1])
+			case x == 61:
+				s += 3
+				if s > len(src) {
+					return nil, ErrCorrupt
+				}
+				x = uint(src[s-2]) | uint(src[s-1])<<8
+			case x == 62:
+				s += 4
+				if s > len(src) {
+					return nil, ErrCorrupt
+				}
+				x = uint(src[s-3]) | uint(src[s-2])<<8 | uint(src[s-1])<<16
+			case x == 63:
+				s += 5
+				if s > len(src) {
+					return nil, ErrCorrupt
+				}
+				x = uint(src[s-4]) | uint(src[s-3])<<8 | uint(src[s-2])<<16 | uint(src[s-1])<<24
+			}
+			length = int(x + 1)
+			if length <= 0 {
+				return nil, errors.New("snappy: unsupported literal length")
+			}
+			if length > len(dst)-d || length > len(src)-s {
+				return nil, ErrCorrupt
+			}
+			copy(dst[d:], src[s:s+length])
+			d += length
+			s += length
+			continue
+
+		case tagCopy1:
+			s += 2
+			if s > len(src) {
+				return nil, ErrCorrupt
+			}
+			length = 4 + int(src[s-2])>>2&0x7
+			offset = int(src[s-2])&0xe0<<3 | int(src[s-1])
+
+		case tagCopy2:
+			s += 3
+			if s > len(src) {
+				return nil, ErrCorrupt
+			}
+			length = 1 + int(src[s-3])>>2
+			offset = int(src[s-2]) | int(src[s-1])<<8
+
+		case tagCopy4:
+			return nil, errors.New("snappy: unsupported COPY_4 tag")
+		}
+
+		end := d + length
+		if offset > d || end > len(dst) {
+			return nil, ErrCorrupt
+		}
+		for ; d < end; d++ {
+			dst[d] = dst[d-offset]
+		}
+	}
+	if d != dLen {
+		return nil, ErrCorrupt
+	}
+	return dst[:d], nil
+}