mirror of
https://github.com/octoleo/restic.git
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213 lines
5.0 KiB
Go
213 lines
5.0 KiB
Go
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package hpack
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import (
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"bytes"
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"errors"
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"io"
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"sync"
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)
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var bufPool = sync.Pool{
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New: func() interface{} { return new(bytes.Buffer) },
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}
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// HuffmanDecode decodes the string in v and writes the expanded
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// result to w, returning the number of bytes written to w and the
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// Write call's return value. At most one Write call is made.
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func HuffmanDecode(w io.Writer, v []byte) (int, error) {
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buf := bufPool.Get().(*bytes.Buffer)
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buf.Reset()
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defer bufPool.Put(buf)
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if err := huffmanDecode(buf, 0, v); err != nil {
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return 0, err
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}
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return w.Write(buf.Bytes())
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}
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// HuffmanDecodeToString decodes the string in v.
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func HuffmanDecodeToString(v []byte) (string, error) {
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buf := bufPool.Get().(*bytes.Buffer)
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buf.Reset()
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defer bufPool.Put(buf)
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if err := huffmanDecode(buf, 0, v); err != nil {
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return "", err
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}
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return buf.String(), nil
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}
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// ErrInvalidHuffman is returned for errors found decoding
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// Huffman-encoded strings.
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var ErrInvalidHuffman = errors.New("hpack: invalid Huffman-encoded data")
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// huffmanDecode decodes v to buf.
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// If maxLen is greater than 0, attempts to write more to buf than
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// maxLen bytes will return ErrStringLength.
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func huffmanDecode(buf *bytes.Buffer, maxLen int, v []byte) error {
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n := rootHuffmanNode
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// cur is the bit buffer that has not been fed into n.
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// cbits is the number of low order bits in cur that are valid.
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// sbits is the number of bits of the symbol prefix being decoded.
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cur, cbits, sbits := uint(0), uint8(0), uint8(0)
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for _, b := range v {
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cur = cur<<8 | uint(b)
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cbits += 8
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sbits += 8
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for cbits >= 8 {
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idx := byte(cur >> (cbits - 8))
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n = n.children[idx]
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if n == nil {
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return ErrInvalidHuffman
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}
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if n.children == nil {
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if maxLen != 0 && buf.Len() == maxLen {
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return ErrStringLength
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}
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buf.WriteByte(n.sym)
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cbits -= n.codeLen
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n = rootHuffmanNode
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sbits = cbits
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} else {
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cbits -= 8
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}
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}
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}
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for cbits > 0 {
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n = n.children[byte(cur<<(8-cbits))]
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if n == nil {
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return ErrInvalidHuffman
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}
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if n.children != nil || n.codeLen > cbits {
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break
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}
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if maxLen != 0 && buf.Len() == maxLen {
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return ErrStringLength
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}
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buf.WriteByte(n.sym)
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cbits -= n.codeLen
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n = rootHuffmanNode
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sbits = cbits
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}
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if sbits > 7 {
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// Either there was an incomplete symbol, or overlong padding.
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// Both are decoding errors per RFC 7541 section 5.2.
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return ErrInvalidHuffman
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}
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if mask := uint(1<<cbits - 1); cur&mask != mask {
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// Trailing bits must be a prefix of EOS per RFC 7541 section 5.2.
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return ErrInvalidHuffman
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}
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return nil
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}
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type node struct {
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// children is non-nil for internal nodes
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children []*node
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// The following are only valid if children is nil:
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codeLen uint8 // number of bits that led to the output of sym
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sym byte // output symbol
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}
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func newInternalNode() *node {
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return &node{children: make([]*node, 256)}
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}
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var rootHuffmanNode = newInternalNode()
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func init() {
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if len(huffmanCodes) != 256 {
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panic("unexpected size")
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}
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for i, code := range huffmanCodes {
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addDecoderNode(byte(i), code, huffmanCodeLen[i])
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}
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}
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func addDecoderNode(sym byte, code uint32, codeLen uint8) {
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cur := rootHuffmanNode
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for codeLen > 8 {
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codeLen -= 8
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i := uint8(code >> codeLen)
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if cur.children[i] == nil {
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cur.children[i] = newInternalNode()
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}
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cur = cur.children[i]
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}
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shift := 8 - codeLen
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start, end := int(uint8(code<<shift)), int(1<<shift)
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for i := start; i < start+end; i++ {
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cur.children[i] = &node{sym: sym, codeLen: codeLen}
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}
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}
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// AppendHuffmanString appends s, as encoded in Huffman codes, to dst
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// and returns the extended buffer.
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func AppendHuffmanString(dst []byte, s string) []byte {
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rembits := uint8(8)
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for i := 0; i < len(s); i++ {
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if rembits == 8 {
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dst = append(dst, 0)
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}
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dst, rembits = appendByteToHuffmanCode(dst, rembits, s[i])
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}
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if rembits < 8 {
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// special EOS symbol
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code := uint32(0x3fffffff)
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nbits := uint8(30)
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t := uint8(code >> (nbits - rembits))
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dst[len(dst)-1] |= t
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}
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return dst
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}
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// HuffmanEncodeLength returns the number of bytes required to encode
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// s in Huffman codes. The result is round up to byte boundary.
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func HuffmanEncodeLength(s string) uint64 {
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n := uint64(0)
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for i := 0; i < len(s); i++ {
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n += uint64(huffmanCodeLen[s[i]])
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}
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return (n + 7) / 8
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}
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// appendByteToHuffmanCode appends Huffman code for c to dst and
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// returns the extended buffer and the remaining bits in the last
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// element. The appending is not byte aligned and the remaining bits
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// in the last element of dst is given in rembits.
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func appendByteToHuffmanCode(dst []byte, rembits uint8, c byte) ([]byte, uint8) {
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code := huffmanCodes[c]
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nbits := huffmanCodeLen[c]
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for {
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if rembits > nbits {
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t := uint8(code << (rembits - nbits))
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dst[len(dst)-1] |= t
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rembits -= nbits
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break
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}
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t := uint8(code >> (nbits - rembits))
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dst[len(dst)-1] |= t
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nbits -= rembits
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rembits = 8
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if nbits == 0 {
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break
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}
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dst = append(dst, 0)
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}
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return dst, rembits
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}
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