251 lines
7.1 KiB
Go
251 lines
7.1 KiB
Go
// 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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"io"
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)
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const (
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uint32Max = ^uint32(0)
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initialHeaderTableSize = 4096
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)
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type Encoder struct {
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dynTab dynamicTable
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// minSize is the minimum table size set by
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// SetMaxDynamicTableSize after the previous Header Table Size
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// Update.
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minSize uint32
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// maxSizeLimit is the maximum table size this encoder
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// supports. This will protect the encoder from too large
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// size.
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maxSizeLimit uint32
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// tableSizeUpdate indicates whether "Header Table Size
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// Update" is required.
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tableSizeUpdate bool
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w io.Writer
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buf []byte
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}
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// NewEncoder returns a new Encoder which performs HPACK encoding. An
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// encoded data is written to w.
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func NewEncoder(w io.Writer) *Encoder {
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e := &Encoder{
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minSize: uint32Max,
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maxSizeLimit: initialHeaderTableSize,
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tableSizeUpdate: false,
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w: w,
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}
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e.dynTab.setMaxSize(initialHeaderTableSize)
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return e
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}
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// WriteField encodes f into a single Write to e's underlying Writer.
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// This function may also produce bytes for "Header Table Size Update"
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// if necessary. If produced, it is done before encoding f.
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func (e *Encoder) WriteField(f HeaderField) error {
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e.buf = e.buf[:0]
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if e.tableSizeUpdate {
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e.tableSizeUpdate = false
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if e.minSize < e.dynTab.maxSize {
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e.buf = appendTableSize(e.buf, e.minSize)
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}
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e.minSize = uint32Max
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e.buf = appendTableSize(e.buf, e.dynTab.maxSize)
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}
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idx, nameValueMatch := e.searchTable(f)
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if nameValueMatch {
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e.buf = appendIndexed(e.buf, idx)
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} else {
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indexing := e.shouldIndex(f)
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if indexing {
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e.dynTab.add(f)
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}
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if idx == 0 {
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e.buf = appendNewName(e.buf, f, indexing)
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} else {
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e.buf = appendIndexedName(e.buf, f, idx, indexing)
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}
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}
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n, err := e.w.Write(e.buf)
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if err == nil && n != len(e.buf) {
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err = io.ErrShortWrite
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}
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return err
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}
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// searchTable searches f in both stable and dynamic header tables.
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// The static header table is searched first. Only when there is no
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// exact match for both name and value, the dynamic header table is
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// then searched. If there is no match, i is 0. If both name and value
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// match, i is the matched index and nameValueMatch becomes true. If
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// only name matches, i points to that index and nameValueMatch
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// becomes false.
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func (e *Encoder) searchTable(f HeaderField) (i uint64, nameValueMatch bool) {
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for idx, hf := range staticTable {
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if !constantTimeStringCompare(hf.Name, f.Name) {
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continue
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}
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if i == 0 {
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i = uint64(idx + 1)
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}
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if f.Sensitive {
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continue
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}
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if !constantTimeStringCompare(hf.Value, f.Value) {
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continue
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}
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i = uint64(idx + 1)
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nameValueMatch = true
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return
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}
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j, nameValueMatch := e.dynTab.search(f)
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if nameValueMatch || (i == 0 && j != 0) {
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i = j + uint64(len(staticTable))
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}
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return
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}
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// SetMaxDynamicTableSize changes the dynamic header table size to v.
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// The actual size is bounded by the value passed to
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// SetMaxDynamicTableSizeLimit.
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func (e *Encoder) SetMaxDynamicTableSize(v uint32) {
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if v > e.maxSizeLimit {
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v = e.maxSizeLimit
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}
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if v < e.minSize {
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e.minSize = v
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}
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e.tableSizeUpdate = true
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e.dynTab.setMaxSize(v)
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}
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// SetMaxDynamicTableSizeLimit changes the maximum value that can be
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// specified in SetMaxDynamicTableSize to v. By default, it is set to
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// 4096, which is the same size of the default dynamic header table
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// size described in HPACK specification. If the current maximum
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// dynamic header table size is strictly greater than v, "Header Table
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// Size Update" will be done in the next WriteField call and the
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// maximum dynamic header table size is truncated to v.
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func (e *Encoder) SetMaxDynamicTableSizeLimit(v uint32) {
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e.maxSizeLimit = v
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if e.dynTab.maxSize > v {
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e.tableSizeUpdate = true
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e.dynTab.setMaxSize(v)
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}
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}
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// shouldIndex reports whether f should be indexed.
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func (e *Encoder) shouldIndex(f HeaderField) bool {
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return !f.Sensitive && f.Size() <= e.dynTab.maxSize
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}
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// appendIndexed appends index i, as encoded in "Indexed Header Field"
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// representation, to dst and returns the extended buffer.
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func appendIndexed(dst []byte, i uint64) []byte {
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first := len(dst)
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dst = appendVarInt(dst, 7, i)
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dst[first] |= 0x80
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return dst
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}
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// appendNewName appends f, as encoded in one of "Literal Header field
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// - New Name" representation variants, to dst and returns the
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// extended buffer.
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//
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// If f.Sensitive is true, "Never Indexed" representation is used. If
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// f.Sensitive is false and indexing is true, "Inremental Indexing"
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// representation is used.
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func appendNewName(dst []byte, f HeaderField, indexing bool) []byte {
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dst = append(dst, encodeTypeByte(indexing, f.Sensitive))
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dst = appendHpackString(dst, f.Name)
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return appendHpackString(dst, f.Value)
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}
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// appendIndexedName appends f and index i referring indexed name
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// entry, as encoded in one of "Literal Header field - Indexed Name"
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// representation variants, to dst and returns the extended buffer.
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//
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// If f.Sensitive is true, "Never Indexed" representation is used. If
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// f.Sensitive is false and indexing is true, "Incremental Indexing"
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// representation is used.
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func appendIndexedName(dst []byte, f HeaderField, i uint64, indexing bool) []byte {
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first := len(dst)
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var n byte
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if indexing {
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n = 6
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} else {
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n = 4
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}
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dst = appendVarInt(dst, n, i)
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dst[first] |= encodeTypeByte(indexing, f.Sensitive)
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return appendHpackString(dst, f.Value)
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}
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// appendTableSize appends v, as encoded in "Header Table Size Update"
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// representation, to dst and returns the extended buffer.
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func appendTableSize(dst []byte, v uint32) []byte {
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first := len(dst)
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dst = appendVarInt(dst, 5, uint64(v))
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dst[first] |= 0x20
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return dst
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}
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// appendVarInt appends i, as encoded in variable integer form using n
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// bit prefix, to dst and returns the extended buffer.
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//
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// See
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// http://http2.github.io/http2-spec/compression.html#integer.representation
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func appendVarInt(dst []byte, n byte, i uint64) []byte {
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k := uint64((1 << n) - 1)
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if i < k {
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return append(dst, byte(i))
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}
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dst = append(dst, byte(k))
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i -= k
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for ; i >= 128; i >>= 7 {
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dst = append(dst, byte(0x80|(i&0x7f)))
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}
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return append(dst, byte(i))
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}
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// appendHpackString appends s, as encoded in "String Literal"
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// representation, to dst and returns the the extended buffer.
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//
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// s will be encoded in Huffman codes only when it produces strictly
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// shorter byte string.
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func appendHpackString(dst []byte, s string) []byte {
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huffmanLength := HuffmanEncodeLength(s)
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if huffmanLength < uint64(len(s)) {
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first := len(dst)
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dst = appendVarInt(dst, 7, huffmanLength)
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dst = AppendHuffmanString(dst, s)
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dst[first] |= 0x80
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} else {
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dst = appendVarInt(dst, 7, uint64(len(s)))
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dst = append(dst, s...)
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}
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return dst
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}
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// encodeTypeByte returns type byte. If sensitive is true, type byte
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// for "Never Indexed" representation is returned. If sensitive is
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// false and indexing is true, type byte for "Incremental Indexing"
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// representation is returned. Otherwise, type byte for "Without
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// Indexing" is returned.
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func encodeTypeByte(indexing, sensitive bool) byte {
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if sensitive {
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return 0x10
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}
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if indexing {
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return 0x40
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}
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return 0
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}
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