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use Huffman encoding for field names and values #16

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Aug 8, 2020
Merged

use Huffman encoding for field names and values #16

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36 changes: 19 additions & 17 deletions encoder.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,8 @@ package qpack

import (
"io"

"golang.org/x/net/http2/hpack"
)

// An Encoder performs QPACK encoding.
Expand Down Expand Up @@ -64,31 +66,31 @@ func (e *Encoder) Close() error {

func (e *Encoder) writeLiteralFieldWithoutNameReference(f HeaderField) {
offset := len(e.buf)
e.buf = appendVarInt(e.buf, 3, uint64(len(f.Name)))
e.buf[offset] ^= 0x20
e.buf = append(e.buf, []byte(f.Name)...)
e.buf = appendVarInt(e.buf, 7, uint64(len(f.Value)))
e.buf = append(e.buf, []byte(f.Value)...)
e.buf = appendVarInt(e.buf, 3, hpack.HuffmanEncodeLength(f.Name))
e.buf[offset] ^= 0x20 ^ 0x8
e.buf = hpack.AppendHuffmanString(e.buf, f.Name)
offset = len(e.buf)
e.buf = appendVarInt(e.buf, 7, hpack.HuffmanEncodeLength(f.Value))
e.buf[offset] ^= 0x80
e.buf = hpack.AppendHuffmanString(e.buf, f.Value)
}

// Encodes a header field whose name is present in one of the
// tables.
func (e *Encoder) writeLiteralFieldWithNameReference(
f *HeaderField, idx uint8) {
// Encodes a header field whose name is present in one of the tables.
func (e *Encoder) writeLiteralFieldWithNameReference(f *HeaderField, id uint8) {
offset := len(e.buf)
e.buf = appendVarInt(e.buf, 4, uint64(idx))
e.buf = appendVarInt(e.buf, 4, uint64(id))
// Set the 01NTxxxx pattern, forcing N to 0 and T to 1
e.buf[offset] ^= 0x50

e.buf = appendVarInt(e.buf, 7, uint64(len(f.Value)))
e.buf = append(e.buf, []byte(f.Value)...)
offset = len(e.buf)
e.buf = appendVarInt(e.buf, 7, hpack.HuffmanEncodeLength(f.Value))
e.buf[offset] ^= 0x80
e.buf = hpack.AppendHuffmanString(e.buf, f.Value)
}

// Encodes an indexed field, meaning it's entirely defined in one of the
// tables.
func (e *Encoder) writeIndexedField(idx uint8) {
// Encodes an indexed field, meaning it's entirely defined in one of the tables.
func (e *Encoder) writeIndexedField(id uint8) {
offset := len(e.buf)
e.buf = appendVarInt(e.buf, 6, uint64(idx))
e.buf = appendVarInt(e.buf, 6, uint64(id))
// Set the 1Txxxxxx pattern, forcing T to 1
e.buf[offset] ^= 0xc0
}
36 changes: 20 additions & 16 deletions encoder_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,8 @@ package qpack
import (
"bytes"

"golang.org/x/net/http2/hpack"

. "github.com/onsi/ginkgo"
. "github.com/onsi/gomega"
)
Expand All @@ -29,41 +31,43 @@ var _ = Describe("Encoder", func() {

checkHeaderField := func(data []byte, hf HeaderField) []byte {
Expect(data[0] & (0x80 ^ 0x40 ^ 0x20)).To(Equal(uint8(0x20))) // 001xxxxx
Expect(data[0] & 0x8).To(BeZero()) // no Huffman encoding
Expect(data[0] & 0x8).ToNot(BeZero()) // Huffman encoding
nameLen, data, err := readVarInt(3, data)
Expect(err).ToNot(HaveOccurred())
Expect(nameLen).To(BeEquivalentTo(len(hf.Name)))
Expect(string(data[:len(hf.Name)])).To(Equal(hf.Name))
valueLen, data, err := readVarInt(7, data[len(hf.Name):])
l := hpack.HuffmanEncodeLength(hf.Name)
Expect(nameLen).To(BeEquivalentTo(l))
Expect(hpack.HuffmanDecodeToString(data[:l])).To(Equal(hf.Name))
valueLen, data, err := readVarInt(7, data[l:])
Expect(err).ToNot(HaveOccurred())
Expect(valueLen).To(BeEquivalentTo(len(hf.Value)))
Expect(string(data[:len(hf.Value)])).To(Equal(hf.Value))
return data[len(hf.Value):]
l = hpack.HuffmanEncodeLength(hf.Value)
Expect(valueLen).To(BeEquivalentTo(l))
Expect(hpack.HuffmanDecodeToString(data[:l])).To(Equal(hf.Value))
return data[l:]
}

// Reads one indexed field line representation from data and verifies it
// matches expected_hf.
// Reads one indexed field line representation from data and verifies it matches hf.
// Returns the leftover bytes from data.
checkIndexedHeaderField := func(data []byte, expected_hf HeaderField) []byte {
checkIndexedHeaderField := func(data []byte, hf HeaderField) []byte {
Expect(data[0] >> 7).To(Equal(uint8(1))) // 1Txxxxxx
index, data, err := readVarInt(6, data)
Expect(err).ToNot(HaveOccurred())
Expect(staticTableEntries[index]).To(Equal(expected_hf))
Expect(staticTableEntries[index]).To(Equal(hf))
return data
}

checkHeaderFieldWithNameRef := func(data []byte, expected_hf HeaderField) []byte {
checkHeaderFieldWithNameRef := func(data []byte, hf HeaderField) []byte {
// read name reference
Expect(data[0] >> 6).To(Equal(uint8(1))) // 01NTxxxx
index, data, err := readVarInt(4, data)
Expect(err).ToNot(HaveOccurred())
Expect(staticTableEntries[index].Name).To(Equal(expected_hf.Name))
Expect(staticTableEntries[index].Name).To(Equal(hf.Name))
// read literal value
valueLen, data, err := readVarInt(7, data)
Expect(err).ToNot(HaveOccurred())
Expect(valueLen).To(BeEquivalentTo(len(expected_hf.Value)))
Expect(string(data[:len(expected_hf.Value)])).To(Equal(expected_hf.Value))
return data[len(expected_hf.Value):]
l := hpack.HuffmanEncodeLength(hf.Value)
Expect(valueLen).To(BeEquivalentTo(l))
Expect(hpack.HuffmanDecodeToString(data[:l])).To(Equal(hf.Value))
return data[l:]
}

It("encodes a single field", func() {
Expand Down
8 changes: 6 additions & 2 deletions integrationtests/self/integration_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -162,7 +162,9 @@ var _ = Describe("Self Tests", func() {
It("uses the static table for field names, for fields with values", func() {
var hf qpack.HeaderField
for {
if entry := staticTable[rand.Intn(len(staticTable))]; len(entry.Value) > 0 {
// Only use values with at least 2 characters.
// This makes sure that Huffman enocding doesn't compress them as much as encoding it using the static table would.
if entry := staticTable[rand.Intn(len(staticTable))]; len(entry.Value) > 1 {
hf = qpack.HeaderField{
Name: entry.Name,
Value: randomString(20),
Expand All @@ -184,7 +186,9 @@ var _ = Describe("Self Tests", func() {
It("uses the static table for field values", func() {
var hf qpack.HeaderField
for {
if entry := staticTable[rand.Intn(len(staticTable))]; len(entry.Value) > 0 {
// Only use values with at least 2 characters.
// This makes sure that Huffman enocding doesn't compress them as much as encoding it using the static table would.
if entry := staticTable[rand.Intn(len(staticTable))]; len(entry.Value) > 1 {
hf = qpack.HeaderField{
Name: entry.Name,
Value: entry.Value,
Expand Down