Implement HPACK encoder that actually compresses header block

This commit implements HPACK encoder that actually compresses header
block.  The encoder supports Huffman encoding strings and table size
update.  The Sensitive in HeaderField struct is also honored and if it
is true, header field is encoded as one of Never Indexed
representation.  SetMaxDynamicTableSizeLimit is use to set an upper
bound for the value set by SetMaxDynamicTableSize.  This is vital
since the value set by SetMaxDynamicTableSize is sent from remote
peer, they might send large value and it might make server exhaust its
memory.  Initially, maxSizeLimit is set to initialHeaderTableSize,
which is 4096.

hpack/encode.go

@@ -6,43 +6,247 @@
 package hpack
 
 import (
-	"errors"
 	"io"
 )
 
+const (
+	uint32Max              = ^uint32(0)
+	initialHeaderTableSize = 4096
+)
+
 type Encoder struct {
-	w   io.Writer
-	buf []byte
+	dynTab dynamicTable
+	// minSize is the minimum table size set by
+	// SetMaxDynamicTableSize after the previous Header Table Size
+	// Update.
+	minSize uint32
+	// maxSizeLimit is the maximum table size this encoder
+	// supports. This will protect the encoder from too large
+	// size.
+	maxSizeLimit uint32
+	// tableSizeUpdate indicates whether "Header Table Size
+	// Update" is required.
+	tableSizeUpdate bool
+	w               io.Writer
+	buf             []byte
 }
 
+// NewEncoder returns a new Encoder which performs HPACK encoding. An
+// encoded data is written to w.
 func NewEncoder(w io.Writer) *Encoder {
-	return &Encoder{w: w}
+	e := &Encoder{
+		minSize:         uint32Max,
+		maxSizeLimit:    initialHeaderTableSize,
+		tableSizeUpdate: false,
+		w:               w,
+	}
+	e.dynTab.setMaxSize(initialHeaderTableSize)
+	return e
 }
 
 // WriteField encodes f into a single Write to e's underlying Writer.
+// This function may also produce bytes for "Header Table Size Update"
+// if necessary.  If produced, it is done before encoding f.
 func (e *Encoder) WriteField(f HeaderField) error {
-	// TODO: write a decent Encoder. This is a quick hack job just to move on
-	// to other pieces. With this encoder, we only write literals.
-	// The form this writes is:
-	// http://http2.github.io/http2-spec/compression.html#rfc.section.6.2.2
-	// In particular, that second table. And no huffman
-	// compression.  Oh, and let's be even lazier for now and
-	// reject keys or values with lengths greather than 126 so we
-	// can save some time by not writing a varint encoder for
-	// now. But I'm wasting time writing this comment.
-	if len(f.Name) > 126 || len(f.Value) > 126 {
-		return errors.New("TODO: finish hpack encoder. names/values too long for current laziness, procrastination, impatience.")
-	}
 	e.buf = e.buf[:0]
-	e.buf = append(e.buf, 0)
-	e.buf = append(e.buf, byte(len(f.Name)))
-	e.buf = append(e.buf, f.Name...)
-	e.buf = append(e.buf, byte(len(f.Value)))
-	e.buf = append(e.buf, f.Value...)
 
+	if e.tableSizeUpdate {
+		e.tableSizeUpdate = false
+		if e.minSize < e.dynTab.maxSize {
+			e.buf = appendTableSize(e.buf, e.minSize)
+		}
+		e.minSize = uint32Max
+		e.buf = appendTableSize(e.buf, e.dynTab.maxSize)
+	}
+
+	idx, nameValueMatch := e.searchTable(f)
+	if nameValueMatch {
+		e.buf = appendIndexed(e.buf, idx)
+	} else {
+		indexing := e.shouldIndex(f)
+		if indexing {
+			e.dynTab.add(f)
+		}
+
+		if idx == 0 {
+			e.buf = appendNewName(e.buf, f, indexing)
+		} else {
+			e.buf = appendIndexedName(e.buf, f, idx, indexing)
+		}
+	}
 	n, err := e.w.Write(e.buf)
 	if err == nil && n != len(e.buf) {
 		err = io.ErrShortWrite
 	}
 	return err
 }
+
+// searchTable searches f in both stable and dynamic header tables.
+// The static header table is searched first. Only when there is no
+// exact match for both name and value, the dynamic header table is
+// then searched. If there is no match, i is 0. If both name and value
+// match, i is the matched index and nameValueMatch becomes true. If
+// only name matches, i points to that index and nameValueMatch
+// becomes false.
+func (e *Encoder) searchTable(f HeaderField) (i uint64, nameValueMatch bool) {
+	for idx, hf := range staticTable {
+		if !constantTimeStringCompare(hf.Name, f.Name) {
+			continue
+		}
+		if i == 0 {
+			i = uint64(idx + 1)
+		}
+		if f.Sensitive {
+			continue
+		}
+		if !constantTimeStringCompare(hf.Value, f.Value) {
+			continue
+		}
+		i = uint64(idx + 1)
+		nameValueMatch = true
+		return
+	}
+
+	j, nameValueMatch := e.dynTab.search(f)
+	if nameValueMatch || (i == 0 && j != 0) {
+		i = j + uint64(len(staticTable))
+	}
+	return
+}
+
+// SetMaxDynamicTableSize changes the dynamic header table size to v.
+// The actual size is bounded by maxSizeLimit parameter passed to
+// NewEncoder.
+func (e *Encoder) SetMaxDynamicTableSize(v uint32) {
+	if v > e.maxSizeLimit {
+		v = e.maxSizeLimit
+	}
+	if v < e.minSize {
+		e.minSize = v
+	}
+	e.tableSizeUpdate = true
+	e.dynTab.setMaxSize(v)
+}
+
+// SetMaxDynamicTableSizeLimit changes the maximum value that can be
+// specified in SetMaxDynamicTableSize to v. By default, it is set to
+// 4096, which is the same size of the default dynamic header table
+// size described in HPACK specification. If the current maximum
+// dynamic header table size is strictly greater than v, "Header Table
+// Size Update" will be done in the next WriteField call and the
+// maximum dynamic header table size is truncated to v.
+func (e *Encoder) SetMaxDynamicTableSizeLimit(v uint32) {
+	e.maxSizeLimit = v
+	if e.dynTab.maxSize > v {
+		e.tableSizeUpdate = true
+		e.dynTab.setMaxSize(v)
+	}
+}
+
+// shouldIndex reports whether f should be indexed.
+func (e *Encoder) shouldIndex(f HeaderField) bool {
+	return !f.Sensitive && f.size() <= e.dynTab.maxSize
+}
+
+// appendIndexed appends index i, as encoded in "Indexed Header Field"
+// representation, to dst and returns the extended buffer.
+func appendIndexed(dst []byte, i uint64) []byte {
+	first := len(dst)
+	dst = appendVarInt(dst, 7, i)
+	dst[first] |= 0x80
+	return dst
+}
+
+// appendNewName appends f, as encoded in one of "Literal Header field
+// - New Name" representation variants, to dst and returns the
+// extended buffer.
+//
+// If f.Sensitive is true, "Never Indexed" representation is used. If
+// f.Sensitive is false and indexing is true, "Inremental Indexing"
+// representation is used.
+func appendNewName(dst []byte, f HeaderField, indexing bool) []byte {
+	dst = append(dst, encodeTypeByte(indexing, f.Sensitive))
+	dst = appendHpackString(dst, f.Name)
+	return appendHpackString(dst, f.Value)
+}
+
+// appendIndexedName appends f and index i referring indexed name
+// entry, as encoded in one of "Literal Header field - Indexed Name"
+// representation variants, to dst and returns the extended buffer.
+//
+// If f.Sensitive is true, "Never Indexed" representation is used. If
+// f.Sensitive is false and indexing is true, "Incremental Indexing"
+// representation is used.
+func appendIndexedName(dst []byte, f HeaderField, i uint64, indexing bool) []byte {
+	first := len(dst)
+	var n byte
+	if indexing {
+		n = 6
+	} else {
+		n = 4
+	}
+	dst = appendVarInt(dst, n, i)
+	dst[first] |= encodeTypeByte(indexing, f.Sensitive)
+	return appendHpackString(dst, f.Value)
+}
+
+// appendTableSize appends v, as encoded in "Header Table Size Update"
+// representation, to dst and returns the extended buffer.
+func appendTableSize(dst []byte, v uint32) []byte {
+	first := len(dst)
+	dst = appendVarInt(dst, 5, uint64(v))
+	dst[first] |= 0x20
+	return dst
+}
+
+// appendVarInt appends i, as encoded in variable integer form using n
+// bit prefix, to dst and returns the extended buffer.
+//
+// See
+// http://http2.github.io/http2-spec/compression.html#integer.representation
+func appendVarInt(dst []byte, n byte, i uint64) []byte {
+	k := uint64((1 << n) - 1)
+	if i < k {
+		return append(dst, byte(i))
+	}
+	dst = append(dst, byte(k))
+	i -= k
+	for ; i >= 128; i >>= 7 {
+		dst = append(dst, byte(0x80|(i&0x7f)))
+	}
+	return append(dst, byte(i))
+}
+
+// appendHpackString appends s, as encoded in "String Literal"
+// representation, to dst and returns the the extended buffer.
+//
+// s will be encoded in Huffman codes only when it produces strictly
+// shorter byte string.
+func appendHpackString(dst []byte, s string) []byte {
+	huffmanLength := HuffmanEncodeLength(s)
+	if huffmanLength < uint64(len(s)) {
+		first := len(dst)
+		dst = appendVarInt(dst, 7, huffmanLength)
+		dst = AppendHuffmanString(dst, s)
+		dst[first] |= 0x80
+	} else {
+		dst = appendVarInt(dst, 7, uint64(len(s)))
+		dst = append(dst, s...)
+	}
+	return dst
+}
+
+// encodeTypeByte returns type byte. If sensitive is true, type byte
+// for "Never Indexed" representation is returned. If sensitive is
+// false and indexing is true, type byte for "Incremental Indexing"
+// representation is returned. Otherwise, type byte for "Without
+// Indexing" is returned.
+func encodeTypeByte(indexing, sensitive bool) byte {
+	if sensitive {
+		return 0x10
+	}
+	if indexing {
+		return 0x40
+	}
+	return 0
+}

hpack/encode_test.go

@@ -7,33 +7,326 @@ package hpack
 
 import (
 	"bytes"
+	"encoding/hex"
 	"reflect"
+	"strings"
 	"testing"
 )
 
-func TestEncoder(t *testing.T) {
-	headers := []HeaderField{
-		HeaderField{Name: "content-type", Value: "text/html"},
-		HeaderField{Name: "x-foo", Value: "x-bar"},
-	}
+func TestEncoderTableSizeUpdate(t *testing.T) {
+	tests := []struct {
+		size1, size2 uint32
+		wantHex      string
+	}{
+		// Should emit 2 table size updates (2048 and 4096)
+		{2048, 4096, "3fe10f 3fe11f 82"},
 
-	var buf bytes.Buffer
-	e := NewEncoder(&buf)
-	for _, hf := range headers {
-		if err := e.WriteField(hf); err != nil {
+		// Should emit 1 table size update (2048)
+		{16384, 2048, "3fe10f 82"},
+	}
+	for _, tt := range tests {
+		var buf bytes.Buffer
+		e := NewEncoder(&buf)
+		e.SetMaxDynamicTableSize(tt.size1)
+		e.SetMaxDynamicTableSize(tt.size2)
+		if err := e.WriteField(pair(":method", "GET")); err != nil {
 			t.Fatal(err)
 		}
+		want := removeSpace(tt.wantHex)
+		if got := hex.EncodeToString(buf.Bytes()); got != want {
+			t.Errorf("e.SetDynamicTableSize %v, %v = %q; want %q", tt.size1, tt.size2, got, want)
+		}
 	}
+}
 
+func TestEncoderWriteField(t *testing.T) {
+	var buf bytes.Buffer
+	e := NewEncoder(&buf)
 	var got []HeaderField
-	_, err := NewDecoder(4<<10, func(f HeaderField) {
+	d := NewDecoder(4<<10, func(f HeaderField) {
 		got = append(got, f)
-	}).Write(buf.Bytes())
-	if err != nil {
-		t.Error("Decoder Write = %v", err)
+	})
+
+	tests := []struct {
+		hdrs []HeaderField
+	}{
+		{[]HeaderField{
+			pair(":method", "GET"),
+			pair(":scheme", "http"),
+			pair(":path", "/"),
+			pair(":authority", "www.example.com"),
+		}},
+		{[]HeaderField{
+			pair(":method", "GET"),
+			pair(":scheme", "http"),
+			pair(":path", "/"),
+			pair(":authority", "www.example.com"),
+			pair("cache-control", "no-cache"),
+		}},
+		{[]HeaderField{
+			pair(":method", "GET"),
+			pair(":scheme", "https"),
+			pair(":path", "/index.html"),
+			pair(":authority", "www.example.com"),
+			pair("custom-key", "custom-value"),
+		}},
+	}
+	for i, tt := range tests {
+		buf.Reset()
+		got = got[:0]
+		for _, hf := range tt.hdrs {
+			if err := e.WriteField(hf); err != nil {
+				t.Fatal(err)
+			}
+		}
+		_, err := d.Write(buf.Bytes())
+		if err != nil {
+			t.Error("%d. Decoder Write = %v", i, err)
+		}
+		if !reflect.DeepEqual(got, tt.hdrs) {
+			t.Errorf("%d. Decoded %+v; want %+v", i, got, tt.hdrs)
+		}
+	}
+}
+
+func TestEncoderSearchTable(t *testing.T) {
+	e := NewEncoder(nil)
+
+	e.dynTab.add(pair("foo", "bar"))
+	e.dynTab.add(pair("blake", "miz"))
+	e.dynTab.add(pair(":method", "GET"))
+
+	tests := []struct {
+		hf        HeaderField
+		wantI     uint64
+		wantMatch bool
+	}{
+		// Name and Value match
+		{pair("foo", "bar"), uint64(len(staticTable) + 3), true},
+		{pair("blake", "miz"), uint64(len(staticTable) + 2), true},
+		{pair(":method", "GET"), 2, true},
+
+		// Only name match because Sensitive == true
+		{HeaderField{":method", "GET", true}, 2, false},
+
+		// Only Name matches
+		{pair("foo", "..."), uint64(len(staticTable) + 3), false},
+		{pair("blake", "..."), uint64(len(staticTable) + 2), false},
+		{pair(":method", "..."), 2, false},
+
+		// None match
+		{pair("foo-", "bar"), 0, false},
 	}
-	if !reflect.DeepEqual(got, headers) {
-		t.Errorf("Decoded %+v; want %+v", got, headers)
+	for _, tt := range tests {
+		if gotI, gotMatch := e.searchTable(tt.hf); gotI != tt.wantI || gotMatch != tt.wantMatch {
+			t.Errorf("d.search(%+v) = %v, %v; want %v, %v", tt.hf, gotI, gotMatch, tt.wantI, tt.wantMatch)
+		}
+	}
+}
+
+func TestAppendVarInt(t *testing.T) {
+	tests := []struct {
+		n    byte
+		i    uint64
+		want []byte
+	}{
+		// Fits in a byte:
+		{1, 0, []byte{0}},
+		{2, 2, []byte{2}},
+		{3, 6, []byte{6}},
+		{4, 14, []byte{14}},
+		{5, 30, []byte{30}},
+		{6, 62, []byte{62}},
+		{7, 126, []byte{126}},
+		{8, 254, []byte{254}},
+
+		// Multiple bytes:
+		{5, 1337, []byte{31, 154, 10}},
+	}
+	for _, tt := range tests {
+		got := appendVarInt(nil, tt.n, tt.i)
+		if !bytes.Equal(got, tt.want) {
+			t.Errorf("appendVarInt(nil, %v, %v) = %v; want %v", tt.n, tt.i, got, tt.want)
+		}
+	}
+}
+
+func TestAppendHpackString(t *testing.T) {
+	tests := []struct {
+		s, wantHex string
+	}{
+		// Huffman encoded
+		{"www.example.com", "8c f1e3 c2e5 f23a 6ba0 ab90 f4ff"},
+
+		// Not Huffman encoded
+		{"a", "01 61"},
+
+		// zero length
+		{"", "00"},
+	}
+	for _, tt := range tests {
+		want := removeSpace(tt.wantHex)
+		buf := appendHpackString(nil, tt.s)
+		if got := hex.EncodeToString(buf); want != got {
+			t.Errorf("appendHpackString(nil, %q) = %q; want %q", tt.s, got, want)
+		}
+	}
+}
+
+func TestAppendIndexed(t *testing.T) {
+	tests := []struct {
+		i       uint64
+		wantHex string
+	}{
+		// 1 byte
+		{1, "81"},
+		{126, "fe"},
+
+		// 2 bytes
+		{127, "ff00"},
+		{128, "ff01"},
+	}
+	for _, tt := range tests {
+		want := removeSpace(tt.wantHex)
+		buf := appendIndexed(nil, tt.i)
+		if got := hex.EncodeToString(buf); want != got {
+			t.Errorf("appendIndex(nil, %v) = %q; want %q", tt.i, got, want)
+		}
 	}
+}
+
+func TestAppendNewName(t *testing.T) {
+	tests := []struct {
+		f        HeaderField
+		indexing bool
+		wantHex  string
+	}{
+		// Incremental indexing
+		{HeaderField{"custom-key", "custom-value", false}, true, "40 88 25a8 49e9 5ba9 7d7f 89 25a8 49e9 5bb8 e8b4 bf"},
+
+		// Without indexing
+		{HeaderField{"custom-key", "custom-value", false}, false, "00 88 25a8 49e9 5ba9 7d7f 89 25a8 49e9 5bb8 e8b4 bf"},
+
+		// Never indexed
+		{HeaderField{"custom-key", "custom-value", true}, true, "10 88 25a8 49e9 5ba9 7d7f 89 25a8 49e9 5bb8 e8b4 bf"},
+		{HeaderField{"custom-key", "custom-value", true}, false, "10 88 25a8 49e9 5ba9 7d7f 89 25a8 49e9 5bb8 e8b4 bf"},
+	}
+	for _, tt := range tests {
+		want := removeSpace(tt.wantHex)
+		buf := appendNewName(nil, tt.f, tt.indexing)
+		if got := hex.EncodeToString(buf); want != got {
+			t.Errorf("appendNewName(nil, %+v, %v) = %q; want %q", tt.f, tt.indexing, got, want)
+		}
+	}
+}
+
+func TestAppendIndexedName(t *testing.T) {
+	tests := []struct {
+		f        HeaderField
+		i        uint64
+		indexing bool
+		wantHex  string
+	}{
+		// Incremental indexing
+		{HeaderField{":status", "302", false}, 8, true, "48 82 6402"},
+
+		// Without indexing
+		{HeaderField{":status", "302", false}, 8, false, "08 82 6402"},
+
+		// Never indexed
+		{HeaderField{":status", "302", true}, 8, true, "18 82 6402"},
+		{HeaderField{":status", "302", true}, 8, false, "18 82 6402"},
+	}
+	for _, tt := range tests {
+		want := removeSpace(tt.wantHex)
+		buf := appendIndexedName(nil, tt.f, tt.i, tt.indexing)
+		if got := hex.EncodeToString(buf); want != got {
+			t.Errorf("appendIndexedName(nil, %+v, %v) = %q; want %q", tt.f, tt.indexing, got, want)
+		}
+	}
+}
+
+func TestAppendTableSize(t *testing.T) {
+	tests := []struct {
+		i       uint32
+		wantHex string
+	}{
+		// Fits into 1 byte
+		{30, "3e"},
+
+		// Extra byte
+		{31, "3f00"},
+		{32, "3f01"},
+	}
+	for _, tt := range tests {
+		want := removeSpace(tt.wantHex)
+		buf := appendTableSize(nil, tt.i)
+		if got := hex.EncodeToString(buf); want != got {
+			t.Errorf("appendTableSize(nil, %v) = %q; want %q", tt.i, got, want)
+		}
+	}
+}
+
+func TestEncoderSetMaxDynamicTableSize(t *testing.T) {
+	var buf bytes.Buffer
+	e := NewEncoder(&buf)
+	tests := []struct {
+		v           uint32
+		wantUpdate  bool
+		wantMinSize uint32
+		wantMaxSize uint32
+	}{
+		// Set new table size to 2048
+		{2048, true, 2048, 2048},
+
+		// Set new table size to 16384, but still limited to
+		// 4096
+		{16384, true, 2048, 4096},
+	}
+	for _, tt := range tests {
+		e.SetMaxDynamicTableSize(tt.v)
+		if got := e.tableSizeUpdate; tt.wantUpdate != got {
+			t.Errorf("e.tableSizeUpdate = %v; want %v", got, tt.wantUpdate)
+		}
+		if got := e.minSize; tt.wantMinSize != got {
+			t.Errorf("e.minSize = %v; want %v", got, tt.wantMinSize)
+		}
+		if got := e.dynTab.maxSize; tt.wantMaxSize != got {
+			t.Errorf("e.maxSize = %v; want %v", got, tt.wantMaxSize)
+		}
+	}
+}
+
+func TestEncoderSetMaxDynamicTableSizeLimit(t *testing.T) {
+	e := NewEncoder(nil)
+	// 4095 < initialHeaderTableSize means maxSize is truncated to
+	// 4095.
+	e.SetMaxDynamicTableSizeLimit(4095)
+	if got, want := e.dynTab.maxSize, uint32(4095); got != want {
+		t.Errorf("e.dynTab.maxSize = %v; want %v", got, want)
+	}
+	if got, want := e.maxSizeLimit, uint32(4095); got != want {
+		t.Errorf("e.maxSizeLimit = %v; want %v", got, want)
+	}
+	if got, want := e.tableSizeUpdate, true; got != want {
+		t.Errorf("e.tableSizeUpdate = %v; want %v", got, want)
+	}
+	// maxSize will be truncated to maxSizeLimit
+	e.SetMaxDynamicTableSize(16384)
+	if got, want := e.dynTab.maxSize, uint32(4095); got != want {
+		t.Errorf("e.dynTab.maxSize = %v; want %v", got, want)
+	}
+	// 8192 > current maxSizeLimit, so maxSize does not change.
+	e.SetMaxDynamicTableSizeLimit(8192)
+	if got, want := e.dynTab.maxSize, uint32(4095); got != want {
+		t.Errorf("e.dynTab.maxSize = %v; want %v", got, want)
+	}
+	if got, want := e.maxSizeLimit, uint32(8192); got != want {
+		t.Errorf("e.maxSizeLimit = %v; want %v", got, want);
+	}
+}
+
 
+func removeSpace(s string) string {
+	return strings.Replace(s, " ", "", -1)
 }

hpack/hpack.go

@@ -141,6 +141,49 @@ func (dt *dynamicTable) evict() {
 	}
 }
 
+// constantTimeStringCompare compares string a and b in a constant
+// time manner.
+func constantTimeStringCompare(a, b string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+
+	c := byte(0)
+
+	for i := 0; i < len(a); i++ {
+		c |= a[i] ^ b[i]
+	}
+
+	return c == 0
+}
+
+// Search searches f in the table. The return value i is 0 if there is
+// no name match. If there is name match or name/value match, i is the
+// index of that entry (1-based). If both name and value match,
+// nameValueMatch becomes true.
+func (dt *dynamicTable) search(f HeaderField) (i uint64, nameValueMatch bool) {
+	l := len(dt.ents)
+	for j := l - 1; j >= 0; j-- {
+		ent := dt.ents[j]
+		if !constantTimeStringCompare(ent.Name, f.Name) {
+			continue
+		}
+		if i == 0 {
+			i = uint64(l - j)
+		}
+		if f.Sensitive {
+			continue
+		}
+		if !constantTimeStringCompare(ent.Value, f.Value) {
+			continue
+		}
+		i = uint64(l - j)
+		nameValueMatch = true
+		return
+	}
+	return
+}
+
 func (d *Decoder) maxTableIndex() int {
 	return len(d.dynTab.ents) + len(staticTable)
 }

hpack/hpack_test.go

@@ -142,6 +142,41 @@ func TestDynamicTableAt(t *testing.T) {
 	}
 }
 
+func TestDynamicTableSearch(t *testing.T) {
+	dt := dynamicTable{}
+	dt.setMaxSize(4096)
+
+	dt.add(pair("foo", "bar"))
+	dt.add(pair("blake", "miz"))
+	dt.add(pair(":method", "GET"))
+
+	tests := []struct {
+		hf        HeaderField
+		wantI     uint64
+		wantMatch bool
+	}{
+		// Name and Value match
+		{pair("foo", "bar"), 3, true},
+		{pair(":method", "GET"), 1, true},
+
+		// Only name match because of Sensitive == true
+		{HeaderField{"blake", "miz", true}, 2, false},
+
+		// Only Name matches
+		{pair("foo", "..."), 3, false},
+		{pair("blake", "..."), 2, false},
+		{pair(":method", "..."), 1, false},
+
+		// None match
+		{pair("foo-", "bar"), 0, false},
+	}
+	for _, tt := range tests {
+		if gotI, gotMatch := dt.search(tt.hf); gotI != tt.wantI || gotMatch != tt.wantMatch {
+			t.Errorf("d.search(%+v) = %v, %v; want %v, %v", tt.hf, gotI, gotMatch, tt.wantI, tt.wantMatch)
+		}
+	}
+}
+
 func TestDynamicTableSizeEvict(t *testing.T) {
 	d := NewDecoder(4096, nil)
 	if want := uint32(0); d.dynTab.size != want {
@@ -521,6 +556,32 @@ func TestHuffmanDecode(t *testing.T) {
 	}
 }
 
+func TestAppendHuffmanString(t *testing.T) {
+	tests := []struct {
+		in, want string
+	}{
+		{"www.example.com", "f1e3 c2e5 f23a 6ba0 ab90 f4ff"},
+		{"no-cache", "a8eb 1064 9cbf"},
+		{"custom-key", "25a8 49e9 5ba9 7d7f"},
+		{"custom-value", "25a8 49e9 5bb8 e8b4 bf"},
+		{"302", "6402"},
+		{"private", "aec3 771a 4b"},
+		{"Mon, 21 Oct 2013 20:13:21 GMT", "d07a be94 1054 d444 a820 0595 040b 8166 e082 a62d 1bff"},
+		{"https://www.example.com", "9d29 ad17 1863 c78f 0b97 c8e9 ae82 ae43 d3"},
+		{"gzip", "9bd9 ab"},
+		{"foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age=3600; version=1",
+			"94e7 821d d7f2 e6c7 b335 dfdf cd5b 3960 d5af 2708 7f36 72c1 ab27 0fb5 291f 9587 3160 65c0 03ed 4ee5 b106 3d50 07"},
+	}
+	for i, tt := range tests {
+		buf := []byte{}
+		want := strings.Replace(tt.want, " ", "", -1)
+		buf = AppendHuffmanString(buf, tt.in)
+		if got := hex.EncodeToString(buf); want != got {
+			t.Errorf("%d. encode = %q; want %q", i, got, want)
+		}
+	}
+}
+
 func TestReadVarInt(t *testing.T) {
 	type res struct {
 		i        uint64

hpack/huffman.go

@@ -91,3 +91,69 @@ func addDecoderNode(sym byte, code uint32, codeLen uint8) {
 		cur.children[i] = &node{sym: sym, codeLen: codeLen}
 	}
 }
+
+// AppendHuffmanString appends s, as encoded in Huffman codes, to dst
+// and returns the extended buffer.
+func AppendHuffmanString(dst []byte, s string) []byte {
+	rembits := uint8(8)
+
+	for i := 0; i < len(s); i++ {
+		if rembits == 8 {
+			dst = append(dst, 0)
+		}
+		dst, rembits = appendByteToHuffmanCode(dst, rembits, s[i])
+	}
+
+	if rembits < 8 {
+		// special EOS symbol
+		code := uint32(0x3fffffff)
+		nbits := uint8(30)
+
+		t := uint8(code >> (nbits - rembits))
+		dst[len(dst)-1] |= t
+	}
+
+	return dst
+}
+
+// HuffmanEncodeLength returns the number of bytes required to encode
+// s in Huffman codes. The result is round up to byte boundary.
+func HuffmanEncodeLength(s string) uint64 {
+	n := uint64(0)
+	for i := 0; i < len(s); i++ {
+		n += uint64(huffmanCodeLen[s[i]])
+	}
+	return (n + 7) / 8
+}
+
+// appendByteToHuffmanCode appends Huffman code for c to dst and
+// returns the extended buffer and the remaining bits in the last
+// element. The appending is not byte aligned and the remaining bits
+// in the last element of dst is given in rembits.
+func appendByteToHuffmanCode(dst []byte, rembits uint8, c byte) ([]byte, uint8) {
+	code := huffmanCodes[c]
+	nbits := huffmanCodeLen[c]
+
+	for {
+		if rembits > nbits {
+			t := uint8(code << (rembits - nbits))
+			dst[len(dst)-1] |= t
+			rembits -= nbits
+			break
+		}
+
+		t := uint8(code >> (nbits - rembits))
+		dst[len(dst)-1] |= t
+
+		nbits -= rembits
+		rembits = 8
+
+		if nbits == 0 {
+			break
+		}
+
+		dst = append(dst, 0)
+	}
+
+	return dst, rembits
+}

server.go

@@ -884,6 +884,7 @@ func (sc *serverConn) processSetting(s Setting) error {
 	switch s.ID {
 	case SettingHeaderTableSize:
 		sc.headerTableSize = s.Val
+		sc.hpackEncoder.SetMaxDynamicTableSize(s.Val)
 		return nil
 	case SettingEnablePush:
 		sc.pushEnabled = s.Val != 0