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package qpack
import (
"bytes"
"errors"
"fmt"
"sync"
"golang.org/x/net/http2/hpack"
)
// A decodingError is something the spec defines as a decoding error.
type decodingError struct {
err error
}
func (de decodingError) Error() string {
return fmt.Sprintf("decoding error: %v", de.err)
}
// An invalidIndexError is returned when an encoder references a table
// entry before the static table or after the end of the dynamic table.
type invalidIndexError int
func (e invalidIndexError) Error() string {
return fmt.Sprintf("invalid indexed representation index %d", int(e))
}
var errNoDynamicTable = decodingError{errors.New("no dynamic table")}
// errNeedMore is an internal sentinel error value that means the
// buffer is truncated and we need to read more data before we can
// continue parsing.
var errNeedMore = errors.New("need more data")
// A Decoder is the decoding context for incremental processing of
// header blocks.
type Decoder struct {
mutex sync.Mutex
emitFunc func(f HeaderField)
readRequiredInsertCount bool
readDeltaBase bool
// buf is the unparsed buffer. It's only written to
// saveBuf if it was truncated in the middle of a header
// block. Because it's usually not owned, we can only
// process it under Write.
buf []byte // not owned; only valid during Write
// saveBuf is previous data passed to Write which we weren't able
// to fully parse before. Unlike buf, we own this data.
saveBuf bytes.Buffer
}
// NewDecoder returns a new decoder
// The emitFunc will be called for each valid field parsed,
// in the same goroutine as calls to Write, before Write returns.
func NewDecoder(emitFunc func(f HeaderField)) *Decoder {
return &Decoder{emitFunc: emitFunc}
}
func (d *Decoder) Write(p []byte) (int, error) {
if len(p) == 0 {
return 0, nil
}
d.mutex.Lock()
n, err := d.writeLocked(p)
d.mutex.Unlock()
return n, err
}
func (d *Decoder) writeLocked(p []byte) (int, error) {
// Only copy the data if we have to. Optimistically assume
// that p will contain a complete header block.
if d.saveBuf.Len() == 0 {
d.buf = p
} else {
d.saveBuf.Write(p)
d.buf = d.saveBuf.Bytes()
d.saveBuf.Reset()
}
if err := d.decode(); err != nil {
if err != errNeedMore {
return 0, err
}
// TODO: limit the size of the buffer
d.saveBuf.Write(d.buf)
}
return len(p), nil
}
// DecodeFull decodes an entire block.
func (d *Decoder) DecodeFull(p []byte) ([]HeaderField, error) {
if len(p) == 0 {
return []HeaderField{}, nil
}
d.mutex.Lock()
defer d.mutex.Unlock()
saveFunc := d.emitFunc
defer func() { d.emitFunc = saveFunc }()
var hf []HeaderField
d.emitFunc = func(f HeaderField) { hf = append(hf, f) }
if _, err := d.writeLocked(p); err != nil {
return nil, err
}
if err := d.Close(); err != nil {
return nil, err
}
return hf, nil
}
// Close declares that the decoding is complete and resets the Decoder
// to be reused again for a new header block. If there is any remaining
// data in the decoder's buffer, Close returns an error.
func (d *Decoder) Close() error {
if d.saveBuf.Len() > 0 {
d.saveBuf.Reset()
return decodingError{errors.New("truncated headers")}
}
d.readRequiredInsertCount = false
d.readDeltaBase = false
return nil
}
func (d *Decoder) decode() error {
if !d.readRequiredInsertCount {
requiredInsertCount, rest, err := readVarInt(8, d.buf)
if err != nil {
return err
}
d.readRequiredInsertCount = true
if requiredInsertCount != 0 {
return decodingError{errors.New("expected Required Insert Count to be zero")}
}
d.buf = rest
}
if !d.readDeltaBase {
base, rest, err := readVarInt(7, d.buf)
if err != nil {
return err
}
d.readDeltaBase = true
if base != 0 {
return decodingError{errors.New("expected Base to be zero")}
}
d.buf = rest
}
if len(d.buf) == 0 {
return errNeedMore
}
for len(d.buf) > 0 {
b := d.buf[0]
var err error
switch {
case b&0x80 > 0: // 1xxxxxxx
err = d.parseIndexedHeaderField()
case b&0xc0 == 0x40: // 01xxxxxx
err = d.parseLiteralHeaderField()
case b&0xe0 == 0x20: // 001xxxxx
err = d.parseLiteralHeaderFieldWithoutNameReference()
default:
err = fmt.Errorf("unexpected type byte: %#x", b)
}
if err != nil {
return err
}
}
return nil
}
func (d *Decoder) parseIndexedHeaderField() error {
buf := d.buf
if buf[0]&0x40 == 0 {
return errNoDynamicTable
}
index, buf, err := readVarInt(6, buf)
if err != nil {
return err
}
hf, ok := d.at(index)
if !ok {
return decodingError{invalidIndexError(index)}
}
d.emitFunc(hf)
d.buf = buf
return nil
}
func (d *Decoder) parseLiteralHeaderField() error {
buf := d.buf
if buf[0]&0x20 > 0 || buf[0]&0x10 == 0 {
return errNoDynamicTable
}
index, buf, err := readVarInt(4, buf)
if err != nil {
return err
}
hf, ok := d.at(index)
if !ok {
return decodingError{invalidIndexError(index)}
}
if len(buf) == 0 {
return errNeedMore
}
usesHuffman := buf[0]&0x80 > 0
val, buf, err := d.readString(buf, 7, usesHuffman)
if err != nil {
return err
}
hf.Value = val
d.emitFunc(hf)
d.buf = buf
return nil
}
func (d *Decoder) parseLiteralHeaderFieldWithoutNameReference() error {
buf := d.buf
usesHuffmanForName := buf[0]&0x8 > 0
name, buf, err := d.readString(buf, 3, usesHuffmanForName)
if err != nil {
return err
}
if len(buf) == 0 {
return errNeedMore
}
usesHuffmanForVal := buf[0]&0x80 > 0
val, buf, err := d.readString(buf, 7, usesHuffmanForVal)
if err != nil {
return err
}
d.emitFunc(HeaderField{Name: name, Value: val})
d.buf = buf
return nil
}
func (d *Decoder) readString(buf []byte, n uint8, usesHuffman bool) (string, []byte, error) {
l, buf, err := readVarInt(n, buf)
if err != nil {
return "", nil, err
}
if uint64(len(buf)) < l {
return "", nil, errNeedMore
}
var val string
if usesHuffman {
var err error
val, err = hpack.HuffmanDecodeToString(buf[:l])
if err != nil {
return "", nil, err
}
} else {
val = string(buf[:l])
}
buf = buf[l:]
return val, buf, nil
}
func (d *Decoder) at(i uint64) (hf HeaderField, ok bool) {
if i >= uint64(len(staticTableEntries)) {
return
}
return staticTableEntries[i], true
}
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