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reader.go
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reader.go
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package wsutil
import (
"errors"
"io"
"io/ioutil"
"github.com/gobwas/ws"
)
// ErrNoFrameAdvance means that Reader's Read() method was called without
// preceding NextFrame() call.
var ErrNoFrameAdvance = errors.New("no frame advance")
// FrameHandlerFunc handles parsed frame header and its body represented by
// io.Reader.
//
// Note that reader represents already unmasked body.
type FrameHandlerFunc func(ws.Header, io.Reader) error
// Reader is a wrapper around source io.Reader which represents WebSocket
// connection. It contains options for reading messages from source.
//
// Reader implements io.Reader, which Read() method reads payload of incoming
// WebSocket frames. It also takes care on fragmented frames and possibly
// intermediate control frames between them.
//
// Note that Reader's methods are not goroutine safe.
type Reader struct {
Source io.Reader
State ws.State
// SkipHeaderCheck disables checking header bits to be RFC6455 compliant.
SkipHeaderCheck bool
OnContinuation FrameHandlerFunc
OnIntermediate FrameHandlerFunc
opCode ws.OpCode // Used to store message op code on fragmentation.
frame io.Reader // Used to as frame reader.
raw io.LimitedReader // Used to discard frames without cipher.
}
// NewReader creates new frame reader that reads from r keeping given state to
// make some protocol validity checks when it needed.
func NewReader(r io.Reader, s ws.State) *Reader {
return &Reader{
Source: r,
State: s,
}
}
// Read implements io.Reader. It reads the next message payload into p.
// It takes care on fragmented messages.
//
// The error is io.EOF only if all of message bytes were read.
// If an io.EOF happens during reading some but not all the message bytes
// Read() returns io.ErrUnexpectedEOF.
//
// The error is ErrNoFrameAdvance if no NextFrame() call was made before
// reading next message bytes.
func (r *Reader) Read(p []byte) (n int, err error) {
if r.frame == nil {
if !r.fragmented() {
// Every new Read() must be preceded by NextFrame() call.
return 0, ErrNoFrameAdvance
}
// Read next continuation or intermediate control frame.
_, err := r.NextFrame()
if err != nil {
return 0, err
}
if r.frame == nil {
// We handled intermediate control and now got nothing to read.
return 0, nil
}
}
n, err = r.frame.Read(p)
if err != nil && err != io.EOF {
return
}
if err == nil && r.raw.N != 0 {
return
}
switch {
case r.raw.N != 0:
err = io.ErrUnexpectedEOF
case r.fragmented():
err = nil
r.resetFragment()
default:
r.reset()
err = io.EOF
}
return
}
// Discard discards current message unread bytes.
// It discards all frames of fragmented message.
func (r *Reader) Discard() (err error) {
for {
_, err = io.Copy(ioutil.Discard, &r.raw)
if err != nil {
break
}
if !r.fragmented() {
break
}
if _, err = r.NextFrame(); err != nil {
break
}
}
r.reset()
return err
}
// NextFrame prepares r to read next message. It returns received frame header
// and non-nil error on failure.
//
// Note that next NextFrame() call must be done after receiving or discarding
// all current message bytes.
func (r *Reader) NextFrame() (hdr ws.Header, err error) {
hdr, err = ws.ReadHeader(r.Source)
if err == io.EOF && r.fragmented() {
// If we are in fragmented state EOF means that is was totally
// unexpected.
//
// NOTE: This is necessary to prevent callers such that
// ioutil.ReadAll to receive some amount of bytes without an error.
// ReadAll() ignores an io.EOF error, thus caller may think that
// whole message fetched, but actually only part of it.
err = io.ErrUnexpectedEOF
}
if err == nil && !r.SkipHeaderCheck {
err = ws.CheckHeader(hdr, r.State)
}
if err != nil {
return hdr, err
}
// Save raw reader to use it on discarding frame without ciphering and
// other streaming checks.
r.raw = io.LimitedReader{R: r.Source, N: hdr.Length}
frame := io.Reader(&r.raw)
if hdr.Masked {
frame = NewCipherReader(frame, hdr.Mask)
}
if r.fragmented() {
if hdr.OpCode.IsControl() {
if cb := r.OnIntermediate; cb != nil {
err = cb(hdr, frame)
}
if err == nil {
// Ensure that src is empty.
_, err = io.Copy(ioutil.Discard, &r.raw)
}
return
}
} else {
r.opCode = hdr.OpCode
}
// Save reader with ciphering and other streaming checks.
r.frame = frame
if hdr.OpCode == ws.OpContinuation {
if cb := r.OnContinuation; cb != nil {
err = cb(hdr, frame)
}
}
if hdr.Fin {
r.State = r.State.Clear(ws.StateFragmented)
} else {
r.State = r.State.Set(ws.StateFragmented)
}
return
}
func (r *Reader) fragmented() bool {
return r.State.Fragmented()
}
func (r *Reader) resetFragment() {
r.raw = io.LimitedReader{}
r.frame = nil
}
func (r *Reader) reset() {
r.raw = io.LimitedReader{}
r.frame = nil
r.opCode = 0
}