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read.go

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package ws

import (

"encoding/binary"

"fmt"

"io"

)

// Errors used by frame reader.

var (

ErrHeaderLengthMSB = fmt.Errorf("header error: the most significant bit must be 0")

ErrHeaderLengthUnexpected = fmt.Errorf("header error: unexpected payload length bits")

)

// ReadHeader reads a frame header from r.

func ReadHeader(r io.Reader) (h Header, err error) {

// Make slice of bytes with capacity 12 that could hold any header.

//

// The maximum header size is 14, but due to the 2 hop reads,

// after first hop that reads first 2 constant bytes, we could reuse 2 bytes.

// So 14 - 2 = 12.

bts := make([]byte, 2, MaxHeaderSize-2)

// Prepare to hold first 2 bytes to choose size of next read.

_, err = io.ReadFull(r, bts)

if err != nil {

return h, err

}

h.Fin = bts[0]&bit0 != 0

h.Rsv = (bts[0] & 0x70) >> 4

h.OpCode = OpCode(bts[0] & 0x0f)

var extra int

if bts[1]&bit0 != 0 {

h.Masked = true

extra += 4

}

length := bts[1] & 0x7f

switch {

case length < 126:

h.Length = int64(length)

case length == 126:

extra += 2

case length == 127:

extra += 8

default:

err = ErrHeaderLengthUnexpected

return h, err

}

if extra == 0 {

return h, err

}

// Increase len of bts to extra bytes need to read.

// Overwrite first 2 bytes that was read before.

bts = bts[:extra]

_, err = io.ReadFull(r, bts)

if err != nil {

return h, err

}

switch {

case length == 126:

h.Length = int64(binary.BigEndian.Uint16(bts[:2]))

bts = bts[2:]

case length == 127:

if bts[0]&0x80 != 0 {

err = ErrHeaderLengthMSB

return h, err

}

h.Length = int64(binary.BigEndian.Uint64(bts[:8]))

bts = bts[8:]

}

if h.Masked {

copy(h.Mask[:], bts)

}

return h, nil

}

// ReadFrame reads a frame from r.

// It is not designed for high optimized use case cause it makes allocation

// for frame.Header.Length size inside to read frame payload into.

//

// Note that ReadFrame does not unmask payload.

func ReadFrame(r io.Reader) (f Frame, err error) {

f.Header, err = ReadHeader(r)

if err != nil {

return f, err

}

if f.Header.Length > 0 {

// int(f.Header.Length) is safe here cause we have

// checked it for overflow above in ReadHeader.

f.Payload = make([]byte, int(f.Header.Length))

_, err = io.ReadFull(r, f.Payload)

}

return f, err

}

// MustReadFrame is like ReadFrame but panics if frame can not be read.

func MustReadFrame(r io.Reader) Frame {

f, err := ReadFrame(r)

if err != nil {

panic(err)

}

return f

}

// ParseCloseFrameData parses close frame status code and closure reason if any provided.

// If there is no status code in the payload

// the empty status code is returned (code.Empty()) with empty string as a reason.

func ParseCloseFrameData(payload []byte) (code StatusCode, reason string) {

if len(payload) < 2 {

// We returning empty StatusCode here, preventing the situation

// when endpoint really sent code 1005 and we should return ProtocolError on that.

//

// In other words, we ignoring this rule [RFC6455:7.1.5]:

// If this Close control frame contains no status code, _The WebSocket

// Connection Close Code_ is considered to be 1005.

return code, reason

}

code = StatusCode(binary.BigEndian.Uint16(payload))

reason = string(payload[2:])

return code, reason

}

// ParseCloseFrameDataUnsafe is like ParseCloseFrameData except the thing

// that it does not copies payload bytes into reason, but prepares unsafe cast.

func ParseCloseFrameDataUnsafe(payload []byte) (code StatusCode, reason string) {

if len(payload) < 2 {

return code, reason

}

code = StatusCode(binary.BigEndian.Uint16(payload))

reason = btsToString(payload[2:])

return code, reason

}