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frame.go
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186 lines (170 loc) · 3.93 KB
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package zsocket
import (
"bufio"
"crypto/rand"
"encoding/binary"
"errors"
"fmt"
"io"
)
// WebSocket opcodes.
const (
opContinuation = 0x0
opText = 0x1
opBinary = 0x2
opClose = 0x8
opPing = 0x9
opPong = 0xA
)
var (
errMaskedExpected = errors.New("zsocket: client-to-server frames must be masked")
errRSVNonZero = errors.New("zsocket: RSV bits must be zero (extensions not implemented)")
errControlTooLarge = errors.New("zsocket: control frame payload too large")
errUnexpectedOpcode = errors.New("zsocket: unexpected opcode in fragmented message")
errFragmentState = errors.New("zsocket: invalid fragmentation state")
)
// readFrame reads a single frame from br.
func readFrame(br *bufio.Reader, readLimit int64, expectMasked bool, allowRSV1 bool) (fin bool, rsv1 bool, opcode byte, payload []byte, err error) {
// First 2 bytes: FIN/RSV/Opcode, MASK/Len
var b0, b1 byte
if b0, err = br.ReadByte(); err != nil {
return
}
if b1, err = br.ReadByte(); err != nil {
return
}
fin = (b0 & 0x80) != 0
rsv1 = (b0 & 0x40) != 0
rsv23 := (b0 & 0x30) != 0
opcode = b0 & 0x0F
masked := (b1 & 0x80) != 0
length := int64(b1 & 0x7F)
if rsv23 || (rsv1 && !allowRSV1) {
err = errRSVNonZero
return
}
if expectMasked && !masked {
err = errMaskedExpected
return
}
switch length {
case 126:
var ext uint16
if err = binary.Read(br, binary.BigEndian, &ext); err != nil {
return
}
length = int64(ext)
case 127:
var ext uint64
if err = binary.Read(br, binary.BigEndian, &ext); err != nil {
return
}
// spec forbids lengths using MSB to avoid negatives; we assume input is sane here.
length = int64(ext)
}
// Control frames must have payload <= 125 and not be fragmented.
isControl := opcode == opClose || opcode == opPing || opcode == opPong
if isControl && (length > 125 || !fin) {
err = errControlTooLarge
return
}
// Enforce read limit if set (0 means unlimited).
if readLimit > 0 && length > readLimit {
err = ErrReadLimit
return
}
var maskKey [4]byte
if masked {
if _, err = io.ReadFull(br, maskKey[:]); err != nil {
return
}
}
payload = make([]byte, length)
if _, err = io.ReadFull(br, payload); err != nil {
return
}
if masked {
for i := int64(0); i < length; i++ {
payload[i] ^= maskKey[i%4]
}
}
return
}
// writeFrame writes a single frame to bw.
func writeFrame(bw *bufio.Writer, fin bool, opcode byte, payload []byte, mask bool, rsv1 bool) error {
// b0: FIN + RSV(0) + opcode
b0 := byte(0)
if fin {
b0 |= 0x80
}
if rsv1 {
b0 |= 0x40
}
b0 |= opcode
if err := bw.WriteByte(b0); err != nil {
return err
}
// b1: MASK bit + length
l := len(payload)
b1Mask := byte(0)
if mask {
b1Mask = 0x80
}
if l <= 125 {
if err := bw.WriteByte(b1Mask | byte(l)); err != nil {
return err
}
} else if l <= 65535 {
if err := bw.WriteByte(b1Mask | 126); err != nil {
return err
}
if err := binary.Write(bw, binary.BigEndian, uint16(l)); err != nil {
return err
}
} else {
if err := bw.WriteByte(b1Mask | 127); err != nil {
return err
}
if err := binary.Write(bw, binary.BigEndian, uint64(l)); err != nil {
return err
}
}
if mask {
var maskKey [4]byte
if _, err := io.ReadFull(rand.Reader, maskKey[:]); err != nil {
return err
}
if _, err := bw.Write(maskKey[:]); err != nil {
return err
}
if l > 0 {
masked := make([]byte, l)
for i := 0; i < l; i++ {
masked[i] = payload[i] ^ maskKey[i%4]
}
if _, err := bw.Write(masked); err != nil {
return err
}
}
return nil
}
if l > 0 {
if _, err := bw.Write(payload); err != nil {
return err
}
}
return nil
}
// CloseError is returned when a close frame is received or needs to be sent.
type CloseError struct {
Code CloseCode
Text string
Reason string
}
func (e CloseError) Error() string {
text := e.Text
if text == "" {
text = e.Reason
}
return fmt.Sprintf("zsocket: close code=%d reason=%q", e.Code, text)
}