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websocket.go
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websocket.go
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package cdp
import (
"bufio"
"context"
"crypto/tls"
"fmt"
"io"
"io/ioutil"
"net"
"net/http"
"net/url"
)
// Dialer interface for WebSocket connection
type Dialer interface {
DialContext(ctx context.Context, network, address string) (net.Conn, error)
}
var _ WebSocketable = &WebSocket{}
// WebSocket client for chromium. It only implements a subset of WebSocket protocol.
// Limitation: https://bugs.chromium.org/p/chromium/issues/detail?id=1069431
// Ref: https://tools.ietf.org/html/rfc6455
type WebSocket struct {
// Dialer is usually used for proxy
Dialer Dialer
close func()
conn net.Conn
r *bufio.Reader
header [18]byte // Send is thread-safe, so we can safely share a header for all frames
mask []byte
}
// Connect to browser
func (ws *WebSocket) Connect(ctx context.Context, wsURL string, header http.Header) error {
ctx, cancel := context.WithCancel(ctx)
ws.close = cancel
u, err := url.Parse(wsURL)
if err != nil {
return err
}
ws.initDialer(u)
conn, err := ws.Dialer.DialContext(ctx, "tcp", u.Host)
if err != nil {
return err
}
go func() {
<-ctx.Done()
_ = conn.Close()
}()
ws.initConstants()
ws.conn = conn
ws.r = bufio.NewReader(conn)
return ws.handshake(ctx, u, header)
}
func (ws *WebSocket) initDialer(u *url.URL) {
if ws.Dialer != nil {
return
}
if u.Scheme == "wss" {
ws.Dialer = &tlsDialer{}
if u.Port() == "" {
u.Host += ":443"
}
} else {
ws.Dialer = &net.Dialer{}
}
}
func (ws *WebSocket) initConstants() {
// FIN is alway true, Opcode is always text frame.
ws.header = [18]byte{0b1000_0001}
ws.mask = []byte{0, 1, 2, 3}
}
// Send a message to browser.
// Because we use zero-copy design, it will modify the content of the msg.
// It won't allocate new memory.
func (ws *WebSocket) Send(msg []byte) error {
ws.header[1] = 0b1000_0000
size := len(msg)
fieldLen := 0
switch {
case size <= 125:
ws.header[1] |= byte(size)
case size < 65536:
ws.header[1] |= 126
fieldLen = 2
default:
ws.header[1] |= 127
fieldLen = 8
}
var i int
for i = 0; i < fieldLen; i++ {
digit := (fieldLen - i - 1) * 8
ws.header[i+2] = byte((size >> digit) & 0xff)
}
copy(ws.header[i+2:], ws.mask)
_, err := ws.conn.Write(ws.header[:i+6])
if err != nil {
return ws.checkClose(err)
}
for i := range msg {
msg[i] = msg[i] ^ ws.mask[i%4]
}
_, err = ws.conn.Write(msg)
return ws.checkClose(err)
}
// Read a message from browser
func (ws *WebSocket) Read() ([]byte, error) {
_, _ = ws.r.ReadByte()
b, err := ws.r.ReadByte()
if err != nil {
return nil, ws.checkClose(err)
}
size := 0
fieldLen := 0
b &= 0x7f
switch {
case b <= 125:
size = int(b)
case b == 126:
fieldLen = 2
case b == 127:
fieldLen = 8
}
for i := 0; i < fieldLen; i++ {
b, err := ws.r.ReadByte()
if err != nil {
return nil, ws.checkClose(err)
}
size = size<<8 + int(b)
}
data := make([]byte, size)
_, err = io.ReadFull(ws.r, data)
return data, ws.checkClose(err)
}
// ErrBadHandshake type
type ErrBadHandshake struct {
*http.Response
}
func (e *ErrBadHandshake) Error() string {
body, _ := ioutil.ReadAll(e.Response.Body)
return fmt.Sprintf(
"websocket bad handshake: %s. %s",
e.Response.Status, body,
)
}
func (ws *WebSocket) handshake(ctx context.Context, u *url.URL, header http.Header) error {
req := (&http.Request{Method: http.MethodGet, URL: u, Header: http.Header{
"Upgrade": {"websocket"},
"Connection": {"Upgrade"},
"Sec-WebSocket-Key": {"nil"},
"Sec-WebSocket-Version": {"13"},
}}).WithContext(ctx)
for k, vs := range header {
if k == "Host" && len(vs) > 0 {
req.Host = vs[0]
} else {
req.Header[k] = vs
}
}
err := req.Write(ws.conn)
if err != nil {
return ws.checkClose(err)
}
res, err := http.ReadResponse(ws.r, req)
if err != nil {
return ws.checkClose(err)
}
if res.StatusCode != http.StatusSwitchingProtocols ||
res.Header.Get("Sec-Websocket-Accept") != "Q67D9eATKx531lK8F7u2rqQNnNI=" {
return &ErrBadHandshake{res}
}
return nil
}
func (ws *WebSocket) checkClose(err error) error {
if err != nil {
ws.close()
}
return err
}
// TODO: replace it with tls.Dialer once golang v1.15 is widely used.
type tlsDialer struct{}
func (d *tlsDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
return tls.Dial(network, address, nil)
}