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client.go
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client.go
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package peasocket
import (
"bufio"
"context"
"crypto/sha1"
"encoding/base64"
"errors"
"fmt"
"io"
"net"
"net/http"
"net/url"
"strings"
"sync"
"unsafe"
)
// flag error for when server gracefully closes the websocket connection with a Close frame.
var (
errServerGracefulClose = errors.New("server closure")
errClientGracefulClose = errors.New("client closure")
errUnexpectedPong = errors.New("unexpected pong")
)
// Client is a client websocket implementation.
//
// Users should use Client in no more than two goroutines unless calling the
// explicitly stated as concurrency safe methods i.e: Err, IsConnected.
// These two goroutines should be separated by responsability:
// - Read goroutine should call methods that read received messages
// - Write goroutine should call methods that write to the connection.
//
// Client automatically takes care of incoming Ping and Close frames during ReadNextFrame
type Client struct {
// Tx mutex.
muTx sync.Mutex
tx TxBuffered
state connState
rx Rx
ServerURL string
entropy func() uint32
}
// NewClient creates a new Client ready to connect to a websocket enabled server.
// serverURL can start with wss:// or ws:// to enable TLS (secure websocket protocol).
// entropy is a function that returns randomized 32 bit integers from a high-entropy source.
// userBuffer will be used as scratch space to copy messages.
//
// If entropy is nil then a default will be used.
// If userBuffer is zero-lengthed one will be automatically allocated.
func NewClient(serverURL string, userBuffer []byte, entropy func() uint32) *Client {
if entropy == nil {
entropy = defaultEntropy
}
L := len(userBuffer)
if userBuffer == nil {
userBuffer = make([]byte, 32*1024)
} else if L < MaxControlPayload*3 {
panic("user buffer length too short, must be at least 3*125")
}
ctl1 := userBuffer[0:0:MaxControlPayload]
ctl2 := userBuffer[MaxControlPayload : MaxControlPayload : 2*MaxControlPayload]
c := &Client{
ServerURL: serverURL,
entropy: entropy,
state: connState{
pendingPingOrClose: ctl1,
expectedPong: ctl2,
closeErr: errClientGracefulClose,
copyBuf: userBuffer[2*MaxControlPayload:],
},
}
rxc, txc := c.state.callbacks(true)
c.rx.RxCallbacks = rxc
c.tx.TxCallbacks = txc
return c
}
// Dial not yet tested. Performs websocket handshake over net.Conn.
func (c *Client) Dial(ctx context.Context, overwriteHeaders http.Header) error {
if !c.state.IsClosed() {
return errors.New("must first close existing connection before starting a new one")
}
remoteAddr, err := net.ResolveTCPAddr("tcp", strings.TrimPrefix(c.ServerURL, "ws://"))
if err != nil {
return err
}
conn, err := net.DialTCP("tcp", nil, remoteAddr)
if err != nil {
return err
}
secureWebsocketKey := c.secureKeyString()
req, err := c.makeRequest(context.Background(), secureWebsocketKey, overwriteHeaders)
if err != nil {
return err
}
err = req.Write(conn) // Write HTTP/1.1 request with challenge.
if err != nil {
return err
}
resp, err := http.ReadResponse(bufio.NewReaderSize(conn, 256), req)
if err != nil {
return err
}
if err := validateServerResponse(resp, secureWebsocketKey); err != nil {
return err
}
c.tx.SetTxTransport(conn)
c.rx.SetRxTransport(conn)
c.state.closeErr = nil
return nil
}
// DialViaHTTPClient completes a websocket handshake and returns an error if
// the handshake failed. After a successful handshake the Client is ready to begin
// communicating with the server via websocket protocol.
func (c *Client) DialViaHTTPClient(ctx context.Context, overwriteHeaders http.Header) error {
if !c.state.IsClosed() {
return errors.New("must first close existing connection before starting a new one")
}
if ctx == nil {
return errors.New("nil context")
}
secureWebsocketKey := c.secureKeyString()
req, err := c.makeRequest(ctx, secureWebsocketKey, overwriteHeaders)
if err != nil {
return err
}
client := http.DefaultClient
resp, err := client.Do(req)
if err != nil {
return fmt.Errorf("failed handshake GET: %w", err)
}
if err := validateServerResponse(resp, secureWebsocketKey); err != nil {
return err
}
// TODO(soypat): use net.Conn instead.
rwc, ok := resp.Body.(io.ReadWriteCloser)
if !ok {
return fmt.Errorf("response body not an io.ReadWriteCloser: %T", resp.Body)
}
c.tx.SetTxTransport(rwc)
c.rx.SetRxTransport(rwc)
c.state.OnConnect()
return nil
}
// IsConnected returns true if the underlying transport of the websocket is ready to send/receive messages.
// It is shorthand for c.Err() == nil.
//
// IsConnected is safe for concurrent use.
func (c *Client) IsConnected() bool { return c.state.IsConnected() }
// Err returns the error that closed the connection.
// It only returns an error while the connection is closed.
// One can test if the server gracefully closed the connection with
//
// errors.As(err, &peasocket.CloseErr{})
//
// Err is safe for concurrent use.
func (c *Client) Err() error {
c.state.mu.Lock()
defer c.state.mu.Unlock()
if c.state.closeErr == errServerGracefulClose {
return fmt.Errorf("server closed websocket: %w", c.state.makeCloseErr())
}
return c.state.closeErr
}
// BufferedMessages returns the amount of received messages N that are ready to be read
// such that the user is guaranteed to not get an error calling NextMessageReader N times.
//
// BufferedMessages is safe for concurrent use.
func (c *Client) BufferedMessages() int {
return c.state.BufferedMessages()
}
// Buffered returns the amount of bytes ready to be read in the received message buffer.
//
// Buffered is safe for concurrent use.
func (c *Client) Buffered() int {
return c.state.Buffered()
}
// HandleNextFrame reads next frame in connection. Should be called in a loop
func (c *Client) HandleNextFrame() error {
if !c.IsConnected() {
return c.Err()
}
_, err := c.rx.ReadNextFrame()
if err != nil {
return err
}
c.muTx.Lock()
err = c.state.ReplyOutstandingFrames(c.entropy(), &c.tx)
c.muTx.Unlock()
if err != nil {
c.CloseConn(err)
return err
}
return nil
}
// BufferedMessageReader returns a reader to a complete websocket message. It copies
// the whole contents of the received message to a new buffer which is returned
// to the caller.
// The returned message may have been fragmented over the wire.
func (c *Client) BufferedMessageReader() (io.Reader, FrameType, error) {
return c.state.NextMessage()
}
// WriteBufferedMessageTo writes the next received message in the queue to the argument writer.
func (c *Client) WriteBufferedMessageTo(w io.Writer) (FrameType, int64, error) {
return c.state.WriteNextMessageTo(w)
}
// WriteFragmentedMessage writes contents of r over the wire using the userBuffer
// as scratch memory. This function does not allocate memory unless userBuffer is nil.
func (c *Client) WriteFragmentedMessage(r io.Reader, userBuffer []byte) (int, error) {
c.muTx.Lock()
defer c.muTx.Unlock()
err := c.state.ReplyOutstandingFrames(c.entropy(), &c.tx)
if err != nil {
c.CloseConn(err)
return 0, err
}
return c.tx.WriteFragmentedMessage(c.entropy(), r, userBuffer)
}
// WriteMessage writes a binary message over the websocket connection.
func (c *Client) WriteMessage(payload []byte) error {
c.muTx.Lock()
defer c.muTx.Unlock()
err := c.state.ReplyOutstandingFrames(c.entropy(), &c.tx)
if err != nil {
c.CloseConn(err)
return err
}
_, err = c.tx.writeMessage(c.entropy(), payload, false)
return err
}
// WriteTextMessage writes a utf-8 message over the websocket connection.
func (c *Client) WriteTextMessage(payload []byte) error {
c.muTx.Lock()
defer c.muTx.Unlock()
err := c.state.ReplyOutstandingFrames(c.entropy(), &c.tx)
if err != nil {
c.CloseConn(err)
return err
}
_, err = c.tx.writeMessage(c.entropy(), payload, true)
return err
}
// makeRequest creates the HTTP handshake required to initiate a websocket connection
// with a server.
func (c *Client) makeRequest(ctx context.Context, secureWebsocketKey string, overwriteHeaders http.Header) (*http.Request, error) {
u, err := url.Parse(c.ServerURL)
if err != nil {
return nil, err
}
switch u.Scheme {
case "ws":
u.Scheme = "http"
case "wss":
u.Scheme = "https"
case "http", "https":
default:
return nil, fmt.Errorf("unexpected url scheme: %q", u.Scheme)
}
req := &http.Request{
Method: http.MethodGet,
URL: u,
Proto: httpProto,
ProtoMajor: httpProtoMajor,
ProtoMinor: httpProtoMinor,
Header: make(http.Header),
Host: u.Host,
}
req = req.WithContext(ctx)
hd, err := makeWSHeader(overwriteHeaders)
if err != nil {
return nil, err
}
hd["Sec-WebSocket-Key"] = []string{secureWebsocketKey}
req.Header = hd
return req, nil
}
// CloseConn closes the underlying transport without sending websocket frames.
//
// If err is nil CloseConn will panic.
func (c *Client) CloseConn(err error) error {
w := c.tx.trp
r := c.rx.trp
if w != nil && r != nil {
c.state.CloseConn(err)
w.Close()
r.Close()
return nil
}
return errors.New("transport(s) nil, will not attempt to close. this may be a bug in peasocket")
}
// CloseWebsocket sends a close control frame over the websocket connection. Does
// not attempt to close the underlying transport.
// If CloseWebsocket received a [*CloseErr] type no memory allocation is performed and it's
// status code and reason is used in the websocket close frame.
//
// If err is nil CloseWebsocket panics.
func (c *Client) CloseWebsocket(err error) error {
c.muTx.Lock()
defer c.muTx.Unlock()
return c.state.CloseWebsocket(err, c.entropy(), &c.tx)
}
func validateServerResponse(resp *http.Response, secureWebsocketKey string) error {
if resp.StatusCode != http.StatusSwitchingProtocols {
return fmt.Errorf("expected %v switching protocol http status, got %v", http.StatusSwitchingProtocols, resp.StatusCode)
}
if !strings.EqualFold(resp.Header.Get("Connection"), "Upgrade") || !strings.EqualFold(resp.Header.Get("Upgrade"), "websocket") ||
!strings.EqualFold(resp.Header.Get("Sec-WebSocket-Accept"), serverProofOfReceipt(secureWebsocketKey)) {
// resp.Header.Get("Sec-Websocket-Version") != "13" TODO(soypat): Add this once done testing since Nhooyr's library sometimes does not set this field.
return fmt.Errorf(`invalid header field(s) "Sec-Websocket-Version:13", "Connection:Upgrade", "Upgrade:websocket" or "Sec-WebSocket-Accept":<secure concatenated hash>, got %v`, resp.Header)
}
return nil
}
// On the Sec-WebSocket-Key header field, which the server uses to
// prove it received the handshake:
//
// For this header field, the server has to take the value (as present
// in the header field as sent by client, e.g., the base64-encoded [RFC4648] version minus
// any leading and trailing whitespace) and concatenate this with the
// Globally Unique Identifier (GUID, [RFC4122]) "258EAFA5-E914-47DA-
// 95CA-C5AB0DC85B11" in string form, which is unlikely to be used by
// network endpoints that do not understand the WebSocket Protocol. A
// SHA-1 hash (160 bits) [FIPS.180-3], base64-encoded (see Section 4 of
// [RFC4648]), of this concatenation is then returned in the server's
// handshake.
var predefinedGUID = []byte("258EAFA5-E914-47DA-95CA-C5AB0DC85B11")
func serverProofOfReceipt(clientSecureWSKey string) string {
clientSecureWSKey = strings.TrimSpace(clientSecureWSKey)
h := sha1.New()
h.Write([]byte(clientSecureWSKey))
h.Write(predefinedGUID)
return base64.StdEncoding.EncodeToString(h.Sum(nil))
}
func (c *Client) secureKeyString() string {
key := c.secureKey()
return base64.StdEncoding.EncodeToString(key[:])
}
func (c *Client) secureKey() [16]byte {
const u32size = unsafe.Sizeof(uint32(0))
k32 := [4]uint32{c.entropy(), c.entropy(), c.entropy(), c.entropy()}
return *(*[4 * u32size]byte)(unsafe.Pointer(&k32))
}
func makeWSHeader(overwriteHeaders http.Header) (http.Header, error) {
header := make(http.Header)
header["Upgrade"] = []string{"websocket"}
header["Connection"] = []string{"Upgrade"}
header["Sec-WebSocket-Version"] = []string{"13"}
for k, v := range overwriteHeaders {
if len(v) == 0 {
return nil, errors.New("overwrite header key " + k + " empty")
}
header.Set(k, v[0])
for _, v0 := range v[1:] {
header.Add(k, v0)
}
}
return header, nil
}