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package yamux
import (
"bufio"
"fmt"
"io"
"io/ioutil"
"log"
"math"
"net"
"strings"
"sync"
"sync/atomic"
"time"
)
// Session is used to wrap a reliable ordered connection and to
// multiplex it into multiple streams.
type Session struct {
// remoteGoAway indicates the remote side does
// not want futher connections. Must be first for alignment.
remoteGoAway int32
// localGoAway indicates that we should stop
// accepting futher connections. Must be first for alignment.
localGoAway int32
// nextStreamID is the next stream we should
// send. This depends if we are a client/server.
nextStreamID uint32
// config holds our configuration
config *Config
// logger is used for our logs
logger *log.Logger
// conn is the underlying connection
conn io.ReadWriteCloser
// bufRead is a buffered reader
bufRead *bufio.Reader
// pings is used to track inflight pings
pings map[uint32]chan struct{}
pingID uint32
pingLock sync.Mutex
// streams maps a stream id to a stream, and inflight has an entry
// for any outgoing stream that has not yet been established. Both are
// protected by streamLock.
streams map[uint32]*Stream
inflight map[uint32]struct{}
streamLock sync.Mutex
// synCh acts like a semaphore. It is sized to the AcceptBacklog which
// is assumed to be symmetric between the client and server. This allows
// the client to avoid exceeding the backlog and instead blocks the open.
synCh chan struct{}
// acceptCh is used to pass ready streams to the client
acceptCh chan *Stream
// sendCh is used to mark a stream as ready to send,
// or to send a header out directly.
sendCh chan sendReady
// recvDoneCh is closed when recv() exits to avoid a race
// between stream registration and stream shutdown
recvDoneCh chan struct{}
// shutdown is used to safely close a session
shutdown bool
shutdownErr error
shutdownCh chan struct{}
shutdownLock sync.Mutex
}
// sendReady is used to either mark a stream as ready
// or to directly send a header
type sendReady struct {
Hdr []byte
Body io.Reader
Err chan error
}
// newSession is used to construct a new session
func newSession(config *Config, conn io.ReadWriteCloser, client bool) *Session {
s := &Session{
config: config,
logger: log.New(config.LogOutput, "", log.LstdFlags),
conn: conn,
bufRead: bufio.NewReader(conn),
pings: make(map[uint32]chan struct{}),
streams: make(map[uint32]*Stream),
inflight: make(map[uint32]struct{}),
synCh: make(chan struct{}, config.AcceptBacklog),
acceptCh: make(chan *Stream, config.AcceptBacklog),
sendCh: make(chan sendReady, 64),
recvDoneCh: make(chan struct{}),
shutdownCh: make(chan struct{}),
}
if client {
s.nextStreamID = 1
} else {
s.nextStreamID = 2
}
go s.recv()
go s.send()
if config.EnableKeepAlive {
go s.keepalive()
}
return s
}
// IsClosed does a safe check to see if we have shutdown
func (s *Session) IsClosed() bool {
select {
case <-s.shutdownCh:
return true
default:
return false
}
}
// CloseChan returns a read-only channel which is closed as
// soon as the session is closed.
func (s *Session) CloseChan() <-chan struct{} {
return s.shutdownCh
}
// NumStreams returns the number of currently open streams
func (s *Session) NumStreams() int {
s.streamLock.Lock()
num := len(s.streams)
s.streamLock.Unlock()
return num
}
// Open is used to create a new stream as a net.Conn
func (s *Session) Open() (net.Conn, error) {
conn, err := s.OpenStream()
if err != nil {
return nil, err
}
return conn, nil
}
// OpenStream is used to create a new stream
func (s *Session) OpenStream() (*Stream, error) {
if s.IsClosed() {
return nil, ErrSessionShutdown
}
if atomic.LoadInt32(&s.remoteGoAway) == 1 {
return nil, ErrRemoteGoAway
}
// Block if we have too many inflight SYNs
select {
case s.synCh <- struct{}{}:
case <-s.shutdownCh:
return nil, ErrSessionShutdown
}
GET_ID:
// Get an ID, and check for stream exhaustion
id := atomic.LoadUint32(&s.nextStreamID)
if id >= math.MaxUint32-1 {
return nil, ErrStreamsExhausted
}
if !atomic.CompareAndSwapUint32(&s.nextStreamID, id, id+2) {
goto GET_ID
}
// Register the stream
stream := newStream(s, id, streamInit)
s.streamLock.Lock()
s.streams[id] = stream
s.inflight[id] = struct{}{}
s.streamLock.Unlock()
// Send the window update to create
if err := stream.sendWindowUpdate(); err != nil {
select {
case <-s.synCh:
default:
s.logger.Printf("[ERR] yamux: aborted stream open without inflight syn semaphore")
}
return nil, err
}
return stream, nil
}
// Accept is used to block until the next available stream
// is ready to be accepted.
func (s *Session) Accept() (net.Conn, error) {
conn, err := s.AcceptStream()
if err != nil {
return nil, err
}
return conn, err
}
// AcceptStream is used to block until the next available stream
// is ready to be accepted.
func (s *Session) AcceptStream() (*Stream, error) {
select {
case stream := <-s.acceptCh:
if err := stream.sendWindowUpdate(); err != nil {
return nil, err
}
return stream, nil
case <-s.shutdownCh:
return nil, s.shutdownErr
}
}
// Close is used to close the session and all streams.
// Attempts to send a GoAway before closing the connection.
func (s *Session) Close() error {
s.shutdownLock.Lock()
defer s.shutdownLock.Unlock()
if s.shutdown {
return nil
}
s.shutdown = true
if s.shutdownErr == nil {
s.shutdownErr = ErrSessionShutdown
}
close(s.shutdownCh)
s.conn.Close()
<-s.recvDoneCh
s.streamLock.Lock()
defer s.streamLock.Unlock()
for _, stream := range s.streams {
stream.forceClose()
}
return nil
}
// exitErr is used to handle an error that is causing the
// session to terminate.
func (s *Session) exitErr(err error) {
s.shutdownLock.Lock()
if s.shutdownErr == nil {
s.shutdownErr = err
}
s.shutdownLock.Unlock()
s.Close()
}
// GoAway can be used to prevent accepting further
// connections. It does not close the underlying conn.
func (s *Session) GoAway() error {
return s.waitForSend(s.goAway(goAwayNormal), nil)
}
// goAway is used to send a goAway message
func (s *Session) goAway(reason uint32) header {
atomic.SwapInt32(&s.localGoAway, 1)
hdr := header(make([]byte, headerSize))
hdr.encode(typeGoAway, 0, 0, reason)
return hdr
}
// Ping is used to measure the RTT response time
func (s *Session) Ping() (time.Duration, error) {
// Get a channel for the ping
ch := make(chan struct{})
// Get a new ping id, mark as pending
s.pingLock.Lock()
id := s.pingID
s.pingID++
s.pings[id] = ch
s.pingLock.Unlock()
// Send the ping request
hdr := header(make([]byte, headerSize))
hdr.encode(typePing, flagSYN, 0, id)
if err := s.waitForSend(hdr, nil); err != nil {
return 0, err
}
// Wait for a response
start := time.Now()
select {
case <-ch:
case <-time.After(s.config.ConnectionWriteTimeout):
s.pingLock.Lock()
delete(s.pings, id) // Ignore it if a response comes later.
s.pingLock.Unlock()
return 0, ErrTimeout
case <-s.shutdownCh:
return 0, ErrSessionShutdown
}
// Compute the RTT
return time.Now().Sub(start), nil
}
// keepalive is a long running goroutine that periodically does
// a ping to keep the connection alive.
func (s *Session) keepalive() {
for {
select {
case <-time.After(s.config.KeepAliveInterval):
_, err := s.Ping()
if err != nil {
if err != ErrSessionShutdown {
s.logger.Printf("[ERR] yamux: keepalive failed: %v", err)
s.exitErr(ErrKeepAliveTimeout)
}
return
}
case <-s.shutdownCh:
return
}
}
}
// waitForSendErr waits to send a header, checking for a potential shutdown
func (s *Session) waitForSend(hdr header, body io.Reader) error {
errCh := make(chan error, 1)
return s.waitForSendErr(hdr, body, errCh)
}
// waitForSendErr waits to send a header with optional data, checking for a
// potential shutdown. Since there's the expectation that sends can happen
// in a timely manner, we enforce the connection write timeout here.
func (s *Session) waitForSendErr(hdr header, body io.Reader, errCh chan error) error {
t := timerPool.Get()
timer := t.(*time.Timer)
timer.Reset(s.config.ConnectionWriteTimeout)
defer func() {
timer.Stop()
select {
case <-timer.C:
default:
}
timerPool.Put(t)
}()
ready := sendReady{Hdr: hdr, Body: body, Err: errCh}
select {
case s.sendCh <- ready:
case <-s.shutdownCh:
return ErrSessionShutdown
case <-timer.C:
return ErrConnectionWriteTimeout
}
select {
case err := <-errCh:
return err
case <-s.shutdownCh:
return ErrSessionShutdown
case <-timer.C:
return ErrConnectionWriteTimeout
}
}
// sendNoWait does a send without waiting. Since there's the expectation that
// the send happens right here, we enforce the connection write timeout if we
// can't queue the header to be sent.
func (s *Session) sendNoWait(hdr header) error {
t := timerPool.Get()
timer := t.(*time.Timer)
timer.Reset(s.config.ConnectionWriteTimeout)
defer func() {
timer.Stop()
select {
case <-timer.C:
default:
}
timerPool.Put(t)
}()
select {
case s.sendCh <- sendReady{Hdr: hdr}:
return nil
case <-s.shutdownCh:
return ErrSessionShutdown
case <-timer.C:
return ErrConnectionWriteTimeout
}
}
// send is a long running goroutine that sends data
func (s *Session) send() {
for {
select {
case ready := <-s.sendCh:
// Send a header if ready
if ready.Hdr != nil {
sent := 0
for sent < len(ready.Hdr) {
n, err := s.conn.Write(ready.Hdr[sent:])
if err != nil {
s.logger.Printf("[ERR] yamux: Failed to write header: %v", err)
asyncSendErr(ready.Err, err)
s.exitErr(err)
return
}
sent += n
}
}
// Send data from a body if given
if ready.Body != nil {
_, err := io.Copy(s.conn, ready.Body)
if err != nil {
s.logger.Printf("[ERR] yamux: Failed to write body: %v", err)
asyncSendErr(ready.Err, err)
s.exitErr(err)
return
}
}
// No error, successful send
asyncSendErr(ready.Err, nil)
case <-s.shutdownCh:
return
}
}
}
// recv is a long running goroutine that accepts new data
func (s *Session) recv() {
if err := s.recvLoop(); err != nil {
s.exitErr(err)
}
}
// Ensure that the index of the handler (typeData/typeWindowUpdate/etc) matches the message type
var (
handlers = []func(*Session, header) error{
typeData: (*Session).handleStreamMessage,
typeWindowUpdate: (*Session).handleStreamMessage,
typePing: (*Session).handlePing,
typeGoAway: (*Session).handleGoAway,
}
)
// recvLoop continues to receive data until a fatal error is encountered
func (s *Session) recvLoop() error {
defer close(s.recvDoneCh)
hdr := header(make([]byte, headerSize))
for {
// Read the header
if _, err := io.ReadFull(s.bufRead, hdr); err != nil {
if err != io.EOF && !strings.Contains(err.Error(), "closed") && !strings.Contains(err.Error(), "reset by peer") {
s.logger.Printf("[ERR] yamux: Failed to read header: %v", err)
}
return err
}
// Verify the version
if hdr.Version() != protoVersion {
s.logger.Printf("[ERR] yamux: Invalid protocol version: %d", hdr.Version())
return ErrInvalidVersion
}
mt := hdr.MsgType()
if mt < typeData || mt > typeGoAway {
return ErrInvalidMsgType
}
if err := handlers[mt](s, hdr); err != nil {
return err
}
}
}
// handleStreamMessage handles either a data or window update frame
func (s *Session) handleStreamMessage(hdr header) error {
// Check for a new stream creation
id := hdr.StreamID()
flags := hdr.Flags()
if flags&flagSYN == flagSYN {
if err := s.incomingStream(id); err != nil {
return err
}
}
// Get the stream
s.streamLock.Lock()
stream := s.streams[id]
s.streamLock.Unlock()
// If we do not have a stream, likely we sent a RST
if stream == nil {
// Drain any data on the wire
if hdr.MsgType() == typeData && hdr.Length() > 0 {
s.logger.Printf("[WARN] yamux: Discarding data for stream: %d", id)
if _, err := io.CopyN(ioutil.Discard, s.bufRead, int64(hdr.Length())); err != nil {
s.logger.Printf("[ERR] yamux: Failed to discard data: %v", err)
return nil
}
} else {
s.logger.Printf("[WARN] yamux: frame for missing stream: %v", hdr)
}
return nil
}
// Check if this is a window update
if hdr.MsgType() == typeWindowUpdate {
if err := stream.incrSendWindow(hdr, flags); err != nil {
if sendErr := s.sendNoWait(s.goAway(goAwayProtoErr)); sendErr != nil {
s.logger.Printf("[WARN] yamux: failed to send go away: %v", sendErr)
}
return err
}
return nil
}
// Read the new data
if err := stream.readData(hdr, flags, s.bufRead); err != nil {
if sendErr := s.sendNoWait(s.goAway(goAwayProtoErr)); sendErr != nil {
s.logger.Printf("[WARN] yamux: failed to send go away: %v", sendErr)
}
return err
}
return nil
}
// handlePing is invokde for a typePing frame
func (s *Session) handlePing(hdr header) error {
flags := hdr.Flags()
pingID := hdr.Length()
// Check if this is a query, respond back in a separate context so we
// don't interfere with the receiving thread blocking for the write.
if flags&flagSYN == flagSYN {
go func() {
hdr := header(make([]byte, headerSize))
hdr.encode(typePing, flagACK, 0, pingID)
if err := s.sendNoWait(hdr); err != nil {
s.logger.Printf("[WARN] yamux: failed to send ping reply: %v", err)
}
}()
return nil
}
// Handle a response
s.pingLock.Lock()
ch := s.pings[pingID]
if ch != nil {
delete(s.pings, pingID)
close(ch)
}
s.pingLock.Unlock()
return nil
}
// handleGoAway is invokde for a typeGoAway frame
func (s *Session) handleGoAway(hdr header) error {
code := hdr.Length()
switch code {
case goAwayNormal:
atomic.SwapInt32(&s.remoteGoAway, 1)
case goAwayProtoErr:
s.logger.Printf("[ERR] yamux: received protocol error go away")
return fmt.Errorf("yamux protocol error")
case goAwayInternalErr:
s.logger.Printf("[ERR] yamux: received internal error go away")
return fmt.Errorf("remote yamux internal error")
default:
s.logger.Printf("[ERR] yamux: received unexpected go away")
return fmt.Errorf("unexpected go away received")
}
return nil
}
// incomingStream is used to create a new incoming stream
func (s *Session) incomingStream(id uint32) error {
// Reject immediately if we are doing a go away
if atomic.LoadInt32(&s.localGoAway) == 1 {
hdr := header(make([]byte, headerSize))
hdr.encode(typeWindowUpdate, flagRST, id, 0)
return s.sendNoWait(hdr)
}
// Allocate a new stream
stream := newStream(s, id, streamSYNReceived)
s.streamLock.Lock()
defer s.streamLock.Unlock()
// Check if stream already exists
if _, ok := s.streams[id]; ok {
s.logger.Printf("[ERR] yamux: duplicate stream declared")
if sendErr := s.sendNoWait(s.goAway(goAwayProtoErr)); sendErr != nil {
s.logger.Printf("[WARN] yamux: failed to send go away: %v", sendErr)
}
return ErrDuplicateStream
}
// Register the stream
s.streams[id] = stream
// Check if we've exceeded the backlog
select {
case s.acceptCh <- stream:
return nil
default:
// Backlog exceeded! RST the stream
s.logger.Printf("[WARN] yamux: backlog exceeded, forcing connection reset")
delete(s.streams, id)
stream.sendHdr.encode(typeWindowUpdate, flagRST, id, 0)
return s.sendNoWait(stream.sendHdr)
}
}
// closeStream is used to close a stream once both sides have
// issued a close. If there was an in-flight SYN and the stream
// was not yet established, then this will give the credit back.
func (s *Session) closeStream(id uint32) {
s.streamLock.Lock()
if _, ok := s.inflight[id]; ok {
select {
case <-s.synCh:
default:
s.logger.Printf("[ERR] yamux: SYN tracking out of sync")
}
}
delete(s.streams, id)
s.streamLock.Unlock()
}
// establishStream is used to mark a stream that was in the
// SYN Sent state as established.
func (s *Session) establishStream(id uint32) {
s.streamLock.Lock()
if _, ok := s.inflight[id]; ok {
delete(s.inflight, id)
} else {
s.logger.Printf("[ERR] yamux: established stream without inflight SYN (no tracking entry)")
}
select {
case <-s.synCh:
default:
s.logger.Printf("[ERR] yamux: established stream without inflight SYN (didn't have semaphore)")
}
s.streamLock.Unlock()
}
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