Closed
Description
Summary
if client close tcp connection directly when server write data with background context.
the goroutine do Write may block forever, and succeed Write may block too.
Solution
DO NOT call Write method with context.Background,
AND DO Read in goroutine once connection established.
analysis
in Conn.writeFrame if real write to tcp failed.
in defer func, it wait closed or context.Done.
if there is no read goroutine, no closed event
defer func() {
if err != nil {
select {
case <-c.closed:
err = c.closeErr
case <-ctx.Done():
err = ctx.Err()
}
c.close(err)
err = fmt.Errorf("failed to write frame: %w", err)
}
}()first stucked write stack may like
# 0x14837f8 nhooyr.io/websocket.(*Conn).writeFrame.func1+0x98 /go/pkg/mod/nhooyr.io/websocket@v1.8.7/write.go:276
# 0x148349a nhooyr.io/websocket.(*Conn).writeFrame+0x6ba /go/pkg/mod/nhooyr.io/websocket@v1.8.7/write.go:318
# 0x1481e5b nhooyr.io/websocket.(*Conn).write+0x19b /go/pkg/mod/nhooyr.io/websocket@v1.8.7/write.go:129
# 0x1481944 nhooyr.io/websocket.(*Conn).Write+0x24 /go/pkg/mod/nhooyr.io/websocket@v1.8.7/write.go:42
succeed stack may like
# 0x147d46c nhooyr.io/websocket.(*mu).lock+0xac /go/pkg/mod/nhooyr.io/websocket@v1.8.7/conn_notjs.go:238
# 0x1481fd6 nhooyr.io/websocket.(*msgWriterState).reset+0x36 /go/pkg/mod/nhooyr.io/websocket@v1.8.7/write.go:142
# 0x1481c2b nhooyr.io/websocket.(*Conn).writer+0x2b /go/pkg/mod/nhooyr.io/websocket@v1.8.7/write.go:111
# 0x1481d2c nhooyr.io/websocket.(*Conn).write+0x6c /go/pkg/mod/nhooyr.io/websocket@v1.8.7/write.go:122
# 0x1481944 nhooyr.io/websocket.(*Conn).Write+0x24 /go/pkg/mod/nhooyr.io/websocket@v1.8.7/write.go:42
reproduce code
package main
import (
"context"
"flag"
ws "github.com/gorilla/websocket"
"log"
"net/http"
_ "net/http/pprof"
"nhooyr.io/websocket"
"sync"
"time"
)
var (
concurrency = flag.Int("c", 1, "concurrency")
wait = flag.Int("w", 1, "wait milliseconds before close")
)
func startupServer(connWg *sync.WaitGroup) {
http.HandleFunc("/ws", func(w http.ResponseWriter, r *http.Request) {
connWg.Add(1)
defer connWg.Done()
c, err := websocket.Accept(w, r, &websocket.AcceptOptions{
InsecureSkipVerify: true,
CompressionMode: websocket.CompressionDisabled,
})
if err != nil {
log.Printf("websocket accept error: %v", err)
return
}
var wg sync.WaitGroup
// uncomment below for resolving the issue
//wg.Add(1)
//go func() { // read goroutine
// defer wg.Done()
// time.Sleep(time.Millisecond * time.Duration(*wait) * 2)
// for {
// _, _, err := c.Read(context.Background())
// if err != nil {
// return
// }
// }
//}()
for i := 0; i < *concurrency; i++ { // multi write goroutine
wg.Add(1)
go func() {
defer wg.Done()
for j := 0; j < 100; j++ {
// NOTICE background may block forever
if err := c.Write(context.Background(), websocket.MessageText, []byte("hello")); err != nil {
return
}
}
}()
}
wg.Wait() // wait all write goroutine end
// do some read after write
for {
_, _, err := c.Read(context.Background())
if err != nil {
return
}
}
})
go http.ListenAndServe("127.0.0.1:40000", nil)
}
func main() {
log.SetFlags(log.Lmicroseconds)
flag.Parse()
var connWg sync.WaitGroup
startupServer(&connWg)
c, _, err := ws.DefaultDialer.Dial("ws://127.0.0.1:40000/ws", nil)
if err != nil {
panic(err)
}
go func() {
for {
_, _, err := c.ReadMessage()
if err != nil {
log.Println("client, read error", err)
return
}
}
}()
time.Sleep(time.Millisecond * time.Duration(*wait))
log.Println("client close", c.Close())
connWg.Wait() // wait for server end
}