some code path didn't check closed state

[zhangyoufu]

Everywhere we got an error when read from / write into underlying transport (incl. flush write buffer), we should check if we have closed the connection, and wrap a CloseError.

How to reproduce

package main

import (
	"context"
	"log"
	"net/http"
	"net/http/httptest"
	"strings"
	"time"

	"nhooyr.io/websocket"
)

func handleHTTP(w http.ResponseWriter, r *http.Request) {
	ws, err := websocket.Accept(w, r, nil)
	if err == nil {
		go handleWS(ws)
	}
}

func handleWS(conn *websocket.Conn) {
	defer conn.Close(websocket.StatusInternalError, "oops")
	ctx := context.Background()
	for {
		_, _, err := conn.Read(ctx)
		if err != nil {
			return
		}
	}
}

func main() {
	ctx := context.Background()

	server := httptest.NewServer(http.HandlerFunc(handleHTTP))
	defer server.Close()

	url := strings.Replace(server.URL, "http", "ws", 1)
	client, _, _ := websocket.Dial(ctx, url, nil)

	// write something in background
	joinCh := make(chan struct{})
	go func() {
		defer close(joinCh)
		for {
			err := client.Write(ctx, websocket.MessageText, []byte("test"))
			if err != nil {
				log.Print("client write error: ", err)
				log.Print("client close status code: ", websocket.CloseStatus(err))
				return
			}
		}
	}()

	// close after some time
	time.Sleep(time.Millisecond)
	_ = client.Close(websocket.StatusNormalClosure, "bye")

	<- joinCh
}

Expected output

2020/03/15 21:20:23 client write error: failed to write msg: failed to close writer: failed to write fin frame: failed to write frame: WebSocket closed: sent close frame: status = StatusNormalClosure and reason = "bye"
2020/03/15 21:20:23 client close status code: StatusNormalClosure

Unexpected output

2020/03/15 21:20:21 client write error: failed to write msg: failed to close writer: failed to write fin frame: failed to write frame: failed to flush: write tcp 127.0.0.1:59943->127.0.0.1:59942: use of closed network connection
2020/03/15 21:20:21 client close status code: StatusCode(-1)

[nhooyr]

Thanks for reporting. Will close with #215.