panic: read websocket after it was closed

[keeword]

I write a example like that:

package main

import (
	aria2 "github.com/siku2/arigo"
)

func Get() error {
	url := "ws://127.0.0.1:6800/jsonrpc"
	conn, err := aria2.Dial(url, "")
	if err != nil {
		return err
	}
	defer conn.Close()

	if _, err := conn.TellActive("gid"); err != nil {
		return err
	}

	return nil
}

func main() {
	for {
		if err := Get(); err != nil {
			panic(err)
		}
	}
}

And got panic:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0xc0 pc=0x63757d]

goroutine 34 [running]:
github.com/gorilla/websocket.(*Conn).NextReader(0x0)
        /root/go/pkg/mod/github.com/gorilla/websocket@v1.5.0/conn.go:1000 +0x1d
github.com/siku2/arigo/internal/pkg/wsrpc.(*ReadWriteCloser).Read(0xc0002061b0, {0xc0001a0200, 0x200, 0x200})
        /root/go/pkg/mod/github.com/siku2/arigo@v0.2.1-0.20221203162025-97cc8d79dcf4/internal/pkg/wsrpc/rwc.go:26 +0x45
encoding/json.(*Decoder).refill(0xc00022e000)
        /usr/local/go/src/encoding/json/stream.go:165 +0x188
encoding/json.(*Decoder).readValue(0xc00022e000)
        /usr/local/go/src/encoding/json/stream.go:140 +0xbb
encoding/json.(*Decoder).Decode(0xc00022e000, {0x652b20, 0xc000230020})
        /usr/local/go/src/encoding/json/stream.go:63 +0x78
github.com/cenkalti/rpc2/jsonrpc.(*jsonCodec).ReadHeader(0xc000230000, 0xc0000121c8, 0xc0000121e0)
        /root/go/pkg/mod/github.com/cenkalti/rpc2@v0.0.0-20180727162946-9642ea02d0aa/jsonrpc/jsonrpc.go:93 +0x85
github.com/cenkalti/rpc2.(*Client).readLoop(0xc000216070)
        /root/go/pkg/mod/github.com/cenkalti/rpc2@v0.0.0-20180727162946-9642ea02d0aa/client.go:87 +0x12d
github.com/cenkalti/rpc2.(*Client).Run(...)
        /root/go/pkg/mod/github.com/cenkalti/rpc2@v0.0.0-20180727162946-9642ea02d0aa/client.go:62
github.com/siku2/arigo.(*Client).Run(0x0?)
        /root/go/pkg/mod/github.com/siku2/arigo@v0.2.1-0.20221203162025-97cc8d79dcf4/client.go:97 +0x1c
created by github.com/siku2/arigo.DialContext
        /root/go/pkg/mod/github.com/siku2/arigo@v0.2.1-0.20221203162025-97cc8d79dcf4/client.go:82 +0x40a
exit status 2

Maybe we shoule use a Mutex to protect the websocket from reading after it was closed?