What causes "read from closed connection" in ginuerzh/gost?

Exit the read loop when this error is returned — the connection is closed and will produce no more data.

read from closed connection

Error message

read from closed connection

What it means

udpConn.ReadFrom returns this error when the connection's `closed` channel has been signaled, meaning ReadFrom was called on an already-closed UDP connection. Any buffered packets in rChan are discarded once closed, so subsequent reads fail with this sentinel.

Source

Thrown at udp.go:249

	}
	go c.ttlWait()
	return c
}

func (c *udpServerConn) Read(b []byte) (n int, err error) {
	n, _, err = c.ReadFrom(b)
	return
}

func (c *udpServerConn) ReadFrom(b []byte) (n int, addr net.Addr, err error) {
	select {
	case bb := <-c.rChan:
		n = copy(b, bb)
		if cap(bb) == mediumBufferSize {
			mPool.Put(bb[:cap(bb)])
		}
	case <-c.closed:
		err = errors.New("read from closed connection")
		return
	}

	select {
	case c.nopChan <- n:
	default:
	}

	addr = c.raddr

	return
}

func (c *udpServerConn) Write(b []byte) (n int, err error) {
	return c.WriteTo(b, c.raddr)
}

func (c *udpServerConn) WriteTo(b []byte, addr net.Addr) (n int, err error) {

View on GitHub (pinned to a33fdbf4c9)

Solutions

Exit the read loop when this error is returned — the connection is closed and will produce no more data.
Cancel read goroutines (context or done channel) before or atomically with closing the connection.
Treat this error as io.EOF/io.ErrClosedPipe equivalent and stop reading rather than retrying.

Example fix

// before
for {
    n, addr, err := conn.ReadFrom(buf)
    if err != nil {
        log.Println(err)
        continue // spins on closed conn
    }
}
// after
for {
    n, addr, err := conn.ReadFrom(buf)
    if err != nil {
        return // conn closed; stop reading
    }
}

Defensive patterns

Strategy: type-guard

Validate before calling

select {
case <-c.done:
    return // skip reads after shutdown signaled
default:
}

Type guard

func isConnClosedReadErr(err error) bool {
    return err != nil && strings.Contains(err.Error(), "read from closed connection")
}

Try / catch

n, addr, err := conn.ReadFrom(buf)
if err != nil {
    if isConnClosedReadErr(err) { return } // expected during shutdown
    log.Printf("read: %v", err)
}

Prevention

Cancel all reader goroutines before/when closing the connection.
Treat this error like io.EOF: stop reading, don't retry.
Centralize the read loop so close/read teardown is ordered once.
Use context.Done() alongside read completion to avoid races.

When it happens

Trigger: Calling Read/ReadFrom on a *udpConn after Close() has completed; a read goroutine still blocked on rChan when another goroutine closes the connection.

Common situations: Relay/pump goroutines not cancelled before connection close; closing the conn in a timeout handler while a reader is active; double-close cleanup paths.

Related errors

AI-assisted analysis of ginuerzh/gost@a33fdbf4c9 (2026-09-02). Data as JSON: /api/errors/0ec4126e7f4edecc. Report an issue: GitHub.