func()

in audit.go [505:560]

• 39 lines of code
• 8 McCabe index (conditional complexity)

func (c *AuditClient) closeAndUnsetPid() error {
	msg := syscall.NetlinkMessage{
		Header: syscall.NlMsghdr{
			Type:  AuditSet,
			Flags: syscall.NLM_F_REQUEST,
		},
		Data: AuditStatus{
			Mask: AuditStatusPID,
			PID:  0,
		}.toWireFormat(),
	}

	// If our request to unset the PID would block, then try to drain events from
	// the netlink socket, resend, try again.
	// In netlink, EAGAIN usually indicates our read buffer is full.
	// The auditd code (which I'm using as a reference implementation) doesn't wait for a response when unsetting the audit pid.
	// The retry count here is largely arbitrary, and provides a buffer for either transient errors (EINTR) or retries.
	retries := 5
outer:
	for i := 0; i < retries; i++ {
		_, err := c.Netlink.SendNoWait(msg)
		switch {
		case err == nil:
			return nil
		case errors.Is(err, syscall.EINTR):
			// got a transient interrupt, try again
			continue
		case errors.Is(err, syscall.EAGAIN):
			// send would block, try to drain the receive socket. The recv count here is just so we have enough of a buffer to attempt a send again/
			// The number is just here so we ideally have enough of a buffer to attempt the send again.
			maxRecv := 10000
			for i := 0; i < maxRecv; i++ {
				_, err = c.Netlink.Receive(true, noParse)
				switch {
				case err == nil, errors.Is(err, syscall.EINTR), errors.Is(err, syscall.ENOBUFS):
					// continue with receive, try to read more data
					continue
				case errors.Is(err, syscall.EAGAIN):
					// receive would block, try to send again
					continue outer
				default:
					// if receive returns an other error, just return that.
					return err
				}
			}
		default:
			// if Send returns and other error, just return that
			return err
		}

	}
	// we may not want to treat this as a hard error?
	// It's not a massive error if this fails, since the kernel will unset the PID if it can't communicate with the process,
	// so this is largely for neatness.
	return fmt.Errorf("could not unset pid from audit after retries")
}