You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: conn_check.go
    path of file: ./repos/streamdal/apps/server/vendor/github.com/redis/go-redis/v9/internal/pool
    
    the code of the file until where you have to start completion: //go:build linux || darwin || dragonfly || freebsd || netbsd || openbsd || solaris || illumos

package pool

import (
	"errors"
	"io"
	"net"
	"syscall"
	"time"
)

var errUnexpectedRead = errors.New("unexpected read from socket")

func connCheck(conn net.Conn) error {
	// Reset previous timeout.
	_ = conn.SetDeadline(time.Time{})

	sysConn, ok := conn.(syscall.Conn)
	if !ok {
		return nil
	}
	rawConn, err := sysConn.Sysc
    
func connCheck(conn net.Conn) error {
	// Reset previous timeout.
	_ = conn.SetDeadline(time.Time{})

	sysConn, ok := conn.(syscall.Conn)
	if !ok {
		return nil
	}
	rawConn, err := sysConn.SyscallConn()
	if err != nil {
		return err
	}

	var sysErr error

	if err := rawConn.Read(func(fd uintptr) bool {
		var buf [1]byte
		n, err := syscall.Read(int(fd), buf[:])
		switch {
		case n == 0 && err == nil:
			sysErr = io.EOF
		case n > 0:
			sysErr = errUnexpectedRead
		case err == syscall.EAGAIN || err == syscall.EWOULDBLOCK:
			sysErr = nil
		default:
			sysErr = err
		}
		return true
	}); err != nil {
		return err
	}

	return sysErr
}