Updated Go MySQL driver library

vendor/github.com/go-sql-driver/mysql/conncheck.go

@@ -0,0 +1,53 @@
+// Go MySQL Driver - A MySQL-Driver for Go's database/sql package
+//
+// Copyright 2019 The Go-MySQL-Driver Authors. All rights reserved.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+// +build !windows,!appengine
+
+package mysql
+
+import (
+	"errors"
+	"io"
+	"net"
+	"syscall"
+)
+
+var errUnexpectedRead = errors.New("unexpected read from socket")
+
+func connCheck(c net.Conn) error {
+	var (
+		n    int
+		err  error
+		buff [1]byte
+	)
+
+	sconn, ok := c.(syscall.Conn)
+	if !ok {
+		return nil
+	}
+	rc, err := sconn.SyscallConn()
+	if err != nil {
+		return err
+	}
+	rerr := rc.Read(func(fd uintptr) bool {
+		n, err = syscall.Read(int(fd), buff[:])
+		return true
+	})
+	switch {
+	case rerr != nil:
+		return rerr
+	case n == 0 && err == nil:
+		return io.EOF
+	case n > 0:
+		return errUnexpectedRead
+	case err == syscall.EAGAIN || err == syscall.EWOULDBLOCK:
+		return nil
+	default:
+		return err
+	}
+}