"unsafe"

	"golang.org/x/net/dns/dnsmessage"
)

// cgoAvailable set to true to indicate that the cgo resolver
// is available on this system.
const cgoAvailable = true

// An addrinfoErrno represents a getaddrinfo, getnameinfo-specific
// error number. It's a signed number and a zero value is a non-error
// by convention.
type addrinfoErrno int

func (eai addrinfoErrno) Error() string   { return _C_gai_strerror(_C_int(eai)) }

It can use a pure Go resolver that sends DNS requests directly to the servers
listed in /etc/resolv.conf, or it can use a cgo-based resolver that calls C
library routines such as getaddrinfo and getnameinfo.

On Unix the pure Go resolver is preferred over the cgo resolver, because a blocked DNS
request consumes only a goroutine, while a blocked C call consumes an operating system thread.

	"io/fs"
	"os"
	"runtime"
	"sync"
	"syscall"
)

// The net package's name resolution is rather complicated.
// There are two main approaches, go and cgo.
// The cgo resolver uses C functions like getaddrinfo.
// The go resolver reads system files directly and
// sends DNS packets directly to servers.
//
// The netgo build tag prefers the go resolver.
// The netcgo build tag prefers the cgo resolver.
//

	_ "github.com/envoyproxy/go-control-plane/envoy/extensions/network/dns_resolver/cares/v3"
	_ "github.com/envoyproxy/go-control-plane/envoy/extensions/network/dns_resolver/getaddrinfo/v3"
	_ "github.com/envoyproxy/go-control-plane/envoy/extensions/network/socket_interface/v3"
	_ "github.com/envoyproxy/go-control-plane/envoy/extensions/outlier_detection_monitors/common/v3"

		start := time.Now()

		var e error
		for i := 0; i < dnsConf.attempts; i++ {
			e = syscall.GetAddrInfoW(name16p, nil, &hints, &result)
			if e == nil || e != _WSATRY_AGAIN || time.Since(start) > dnsConf.timeout {
				break
			}
		}
		if e != nil {
			return nil, newDNSError(winError("getaddrinfow", e), name, "")
		}
		defer syscall.FreeAddrInfoW(result)
		addrs := make([]IPAddr, 0, 5)