go/vendor/google.golang.org/grpc/resolver/dns/go19.go

// +build go1.9

/*
 *
 * Copyright 2018 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package dns

import (
	"net"

	"golang.org/x/net/context"
)

var (
	defaultResolver netResolver = net.DefaultResolver
)

const defaultDNSSvrPort = "53"

var customAuthorityDialler = func(authority string) func(ctx context.Context, network, address string) (net.Conn, error) {
	return func(ctx context.Context, network, address string) (net.Conn, error) {
		var dialer net.Dialer
		return dialer.DialContext(ctx, network, authority)
	}
}

var customAuthorityResolver = func(authority string) (netResolver, error) {
	host, port, err := parseTarget(authority, defaultDNSSvrPort)
	if err != nil {
		return nil, err
	}

	authorityWithPort := net.JoinHostPort(host, port)

	return &net.Resolver{
		PreferGo: true,
		Dial:     customAuthorityDialler(authorityWithPort),
	}, nil
}