cloudflared-mirror/tunneldns/https_upstream.go

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package tunneldns
import (
"bytes"
"context"
"crypto/tls"
"fmt"
"io/ioutil"
"net"
"net/http"
"net/url"
"time"
"github.com/miekg/dns"
"github.com/pkg/errors"
"github.com/rs/zerolog"
"golang.org/x/net/http2"
)
const (
defaultTimeout = 5 * time.Second
)
// UpstreamHTTPS is the upstream implementation for DNS over HTTPS service
type UpstreamHTTPS struct {
client *http.Client
endpoint *url.URL
bootstraps []string
log *zerolog.Logger
}
// NewUpstreamHTTPS creates a new DNS over HTTPS upstream from endpoint
func NewUpstreamHTTPS(endpoint string, bootstraps []string, log *zerolog.Logger) (Upstream, error) {
u, err := url.Parse(endpoint)
if err != nil {
return nil, err
}
return &UpstreamHTTPS{client: configureClient(u.Hostname()), endpoint: u, bootstraps: bootstraps, log: log}, nil
}
// Exchange provides an implementation for the Upstream interface
func (u *UpstreamHTTPS) Exchange(ctx context.Context, query *dns.Msg) (*dns.Msg, error) {
queryBuf, err := query.Pack()
if err != nil {
return nil, errors.Wrap(err, "failed to pack DNS query")
}
if len(query.Question) > 0 && query.Question[0].Name == fmt.Sprintf("%s.", u.endpoint.Hostname()) {
for _, bootstrap := range u.bootstraps {
endpoint, client, err := configureBootstrap(bootstrap)
if err != nil {
u.log.Err(err).Msgf("failed to configure boostrap upstream %s", bootstrap)
continue
}
msg, err := exchange(queryBuf, query.Id, endpoint, client, u.log)
if err != nil {
u.log.Err(err).Msgf("failed to connect to a boostrap upstream %s", bootstrap)
continue
}
return msg, nil
}
return nil, fmt.Errorf("failed to reach any bootstrap upstream: %v", u.bootstraps)
}
return exchange(queryBuf, query.Id, u.endpoint, u.client, u.log)
}
func exchange(msg []byte, queryID uint16, endpoint *url.URL, client *http.Client, log *zerolog.Logger) (*dns.Msg, error) {
// No content negotiation for now, use DNS wire format
buf, backendErr := exchangeWireformat(msg, endpoint, client)
if backendErr == nil {
response := &dns.Msg{}
if err := response.Unpack(buf); err != nil {
return nil, errors.Wrap(err, "failed to unpack DNS response from body")
}
response.Id = queryID
return response, nil
}
log.Err(backendErr).Msgf("failed to connect to an HTTPS backend %q", endpoint)
return nil, backendErr
}
// Perform message exchange with the default UDP wireformat defined in current draft
// https://datatracker.ietf.org/doc/draft-ietf-doh-dns-over-https
func exchangeWireformat(msg []byte, endpoint *url.URL, client *http.Client) ([]byte, error) {
req, err := http.NewRequest("POST", endpoint.String(), bytes.NewBuffer(msg))
if err != nil {
return nil, errors.Wrap(err, "failed to create an HTTPS request")
}
req.Header.Add("Content-Type", "application/dns-message")
req.Host = endpoint.Host
resp, err := client.Do(req)
if err != nil {
return nil, errors.Wrap(err, "failed to perform an HTTPS request")
}
// Check response status code
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return nil, fmt.Errorf("returned status code %d", resp.StatusCode)
}
// Read wireformat response from the body
buf, err := ioutil.ReadAll(resp.Body)
if err != nil {
return nil, errors.Wrap(err, "failed to read the response body")
}
return buf, nil
}
func configureBootstrap(bootstrap string) (*url.URL, *http.Client, error) {
b, err := url.Parse(bootstrap)
if err != nil {
return nil, nil, err
}
if ip := net.ParseIP(b.Hostname()); ip == nil {
return nil, nil, fmt.Errorf("bootstrap address of %s must be an IP address", b.Hostname())
}
return b, configureClient(b.Hostname()), nil
}
// configureClient will configure a HTTPS client for upstream DoH requests
func configureClient(hostname string) *http.Client {
// Update TLS and HTTP client configuration
tlsConfig := &tls.Config{ServerName: hostname}
transport := &http.Transport{
TLSClientConfig: tlsConfig,
DisableCompression: true,
MaxIdleConns: 1,
Proxy: http.ProxyFromEnvironment,
}
_ = http2.ConfigureTransport(transport)
return &http.Client{
Timeout: defaultTimeout,
Transport: transport,
}
}