cloudflared-mirror/tunneldns/https_upstream.go

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package tunneldns
import (
"bytes"
"crypto/tls"
"fmt"
"io/ioutil"
"net/http"
"net/url"
"time"
"github.com/miekg/dns"
"github.com/pkg/errors"
log "github.com/sirupsen/logrus"
"golang.org/x/net/context"
"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
}
// NewUpstreamHTTPS creates a new DNS over HTTPS upstream from hostname
func NewUpstreamHTTPS(endpoint string) (Upstream, error) {
u, err := url.Parse(endpoint)
if err != nil {
return nil, err
}
// Update TLS and HTTP client configuration
tls := &tls.Config{ServerName: u.Hostname()}
transport := &http.Transport{
TLSClientConfig: tls,
DisableCompression: true,
MaxIdleConns: 1,
}
http2.ConfigureTransport(transport)
client := &http.Client{
Timeout: defaultTimeout,
Transport: transport,
}
return &UpstreamHTTPS{client: client, endpoint: u}, 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")
}
// No content negotiation for now, use DNS wire format
buf, backendErr := u.exchangeWireformat(queryBuf)
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 = query.Id
return response, nil
}
log.WithError(backendErr).Errorf("failed to connect to an HTTPS backend %q", u.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 (u *UpstreamHTTPS) exchangeWireformat(msg []byte) ([]byte, error) {
req, err := http.NewRequest("POST", u.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-udpwireformat")
req.Host = u.endpoint.Hostname()
resp, err := u.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
}