128 lines
3.3 KiB
Go
128 lines
3.3 KiB
Go
package upstream
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import (
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"bytes"
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"crypto/tls"
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"fmt"
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"github.com/miekg/dns"
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"github.com/pkg/errors"
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"golang.org/x/net/context"
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"golang.org/x/net/http2"
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"io/ioutil"
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"log"
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"net"
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"net/http"
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"net/url"
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"time"
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)
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const (
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dnsMessageContentType = "application/dns-message"
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defaultKeepAlive = 30 * time.Second
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)
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// HttpsUpstream is the upstream implementation for DNS-over-HTTPS
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type HttpsUpstream struct {
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client *http.Client
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endpoint *url.URL
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}
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// NewHttpsUpstream creates a new DNS-over-HTTPS upstream from the specified url
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func NewHttpsUpstream(endpoint string, bootstrap string) (Upstream, error) {
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u, err := url.Parse(endpoint)
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if err != nil {
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return nil, err
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}
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// Initialize bootstrap resolver
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bootstrapResolver := CreateResolver(bootstrap)
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dialer := &net.Dialer{
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Timeout: defaultTimeout,
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KeepAlive: defaultKeepAlive,
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DualStack: true,
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Resolver: bootstrapResolver,
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}
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// Update TLS and HTTP client configuration
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tlsConfig := &tls.Config{ServerName: u.Hostname()}
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transport := &http.Transport{
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TLSClientConfig: tlsConfig,
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DisableCompression: true,
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MaxIdleConns: 1,
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DialContext: dialer.DialContext,
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}
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http2.ConfigureTransport(transport)
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client := &http.Client{
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Timeout: defaultTimeout,
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Transport: transport,
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}
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return &HttpsUpstream{client: client, endpoint: u}, nil
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}
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// Exchange provides an implementation for the Upstream interface
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func (u *HttpsUpstream) Exchange(ctx context.Context, query *dns.Msg) (*dns.Msg, error) {
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queryBuf, err := query.Pack()
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if err != nil {
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return nil, errors.Wrap(err, "failed to pack DNS query")
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}
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// No content negotiation for now, use DNS wire format
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buf, backendErr := u.exchangeWireformat(queryBuf)
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if backendErr == nil {
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response := &dns.Msg{}
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if err := response.Unpack(buf); err != nil {
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return nil, errors.Wrap(err, "failed to unpack DNS response from body")
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}
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response.Id = query.Id
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return response, nil
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}
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log.Printf("failed to connect to an HTTPS backend %q due to %s", u.endpoint, backendErr)
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return nil, backendErr
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}
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// Perform message exchange with the default UDP wireformat defined in current draft
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// https://tools.ietf.org/html/draft-ietf-doh-dns-over-https-10
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func (u *HttpsUpstream) exchangeWireformat(msg []byte) ([]byte, error) {
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req, err := http.NewRequest("POST", u.endpoint.String(), bytes.NewBuffer(msg))
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if err != nil {
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return nil, errors.Wrap(err, "failed to create an HTTPS request")
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}
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req.Header.Add("Content-Type", dnsMessageContentType)
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req.Header.Add("Accept", dnsMessageContentType)
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req.Host = u.endpoint.Hostname()
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resp, err := u.client.Do(req)
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if err != nil {
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return nil, errors.Wrap(err, "failed to perform an HTTPS request")
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}
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// Check response status code
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defer resp.Body.Close()
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if resp.StatusCode != http.StatusOK {
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return nil, fmt.Errorf("returned status code %d", resp.StatusCode)
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}
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contentType := resp.Header.Get("Content-Type")
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if contentType != dnsMessageContentType {
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return nil, fmt.Errorf("return wrong content type %s", contentType)
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}
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// Read application/dns-message response from the body
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buf, err := ioutil.ReadAll(resp.Body)
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if err != nil {
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return nil, errors.Wrap(err, "failed to read the response body")
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}
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return buf, nil
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}
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// Clear resources
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func (u *HttpsUpstream) Close() error {
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return nil
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}
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