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package http
import (
"bytes"
"fmt"
"io/ioutil"
"net/http"
"net/url"
"time"
"github.com/miekg/dns"
)
// RFC8484 (https://tools.ietf.org/html/rfc8484) claims that application/dns-message should be used, as does
// https://developers.cloudflare.com/1.1.1.1/dns-over-https/wireformat/
//
// However, Cloudflares service only accept this media type from one of the older RFC drafts
// (https://tools.ietf.org/html/draft-ietf-doh-dns-over-https-05).
const mimeType = "application/dns-udpwireformat"
// Client is a DNS-over-HTTPS client.
type Client struct {
httpClient *http.Client
}
// NewClient creates a new DNS-over-HTTPS client.
func NewClient(timeout time.Duration) *Client {
return &Client{httpClient: &http.Client{Timeout: timeout}}
}
// Exchange sends the DNS message msg to the DNS-over-HTTPS endpoint addr and returns the response.
func (c *Client) Exchange(msg *dns.Msg, addr string) (*dns.Msg, time.Duration, error) {
u, err := url.Parse(addr)
if err != nil {
return nil, 0, fmt.Errorf("invalid url: %w", err)
}
p, err := msg.Pack()
if err != nil {
return nil, 0, err
}
r, err := http.NewRequest(http.MethodPost, u.String(), bytes.NewReader(p))
if err != nil {
return nil, 0, err
}
r.Header.Set("Content-Type", mimeType)
r.Header.Set("Accept", mimeType)
t := time.Now()
resp, err := c.httpClient.Do(r)
if err != nil {
return nil, 0, err
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return nil, 0, fmt.Errorf("server returned HTTP %d error: %q", resp.StatusCode, resp.Status)
}
if contentType := resp.Header.Get("Content-Type"); contentType != mimeType {
return nil, 0, fmt.Errorf("server returned unexpected ContentType %q, want %q", contentType, mimeType)
}
p, err = ioutil.ReadAll(resp.Body)
if err != nil {
return nil, 0, err
}
rtt := time.Since(t)
reply := dns.Msg{}
if err := reply.Unpack(p); err != nil {
return nil, 0, err
}
return &reply, rtt, nil
}
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