doggo/pkg/resolvers/doh.go

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package resolvers
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import (
"bytes"
"fmt"
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"io/ioutil"
"net/http"
"net/url"
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"time"
"github.com/miekg/dns"
)
// DOHResolver represents the config options for setting up a DOH based resolver.
type DOHResolver struct {
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client *http.Client
server string
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}
type DOHResolverOpts struct {
Timeout time.Duration
}
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// NewDOHResolver accepts a nameserver address and configures a DOH based resolver.
func NewDOHResolver(server string, opts DOHResolverOpts) (Resolver, error) {
// do basic validation
u, err := url.ParseRequestURI(server)
if err != nil {
return nil, fmt.Errorf("%s is not a valid HTTPS nameserver", server)
}
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if u.Scheme != "https" {
return nil, fmt.Errorf("missing https in %s", server)
}
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httpClient := &http.Client{
Timeout: opts.Timeout,
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}
return &DOHResolver{
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client: httpClient,
server: server,
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}, nil
}
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func (d *DOHResolver) Lookup(questions []dns.Question) ([]Response, error) {
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var (
messages = prepareMessages(questions)
responses []Response
)
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for _, msg := range messages {
// get the DNS Message in wire format.
b, err := msg.Pack()
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if err != nil {
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return nil, err
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}
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now := time.Now()
// Make an HTTP POST request to the DNS server with the DNS message as wire format bytes in the body.
resp, err := d.client.Post(d.server, "application/dns-message", bytes.NewBuffer(b))
if err != nil {
return nil, err
}
if resp.StatusCode != http.StatusOK {
return nil, fmt.Errorf("error from nameserver %s", resp.Status)
}
rtt := time.Since(now)
// extract the binary response in DNS Message.
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
return nil, err
}
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err = msg.Unpack(body)
if err != nil {
return nil, err
}
rsp := Response{
Message: msg,
RTT: rtt,
Nameserver: d.server,
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}
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responses = append(responses, rsp)
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}
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return responses, nil
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}