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| 1 | +package tinydoh |
| 2 | + |
| 3 | +import ( |
| 4 | + "errors" |
| 5 | + "fmt" |
| 6 | + "io" |
| 7 | + "net" |
| 8 | + "net/http" |
| 9 | + "strings" |
| 10 | + |
| 11 | + "golang.org/x/net/dns/dnsmessage" |
| 12 | +) |
| 13 | + |
| 14 | +type Resolver struct { |
| 15 | + URL string |
| 16 | + HTTPClient *http.Client |
| 17 | +} |
| 18 | + |
| 19 | +func (r *Resolver) lookup(dnsType dnsmessage.Type, host string) ([]dnsmessage.Resource, error) { |
| 20 | + url := r.URL |
| 21 | + if url == "" { |
| 22 | + return nil, errors.New("no DoH URL provided") |
| 23 | + } |
| 24 | + client := r.HTTPClient |
| 25 | + if client == nil { |
| 26 | + client = http.DefaultClient |
| 27 | + } |
| 28 | + if !strings.HasSuffix(host, ".") { |
| 29 | + host += "." |
| 30 | + } |
| 31 | + name, err := dnsmessage.NewName(host) |
| 32 | + if err != nil { |
| 33 | + return nil, fmt.Errorf("failed to parse host %s: %w", host, err) |
| 34 | + } |
| 35 | + |
| 36 | + reqBuilder := dnsmessage.NewBuilder(nil, dnsmessage.Header{ |
| 37 | + RecursionDesired: true, |
| 38 | + }) |
| 39 | + reqBuilder.EnableCompression() |
| 40 | + err = reqBuilder.StartQuestions() |
| 41 | + if err != nil { |
| 42 | + return nil, fmt.Errorf("failed to start dns questions for host %s: %w", host, err) |
| 43 | + } |
| 44 | + err = reqBuilder.Question(dnsmessage.Question{ |
| 45 | + Name: name, |
| 46 | + Type: dnsType, |
| 47 | + Class: dnsmessage.ClassINET, |
| 48 | + }) |
| 49 | + if err != nil { |
| 50 | + return nil, fmt.Errorf("failed to build dns question for host %s: %w", host, err) |
| 51 | + } |
| 52 | + reqMsg, err := reqBuilder.Finish() |
| 53 | + if err != nil { |
| 54 | + return nil, fmt.Errorf("failed to finish dns message for host %s: %w", host, err) |
| 55 | + } |
| 56 | + httpReq, err := http.NewRequest("POST", url, strings.NewReader(string(reqMsg))) |
| 57 | + if err != nil { |
| 58 | + return nil, fmt.Errorf("failed to create http request for host %s: %w", host, err) |
| 59 | + } |
| 60 | + httpReq.Header.Set("Content-Type", "application/dns-message") |
| 61 | + |
| 62 | + httpResp, err := client.Do(httpReq) |
| 63 | + if err != nil { |
| 64 | + return nil, fmt.Errorf("failed to perform http request for host %s: %w", host, err) |
| 65 | + } |
| 66 | + defer httpResp.Body.Close() |
| 67 | + if httpResp.StatusCode != http.StatusOK { |
| 68 | + return nil, fmt.Errorf("non-200 status-code=%d for host %s", httpResp.StatusCode, host) |
| 69 | + } |
| 70 | + if httpResp.Header.Get("Content-Type") != "application/dns-message" { |
| 71 | + return nil, fmt.Errorf("unexpected content-type=%s for host %s", httpResp.Header.Get("Content-Type"), host) |
| 72 | + } |
| 73 | + |
| 74 | + // 64KB should be enough for all DNS response |
| 75 | + limitedBody := io.LimitReader(httpResp.Body, 65536) |
| 76 | + respMsg, err := io.ReadAll(limitedBody) |
| 77 | + if err != nil { |
| 78 | + return nil, fmt.Errorf("failed to read http response body for host %s: %w", host, err) |
| 79 | + } |
| 80 | + parser := dnsmessage.Parser{} |
| 81 | + header, err := parser.Start(respMsg) |
| 82 | + if err != nil { |
| 83 | + return nil, fmt.Errorf("failed to parse dns message header for host %s: %w", host, err) |
| 84 | + } |
| 85 | + if header.RCode != dnsmessage.RCodeSuccess { |
| 86 | + return nil, fmt.Errorf("dns query failed with %s for host %s", header.RCode, host) |
| 87 | + } |
| 88 | + err = parser.SkipAllQuestions() |
| 89 | + if err != nil { |
| 90 | + return nil, fmt.Errorf("failed to skip dns questions for host %s: %w", host, err) |
| 91 | + } |
| 92 | + answers, err := parser.AllAnswers() |
| 93 | + if err != nil { |
| 94 | + return nil, fmt.Errorf("failed to parse dns answers for host %s: %w", host, err) |
| 95 | + } |
| 96 | + return answers, nil |
| 97 | +} |
| 98 | + |
| 99 | +func (r *Resolver) LookupA(host string) ([]net.IP, error) { |
| 100 | + answers, err := r.lookup(dnsmessage.TypeA, host) |
| 101 | + if err != nil { |
| 102 | + return nil, err |
| 103 | + } |
| 104 | + var results []net.IP |
| 105 | + for _, rr := range answers { |
| 106 | + if rr.Header.Type == dnsmessage.TypeA { |
| 107 | + a := rr.Body.(*dnsmessage.AResource) |
| 108 | + results = append(results, a.A[:]) |
| 109 | + } |
| 110 | + } |
| 111 | + return results, nil |
| 112 | +} |
| 113 | + |
| 114 | +func (r *Resolver) LookupAAAA(host string) ([]net.IP, error) { |
| 115 | + answers, err := r.lookup(dnsmessage.TypeAAAA, host) |
| 116 | + if err != nil { |
| 117 | + return nil, err |
| 118 | + } |
| 119 | + var results []net.IP |
| 120 | + for _, rr := range answers { |
| 121 | + if rr.Header.Type == dnsmessage.TypeAAAA { |
| 122 | + aaaa := rr.Body.(*dnsmessage.AAAAResource) |
| 123 | + results = append(results, aaaa.AAAA[:]) |
| 124 | + } |
| 125 | + } |
| 126 | + return results, nil |
| 127 | +} |
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