github.com/icodeface/tls@v0.0.0-20230910023335-34df9250cd12/internal/x/net/dns/dnsmessage/example_test.go (about)

     1  // Copyright 2017 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package dnsmessage_test
     6  
     7  import (
     8  	"fmt"
     9  	"net"
    10  	"strings"
    11  
    12  	"github.com/icodeface/tls/internal/x/net/dns/dnsmessage"
    13  )
    14  
    15  func mustNewName(name string) dnsmessage.Name {
    16  	n, err := dnsmessage.NewName(name)
    17  	if err != nil {
    18  		panic(err)
    19  	}
    20  	return n
    21  }
    22  
    23  func ExampleParser() {
    24  	msg := dnsmessage.Message{
    25  		Header: dnsmessage.Header{Response: true, Authoritative: true},
    26  		Questions: []dnsmessage.Question{
    27  			{
    28  				Name:  mustNewName("foo.bar.example.com."),
    29  				Type:  dnsmessage.TypeA,
    30  				Class: dnsmessage.ClassINET,
    31  			},
    32  			{
    33  				Name:  mustNewName("bar.example.com."),
    34  				Type:  dnsmessage.TypeA,
    35  				Class: dnsmessage.ClassINET,
    36  			},
    37  		},
    38  		Answers: []dnsmessage.Resource{
    39  			{
    40  				Header: dnsmessage.ResourceHeader{
    41  					Name:  mustNewName("foo.bar.example.com."),
    42  					Type:  dnsmessage.TypeA,
    43  					Class: dnsmessage.ClassINET,
    44  				},
    45  				Body: &dnsmessage.AResource{A: [4]byte{127, 0, 0, 1}},
    46  			},
    47  			{
    48  				Header: dnsmessage.ResourceHeader{
    49  					Name:  mustNewName("bar.example.com."),
    50  					Type:  dnsmessage.TypeA,
    51  					Class: dnsmessage.ClassINET,
    52  				},
    53  				Body: &dnsmessage.AResource{A: [4]byte{127, 0, 0, 2}},
    54  			},
    55  		},
    56  	}
    57  
    58  	buf, err := msg.Pack()
    59  	if err != nil {
    60  		panic(err)
    61  	}
    62  
    63  	wantName := "bar.example.com."
    64  
    65  	var p dnsmessage.Parser
    66  	if _, err := p.Start(buf); err != nil {
    67  		panic(err)
    68  	}
    69  
    70  	for {
    71  		q, err := p.Question()
    72  		if err == dnsmessage.ErrSectionDone {
    73  			break
    74  		}
    75  		if err != nil {
    76  			panic(err)
    77  		}
    78  
    79  		if q.Name.String() != wantName {
    80  			continue
    81  		}
    82  
    83  		fmt.Println("Found question for name", wantName)
    84  		if err := p.SkipAllQuestions(); err != nil {
    85  			panic(err)
    86  		}
    87  		break
    88  	}
    89  
    90  	var gotIPs []net.IP
    91  	for {
    92  		h, err := p.AnswerHeader()
    93  		if err == dnsmessage.ErrSectionDone {
    94  			break
    95  		}
    96  		if err != nil {
    97  			panic(err)
    98  		}
    99  
   100  		if (h.Type != dnsmessage.TypeA && h.Type != dnsmessage.TypeAAAA) || h.Class != dnsmessage.ClassINET {
   101  			continue
   102  		}
   103  
   104  		if !strings.EqualFold(h.Name.String(), wantName) {
   105  			if err := p.SkipAnswer(); err != nil {
   106  				panic(err)
   107  			}
   108  			continue
   109  		}
   110  
   111  		switch h.Type {
   112  		case dnsmessage.TypeA:
   113  			r, err := p.AResource()
   114  			if err != nil {
   115  				panic(err)
   116  			}
   117  			gotIPs = append(gotIPs, r.A[:])
   118  		case dnsmessage.TypeAAAA:
   119  			r, err := p.AAAAResource()
   120  			if err != nil {
   121  				panic(err)
   122  			}
   123  			gotIPs = append(gotIPs, r.AAAA[:])
   124  		}
   125  	}
   126  
   127  	fmt.Printf("Found A/AAAA records for name %s: %v\n", wantName, gotIPs)
   128  
   129  	// Output:
   130  	// Found question for name bar.example.com.
   131  	// Found A/AAAA records for name bar.example.com.: [127.0.0.2]
   132  }