85 lines
1.9 KiB
Go
85 lines
1.9 KiB
Go
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package resolvers
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import (
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"fmt"
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"net"
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"github.com/miekg/dns"
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)
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// SystemResolver represents the config options based on the
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// resolvconf file.
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type SystemResolver struct {
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client *dns.Client
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config *dns.ClientConfig
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servers []string
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}
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// NewSystemResolver loads the configuration from resolv config file
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// and initialises a DNS resolver.
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func NewSystemResolver(resolvFilePath string) (Resolver, error) {
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if resolvFilePath == "" {
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resolvFilePath = DefaultResolvConfPath
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}
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cfg, err := dns.ClientConfigFromFile(resolvFilePath)
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if err != nil {
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return nil, err
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}
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servers := make([]string, 0, len(cfg.Servers))
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for _, s := range cfg.Servers {
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ip := net.ParseIP(s)
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// handle IPv6
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if ip != nil && ip.To4() != nil {
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servers = append(servers, fmt.Sprintf("%s:%s", s, cfg.Port))
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} else {
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servers = append(servers, fmt.Sprintf("[%s]:%s", s, cfg.Port))
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}
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}
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client := &dns.Client{}
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return &SystemResolver{
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client: client,
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servers: servers,
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config: cfg,
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}, nil
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}
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// Lookup prepare a list of DNS messages to be sent to the server.
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// It's possible to send multiple question in one message
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// but some nameservers are not able to
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func (s *SystemResolver) Lookup(questions []dns.Question) ([]Response, error) {
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for _, q := range questions {
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domains := s.config.NameList(q.Name)
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for _, d := range domains {
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ques := dns.Question{
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Name: d,
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Qtype: q.Qtype,
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Qclass: q.Qclass,
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}
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questions = append(questions, ques)
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}
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}
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var (
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messages = prepareMessages(questions)
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responses []Response
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)
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for _, msg := range messages {
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for _, srv := range s.servers {
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in, rtt, err := s.client.Exchange(&msg, srv)
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if err != nil {
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return nil, err
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}
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msg.Answer = in.Answer
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rsp := Response{
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Message: msg,
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RTT: rtt,
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Nameserver: srv,
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}
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responses = append(responses, rsp)
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}
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}
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return responses, nil
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}
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