92 lines
2.2 KiB
Go
92 lines
2.2 KiB
Go
package resolve
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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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// Resolver holds the configuration for a dns.Client
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type Resolver struct {
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client *dns.Client
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servers []string
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}
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//DefaultResolvConfPath specifies path to default resolv config file on UNIX.
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const DefaultResolvConfPath = "/etc/resolv.conf"
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// NewResolver accepts a list of nameservers and configures a DNS resolver.
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func NewResolver(servers []string) *Resolver {
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client := &dns.Client{}
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return &Resolver{
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client: client,
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servers: servers,
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}
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}
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// NewResolverFromResolvFile loads the configuration from resolv config file
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// and initialises a DNS resolver.
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func NewResolverFromResolvFile(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 &Resolver{
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client: client,
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servers: servers,
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}, nil
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}
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func (r *Resolver) Lookup(domains []string) []error {
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// 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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var messages = make([]dns.Msg, 0, len(domains))
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for _, d := range domains {
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msg := dns.Msg{}
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msg.Id = dns.Id()
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msg.RecursionDesired = true
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// It's recommended to only send 1 question for 1 DNS message.
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msg.Question = []dns.Question{(dns.Question{
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Name: dns.Fqdn(d),
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Qtype: dns.TypeA,
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Qclass: dns.ClassINET,
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})}
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messages = append(messages, msg)
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}
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var errors []error
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for _, msg := range messages {
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for _, srv := range r.servers {
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in, rtt, err := r.client.Exchange(&msg, srv)
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if err != nil {
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errors = append(errors, err)
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}
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for _, ans := range in.Answer {
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if t, ok := ans.(*dns.A); ok {
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fmt.Println(t.String())
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}
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}
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fmt.Println("rtt is", rtt, msg.Question)
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}
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}
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return errors
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}
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