96 lines
2.2 KiB
Go
96 lines
2.2 KiB
Go
package resolvers
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import (
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"net"
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"time"
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"github.com/miekg/dns"
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)
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const (
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// DefaultUDPPort specifies the default port for a DNS server connecting over UDP
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DefaultUDPPort = "53"
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//DefaultResolvConfPath specifies path to default resolv config file on UNIX.
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DefaultResolvConfPath = "/etc/resolv.conf"
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)
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// UDPResolver represents the config options for setting up a Resolver.
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type UDPResolver struct {
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client *dns.Client
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servers []string
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}
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// UDPResolverOpts holds options for setting up a Classic resolver.
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type UDPResolverOpts struct {
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IPv4Only bool
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IPv6Only bool
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Timeout time.Duration
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}
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// NewUDPResolver accepts a list of nameservers and configures a DNS resolver.
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func NewUDPResolver(servers []string, opts UDPResolverOpts) (Resolver, error) {
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client := &dns.Client{
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Timeout: opts.Timeout,
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}
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var nameservers []string
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// load list of nameservers to the config
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if len(servers) == 0 {
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ns, err := getDefaultServers()
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if err != nil {
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return nil, err
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}
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nameservers = ns
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} else {
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// load the list of servers that user specified.
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for _, srv := range servers {
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if i := net.ParseIP(srv); i != nil {
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// if no port specified in nameserver, append defaults.
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nameservers = append(nameservers, net.JoinHostPort(srv, DefaultUDPPort))
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} else {
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// use the port user specified.
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nameservers = append(nameservers, srv)
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}
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}
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}
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client.Net = "udp"
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if opts.IPv4Only {
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client.Net = "udp4"
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}
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if opts.IPv6Only {
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client.Net = "udp6"
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}
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return &UDPResolver{
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client: client,
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servers: nameservers,
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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 (c *UDPResolver) Lookup(questions []dns.Question) ([]Response, error) {
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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 c.servers {
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in, rtt, err := c.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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