wenyifan
109 lines
1.9 KiB
Go
109 lines
1.9 KiB
Go
package exchanger
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import (
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"context"
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"errors"
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"net"
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"strings"
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"time"
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"github.com/miekg/dns"
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)
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type systemExchanger struct {
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rawAddr string
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timeout time.Duration
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lookupIP func(ctx context.Context, network, host string) ([]net.IP, error)
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}
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func newSystemExchanger(rawAddr string, opts Options) Exchanger {
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if opts.timeout <= 0 {
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opts.timeout = 5 * time.Second
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}
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ex := &systemExchanger{
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rawAddr: rawAddr,
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timeout: opts.timeout,
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}
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ex.lookupIP = net.DefaultResolver.LookupIP
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return ex
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}
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func (ex *systemExchanger) Exchange(ctx context.Context, msg []byte) ([]byte, error) {
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mq := new(dns.Msg)
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if err := mq.Unpack(msg); err != nil {
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return nil, err
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}
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mr := new(dns.Msg)
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mr.SetReply(mq)
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mr.RecursionAvailable = true
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if len(mq.Question) == 0 {
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return mr.Pack()
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}
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q := mq.Question[0]
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network := "ip"
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switch q.Qtype {
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case dns.TypeA:
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network = "ip4"
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case dns.TypeAAAA:
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network = "ip6"
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default:
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return mr.Pack()
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}
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if ex.timeout > 0 {
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var cancel context.CancelFunc
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ctx, cancel = context.WithTimeout(ctx, ex.timeout)
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defer cancel()
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}
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host := strings.TrimSuffix(q.Name, ".")
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ips, err := ex.lookupIP(ctx, network, host)
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if err != nil {
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var dnsErr *net.DNSError
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if !errors.As(err, &dnsErr) || !dnsErr.IsNotFound {
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return nil, err
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}
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}
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for _, ip := range ips {
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switch q.Qtype {
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case dns.TypeA:
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if ip4 := ip.To4(); ip4 != nil {
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mr.Answer = append(mr.Answer, &dns.A{
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Hdr: dns.RR_Header{
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Name: q.Name,
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Rrtype: dns.TypeA,
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Class: q.Qclass,
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},
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A: ip4,
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})
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}
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case dns.TypeAAAA:
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if ip.To4() == nil {
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if ip16 := ip.To16(); ip16 != nil {
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mr.Answer = append(mr.Answer, &dns.AAAA{
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Hdr: dns.RR_Header{
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Name: q.Name,
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Rrtype: dns.TypeAAAA,
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Class: q.Qclass,
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},
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AAAA: ip16,
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})
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}
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}
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}
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}
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return mr.Pack()
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}
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func (ex *systemExchanger) String() string {
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if ex.rawAddr == "" {
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return "system"
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}
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return ex.rawAddr
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}
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